Antiviral ethers of aspartate protease substrate isosteres

Abstract: Antiretroviral compounds (which are effective, for example, against HIV) of the formula I in which R 1 is an acyl radical lower-alkoxy-lower-alkanoyl whose lower alkoxy radical is unsubstituted or is substituted by halogen, phenyl, lower alkoxy or a heterocyclic radical selected from piperidinyl, pyrrolidinyl, tetrahydropyranyl, tetrahydrofuranyl, thiazolidinyl, thiazolyl, indolyl or 4H-1-benzopyranyl which is unsubstituted or substituted by oxo, hydroxyl, amino, lower alkyl, lower-alkoxycarbonyl and/or phenyl-lower-alkoxycarbonyl; lower alkanoyl which is unsubstituted or is substituted by one of the said unsubstituted or substituted heterocyclic radicals; arylcarbonyl or heterocyclylcarbonyl which are substituted by heterocyclyl or heterocyclyl-lower-alkyl; phenyl-lower-alkanoyl which is substituted by hydroxyl and lower alkyl; or arylsulfonyl; or the residue of an amino acid which is defined in accordance with the description (and which may be acylated on the amino nitrogen by one of the abovementioned acyl radicals); R 2 and R 3 are in each case cyclohexyl, cyclohexenyl, phenyl, naphthyl or tetrahydronaphthyl which are unsubstituted or substituted by lower alkyl, phenyl, cyanophenyl, phenyl-lower-alkyl, halogen, halo-lower-alkyl, cyano, hydroxyl, lower alkoxy, phenyl-lower-alkoxyl, pyridyl-lower-alkoxy, lower-alkoxy-lower-alkoxy, lower-alkoxycarbonyl-lower-alkoxy, carboxyl-lower-alkoxy, hydroxyl-lower-alkoxy, carbamoyl-lower-alkoxy, cyano-lower-alkoxy, and phenyl-lower-alkanesulfonyl which is unsubstituted or substituted by halogen; R 4 is lower alkyl, cyclohexyl or phenyl; and R 5 is lower alkyl; and n is 1 or 2, or salts thereof, are novel.

Description: Resumé and field of the invention The invention relates to ethers of aspartate protease substrate isosteres and their salts, to processes for preparing these compounds and the salts thereof, to pharmaceutical preparations which comprise these compounds or the salts thereof, and to the use of these compounds or the salts thereof (either alone or in combination with other active compounds which are effective against retroviruses) for the therapeutic or diagnostic treatment of the human or animal body or for producing pharmaceutical preparations. Background of the invention According to WHO estimates, considerably more than 15 million people are currently infected with HIV-1 or HIV-2. Inhibitors of reverse transcriptase, an enzyme which converts retroviral RNA into DNA, such as 3'-azido-3'-deoxythymidine (AZT) or dideoxyinosine (DDI), and also trisodium phosphonoformate, ammonium 21-tungsto-9-antimoniate, 1-β-D-ribofuranoxyl-1,2,4-triazole-3-carboxamide and dideoxycytidine, and also adriamycin, have primarily been used hitherto for treating retroviral diseases such as AIDS. Attempts are also being made to introduce the T4 cell receptor, which is present in the human body on certain cells of the immune system and which is responsible for anchoring infectious viral particles and introducing them into these cells, and is consequently responsible for their ability to infect, into the body, for example as a recombinant molecule or molecular fragment. This would have the effect of titrating out binding sites for the virus so that the virions would no longer be able to bind to the cells. Compounds which use other means to prevent the virus penetrating through the cell membrane, such as polymannoacetate, are also used. In addition to this, the first clinical experiments in which a hydroxyethylene isostere, N-tert-butyldecahydro-2-[2(R)-hydroxy-4-phenyl-3(S)-[[N-2-quinolylcarbonyl-L-asparaginyl]amino]butyl]-(4aS,8aS)-isoquinoline-3(S)-carboxamide (Ro 31-8959) is used as an inhibitor of the HIV protease have been reported. This compound had an inhibitory effect on HIV protease in vitro and suppressed viral replication in cell experiments, and useful blood levels were achieved in rodents even with oral administration (see Roberts, N. A., et al., Biochemical Soc. Transactions 20 , 513-516 (1992)); useful blood levels were also achieved in humans (see, for example, G.J. Muirhead et al., Brit. J. Clin. Pharmacol. 34 , 170P-171P (1992)). A so-called "surrogate marker" (titre of the CD4 lymphocytes in the blood, whose decline in untreated patients represents a measure of the development of the AIDS disease) demonstrated the first positive effects in AIDS patients (see "Roche statement on HIV Proteinase Inhibitor (Ro 31-8959) European Trials Results", which was distributed to participants at the 9th International Congress on AIDS in Berlin, June 7 - 11, 1993). Previously de Solms et al. (J. Med. Chem. 1991, vol. 34 (9); 2852-7 (1991)) described the synthesis of a series of tetrapeptide analogues of the known HIV protease inhibitor L-682,679, in which the P 2 ' amino acid (Leucine) is varied and the P 3 ' amino acid (Phenylalanine) is eliminated or replaced, including compounds in which the P 3 ' amino add is replaced by -CH 2 -CH 2 -OH. The most potent compound described by de Solms et al., compound 12, has an α-branched amino acid in the P 2 '-position (Isoleucine) and aminomethyl)benzimidazole at the carboxy terminus. In the AIDS viruses, HIV-1 and HIV-2, and in other retroviruses, for example the corresponding viruses in cats (FIV) and monkeys (SIV), proteolytic maturation, for example of the core proteins of the virus, is effected by an aspartate protease, such as the HIV protease. No infectious viral particles can be produced without this proteolytic maturation. On the basis of the central role played by the said aspartate proteases, such as HIV-1 protease or HIV-2 protease, in viral maturation, and on the basis of experimental results, for example obtained with infected cell cultures, it is assumed that effective prevention in vivo of the maturation step which is brought about by this protease will prevent mature virions from being assembled. Consequently, appropriate inhibitors can be employed therapeutically. It is the object of the present invention to prepare a novel class of compounds which also possess, in particular, favourable pharmacological properties, such as good pharmacokinetics, bioavailability and/or good tolerability. Detailed description of the invention The novel ethers of aspartate protease substrate isosteres are compounds of the formula I, in which R 1 is lower-alkoxy-lower-alkanoyl (including lower-alkoxycarbonyl); R 2 and R 3 are, independently of each other, phenyl which is unsubstituted or is substituted by one or more radicals selected, independently of each other, from lower alkyl, phenyl, cyanophenyl, phenyl-lower-alkyl, halogen, halo-lower-alkyl, cyano, hydroxyl, lower alkoxy, phenyl-lower-alkoxyl, pyridyl-lower-alkoxy, in which pyridyl is bonded via a ring carbon atom, lower-alkoxy-lower-alkoxy, lower-alkoxycarbonyl-lower-alkoxy, carboxyl-lower- alkoxy, hydroxyl-lower-alkoxy having at least two carbon atoms, in which hydroxyl is not bonded in the 1 position, carbamoyl-lower-alkoxy, cyano-lower-alkoxy and lower- alkylenedioxy; R 4 is lower alkyl; R 5 is lower alkyl; n is 1 or 2, and "lower" denotes a radical having not more than 7 carbon atoms, or salts thereof, provided at least one salt-forming group is present. Within the scope of the present application, the general terms used above and below preferably have the following meanings unless otherwise indicated: The prefix "lower" or the word component "lower", for example in lower alkyl, lower alkoxy, lower alkanoyl or phenyl-lower-alkyl, denote a radical having not more than 7, in particular not more than 4, carbon atoms, it being possible for the radicals concerned to be unbranched or to be branched once or more than once. When compounds or salts are mentioned, these terms also mean a compound or a salt. Asymmetric carbon atoms which may be present, including those in the substituents R 1 , R 2 , R 3 , R 4 and R 5 , can be in the (R), (S) or (R,S) configurations, preferably in the (R) configuration or (S) configuration. The present compounds can consequently exist as isomeric mixtures or as pure isomers, in particular as diastereomeric mixtures, enantiomeric mixtures or, preferably, pure enantiomers. The additional statement "altematively or additionally" means either that the corresponding designated substituent meanings combined with the respective groups of substituent meanings which are not designated with this additional statement together form a group of substituents, or that the correspondingly designated substituent meanings form a group on their own, or that the meanings which are not designated with this additional statement also on their own form a group of substituent meanings. Preferably, the compounds of the formula I have the formula I', in which the radicals have the meanings given for compounds of the formula I. In lower alkoxy-lower-alkanoyl, R 1 is the lower-alkoxy radical, preferably methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, isobutoxy, seo-butoxy or tert-butoxy, while lower alkanoyl is preferably formyl (the corresponding radical is then a lower-alkoxycarbonyl radical, in particular methoxycarbonyl, ethoxycarbonyl or tert-butoxycarbonyl), acetyl or proplonyl. Halogen is fluorine, chlorine, bromine or iodine, in particular fluorine or chlorine. R 1 is primarily tert-butoxycarbonyl. Preferably, R 2 and R 3 are selected from phenyl, phenyl-lower-alkoxy-phenyl, in particular 4-phenyl-lower-alkoxyphenyl, such as 4-(benzyloxy)phenyl, difluorophenyl, in particular 2,4-difluorophenyl, cyanophenyl, in particular 4-cyanophenyl, lower-alkoxyphenyl, such as 2-, 3-or 4-lower-alkoxyphenyl, for example 4-isobutyloxyphenyl and, in particular, 2-, 3- and, in particular, 4-methoxyphenyl, tri-lower-alkoxy-phenyl, In particular trimethoxyphenyl, for example having the lower-alkoxy substituents in the 3,4,5 positions, as in 3,4,5-trimethoxyphenyl, in the 2,4,5 positions, as in 2,4,5-trimethoxyphenyl, in 2,4,6 positions, as in 2,4,6-trimethoxyphenyl, where the tri-lower alkoxy radicals or methoxy radicals preferably being bonded asymmetrically on the phenyl ring, primarily in the 2,3,4 positions, for example in 2,3,4-trimethoxyphenyl, lower-alkoxy-lower-alkoxy-phenyl, such as 4-(lower-alkoxy-lower-alkoxy)phenyl, especially 4-(2-methoxy-ethoxy)phenyl, lower-alkylenedioxyphenyl, in which the lower-alkylenedioxy radical is bonded via its two oxygen atoms to two adjacent carbon atoms of the phenyl ring, for example methylenedioxyphenyl, such as 3,4-methylenedioxyphenyl, and pyridyl-lower-alkoxyphenyl, such as 4-(pyridin-2- or pyridin-3-yl-lower-alkoxy)phenyl, in particular pyridin-3-yl-loweralkoxyphenyl, for example pyridin-3-yl-methoxyphenyl; and, in addition, from 4-lower-alkoxy-2-fluorophenyl, such as 4-methoxy-2-fluorophenyl, 4-fluoro-2-loweralkoxyphenyl, such as 4-fluoro-2-methoxyphenyl, 4-lower-alkoxy-2-hydroxyphenyl, such as 4-methoxy-2-hydroxyphenyl, phenyl which is substituted not more than three times by lower alkyl, such as methyl, and lower alkoxy, such as methoxy, such as 4-lower-alkoxy-2,3-di-lower-alkylphenyl, for example 4-methoxy-2,3-dimethylphenyl, phenyl-lower-alkylphenyl, such as 4-phenyl-lower-alkylphenyl, for example 4-(2-phenylethyl)-phenyl, fluorophenyl, such as 2-fluorophenyl, hydroxyphenyl, such as 4-hydroxyphenyl, di-lower-alkoxyphenyl, in particular dimethoxyphenyl, for example 2,4-di-lower-alkoxyphenyl, such as 2,4-dimethoxyphenyl, 3,4-di-lower-alkoxyphenyl, such as 3,4-dimethoxyphenyl, 2,5-di-lower-alkoxyphenyl, such as 2,5-dimethoxyphenyl, or 2,6-di-lower-alkoxyphenyl, such as 2,6-dimethoxyphenyl. Compounds of the formula I are particularly preferred in which R 3 is 2,3,4-tri-lower-alkoxyphenyl, in particular 2,3,4-trimethoxyphenyl, while the remaining radicals R 1 , R 2 , R 4 , R 5 and n are as defined above or below. Compounds of the formula I are preferred in which the following combinations of R 2 and R 3 are present: Radical R 2 Radical R 3 1) 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-(benzyloxy)phenyl 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-(benzyloxy)phenyl 2) Phenyl Cyanophenyl, in particular 4-cyanophenyl 3) Phenyl 2-Fluorophenyl 4) Phenyl 2,4-Difluorophenyl 5) Phenyl 4-Phenyl-lower-alkylphenyl, in particular 4-(2-phenylethyl)phenyl 6) Phenyl 4-Lower-alkoxyphenyl, in particular 4-methoxyphenyl or, in addition, 4-isobutoxyphenyl 7) Phenyl Dichlorophenyl-lower-alkanesulfonylphenyl, in particular 4-(2,6-dichlorobenzyl sulfonyl)phenyl 8) 4-(Lower alkoxy-lower-alkoxy)phenyl, in particular 4-(2-methoxyethoxy)phenyl 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-(benzyloxy)phenyl 9) 4-(Lower-alkoxy-lower-alkoxy)phenyl, in particular 4-(2-methoxyethoxy)phenyl Hydroxyphenyl, in particular 4-hydroxyphenyl 10) 4-(Lower-alkoxy-lower- 4-(Lower alkoxy)phenyl, 10) 4-(Lower-alkoxy-lower-alkoxy) )phenyl, in particular 4-(2-methoxyethoxy)phenyl 4-(Lower alkoxy)phenyl, in particular 4-methoxyphenyl 11) 4-(Lower-alkoxy-lower-alkoxy)phenyl, in particular 4-(2-methoxyethoxy)phenyl 4-(Lower-alkoxy-lower-alkoxy)phenyl, in particular 4-(2-methoxyethoxy)phenyl 12) 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-(benzyloxy)phenyl 4-(Lower alkoxy)phenyl, in particular 4-methoxyphenyl 13) 4-Hydroxyphenyl 4-(Lower alkoxy)-phenyl, in particular 4-methoxyphenyl 14) 4-(Lower alkoxy)phenyl, in particular 4-methoxyphenyl or 4-isobutoxyphenyl 4-Lower alkoxyphenyl, in particular 4-methoxyphenyl 15) 4-(Lower alkoxy)phenyl, in particular 4-methoxyphenyl Phenyl 16) Phenyl 4-Lower-alkoxy-2-fluorophenyl, in particular 4-methoxy-2-fluorophenyl 17) Phenyl 4-Fluoro-2-lower-alkoxyphenyl, in particular 4-fluoro-2-methoxyphenyl 18) Phenyl 4-Lower-alkoxy-2-hydroxyphenyl, in particular 4-methoxy-2-hydroxyphenyl 19) Phenyl Phenyl 20) Phenyl 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-(benzyloxy)phenyl 21) Phenyl 4-((Pyridin-2-yl- or pyridin-3-yl)lower alkoxy)phenyl, in particular 4-(pyridin-2-yl- or, especially, pyridin-3-yl)methoxyphenyl 22) Phenyl 3,4-Lower-alkylenedioxyphenyl, in particular 3,4-methylenedioxyphenyl 23) Phenyl 3,4-Di-lower-alkoxyphenyl, in particular 3,4-dimethoxyphenyl 24) Phenyl 3-Lower-alkoxyphenyl, in particular 3-methoxyphenyl 25) Phenyl 2,3,4-Tri-lower-alkoxyphenyl, in particular 2,3,4-trimethoxyphenyl 26) Phenyl 3,4,5-Tri-lower-alkoxyphenyl, in particular 3,4,5-trimethoxyphenyl 27) Phenyl 2,4-Di-lower-alkoxyphenyl, in particular 2,4-dimethoxyphenyl 28) Phenyl 2-(Lower alkoxy)phenyl, in particular 2-methoxyphenyl 29) Phenyl 4-Lower-alkoxy-2,3-di-lower-alkylphenyl, in particular 4-methoxy-2,3-dimethylphenyl 30) Phenyl 2,4,5-Tri-lower-alkoxyphenyl, in particular 2,4,5-trimethoxyphenyl 31) Phenyl 2,4,6-Tri-lower-alkoxyphenyl, in particular 2,4,6-trimethoxyphenyl 32) Phenyl 5,6,7,8-Tetrahydro-1-naphthyl 33) Phenyl 2,5-Di-lower-alkoxyphenyl, in particular 2,5-dimethoxyphenyl 34) Phenyl 2,6-Di-lower-alkoxyphenyl, in particular 2,6-dimethoxyphenyl or alternatively or additionally: 35) Phenyl Biphenylyl, in particular 4-biphenylyl 36) 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-benzyloxyphenyl Biphenylyl, in particular 4-biphenylyl 37) 4-Hydroxyphenyl Biphenylyl, in particular 4-biphenylyl 38) 4-Lower-alkoxyphenyl, in particular 4-methoxyphenyl Biphenylyl, in particular 4-biphenylyl 39) Phenyl (Cyanophenyl)phenyl, in particular 2'-cyanobiphenyl-4-yl 40) 4-(Phenyl-lower-alkoxy)phenyl, in particular 4-benzyloxyphenyl (Cyanophenyl)phenyl, in particular 2'-cyanobiphenyl-4-yl 41) 4-Hydroxyphenyl (Cyanophenyl)phenyl, in particular 2'-cyanobiphenyl-4-yl 42) 4-Lower-alkoxyphenyl, in particular 4-methoxyphenyl (Cyanophenyl)phenyl, in particular 2'-cyanobiphenyl-4-yl 43) Phenyl 4-Hydroxyphenyl The combinations R 2 and R 3 which are very particularly preferred are those mentioned immediately above under numbers 2), 4), 6), 8), 19), 20), 21), 22) and 25), especially those mentioned under 6) and, in particular, under 25). R 4 is preferably lower alkyl, in particular methyl or isopropyl, or else sec-butyl (=1-methylpropyl). Lower alkyl R 5 is preferably methyl or else ethyl. The variable n is preferably 1. Salts of compounds of the formula I are, in particular (when basic groups are present in compounds of the formula I), add addition salts, salts with bases (when acidic groups are present in compounds of the formula I) or else possibly mixed salts or internal salts when several salt-forming groups are present. Salts are primarily the pharmaceutically utilizable, non-toxic salts of compounds of the formula I. Such salts are formed, for example, from compounds of the formula I having an acidic group, for example a carboxyl group, a sulfo group or a phosphoryl group which is substituted by one or two hydroxyl groups, and are, for example, their salts with suitable bases, such as non-toxic metal salts derived from metals of groups Ia, Ib, IIa and lib of the periodic system of the elements, primarily suitable alkali metal salts, for example lithium, sodium or potassium salts, or alkaline earth metal salts, for example magnesium or calcium salts, and also zinc salts or ammonium salts, and also those salts which are formed with organic amines, such as mono-, di- or trialkylamines, In particular mono-, di- or tri-lower-alkylamines, which are unsubstituted or substituted by hydroxyl, or with quatemary ammonium compounds, for example with N-methyl-N-ethylamine, diethylamine, triethylamine, mono-, bis- or tris-(2-hydroxy-lower-alkyl)amines, such as mono-, bis- or tris-(2-hydroxyethyl)amine, 2-hydroxy-tert-butylamine or tris(hydroxymethyl)methylamine, N,N-di-lower-alkyl-N-(hydroxy-lower-alkyl)amines, such as N,N-dimethyl-N-(2-hydroxyethyl)amine or tri-(2-hydroxyethyl)amine, N-methyl-D-glucamine or quaternary ammonium salts, such as tetrabutylammonium salts. The compounds of the formula I which have a basic group, for example an amino group, can form acid addition salts, for example with Inorganic acids, for example hydrohalic acid, such as hydrochloric acid, sulfuric acid or phosphoric acid, or with organic carboxylic, sulfonic, sulfato (-O-SO 3 H) or phospho acids or N-substituted sulfamic acids, for example acetic acid, propionic acid, glycolic acid, succinic acid, maleic acid, hydroxymaleic acid, methylmaleic acid, fumaric acid, malic acid, tartaric acid, gluconic acid, glucaric acid, glucuronic acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, salicylic add, 4-aminosalicylic acid, 2-phenoxybenzoic acid, 2-acetoxybenzoic acid, embonic acid, nicotinic acid or isonicotinic acid, and, in addition, with amino acids, for example the α-amino acids mentioned above, in particular glutamic acid and aspartic acid, and also with methanesulfonic acid, ethanesulfonic acid, 2-hydroxyethanesulfonic acid, ethane-1,2-disulfonic acid, benzenesulfonic acid, 4-methylbenzenesulfonic acid, naphthalene-2-sulfonic acid, 2- or 3-phosphoglycerate, glucose-6-phosphate or N-cyclohexylsulfamic acid (with the formation of cyclamates), or with other acidic organic compounds, such as ascorbic acid. Compounds of the formula I which possess acidic and basic groups can also form internal salts. Pharmaceutically unsuitable salts, for example perchlorates or picrates, may also be used for isolation or purification. Only the pharmaceutically utilizable salts, which are non-toxic when properly used, are suitable for therapeutic use, and are, therefore, preferred. The compounds of the formula I have valuable pharmacological properties. They possess anti-retroviral activity, particularly against the HIV-1 and HIV-2 viruses, which are considered to be causative agents of AIDS, and surprisingly have synergistic effects when used in combination with other compounds which possess activity against retroviral aspartate proteases. The compounds of the formula I are inhibitors of retroviral aspartate proteases, in particular inhibitors of the aspartate protease of HIV-1 or HIV-2, and are therefore suitable for treating retroviral diseases, such as AIDS or its preliminary stages (e.g. ARDS). Compounds of the formula I also have an effect against corresponding animal retroviruses, such as SIV (in monkeys) or FIV (in cats). In this context, compounds of the formula I have particularly advantageous pharmacodynamic properties, for example good pharmacodynamics, such as a high bioavailability and/or high blood levels (especially when administered orally), and/or good tolerability. The inhibitory effect of the compounds of the formula I on the proteolytic activity of HIV-1 protease can be demonstrated, for example, using a method analogous to that described by A. D. Richards et al., J. Biol. Chem. 265 (14), 7733-7736 (1990). In this case, inhibition of the action of the HIV-1 protease (prepared in accordance with S. Billich et al., J. Biol. Chem. 263 (34), 17905-17908 (1990)) is measured in the presence of the icosapeptide RRSNQVSQNYPIVQNIQGRR (an artificial substrate of HIV-1 protease, prepared by peptide synthesis using known methods, see J. Schneider et al., Cell 54 , 363-368 (1988)), which, as a substrate analogue, comprises one of the cleavage sites of the gag precursor protein (natural substrate of the HIV-1 protease). This substrate and its cleavage products are analysed by high performance liquid chromatography (HPLC). The active compound to be tested is dissolved in dimethyl sulfoxide. The enzymic test is carried out by adding suitable dilutions of the inhibitor in 20 mM β-morpholinoethanesulfonic acid (MES) buffer pH 6.0, to the test mixture. The latter consists of the abovementioned icosapeptide (122 µM) in 20 mM MES buffer, pH 6.0. 100 µl are employed per test mixture. The reaction is started by adding 10 µl of HIV-1 protease solution, and is ended after one hour of incubation at 37°C by adding 10 µl of 0.3 M HClO 4 . After the sample has been centrifuged at 10,000 x g for 5 min, 20µl of the resulting supematant are loaded onto a 125 x 4.6 mm 'Nucleosil C18-5µ HPLC column (reverse-phase material from Macherey & Nagel, Düren, FRG, based on silica gel which is coated with C 18 alkyl chains). The uncleaved icosapeptide and its cleavage products are eluted from the column using the following gradient 100 % eluent 1 -> 50 % eluent 1+50 % eluent 2 (eluent 1: 10 % acetonitrile, 90 % H 2 O, 0.1 % trifluoroacetic acid (TFA); eluent 2: 75 % acetonitrile, 25 % H 2 O, 0.08 % TFA) over 15 min, flow rate 1 ml/min The eluted peptide fragments are quantified by measuring the peak height of the cleavage product at 215 nm. Compounds of the formula I have inhibitory effects in the range from 10 -5 to 10 -9 M. In this context, IC 50 values (IC 50 = that concentration which decreases the activity of the HIV-1 protease by 50 % as compared with the activity of a control without inhibitor) of from about 5 x 10 -5 to 10 -9 M are preferably obtained. In a further test, it can be shown that compounds of the formula I either protect cells which are normally infected by HIV from such an infection or at least retard such an infection. This test uses the human T cell leukaemia cell line MT-2 (Science 229, 563 (1985)), which is extremely sensitive to the cytopathic effect of HIV since it continually produces HTLV-1 (a virus which causes leukaemia). The MT-2 cells are grown in RPMI 1640 medium (Gibco, Scotland; RPMI comprises an amino acid mixture lacking glutamine) which is supplemented with 10 % heat-inactivated foetal calf serum, glutamine and standard antibiotics. The cells are always free of mycoplasmas. The HIV-1 virus (strain LAV) is cultured In A3.01 cells (NIH, Bethesda, USA), a cell line which is used for culturing HIV-1 and which derives from the CEM cell line. Measuring by the test for reverse transcriptase (see below) indicates that the titre of the virus preparation is 2 x 10 7 lU/ml. In order to measure the infection-inhibiting effect of the test compounds, 50 µl of the respective test substance in culture medium and 100 µl of HIV-1 in culture medium (800 TCID50/ml, TCID50 = tissue culture infective dose = dose, which infects 50 % of the MT-2 cells) are added to 10 x 10 4 exponentially growing MT-2 cells which are initially introduced in 50 µl of culture medium on 96-well microtitre plates. After 4 days of incubation, a sample consisting of 10 µl of the supematant is removed from each well for measuring the reverse transcriptase activity. The titre of the reverse transcriptase enzyme, which is specific for retroviruses, is used as a measure of the virus titre. For determining the titre, the samples which have been removed are first added to another 96-well microtitre plate and stored at-20°C until measured. When carrying out the measurement, 30 µl of reverse transcriptase cocktail are added to each well. The reverse transcriptase cocktail consists of 50 mM Tris (α,α,α-tris(hydroxymethyl)methylamine, Ultra pur, Merck, Germany), pH 7.8; 75 mM KCI, 2 mM dithiothreitol, 5 mM MgCl 2 ; 0.1 % Nonidet P-40 (detergent; Sigma, Switzerland), 0.8 mM EDTA, 10 µg/ml poly-A (Pharmacia, Uppsala, Sweden) and 0.16 µg/ml oligo(T) (= pdT(12-18), Pharmacia, Uppsala, Sweden) as template primer. The mixture is filtered through a 0.45 µm Acrodisc filter (Gelman Sciences Inc., Ann Arbor, USA) and stored at -20°C. Prior to the test, 0.1 % (v/v) of [alpha- 32 P]dTTP is added to aliquots of the solution to produce a final radioactivity of 10 µCi/ml. After mixing has taken place, the plate is incubated at 37°C for 2 h. 5 µl of the reaction mixture are then transferred to DE81 paper (Whatman, one filter per well). The dried filters are washed three times for 5 min with 300 mM NaCl/25 mM trisodium citrate and then once with ethanol, and air-dried once again. The radioactivity on the filters is measured in a Packard Matrix 96-well counter (Packard, Zürich, Switzerland). The ED90 values are calculated and are defined as the concentrations of the test compounds which reduce the RT activity by 90 % as compared with that of a control without test compound. In this test, the compounds of the formula I preferably inhibit virus replication at concentrations of from 5 x 10 -5 to 10 -8 M. Thus, the compounds of the formula I are suitable for actively retarding the replication of HIV-1 in cell cultures. It is also possible to measure the blood levels of compounds of the formula I. For this purpose, the compounds of the formula I which are to be investigated are dissolved, for example, in dimethyl sulfoxide (DMSO) at a concentration of 240 mg/ml. The resulting solutions are diluted with 20 % (w/v) hydroxypropyl-β-cyclodextrin (HPβCD) in order to obtain a concentration of the test substance of 12 mg/ml. This solution is administered orally to mice, by means of artificial feeding by gavage, at a dose of 120 mg/kg. The animals are sacrificed at 30, 60, 90 and 120 min after the administration, and blood is removed. From three to four animals are examined at each time point. The blood is heparinized and worked up for the analysis as follows: an internal standard is added to the heparinized blood to give a final concentration of 4 µM. The blood is centrifuged. 0.25 ml of plasma are taken off and deproteinized with an equal volume of acetonitrile. After centrifugation, the supematant is dried in vacuo and the residue is suspended in 20 µl of a 3M solution of NaCl and 100 µl of 0.05 M phthalate buffer having a pH of 3.0. The suspension is extracted firstly with 1 ml, and then with 0.2 ml, of diisopropyl ether. The diisopropyl ether solution is evaporated to dryness and the residue is dissolved in 50 % (v/v) of aqueous acetonitrile. This solution is examined by reversed-phase HPLC. The reversed-phase HPLC analysis is carried out using a 125 x 4.6 mm Nucleosil' C 18 column (reversed-phase material from Macherey-Nagel, Düren, Federal Republic of Germany, based on silica gel which has been derivatized with hydrocarbon residues of 18 carbon atoms), which is equilibrated with a mobile phase of 50 % acetonitrile in water/0.1 % trifluoroacetic acid. The flow rate is 1 ml/min. Detection takes place at 215 nm. Standards for the compounds in blood are worked up in analogy with the blood samples and are used for constructing standard curves which are then employed for determining the in-vivo concentrations. These and related experiments, and also experiments involving parenteral administration, demonstrate that using the compounds of the formula I, blood levels can be obtained which are greater than the ED 90 in the abovementioned cell assay. For this reason, compounds of this nature are also suitable for preventing virus growth in vivo. The combination of aspartate protease inhibition in vitro, inhibition of viral replication in cell culture and measurement of the blood levels in rodents, such as rat or mouse, is used for determining the clinical potential of aspartate protease inhibitors (see, for example, Roberts, N. A., et al., Biochemical Soc. Transactions 20 , 513-516 (1992)). Blood levels which are greater than the ED 90 in the abovementioned cell assay can also be observed when compounds of the formula I are administered (for example orally) to dogs. Consequently, the combination of the data from the cell experiment, the blood levels in rodents and the blood levels in dogs also renders plausible the possibility of using the compounds to treat retroviral diseases, in particular the said diseases, in other mammals, such as humans. The compounds of the formula I can also be used for the prevention, control and therapy of infections due to retroviruses, in particular HIV, such as HIV-1 or HIV-2, in cell cultures, in particular cell cultures of lymphocyte cell lines from mammals, which is particularly advantageous in the case of very valuable cell cultures which, for example, produce specific antibodies, vaccines or messenger substances, such as interleukins etc., and are therefore of great commercial value. Finally, the compounds of the formula I can be used as standards in experiments, for example as HPLC standards or as standards for comparing animal models, in relation to different aspartate protease inhibitors, for example in regard to the blood levels which can be achieved. The compounds of the formula I can be administered alone or else in combination (as a fixed combination of appropriate preparations or as a combination of individual active compounds or individual preparations administered in chronologically staggered sequence) with other substances which are active against retroviruses, in particular HIV, such as HIV-1 or HIV-2, or salts thereof, provided at least one salt-forming group is present; in particular together with inhibitors of reverse transcriptase, especially nucleoside analogues, in particular 3'-azido-3'-deoxythyimidine (= zidovudine = 'RETROVIR, Burroughs-Wellcome), 2',3'-dideoxycytidine (= zalcitabine = 'HIVID, Hoffmann-LaRoche), 2',3'-dideoxyinosine (= didanosine = 'VIDEX, Bristol-Myers-Squibb) or (2R,cis)-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one (= lamivindine, Glaxo) or non-nucleoside analogues, such as 11-cyclopropyl-5,11-dihydro-4-methyl-(6H)-dipyrido[3,2-b;2',3'-e]-[1,4]diazepin-6-one; and in the first place with one or more (in particular one or else two) other inhibitors of retroviral asparate proteases, in particular the aspartate proteases from HIV, such as HIV-1 and HIV-2, in particular one or more (preferably one or two), in particular a) one of the inhibitors named in EP 0 346 847 (published on 20.12.1989) and EP0432695 (published on 10.06.1991; corresponds to US 5,196,438, published on 23.03.1993), in particular the compound with the designation Ro 31-8959 (= saquinavir; Hoffmann-LaRoche) of the formula b) one of the inhibitors named in EP 0 541 168 (published on 12.05.1993; corresponds to US 5,413,999), in particular the compound with the designation L-735,524 (= indinavir = 'CRIXIVAN; Merck & Co., Inc.) of the formula c) one of the inhibitors named in EP 0486 948 (published on 27.05.1992; corresponds to US 5,354,866), in particular the compound with the designation ABT-538 (Abbott) of the formula d) the compound with the designation KVX-478 (or VX-478 or 141W94; Glaxo Wellcome, Vertex and Kissei Pharmaceuticals) of the formula e) the compound with the designation AG-1343 (Agouron) of the formula f) the compound with the designation KNI-272 (Nippon Mining) of the formula g) the compound with the designation U-96988 (Upjohn) of the formula and/or h) the compound with the designation BILA-2011 BS (= palinavir; Boehringer-Ingelheim) of the formula or in each case a salt thereof, provided salt-forming groups are present. Particularly when a compound of the formula I is combined with one or more of the said inhibitors of retroviral aspartate proteases, synergistic effects can actually be observed, which is surprising since the inhibitors act on the same enzyme. The particular advantage of such combinations then resides in the decrease in the dosage quantities which are required and in the more powerful anti-retroviral activity, which can simultaneously be achieved, of the active compounds when used in combination as compared with that which can be achieved using the individual active compounds. This yields advantages with regard to possible side effects of the individual compounds and results in a lower number of viruses in the organism, so that the frequency of mutation can also be lowered and hence the possibility of the development of resistance can be reduced. The activity of the combinations, and, in particular, the synergistic effects, can be verified, for example, by means of experiments using cell lines and peripheral mononuclear blood cells (lymphocytes and monocytes). CEM-SS cells (see Nara, P.L., et al., AIDS Res. Human Retroviruses 3 , 283-302 (1987), or Nara, P.L., et al., Nature 332 , 469-70 (1988)) and the permanently infected cell line H9/HTLV-IIIB NIH 1983 (H9/HIV-1/IIIB cells) of Gallo (see Popovic, M., et al., Science 224, 497-500 (1984); Popovic, M., et al., Lancet (1984) ii, 1472-3; or Ratner, L., et al., Nature 313 , 277-84 (1985)), for example, are employed for the experiments using cell lines . For the experiments using peripheral mononuclear blood cells, the cells are isolated from the blood of healthy HIV-seronegative human subjects using a combination of leukaphoresis and counter-current centrifugal elutriation in accordance with known methods (see Alteri, E., et al., Antimicrob. Agent Chemother. 37 (10), 2087-92 (1993)). The lymphocytotrophic isolate HIV-1/LAV (LAV.04/A.301), for example, is used as the virus (see Science 220 , 868-71 (1983)). The compounds to be tested, for example a compound of the formula I and one of the other inhibitors of retroviral aspartate proteases mentioned above, for example saquinavir or indinavir, are dissolved In dimethyl sulfoxide (= DMSO; 2mM), with further dilutions being made using complete tissue culture medium (see below). The final concentration of free DMSO is less than 0.5 %. The experiments for testing antiviral activity are carried out as follows: When using cell lines: The cell lines are maintained in complete culture medium of the following composition: RPMI 1640 (GIBCO, Paisley, Scotland), supplemented with 10% foetal calf serum (SEROMED, Berlin, Germany), 10mM 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (= HEPES) and 2mM L-glutamine (AMIMED, Muttenz, Switzerland). The antiviral activity of the compounds is tested in a coculture system using CEM-SS cells and permanently infected H9/HIV-1/IIIB cells. The test compounds are tested as individual substances or as a combination of two active substances in defined concentration ratios. H9/HIV-1/IIIB cells are mixed, after having been washed twice and having been suspended in fresh medium, with CEM-SS cells in a ratio of 1:50. 100 µl of the cell mixture are dispensed into each well of 96-well tissue culture plates with the wells in each case containing 400 H9/HIV-1/IIIB cells and 2 x 10 4 CEM-SS cells. Immediately after the cells have been dispensed, two-fold serial dilutions of the test compounds are added (100µl per well) In each case in sets of six. Instead of this, 100µl of medium are added to each well for the virus control (VC); CEM-SS cells on their own (without H9/HIV-1/IIIB cells) are used as the control (CC). The final volume is 200 µl/well. After a 24 h incubation at 37°C and in 5 % CO 2 , 150 µl of each supernatant is removed, without removing any cells, and replaced by 150 µl of fresh medium which contains (or, in the case of the VC does not contain) fresh test substance or fresh test substances. 10 µl samples of the culture supematants are collected on day 4 and added to another 96-well microtitre plate which, if required, is stored at -20°C. The virus production is determined as the virus-associated activity of the reverse transcriptase (RT) in accordance with the following method, which has already been described above (see Alteri, E., et al., Antimicrob. Agent Chemother. 37 (10), 2087-92 (1993)): When carrying out the measurement, 30 µl of reverse transcriptase cocktail are added to each well. The reverse transcriptase cocktail consists of 50mM Tris (α,α,α-tris(hydroxymethyl)methylamine, Ultra pur, Merck, Germany), pH 7.8; 75mM KCI, 2mM dithiothreitol, 5mM MgCl 2 ; 0.1 % Nonidet P-40 (detergent; Sigma, Switzerland), 0.8mM EDTA, 10 µg/ml poly-A (Pharmacia, Uppsala, Sweden) and 0.16µg/ml oligo(T) (= pdT(12-18), Pharmacia, Uppsala, Sweden) as template primer. The mixture is filtered through a 0.45 µm Acrodisc filter (Gelman Sciences Inc., Ann Arbor, USA) and stored at -20°C. Prior to the test, 0.1 % (v/v) [alpha- 32 P]dTTP is added to aliquots of the solution in order to achieve a final radioactivity of 10 µCi/ml. After mixing, the plate is incubated at 37°C for 1.5 h. 5 µl of the reaction mixture are transferred to DE81 paper (Whatman, one filter per well). The dried filters are washed three times for 5 min with 300 mM NaCl/25 mM trisodium citrate and then once with ethanol, and air-dried once again. The radioactivity on the filters is measured in a Packard Matrix 96-well counter (Packard, Zurich, Switzerland). The antiretroviral effect is given as the % reduction in RT activity as compared with the VC values. When peripheral mononuclear blood cells are used: The mixture of mononuclear cells (lymphocytes and monocytes), which is obtained as described above, is cultured, in the presence of 0.25 µg/ml phytohaemagglutinin (Wellcome Diagnostics, Temple Hill, Dartford, England), for two days in RPMI-1640 (GIBCO, Paisley, Scotland), 50 mU/ml penicillin, 50µg/ml streptomycin (ANIMED, Muttenz, Switzerland), 2 mM L-glutamine (AMIMED, Muttenz, Switzerland) and 10 mM HEPES buffer (GIBCO, Paisley, Scotland). Successful activation is monitored by measuring the increase in cell size (scattergram, FCM analysis). The cells are resuspended in complete medium containing 10 % human AB serum (Sigma, St. Louis, USA) and infected with HIV-1 for 6 h. After the viral adsorption, the cells are washed and resuspended in complete medium which is supplemented with 100 U/ml human recombinant IL-2 (Genzyme, Cambridge, USA). 9 x 10 4 cells are plated out per well (0.3 ml) in 96-well plates having U-shaped well bottoms. The antiviral compounds are added either alone or in combination to sets of five cell cultures in each case (pentaplicates) directly following the infection. Two thirds of the culture medium with or without antiviral compound(s) are replaced every three days. The test is concluded on day 13 after infection. The progress of the viral infection is measured by determining the RT activity as described above for the cell lines. In the groups of preferred compounds of the formula I which are mentioned below, definitions of substituents from the abovementioned general definitions can be employed in a meaningful manner, for example to replace more general definitions by more specific definitions or in particular those definitions characterized as being preferred; in each case, those definitions are preferred which are characterized above as being preferred or as being examples. A compound of the formula I (in particular of the formula I') is preferred in which: R 1 is lower-alkoxycarbonyl, especially tert-butoxycarbonyl, ethoxycarbonyl or methoxycarbonyl; R 2 = phenyl and R 3 = 4-lower-alkoxyphenyl, in particular 4-methoxyphenyl, or, preferably, 2,3,4-tri-lower-alkoxyphenyl, in particular 2,3,4-trimethoxycarbonyl; R 4 is isopropyl; R 5 is methyl; and n is 1. Compounds of the formula I which are named in the examples, or pharmaceutically acceptable salts thereof, provided at least one salt-forming group is present, are the most strongly preferred. The compounds of the formula I, or salts of such compounds having at least one salt-forming group, are obtained by processes which are known per se, for example by a) condensing an acid of the formula R 1 -OH or a reactive acid derivative thereof, in which R 1 has the same meanings as R 1 in compounds of the formula I, with an amino compound of the formula (in particular of the formula or a reactive derivative thereof, in which n and the radicals have the meanings specified for compounds of the formula I, with free functional groups, with the exception of those participating in the reaction, being present, if necessary, in protected form in the starting materials of the formulae II and III (or III'), and eliminating protective groups which are present, or b) condensing a carboxylic acid of the formula (in particular of the formula or a reactive derivative thereof, in which the radicals have the meanings specified for compounds of the formula I, with an amino compound of the formula (in particular of the formula or a reactive derivative thereof, in which n and the radicals have the meanings specified for compounds of the formula I, with free functional groups, with the exception of those participating in the reaction, being present, if necessary, in protected form in the starting materials of the formulae V (or V') and VI (or VI'), and protective groups which are present being eliminated, or c) condensing a carboxylic acid of the formula (in particular of the formula or a reactive derivative thereof, in which the radicals have the meanings specified for compounds of the formula I, with an amino compound of the formula or a reactive derivative thereof, in which n and R 5 have the meanings specified for compounds of the formula I, with free functional groups, with the exception of those participating in the reaction, being present, if required, in protected form in the starting materials of the formulae VII (or VII') and VIII, and protective groups which are present being eliminated If desired, or d) either (i) etherifying a hydroxy compound of the formula (in particular of the formula or its alcoholate salt, in which n and the radicals have the meanings specified for compounds of the formula I, with a compound of the formula W 1 -R 5 in which R 5 has the meanings specified for compounds of the formula I and W 1 Is a leaving group, which is a nucleofugic group selected from hydroxyl which is esterified with a strong organic or inorganic acid, or (ii) etherifying a reactive derivative of the hydroxy compound of the formula IX (or IX') with a compound of the formula HO-R 5 or its alcoholate salt, in which R 5 is defined as Immediately above, with free functional groups, with the exception of those participating in the reaction, being present, if necessary, in protected form in the starting materials of the formulae IX (or IX'), X and Xa, and protective groups which are present being eliminated, or e) eliminating protective groups which are present in a compound of the formula I (in particular I'), in which the substituents are as defined above, with the proviso that in the compound of the formula I concerned at least one functional group is protected by protective groups, with it being possible, in the specified process steps a) to e), if not already specifically mentioned, for starting materials also to be employed in the form of salts, provided salt-forming groups are present, and/or converting, if desired, a compound of the formula I (or I'), which is obtained by one of the abovementioned processes a) to e) and which has at least one salt-forming group, into its salt, and/or converting an obtainable salt into the free compound or Into another salt, and/or resolving isomeric mixtures, which may be obtainable, of compounds of the formula I (or I'), and/or transforming a novel compound of the formula I (or I') Into another novel compound of the formula I (or I'). The above-defined processes are described in more detail below: In the description of the respective process steps, the radicals R 1 , R 2 , R 3 , R 4 and R 5 , and n have, both above and below, the meanings specified for compounds of the formula I, unless otherwise indicated. In each case, the preparation of compounds of the formula in which n and the radicals have the meanings specified for compounds of the formula I, is preferred when preparing compounds of the formula I. In the respective processes, the compounds of the apostrophe-labelled formulae I', Ia', III', IIIa', V', VI', VII' and IX', having the stereospecificity indicated, are particularly preferred as compared with the corresponding compounds without an indicated stereospecificity and with the formulae I, la, III, IIIa, V, VI, VII and IX; the corresponding compound mixtures, in which the carbon atoms (in the given sequence C(5), C(2) and C(4)) carrying the radical R 2 -CH 2 -, the radical R 3 -CH 2 - and the OH located between them are in the (2R,4S,5S) configuration and the (2S,4R,5R) configuration and are in each case less preferred than the compounds labelled with an apostrophe but more strongly preferred than the corresponding compounds without any indicated stereospecificity. In that which follows, preferably the corresponding compound mixtures having the (2R,4S,5S) configuration and the (2S,4R,5R) configuration or, in particular the compounds of the formulae which in each case correspond and which are labelled with an apostrophe can in each case be employed in place of the compounds of the formulae I, Ia, III, IIIa, V, VI, VII and IX, provided this is chemically meaningful; this also applies to the section on additional process measures and starting materials. Process a) (preparation of an amide bond) In starting materials of the formulae II and III, functional groups, with the exception of the groups which are to take part in the reaction or do not react under the reaction conditions, are, independently of each other, protected by protective groups. Protective groups for functional groups in starting materials whose reaction is to be avoided, in particular carboxyl, amino, hydroxyl and mercapto groups, include, in particular, those protective groups (conventional protecting groups) which are customarily used in the synthesis of peptide compounds or else of cephalosporins and penicillins, and also nucleic acid derivatives and sugars. These protective groups can already be present in the precursors and are intended to protect the functional groups concerned against unwanted side reactions such as acylations, etherifications, esterifications, oxidations and solvolysis. In certain cases, the protective groups can, in addition to this, have the effect of making the course of reactions selective, for example stereoselective. It is characteristic of protective groups that they are easily detachable, i.e. without undesirable side reactions, for example solvolytically, reductively, photolytically or else enzymically, for example under physiological conditions as well, and that they are not present in the end products. Compounds of the formula I which possess protected functional groups, whose protective groups are detachable under physiological conditions, can have a higher degree of metabolic stability, or pharmacodynamic properties which are otherwise improved, as compared with the corresponding compounds having free functional groups. The protection of functional groups by such protective groups, the protective groups themselves, and also the reactions for eliminating them, are described, for example, in standard works such as J. F. W. McOmie, "Protective Groups in Organic Chemistry", Plenum Press, London and New York 1973, in Th. W. Greene, "Protective Groups in Organic Synthesis", Wiley, New York 1981, in "The Peptides"; Volume 3 (E. Gross and J. Meienhofer, editors), Academic Press, London and New York 1981, in "Methoden der organischen Chemie" (Methods of Organic Chemistry), HoubenWeyl, 4th Edition, Volume 15/l, Georg Thieme Verlag, Stuttgart 1974, in H.-D. Jakubke and H. Jescheit, "Aminosäuren, Peptide, Proteine" (Amino Acids, Peptides and Proteins), Verlag Chemie, Weinheim, Deerfield Beach and Basel 1982, and in Jochen Lehmann, "Chemie der Kohlenhydrate: Monosaccharide und Derivate" (Chemistry of the Carbohydrates: Monosaccharides and Derivatives), Georg Thieme Veriag, Stuttgart 1974. Within the meaning of this application, a polymeric support, as is suitable, for example, for the Merrifield synthesis, and which is bound in an easily detachable manner to the functional group to be protected, for example a carboxyl group, Is also expressly understood to be a protective group, for example a carboxyl protective group. A suitable polymeric support of this nature is, in particular, a polystyrene resin which is weakly cross-connected by copolymerization with divinylbenzene and which carries suitable bridge members for the reversible binding. The adds of the formula II are carboxylic acids and either have a free carboxylic group or are present as a reactive derivative thereof, for example as an activated ester which is derived from the free carboxy compound, as a reactive anhydride, or, in addition, as a reactive cyclic amide. The reactive derivatives can also be formed In situ. Process b) (preparation of an amide bond) In starting materials of the formulae V and VI, functional groups, with the exception of the groups which are to participate in the reaction or which do not react under the reaction conditions, are protected, independently of each other, by protective groups. The protective groups, the free carboxylic acids and their reactive derivatives, the free amines and their reactive derivatives and the processes used for the condensation are completely analogous to those described under process a) for the preparation of an amide bond proceeding from compounds of the formulae II and III, if the carboxylic acids of the formula V are employed there in place of those of the formula II and the amino compounds of the formula VI are employed In place of those of the formula III. In addition to the reactive derivatives in analogy with process a), a reactive derivative of a carboxylic acid of the formula V can also be the corresponding γ-lactone of the formula XXA (in particular of the formula XXA') in which the radicals R 1 , R 2 and R 3 have the meanings specified for compounds of the formula I. The reaction then proceeds directly to yield the end product in the presence of an organic acid which is, if anything, mild, for example a substituted or (preferably) unsubstituted lower-alkanoic acid, such as trihaloacetic acid, for example trichloroacetic acid, or, in particular, acetic acid, or other organic acids of similar acidity, for example 2-hydroxypyridine, at preferred temperatures of between 10 and 100°C, in particular of between 60 and 100°C, in the presence or, preferably, in the absence of solvents, preferably while excluding the atmosphere, for example in bomb tubes. Preferably, the compound of the formula VI, in particular VI', is then employed in a slight excess, for example in from 1.01-fold to 4-fold molar excess, in relation to the compound of the formula XXA, in particular XXA', with the, if anything, mild organic acid on the other hand preferably being employed in slight excess, in equimolar quantity or in slight deficit in relation to the compound of the formula VI, in particular VI', for example in a 0.3-fold to 2-fold molar ratio. The release of functional groups which are protected by protective groups in the resulting compounds of the formula I having protected functions is effected using one or more of the methods specified under process f). Process c) (preparation of an amide bond) In starting materials of the formulae VII and VIII, functional groups, with the exception of the groups which are to participate in the reaction or which do not react under the reaction conditions, are protected, independently of each other, by protective groups. The protective groups, the free carboxylic acids and their reactive derivatives, the free amines and their reactive derivatives and the processes used for the condensation are completely analogous to those described under process a) for the preparation of an amide bond proceeding from compounds of the formulae II and III, if the carboxylic acids of the formula VII are employed there in place of those of the formula II and the amino compounds of the formula VIII are employed in place of those of the formula III. The release of functional groups which are protected by protective groups in the resulting compounds of the formula I having protected functions is effected using one or more of the methods specified under process e). Process d) (preparation of an ether bond - nucleophilic substitution) In starting materials of the formulae IX, X and Xa, functional groups, with the exception of the groups which are to participate in the reaction or which do not react under the reaction conditions, are protected, independently of each other, by protective groups. The protective groups, and the methods for introducing them, correspond to those specified under process a). In the nucleophilic substitution, either, in case (i), the compound of the formula IX has a free hydroxyl group which is to be etherified and W 1 in the compound of the formula X is a leaving group, or, in case (ii), the compound of the formula IX is in the form of a reactive derivative and is reacted with the hydroxyl group which is to be etherified. In this context, the hydroxyl group, which is to be reacted, of the respective hydroxyl compound is converted into its alcoholate salt either in situ or in a previous, independent reaction. In an alcoholate salt, the hydroxyl group (-OH) is present in anionic form (as -O - ), with a suitable counterion principally being a metal cation, such as an alkali metal cation, for example K + , Cs + or, in particular, Na + . A leaving group W 1 is, in particular, a nucleofugic leaving group selected from hydroxyl which is esterified with a strong inorganic or organic acid, such as hydroxyl which is esterified with a mineral acid, for example hydrohalic acid, such as hydrochloric, hydrobromic or hydriodic acid, or with a strong organic sulfonic acid such as a lower-alkanesulfonic acid which is unsubstituted or substituted, for example, by halogen, such as fluorine, or an aromatic sulfonic acid, for example a benzenesulfonic acid which is unsubstituted or substituted by lower alkyl, such as methyl, halogen, such as bromine, and/or nitro, for example a methanesulfonic, p-bromotoluenesulfonic or p-toluenesulfonic acid, or hydroxyl which is esterified with hydrazoic acid. It is also possible to prepare the compound concerned in situ by substituting another corresponding radical W 1 , for example of Cl, by another radical W 1 , for example I (preferably using an alkali metal iodide, such as Nal) and subsequently continuing with the reaction in the resulting reaction mixture. In a reactive derivative of a compound of the formula IX, a leaving group, such as described immediately above for W 1 , is present in place of the hydroxyl group. The etherification preferably takes place in the presence of a relatively mild base, such as an alkali metal carbonate, for example sodium or potassium carbonate, of a strong base, for example a hydroxide-containing base, such as a metal hydroxide, for example an alkali metal hydroxide, such as sodium or potassium hydroxide, or, in particular, using a metal alcoholate of the respective hydroxy compound or its preparation in situ in the presence of a strong base, for example of an alkali metal hydride, such as sodium hydride, or in the presence of an alkali metal, such as sodium, in the absence or presence of suitable solvents or solvent mixtures, in particular aprotic solvents, for example of DMPU, an ether, such as diethyl ether, dioxane or tetrahydrofuran, of a carboxamide, such as dimethylformamide, or of a mixture of two or more of these solvents, at temperatures of between 0°C and reflux temperature, in particular between 20°C and reflux temperature, if necessary under protective gas, such as nitrogen or argon. Depending on the reaction conditions, the substitution can proceed as a nucleophilic substitution of the first or second order. Since a series of side reactions (for example racemization by the formation of carbanions) are possible in the reaction according to process d), this process can sometimes only be carried out under very precisely controlled reaction conditions (for example careful metering-in of the base which is employed or of the respective alcoholate). Possible interfering reactions and suitable reaction conditions are immediately apparent to the person skilled in the art. In a preferred variant of the process according to the invention for preparing compounds of the formula I, process d) is excluded for this reason. The release of functional groups which are protected by protective groups in the resulting compounds of the formula I having protected functions is effected using one or more of the methods specified under process e). Process e) (protective group detachment) Detachment of the protective groups which are not components of the desired end product of the formula I, for example the carboxyl, amino, hydroxyl and/or mercapto protective groups, is effected in a manner known per se, for example using solvolysis, in particular hydrolysis, alcoholysis or acidolysis, or by means of reduction, in particular hydrogenolysis, or by means of other reducing agents, and also photolysis, as desired stepwise or simultaneously, with it also being possible to use enzymic methods. Detachment of the protective groups is described, for example, in the standard works which are mentioned above in the section on "protective groups". Additional process measures In the additional process measures, which are carried out if desired, functional groups of the starting compounds which are not to participate in the reaction can be unprotected or in protected form, for example protected by one or more of the protective groups specified under process a). The protective groups can be detached, in their entirety or in part, using one of the methods specified under process e). Salts of compounds of the formula I having at least one salt-forming group can be prepared in a manner known per se. Thus, salts of compounds of the formula I having acidic groups can be formed, for example, by treating with metal compounds, such as alkali metal salts of suitable organic carboxylic acids, for example the sodium salt of 2-ethylhexanoic acid, with inorganic alkali metal or alkaline earth metal compounds, such as the corresponding hydroxides, carbonates or hydrogen carbonates, such as sodium and potassium hydroxide, carbonate or hydrogen carbonate, with corresponding calcium compounds or with ammonia, or with a suitable organic amine, with stoichiometric quantities, or only a small excess of the salt-forming agent, preferably being used. Acid addition salts of compounds of the formula I are obtained in a customary manner, for example by treating with an acid or a suitable anion exchange reagent. Internal salts of compounds of the formula I which contain acidic and basic salt-forming groups, for example a free carboxylic group and a free amino group, can be formed, for example, by neutralizing salts, such as acid addition salts, to the isoelectric point, for example using weak bases, or by treating with ion exchangers. Salts can be converted into the free compounds in a customary manner; metal salts and ammonium salts can be converted, for example, by treating with suitable acids or acidic ion exchangers, and acid addition salts can be converted, for example, by treating with a suitable basic agent, in particular with inorganic alkali metal or alkaline earth metal compounds, such as the corresponding hydroxides, carbonates or hydrogen-carbonates, such as sodium and potassium hydroxide, carbonate or hydrogen-carbonate, with corresponding calcium compounds or with ammonia or a suitable organic amine, with stoichiometric quantities or only a small excess of the salt-forming agent preferably being used, in suitable solvents, for example halohydrocarbons, such as dichloromethane, in the presence or absence of water; or by means of treating with basic ion exchangers. Stereoisomeric mixtures of compounds of the formula I, that is mixtures of diastereomers and/or enantiomers, for example racemic mixtures, can be resolved into the corresponding isomers in a manner known per se using suitable separation methods. Thus, diastereomeric mixtures, for example, can be resolved into the individual diastereomers by fractional crystallization, chromatography, solvent partition or other suitable methods. Racemates can be separated from each other after converting the optical antipodes into diastereomers, for example by reacting with optically active compounds, for example optically active acids or bases, by chromatography on column materials coated with optically active compounds, or by enzymic methods, for example by the selective reaction of only one of the two enantiomers. This separation can be effected either at the level of one of the starting products or at that of the compounds of the formula I. In a compound of the formula I, in which one of the radicals R 1 , R 2 or R 3 , or several of these radicals, are substituted by 1-phenyl-lower-alkoxy, such as benzyloxy, the 1-phenyl-lower-alkoxy radical can be detached as described under process e). The corresponding compounds of the formula I are obtained in which hydroxyl is present in place of 1-phenyl-lower-alkoxy. In an obtainable compound of the formula I, a carboxyl group which is present in free form or in reactive form can be esterifled, or an esterified carboxyl group can be converted into a free carboxyl group. In order to esterify a carboxyl group in a compound of the formula I, the free acid, if desired, can be used, or the free acid can be converted into one of the reactive derivatives specified above under process a) and can be reacted with a corresponding alcohol, or, for the esterification, the free acid or a reactive salt, for example the caesium salt, can be reacted with a reactive derivative of an alcohol. For example, the caesium salt of a carboxylic add can be reacted with a halide or organic sulfonic acid ester corresponding to the alcohol (with halogen or the radical of an organic sulfonic acid, such as toluenesulfonic acid, in place of the hydroxyl group). The esterification of the carboxyl group can also be effected using other customary alkylating agents, for example using diazomethane, lower-alkyl halides, sulfonic acid esters, Meerwein salts or 1-substituted 3-aryltriazenes. In order to convert an esterified carboxyl group into the free carboxyl group, use can be made of one of the methods described above in association with the detachment of the carboxyl protective groups or, if desired, of an alkaline hydrolysis under customary conditions, such as those specified under process e), preferably in the presence of an alkali metal hydroxide, such as LiOH, in suitable solvents, such as alcohols, for example methanol or ethanol, water or mixtures thereof. A lower-alkoxycarbonyl-lower-alkoxy group which is present as a substituent, for example of phenyl R 2 and/or R 3 , can be converted reductively into a hydroxy-lower-alkoxy group (in which the lower alkyl radical has at least 2 carbon atoms) by, for example, reducing with complex hydrides which selectively reduce the carbonyl ester group under suitable reaction conditions, for example using LiBH 4 in 1,2-dimethoxyethane at temperatures of from 0°C up to the reflux temperature, preferably from about 15 to 30°C. In a compound of the formula I, a free amino or imino group which is present can be acylated. The acylation is effected in analogy with the methods specified above under process a) or in analogy with one of the methods specified for protective groups. In an obtainable compound of the formula I, in which the substituents have the said meanings and there is at least one free hydroxyl group, and additional functional groups are, if necessary, present in protected form, the free hydroxyl group, for example the hydroxyl group on the phenyl R 2 and/or phenyl R 3 , can be etherified, which hydroxyl group can be etherified with the radical of a lower-alkanol, of a phenyl-lower-alkanol, of a lower-alkoxy-carbonyl-lower-alkanol, of a carbamoyl-lower-alkanol, of a pyridyl-lower-alkanol, of a cyano-lower-alkanol or of a lower-alkoxy-lower-alkanol, with the said alcohols preferably being employed in a form in which a nucleofugic leaving group is present in place of the hydroxyl group, for example as defined for W 1 in compounds of the formula X. The etherification can be carried out in analogy with the process conditions according to process e) and is preferably effected using diazomethane or lower-alkyl-, phenyl-lower-alkyl-, lower-alkoxy-lower-alkyl-, carbamoyl-lower-alkyl-, pyridyl-lower-alkyl-, cyano-lower-alkyl- or lower-alkoxy-lower-alkyl-halides or -sulfonic acid esters. The reaction is preferably carried out using appropriate lower-alkyl-, phenyl-lower-alkyl-, lower-alkoxy-lower-alkyl-, carbamoyl-lower-alkyl-, pyridyl-lower-alkyl-, cyano-lower-alkyl- or lower-alkoxy-lower-alkyl-halides, such as -iodides, -bromides or -chlorides, in the presence of bases, preferably of a hydroxyl base, in particular a basic metal hyroxide, such as sodium or potassium hydroxide, or, especially, of a metal carbonate or metal hydrogen carbonate, such as sodium, potassium or, primarily, caesium carbonate in suitable solvents or solvent mixtures, for example in N,N-di-lower-alkyl-lower-alkanoylamides, such as dimethylformamide or dimethylacetamide, ketones, such as lower-alkanones, for example acetone, or ethers, such as dioxane, or mixtures thereof, at temperatures of between -10°C up to the reflux temperature, preferably at from 0 to 60°C, for example at from about 0 to 50°C. In a compound of the formula I, groups which are present and which correspond to protective groups, or, in addition, suitable R 1 radicals, apart from hydrogen, can be detached using one of the methods specified under process e), in particular by hydrolysis, for example in the presence of bases, such as alkali metal or alkaline earth metal hydroxides, for example sodium hydroxide, or acids, such as organic acids or mineral acids, for example hydrohalic acid, such as hydrochloric acid. The hydrolysis is effected under the customary conditions, for example in aqueous solution or in anhydrous solvents, in particular in ethers, such as dioxane, at temperatures of between -50°C and the reflux temperature of the corresponding reaction mixtures, for example between 0°C and 50°C, preferably in the presence of a protective gas, such as argon or nitrogen, or by means of hydrogenolysis (for example in the case of benzyloxycarbonyl radicals), preferably in polar solvents, such as alcohols, for example methanol or ethanol, or of esters, such as lower-alkyl-lower-alkanoates, for example ethyl acetate, at the abovementioned temperatures and in the presence of suitable hydrogenation catalysts, such as a palladium catalyst, which is preferably bound to a support, such as charcoal. Pharmaceutical preparations and methods The invention also relates to pharmaceutical preparations which comprise compounds of the formula I, In particular of the formula I'. The pharmacologically utilizable compounds of the present invention can be used, for example, for producing pharmaceutical preparations which comprise an effective quantity of the active compound together, or in a mixture, with a significant quantity of inorganic or organic, solid or liquid, pharmaceutically utilizable carrier substances. The pharmaceutical preparations according to the invention are those for enteral, such as nasal, buccal, rectal or oral, or parenteral, such as intramuscular or intravenous, administration to mammals (humans and animals) and comprise an effective dose of the pharmacological active compound on its own or together with a significant quantity of a pharmaceutically utilizable carrier material. The dose of the active compound depends on the mammalian species, the body weight, the age and the individual condition, the individual pharmacokinetic circumstances, the disease to be treated and the mode of administration. The invention also relates to pharmaceutical preparations and to a method for treating diseases caused by retroviruses, for example AIDS or its preliminary stages, in particular when HIV-2 or, especially, HIV-1 causes the disease, or, in addition, for treating analogous diseases, or their preliminary stages, in non-human mammals which are caused, for example, by SIV in monkeys or FIV in cats, preferably wherein a quantity, which is therapeutically effective against retroviral diseases, such as AIDS or its preliminary stages, or analogous diseases in non-human mammals, of a novel compound of the formula I or, In particular, I' is included in a pharmaceutical preparation which is suitable for administration to a mammal, in particular humans, for treating a retroviral disease, such as, preferably, AIDS or, in addition, analogous diseases in non-human mammals, or wherein a therapeutically effective quantity of a novel compound of the formula I or, in particular I' is administered, in association with the treatment method, to a mammal, for example humans, which, on account of one of the said diseases, in particular AIDS or its preliminary stages, or, in addition, corresponding diseases in non-human mammals, requires a treatment of this nature, in a quantity which is therapeutically effective against retroviral diseases, such as AIDS or its preliminary stages, or, in addition, corresponding diseases in non-human mammals. The dose quantities to be administered to mammals, for example humans of about 70 kg body weight, are between about 3 mg and about 10 g, preferably between about 20 mg and about 4 g, for example approximately 100 mg to 2.5 g per person and day, distributed, preferably, between 1 to 3 individual doses which can, for example, be of equal size. Customarily, children are given half the dose given to adults. "Therapeutically effective" means, in particular, that the onset of the particular disease can be retarded when compared with the untreated patient, that at least one symptom can be delayed or attenuated, that at least one cell type (for example human CD4 cells) can be fully or partially protected from the disease, or that the disease can even be completely cured. The pharmaceutical preparations comprise from about 1 % to about 95 %, preferably from about 20 % to about 90 %, of the active compound. Pharmaceutical preparations according to the invention can, for example, be present in unit dose form, such as ampoules, vials, suppositories, coated tablets, tablets or capsules. The pharmaceutical preparations of the present Invention are produced in a manner known per se, for example using conventional solubilizing, lyophilizing, mixing, granulating or coating methods. Use Is preferably made of solutions of the active compound, and in addition also suspensions or dispersions, specifically, and in particular, isotonic aqueous solutions, dispersions or suspensions, with it being possible for these, for example in the case of lyophilized preparations, which comprise the active substance alone or together with a carrier material, for example mannitol, to be prepared prior to use. The pharmaceutical preparations can be sterilized and/or comprise auxiliary substances, for example preservatives, stabilizers, crosslinking agents and/or emulsifiers, solubilizers, salts for regulating the osmotic pressure and/or buffers, and are produced in a manner known per se, for example using conventional solubilizing or lyophilizing methods. The said solutions or suspensions can comprise viscosity-increasing substances, such as sodium carboxymethylcellulose, carboxymethylcellulose, dextran, polyvinylpyrrolidone or gelatin. Suspensions in oil contain, as the oily component, the vegetable, synthetic or semi-synthetic oils which are customary for injection purposes. Oils of this nature which are to be mentioned are, in particular, liquid fatty acid esters which, as acid component, contain a long-chain fatty acid having 8-22, in particular 12-22, carbon atoms, for example lauric add, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic add, margaric acid, stearic acid, arachidonic acid, behenic acid, or corresponding unsaturated acids, for example oleic acid, elaidic acid, erucic acid, brassidic acid or linoleic acid, with or without the addition of antioxidants, for example vitamin E, β-carotene or 3,5-di-tert-butyl-4-hydroxytoluene. The alcohol component of these fatty acid esters has at most 6 carbon atoms and is a mono- or poly-hydric, for example monohydric, dihydric or trihydric alcohol, for example methanol, ethanol, propanol, butanol or pentanol, or their isomers, especially, however, glycol and glycerol. Fatty acids which are, therefore, to be mentioned by way of example are: ethyl oleate, isopropyl myristate, isopropyl palmitate, "Labrafil M 2375" (polyoxyethyleneglycerol trioleate from Gattefossé, Paris), "Miglyol 812" (triglyceride of saturated fatty acids of C 8 to C 12 chain length from Hüls AG, Germany), particularly, however, vegetable oils such as cottonseed oil, almond oil, olive oil, castor oil, sesame oil, soya bean oil and, especially, groundnut oil. The production of the injection preparations is effected in a customary manner under sterile conditions, as is their filling into ampoules or vials, and the sealing of the containers. Pharmaceutical preparations for oral use can be obtained by combining the active compound with solid carrier substances, if desired granulating a mixture which is obtained and, if desired or necessary, after having added suitable auxiliary substances, processing into tablets, coated tablet cores or capsules, or else by preparing dispersions, preferably with phospholipids, which are filled into glass vials. At the same time, the active compounds can also be incorporated into synthetic supports which release them in a metered manner or else allow them to diffuse. Suitable carrier substances are, in particular, fillers, such as sugars, for example lactose, sucrose, mannitol or sorbitol, cellulose preparations, and/or calcium phosphates, for example tricalcium phosphate or calcium hydrogen phosphate and, in addition, binders, such as starch pastes using, for example, com starch, wheat starch, rice starch or potato starch, gelatin, tragacanth, methylcellulose, hydroxypropylmethylcellulose, sodium carboxymethylcellulose and/or polyvinylpyrrolidone, and/or, if desired, disintegrants, such as the abovementioned starches, and, in addition, carboxymethyl starch, crosslinked polyvinylpyrrolidone, agar, alginic acid or a salt thereof, such as sodium alginate. Adjuvants are primarily flow regulators and lubricants, for example silicic acid, talc, stearic acid or salts thereof, such as magnesium or calcium stearate, and/or polyethylene glycol. Coated tablet cores are provided with suitable coatings which are or are not resistant to gastric juices, with, inter alia, concentrated sugar solutions, which do or do not contain gum arabic, talc, polyvinylpyrrolidone, polyethylene glycol and/or titanium dioxide, lacquer solutions in suitable organic solvents or, for preparing gastric juice-resistant coatings, solutions of suitable cellulose preparations, such as ethylcellulose phthalate or hydroxypropylmethylcellulose phthalate, being used. Capsules are hard gelatin capsules and also soft, closed capsules made of gelatin and an emollient, such as glycerol or sorbitol. The hard capsules can contain the active compound in the form of a granulate, for example containing fillers, such as lactose, binders, such as starches, and/or glidants, such as talc or magnesium stearate, and, if desired, containing stabilizers. In capsules, the active compound is preferably suspended or dissolved in suitable, oily auxiliary substances, such as customary vegetable, synthetic or semi-synthetic oils. Oils of this nature which are to be mentioned, in particular are liquid fatty esters which contain, as the acid component, a long-chain fatty add, for example having 8-22, in particular 12-22, carbon atoms, for example lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, arachidonic acid, behenic acid, or corresponding unsaturated acids, for example oleic acid, elaidic acid, erucic acid, brassidic acid or linoleic acid, with or without the addition of antioxidants, for example, vitamin E, β-carotene or 3,5-di-tert-butyl-4-hydroxytoluene. The alcohol component of these fatty acid esters has at most 6 carbon atoms and is a mono- or poly-hydric, for example monohydric, dihydric or trihydric alcohol, for example methanol, ethanol, propanol, butanol or pentanol or their isomers, especially, however, ethylene glycol or propylene glycol and glycerol. Fatty acid esters which are to be mentioned therefore, by way of example, are: ethyl oleate, isopropyl myristate, isopropyl palmitate, "Labrafil M 2375" (polyoxyethyleneglycerol trioleate from Gattefossé, Paris), "Miglyol 812" (triglyceride of saturated fatty adds of C 8 to C 12 chain length from Hüls AG, Germany), particularly, however, vegetable oils, such as cottonseed oil, almond oil, olive oil, castor oil, groundnut oil, soya bean oil and, especially, sesame oil. Paraffin oil is also possible. Stabilizers, such as emulsifiers, wetting agents or surfactants, binders, such as starch pastes using, for example, com starch, wheat starch, rice starch or potato starch, gelatin, tragacanth, methylcellulose, hydroxypropylmethylcellulose (preferably), sodium carboxymethylcellulose, cyclodextrin(s) and/or polyvinylpyrrolidone, and/or anti-bacterial agents, can be added. Suitable emulsifiers are, in particular, oleic acid, non-ionic surfactants of the fatty add polyhydroxyalcohol ester type, such as sorbitan monolaurate, -oleate, -stearate or-palmitate, sorbitan tristearate or -trioleate, polyoxyethylene adducts of fatty acid polyhydroxyalcohol esters, such as polyoxyethylenesorbitan monolaurate, -oleate,-stearate, -palmitate, -tristearate or -trioleate, polyethylene glycol fatty acid esters, such as polyoxyethyl stearate, polyoxyethylene glycol-(300 or 400)-stearate, polyethylene glycol-2000-stearate, in particular ethylene oxide-propylene oxide block polymers of the ®Pluronic (Wyandotte Chem. Corp.; trademark of BASF, FRG) or ®Synperonic (ICI) type. If it is not soluble in the said oils, the active substance is preferably present in suspension form, for example with the active substance having a particle size of between about 1 and 100 µm. Dyes or pigments can be added to the tablets or coated tablet coatings and to the capsule shells, for example for identifying or for labelling different doses of active compound. The compounds of the formula I can be present either alone or in combination with other compounds which are effective against retroviruses, and used as mentioned above. The invention also relates, correspondingly, to a process or a method for treating diseases caused by retroviruses, for example AIDS or its preliminary stages, in particular when HIV-2 or, especially, HIV-1 is causing the disease, or, in addition, analogous diseases, or their preliminary stages, in non-human mammals, for example those caused by SIV in monkeys or FIV in cats, which comprises administering a combination, which is therapeutically effective against retroviral diseases, such as AIDS or its preliminary stages, or analogous diseases in non-human mammals, of a) a novel compound of the formula I or, in particular, I' (or else several of these compounds) and b) another compound, or two or more thereof, which is/are effective against retroviruses, in particular several or, preferably, one of the inhibitors, mentioned above as being preferred, of reverse transcriptase or, in particular, retroviral aspartate proteases (which, for example, is included in a pharmaceutical product or preparation which is suitable for administering to a mammal, in particular humans, which are in need of such treatment, for treating a retroviral disease, such as, preferably, AIDS or else analogous diseases in non-human mammals) in a quantity which is therapeutically effective against retroviral diseases, such as AIDS or its preliminary stages, or else corresponding diseases in non-human mammals. The dose quantities of the combined individual active compounds which are to be administered to mammals, for example humans, of about 70 kg body weight are between about 3 mg and about 10g, preferably between about 20mg and about 4g, for example from approximately 50mg to 2.5g per person and day, preferably divided between 1 to 3 individual doses which can, for example, be of equal size. Customarily, children are given half the dose given to adults. "Therapeutically effective" means, in particular, that the onset of the respective disease can be retarded as compared with the untreated patient, that at least one symptom can be delayed or attenuated, that at least one cell type (for example human CD4 cells) can be fully or partially protected from the disease, or that the disease can even be completely cured. The invention also relates to products which comprise a) at least, and preferably, one compound of the formula I, or a salt thereof, providing a salt-forming group is present, and b) one, two (preferred) or more other active compounds which are effective against retroviruses, in particular HIV, such as HIV-1 or HIV-2, selected, in particular, from the abovementioned inhibitors of reverse transcriptase or, especially, from the abovementioned other inhibitors of retroviral aspartate proteases (in particular the inhibitors described above in each case as being preferred), in the presence or absence of one or more pharmaceutically acceptable carrier materials, as combination preparations for simultaneous or chronologically staggered use within a time span which is small enough for the active compounds both of the component a) and of the component b) to be present simultaneously in the patient (for example in blood), for treating a retroviral disease which responds to active compounds of this type. The underlying concept is that synergisms can occur in this way. The invention also relates to pharmaceutical preparations which comprise a (preferably jointly) antiretrovirally active quantity of a) at least (and preferably) one compound of the formula I and b) one or more of the said active compounds which are effective against retroviruses, with or without one or more pharmaceutically acceptable carrier material(s), with the active compounds described above in each case as being preferred being preferred. The invention furthermore relates to the use of a combination of a) a compound of the formula I and b) one or more of the abovementioned active compounds which are effective against retroviruses (in particular HIV, such as HIV-1 or HIV-2) for producing pharmaceutical preparations to be used as compositions against retroviral infections, in particular caused by HIV, such as HIV-1 or HIV-2; with the compounds mentioned in each case as being preferred being preferred. The invention also relates to the provision of the abovementioned product or compound mixture for use in a process for the therapeutic treatment of the human or animal body. In this context, the composition and production of the pharmaceutical preparations for the Individual components of a product for staggered or simultaneous administration, or for the compound mixtures, are analogous to those of the abovementioned pharmaceutical preparations for active compounds of the formula I. In each case, a combination of a) the compound of the formula I having the designation 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethox yphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide and b) one or two of the active compounds saquinavir or indinavir is particularly preferred. The active compounds of the formula I and/or the other active compounds which are effective against retroviruses can in each case be replaced by their pharmaceutically utilizable salts. Starting materials: All starting materials can preferably be prepared in analogy with the methods specified in the examples or else, for example, as described in EP 0 532 466 (published on 17 March 1993) or EP 0 618 222 (published on 5 October 1994); these applications are incorporated into the present text by reference. In the preparation of all the starting materials, free functional groups which are not to participate in the respective reaction can be unprotected or, if necessary, be in protected form, for example protected by the protective groups mentioned above under process a), which groups can be introduced at appropriate stages in analogy with the methods mentioned there. Protective groups, or the protected groups, can be set free at suitable time points in analogy with the methods described under process e). Starting materials and intermediates having salt-forming groups can in each case be used as free compounds or as salts, and salts can, at every stage, be prepared or converted once again into the free compounds. In analogy with the process steps described above for the additional process measures, hydroxyl-substituted phenyl R 2 and/or phenyl R 3 radicals in intermediates can be etherified, at appropriate reaction stages, with the radical of a lower alkanol, a phenyl-lower-alkanol, a lower-alkoxy-carbonyl-lower-alkanol, a carbamoyl-lower-alkanol, a pyridyl-lower-alkanol, a cyano-lower-alkanol or a lower-alkoxy-lower-alkanol. The etherification is preferably effected using diazomethane, or lower-alkyl-, phenyl-lower-alkyl-, lower-alkoxycarbonyl-lower-alkyl-, carbamoyl-lower-alkyl, pyridiyl-lower-alkyl-, cyano-lower-alkyl- or lower-alkoxy-lower-alkyl-halides or -sulfonic acid esters. Preference is given to the reaction with corresponding lower-alkyl-, phenyl-lower-alkyl-, lower-alkoxycarbonyl-lower-alkyl-, carbamoyl-lower-alkyl-, pyridyl-lower-alkyl-, cyano-lower-alkyl- or lower-alkoxy-lower-alkyl-halides, such as -iodides, -bromides or -chlorides, in the presence of bases, preferably of a hydroxyl base, in particular a basic metal hydroxide, such as sodium or potassium hydroxide, or, especially, of a metal carbonate or hydrogen carbonate, such as sodium, potassium or, primarily, caesium carbonate, in suitable solvents or solvent mixtures, for example in N,N-di-lower-alkyl-lower-alkanoylamides, such as dimethylformamide or -acetamide, ketones, such as lower alkanones, for example acetone, or ethers, such as dioxane, or mixtures thereof, at temperatures of from -10°C up to the reflux temperature, preferably at from 0 to 60°C, for example from about 0 to 50°C. In intermediates in which at least one of the radicals R 2 or R 3 is a phenyl group and/or one or more additional phenyl rings are present, with it also being possible for the phenyl radicals in each case to be substituted, as described above, an appropriate phenyl radical can, at suitable reaction stages, in analogy with the process steps described above for the additional process measures, be selectively reduced, i.e. hydrogenated, to corresponding cyclohexyl radicals. The hydrogenation is preferably effected in the presence of a catalyst which permits the selective hydrogenation of double bonds in the presence of peptide bonds, In particular of a catalyst consisting of heavy metal oxides, such as a Rh(III)/Pt(VI) oxide catalyst in accordance with Nishimura (S. Nishimura, Bull, Chem. Soc. Japan 33, 566 (1960), in suitable solvents, in particular water, alcohols, such as methanol or ethanol, esters, such as ethyl acetate, or ethers, such as dioxane, for example in methanol, at temperatures of from 0 to 150°C, preferably of from 10 to 50°C, for example at room temperature, and under hydrogen pressures of from 0.01 to 50 bar, for example under standard pressure or under low pressure. Provided the stereochemistry of asymmetric carbon atoms is not defined directly by the choice of corresponding bond symbols, the configuration of asymmetric carbon atoms which is in each case preferred is designated in the formulae by the configuration designation, selected from (S), (R) and (S,R), which is in each case given in brackets. In addition, other isomers or isomeric mixtures can also be present in place of these. The carboxylic acids of the formulae II and IV, or reactive derivatives thereof, are known, are commercially available or can be prepared by methods which are known per se. The compounds of the formula III and III' are known or can be prepared by methods which are known per se. For example, they can be obtained from compounds of the formula in which R 2 has the meanings given for compounds of the formula I, and Pa is an amino protective group, in particular lower-alkoxycarbonyl, such as tert-butoxycarbonyl, or 1-phenyl-lower-alkoxycarbonyl, such as benzyloxycarbonyl (or analogues thereof in which hydrogen replaces Pa, which analogues can then be protected subsequently), which are in a first step converted by reduction into the corresponding compounds of the formula (or the analogue having hydrogen in place of Pa), in which the radicals are as described above. The reduction of amino acid derivatives of the formula XI to give the corresponding aldehydes XII is effected, for example, by reducing them to the corresponding alcohols and then oxidizing the latter to form the aldehydes of the formula XII. The reduction to the alcohols is effected, in particular, by hydrogenation of the corresponding acid halides or other activated carboxylic acid derivatives which are specified under process a), or by reacting activated carboxylic acid derivatives of the compounds of the formula XI, in particular anhydrides with organic carboxylic acids, preferably those which are obtained with haloformic acid esters, for example isobutyl chloroformate (which are preferably obtained by reacting the compounds of the formula XI in the presence of basic amines, for example tri-lower-alkylamines, such as triethylamine, in organic solvents, such as cyclic ethers, for example dioxane, at temperatures of between -50 and 80°C, preferably of between 0 and 50°C) with complex hydrides, such as alkali metal borohydrides, for example sodium borohydride, in aqueous solution in the presence or absence of the last organic solvents to be used, at temperatures of between -50 and 80°C, preferably of between 0 and 50°C. The subsequent oxidation of the resulting alcohols is preferably effected using those oxidizing agents which selectively convert the hydroxyl group into an aldehyde group, for example chromic acid or its derivatives, such as pyridinium chromate or tert-butyl chromate, dichromate/sulfuric acid, sulfur trioxide in the presence of heterocyclic bases, such as pyridine/SO 3 (preferably dissolved in di-lower-alkyl sulfoxides, such as dimethyl sulfoxide, aromatic solvents, such as toluene, or mixtures of these solvents), and also nitric acid, manganese dioxide or selenium dioxide, in water, aqueous or organic solvents, such as halogenated solvents, for example methylene chloride, carboxamides, such as dimethylformamide, and/or cyclic ethers, such as tetrahydrofuran, in the presence or absence of basic amines, for example tri-lower-alkylamines, such as triethylamine, at temperatures of from -70 to 100°C, preferably of from -70 to 50°C, or from -10 to 50°C, for example as described in European Patent Application EP-A-0236734, or by reaction with dicarbonyl halides, such as oxalyl chloride, and di-lower-alkyl sulfoxides, such as dimethyl sulfoxide, in a halogenated hydrocarbon, such as dichloromethylene, in the presence of a tertiary nitrogen base, such as triethylamine, at preferred temperatures of from about -70 to 0°C, for example at about -60°C. It is also possible directly to reduce the compounds of the formula XI to the aldehydes, for example by hydrogenation in the presence of a partially poisoned palladium catalyst, or by reducing the corresponding amino acid esters, for example the lower-alkyl esters, such as ethyl esters, with complex hydrides, for example borohydrides, such as sodium borohydride or, preferably, aluminium hydrides, for example lithium aluminium hydride, lithium tri-(tert-butoxy)aluminium hydride or, in particular, diisobutylaluminium hydride, in apolar solvents, for example in hydrocarbons or aromatic solvents, such as toluene, at from -100 to 0°C, preferably from -70 to -30°C, and first subsequently converting the products into the corresponding semicarbazones, for example using the corresponding acid salts of semicarbazones, such as semicarbazide hydrochloride, in aqueous solvent systems, such as alcohol/water, for example ethanol/water, at temperatures of between -20 and 60°C, preferably from 10 to 30°C, and then reacting the resulting semicarbazone with a reactive aldehyde, for example formaldehyde, in an inert solvent, for example a polar organic solvent, for example a carboxamide, such as dimethylformamide, at temperatures of between -30 and 60°C, preferably from 0 to 30°C, and then reacting with an acid, for example a strong mineral acid, such as hydrohalic acid, in aqueous solution, in the absence or presence of the solvent which was previously used, at temperatures of between -40 and 50°C, preferably between -10 and 30°C. The corresponding esters are obtained by reacting the amino acids with the corresponding alcohols, for example ethanol, in analogy with the conditions used in the condensation under process b), for example by reacting with inorganic acid halides, such as thionyl chloride, in organic solvent mixtures, such as mixtures of aromatic and alcoholic solvents, for example toluene and ethanol, at temperatures of between -50 and 50°C, preferably of between -10 and 20°C. In order to synthesize the compounds of the formula III or III', the compounds of the formula XII are then reacted with a reactive tetraalkylsilane, preferably a halomethyltri-lower-alkylsilane, such as chloromethyltrimethylsilane, in an inert solvent, for example an ether, such as diethyl ether, a cyclic ether, such as dioxane, or an ester, such as ethyl acetate, at temperatures of between -100 and 50°C, preferably of between -65 and 40°C, with compounds of the formula being obtained, in which R 6 , R 7 and R 8 are lower alkyl, for example methyl, and the remaining radicals are as defined above, the resulting compounds are converted, in the presence of a Lewis acid, such as boron trifluoride ethyl etherate, in an inert solvent, in particular a halogenated hydrocarbon, such as methylene chloride or chloroform, with subsequent aftertreatment with an aqueous base, for example sodium hydroxide solution, at temperatures of between -30 and 80°C, in particular of between 0 and 50°C, with elimination and protective group detachment, into olefinic compounds of the formula in which R 2 has the meanings specified for compounds of the formula I, an amino protective group Pa, for example tert-butoxycarbonyl, is once again introduced into the corresponding olefin, as described under process a) for the introduction of amino protective groups, in particular using an acid anhydride in a chlorinated hydrocarbon, such as methylene chloride or chloroform, at temperatures of between -50 and 80°C, in particular of between 0 and 35°C, with a protected amino-olefin of the formula being obtained in which the radicals are as defined above, the double bond is converted into an oxirane, preferably stereoselectively using peroxides, in particular peroxycarboxylic acids, for example haloperbenzoic acid, such as m-chloroperbenzoic acid, in an inert organic solvent, preferably a halogenated hydrocarbon, such as methylene chloride or chloroform, at temperatures of between -50 and 60°C, in particular of between -10 and 25°C, and, if required, a diastereomer resolution is undertaken, with epoxides of the formula in which the radicals are as defined above, being obtained, a suitable malonic add diester, for example dimethyl malonate or diethyl malonate, is added to the olefins concerned, for example by activating the methylene group of the malonic acid diester by means of an alkali metal, for example sodium, in a polar, anhydrous solvent, such as an alcohol, for example methanol or ethanol, at temperatures of between -50 and 80°C, in particular between 0 and 35°C, and the solution is treated with an acid, for example carboxylic acid, such as citric acid, with a lactone of the formula in which R 9 is lower alkoxy, for example methoxy or ethoxy, and the remaining radicals are as defined above, being obtained, the compounds of the formula XVII which are obtained directly are reacted with a reagent which introduces the R 3 -CH 2 - radical, for example of the formula R 3 -CH 2 -W in which R 3 has the meanings specified for compounds of the formula I and W is a nucleofugic leaving group, preferably selected from hydroxyl which is esterified with a strong inorganic or organic acid, such as hydroxyl which is esterified with a mineral acid, for example hydrohalic acid, such as hydrochloric acid, hydrobromic acid or hydriodic acid, with a strong organic sulfonic acid, such as a lower-alkanesulfonic acid which is unsubstituted or substituted, for example, by halogen, such as fluorine, or an aromatic sulfonic acid, for example a benzenesulfonic acid which is unsubstituted or substituted by lower alkyl, such as methyl, halogen, such as bromine, and/or nitro, for example a methanesulfonic, trimethanesulfonic or p-toluenesulfonic acid, and hydroxyl which is esterified with hydrazoic acid, in particular bromide, in an anhydrous polar solvent, for example an alcohol, such as ethanol, in the presence of an alkali metal, for example sodium, at temperatures of between -50 and 80°C, preferably of between 0 and 35°C, to form compounds of the formula in which the radicals are as defined above, the compounds of the formula XIX are hydrolysed and decarboxylated, for example by hydrolysis with a base, such as an alkali metal hydroxide, for example lithium hydroxide or NaOH, at temperatures of between -50 and 80°C, preferably of between about 0 and 35°C, in an organic solvent, for example an ether, such as 1,2-dimethoxyethane, or an alcohol, such as ethanol, and subsequent decarboxylation by heating in an inert solvent, preferably a hydrocarbon, for example an aromatic hydrocarbon, such as toluene, at temperatures of between 40 and 120°C, preferably of between 70 and 120°C, with a compound of the formula in which the radicals are as defined above, being obtained, the resulting (R,S,S) and (S,S,S) isomers are resolved by column chromatography, the (R,S,S) isomer is reused and, for opening the lactone ring, is reacted with a base, such as an alkali metal hydroxide, for example lithium hydroxide or sodium hydroxide, in an inert solvent, such as an ether, for example dimethoxyethane, or an alcohol, such as ethanol, to form a compound of the formula in which the radicals are as defined above, an hydroxyl protective group Py, for example one of the hydroxyl protective groups specified under process a), in particular a tri-lower-alkylsilyl group, is introduced, under the conditions specified there, Into the resulting compound using the corresponding halo-tri-lower-alkylsilane, for example tert-butyldimethylchlorosilane, in a polar solvent, such as a di-lower-alkyl-lower-alkanoylamide, such as dimethylformamide, in the presence of a sterically hindered amino compound, such as a cyclic amine, for example imidazole, at temperatures of from -50 to 80, preferably from 0 to 35°C, and the carboxyl group which is also silylated at the same time is set free once again by reaction with a basic metal salt, in particular an alkali metal hydroxide or alkali metal hydrogen carbonate or, preferably, an alkali metal carbonate, such as potassium carbonate, preferably in an alcohol, such as methanol or ethanol, a cyclic ether, such as tetrahydrofuran, in water or, in particular, a mixture of 2 or 3 of these solvents, at preferred temperatures of between 0 and 50°C, in particular of from 10 to 35°C, with a compound of the formula being obtained, in which the radicals are as defined above, and the compounds of the formula III or III' having the radicals given under process a) are prepared, for example, from one of the compounds of the formula XXII by condensation with a compound of the formula VI, in which the radicals have the meanings given under process c), under conditions which are analogous to those given for process a), in particular by in-situ reaction in the presence of a condensing agent, such as N,N-dicyclohexylcarbodiimide, ethyl cyanophosphonate, benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate or O-benzotriazol-1-yl-N,N,N',N'-tetramethyluronium hexafluorophosphate, a sterically hindered amine, such as triethylamine or N-methylmorpholine, and, if desired, a racemization-preventing compound, such as 1-hydroxybenzotriazole, in a polar solvent, preferably an acid amide, for example a di-lower-alkylamino-lower-alkanoylamide, such as dimethylformamide, a cyclic ether, such as tetrahydrofuran, or a nitrile, such as acetonitrile, at preferred temperatures of between -50 and 80°C, in particular of between 0 and 35°C, if desired under protective gas, such as argon or nitrogen, and by the subsequent detachment of the protective group Pa under analogous conditions, as described under process e), (provided Pa is not a radical which corresponds to the radical R 1 having the meanings presented above for compounds of the formula I, which would lead directly to compounds of the formula I) and finally, if desired, the detachment of Py and/or further protective groups under analogous conditions to those described under process e). In order to prepare the compounds of the formula III or III', it is also possible successively to condense the compounds of the formula XXII with compounds which introduce the radicals -HN-(CHR 4 )-CO- (starting material: the corresponding amino adds H 2 N-(CHR 4 )-COOH) and -NH-CH 2 -(CH 2 ) n -O-R 5 (starting material: the corresponding amino compound H 2 N-CH 2 -(CH 2 ) n -O-R 5 ) of the compound of the formula III or III', under conditions which are analogous to those specified for process a), preferably by reacting a compound which is analogous to the compound of the formula (i) V or V', (ii) VII or VII' or (iii) IX or IX', in which hydrogen is present in place of R 1 , with a compound of the formula (i) VI or VI' (corresponds to a compound of the formula XXII in which Pa = hydrogen), (ii) VIII or (iii) X, where the remaining radicals in each case have the specified meanings and the starting materials can also be present as the reactive derivatives, in analogy with the conditions specified under (i) process b), (ii) process c) or (iii) process d), with it being possible to detach the protective group Py from compounds of the formula III or III' using one of the methods described under process e). The following route can also be taken for preparing a compound of the formula XX from an abovementioned compound of the formula XVII: Hydrolysis of a racemic compound of the formula XVII (which can be prepared from the racemate of a compound of the formula XV via the corresponding racemate of a compound of the formula XVI) and decarboxylation under conditions analogous to those for the hydrolysis and decarboxylation of compounds of the formula XIX leads to a compound which is analogous to the compound of the formula XIX in which, however, the radicals R 3 -CH 2 - and R 9 -(C=O)- are missing (in both cases, a hydrogen atom Is present instead) and which is present as a racemate (or as a diastereomer mixture providing an additional centre of asymmetry is present in R 3 and/or R 9 ); this latter compound is subsequently reacted with a compound of the formula XVIII, as defined above, in which W is one of the abovementioned nucleofugic leaving groups, in particular halo, such as iodine or, preferably, bromine or chlorine, by first deprotonating it in the presence of a strong base, such as an alkali metal bis(tri-lower-alkylsilyl)amide, for example lithium bis(trimethylsilyl)amide, and then alkylating it with the compound of the formula R 3 -CH 2 -W (preferably obtaining the [1'(S),3(R)-(R 3 -CH 2 -),5(S)]- and the [1'(R),3(S)-(R 3 -CH 2 -),5(R)] compounds of the formula XX, i.e. a racemate as regards the said asymmetric carbon atoms). The abovementioned compounds of the formula XIV can also be present in the (R,S) configuration instead of the indicated (S) configuration at the carbon atom carrying the -NH 2 radical, while the compounds of the formulae XI, XII and XIII and, in particular, those of the formulae XV, XVI, XVII, XIX, XX, XXI and/or XXII can also be present in the (R,S) configuration instead of the (S) configuration at the carbon atom carrying the Pa-NH-radical. The abovementioned compounds of the formulae XV, XVI and XVII can also be present as racemates. Other mixtures of the optical antipodes of the indicated formulae are also possible. Corresponding compounds of the formula V, for example, can be obtained from these racemates or mixtures (for example racemates or antipode mixtures if R 1 does not contain any centres of assymetry), so that, in this way, compounds of the formula I or I' are accessible in which either the carbon atom carrying R 2 -CH 2 - is in the (S) configuration, the carbon atom carrying HO- is in the (S) configuration and the carbon atom carrying R 3 -CH 2 - is in the (R) configuration (2R,4S,5S), or the said carbon atoms have the opposite configuration (2S,4R,5R); or else mixtures of compounds of the formula V or I are present which have both these configurations. Corresponding racemic mixtures or diastereomer mixtures can be dissolved at suitable stages (preferably) into individual isomers. Compounds of the formula XX, in which the radicals have the said meanings, are prepared from compounds of the formula XII, in which the radicals have the said meanings, by reacting the aldehydes of the formula XII with 2-halopropionic acid esters, in particular lower-alkyl 2-iodopropionates, such as ethyl 2-iodopropionate, with the compounds of the formula being obtained, in which the radicals have the said meanings and in which the carbon atom carrying the Pa-NH- radical can also, altematively, be present, for example, in the (R,S) configuration. The reaction initially takes place with the formation of the homoenolate of the 2-halopropionic acid-lower-alkyl(such as ethyl) ester In the presence of a mixture of Zn/Cu in a di-lower-alkyl-lower-alkanoylamide, such as dimethylacetamide, or of an aromatic hydrocarbon, such as toluene, or mixtures thereof, at temperatures of between 0 and 100°C, in particular of between 20 and 80°C, if desired under protective gas, such as argon or N 2 . In a subsequent reaction mixture, a suitable tetra-lower-alkyl orthotitanate, such as tetraisopropyl orthotitanate, is treated, preferably under a protective gas, such as nitrogen or argon, in an aromatic solvent, such as toluene or xylene, in the presence of a halohydrocarbon, such as methylene chloride, with a titanium tetrahalide, such as titanium tetrachloride, at from -50 to 50°C, preferably at from -40 to 25°C, and the mixture is stirred, with the corresponding dihalo-titanium-di-lower-alkylate or, preferably, the trihalo-titanium-lower-alkylate, in particular trichlorotitanium diisopropylate, being formed. The Zn-homoenolate solution is added dropwise to the latter at temperatures of between -50 and 0°C, in particular of from -40 to -25°C, and the aldehyde of the formula XII in a halohydrocarbon, for example methylene chloride, is subsequently added dropwise, with the reaction taking place at from -50 to 30°C, preferably at from about -40 to 5°C, with the formation of the lower-alkyl-(in particular ethyl) ester precursor, in particular the ethyl ester, of the compound of the formula XXIII. This ester is then hydrolysed and cyclized with the formation of the compound of the formula XXIII, as defined above, preferably in an organic solvent, such as an aromatic compound, for example in toluene or xylene, in the presence of an acid, such as a carboxylic acid, for example acetic acid, at temperatures of between 20°C and the boiling point of the reaction mixture, in particular between 70 and 100°C. If necessary, the diastereomers are separated, for example by means of chromatography, for example on silica gel using an organic solvent mixture, such as a mixture of alkane and ester, such as lower alkane and lower-alkyl-lower-alkanoyl ester, such as hexane/ethyl acetate. The corresponding compound of the formula XX is then obtained from the compound of the formula XXIII by deprotonation with a strong base, with the formation of the carbanion at the α-carbon next to the oxo group of the lactone, and subsequent nucleophilic substitution of the W radical of a compound of the formula XVIII, in which R 3 and W are defined as above in association with the preparation of compounds of the formula XIX (W is, in particular, bromo), with the reaction preferably leading stereoselectively to the (R) configuration at the carbon atom in the compound of the formula XX which carries the R 3 -CH 2 - radical. The reaction with the strong base, in particular with an alkali metal-organosilicon amide compound, for example an alkali metal bis(tri-lower-alkylsilyl)amide, such as lithium bis(trimethylsilyl)amide, or else an alkali metal di-lower-alkylamide, such as lithium diisopropylamide, is preferably carried out in an inert organic solvent, in particular an ether, for example a cyclic ether, such as tetrahydrofuran, or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), or mixtures of these solvents, at temperatures of between -100 and 0°C, preferably of between -78 and -50°C, while the nudeophilic substitution is carried out in situ by adding the compound of the formula R 3 -CH 2 -W in the same solvent and at temperatures of between -100 and 0°C, preferably of between -60 and -40°C. A compound of the formula XIV, in which the radicals have the said meanings, and in which the carbon atom carrying the -NH 2 group is preferably in the (R,S) configuration, can also be obtained by converting a formic acid ester, for example lower-alkyl formate, such as ethyl formate, into formic acid allylamide by reacting it with allylamine at temperatures of between 20 and 70°C, in particular of between 50 and 60°C. This amide is then dehydrated under a protective gas, such as nitrogen or argon, preferably using an acid halide, such as phosphorus oxychloride, phosgene or, in particular, an organic sulfonyl halide, for example an arylsulfonyl chloride, such as toluenesulfonyl chloride, in the presence of a base, for example a tri-lower-alkylamine, such as triethylamine, or, in particular, a mono- or bi-cyclic amine, such as pyridine or quinoline, at temperatures of between 50 and 100°C, in particular of between about 80 and about 100°C. This results in the formation of allyl isocyanide, which is converted into the corresponding lithium salt by reaction with an organolithium salt, for example lower-alkyllithium, such as n-butyllithium, with the reaction preferably being carried out in an inert organic solvent, in particular an ether, such as dioxane or diethyl ether, or an alkane, for example hexane, or a mixture of these solvents, at temperatures of from -120 to -50, in particular of from about -100 to -70°C. The lithium salt which has been formed is then reacted in situ with a compound of the formula R 2 -CH 2 -W, in which R 2 has the meanings specified for compounds of the formula I and W has the meanings specified above for compounds of the formula XVIII, in particular bromine, preferably by adding R 2 -CH 2 -W dropwise in an organic solvent, for example an ether, such as tetrahydrofuran, at the temperatures mentioned immediately above, and then warming to from 0 to 50°C, preferably to from 20 to 30°C. This results in the formation of an isocyanide of the formula in which the radicals have the said meanings. The compound of the formula XXIV is subsequently hydrolysed, preferably in aqueous solution to which an acid is added, for example in aqueous hydrohalic acid, such as hydrochloric acid, in particular in concentrated hydrochloric acid, at temperatures of between -20 and 30°C, in particular of between about 0 and 10°C, and the compound of the formula XIV is obtained, in which the radicals are defined as most recently above and in which the carbon atom carrying the -NH 2 group is preferably in the (R,S) configuration. Amino compounds of the formula IIIa or IIIa', or their reactive derivatives, are known or can be prepared by methods which are known per se, for example by condensing amino acids of the formula H-B 1 -OH, in which B 1 has the meanings specified for compounds of the formula III or III', or reactive derivatives thereof, with amino compounds of the formula III or III', or reactive derivatives thereof, with the reactive derivatives and the condensation conditions being analogous to those described under process a). Compounds of the formula V or V' are prepared, for example, provided the protective group Pa in formula XXI or XXII does not correspond directly to an R 1 radical, from the amino compounds of the formula XXI or XXII, for example by introducing a carboxyl protective group, as described under process e), and detaching the protective group Pa, as described under process e), by condensation with a carboxylic acid of the formula R 1 -OH, or a reactive derivative thereof, in which the radicals have the meanings specified for compounds of the formula I, under conditions which are analogous to the condensation conditions specified for process a). Compounds of the formula XXA or XXA' are prepared, for example, provided the protective group Pa in the formula XX does not correspond directly to an R 1 radical, from the γ-lactone compounds of the formula XX (preferably from the (R,S,S) isomer), for example by detaching the protective group Pa, as described under process e), by condensation with a carboxylic acid of the formula R 1 -OH, or a reactive derivative thereof, in which the radicals have the meanings specified for compounds of the formula I, under conditions which are analogous to the condensation conditions specified for process a). Compounds of the formula VI (or VI') are prepared, for example, from the corresponding amino acids of the formula (in particular of the formula in which the radicals have the said meanings, or reactive acid derivatives thereof, and the amino component of the formula VIII, in which the radicals are in each case defined as above, or reactive derivatives thereof, by condensation in analogy with the method described under process a) and, if desired, using analogous reactive derivatives. Compounds of the formula VII (or VII') can be prepared, for example, from compounds of the formula V (or V') by condensation with an amino acid of the formula XXV (or XXV'), as defined immediately above, which introduces the radical -NH-CH(R 4 )-COOH. The reaction is carried out in analogy with the conditions described under process a) using the corresponding free compounds or their reactive derivatives; or they can be prepared from compounds of the formula XXA (or XXA') by condensation with an amino acid of the formula XXV (or XXV'), as defined immediately above, which introduces the radical -NH-CH(R 4 )-COOH. The reaction is carried out in analogy with the conditions described under process b) using the corresponding γ-lactones of the formula XXA, in particular XXA'. The amino compound of the formula VIII is known or is prepared by methods which are known per se. Compounds of the formula IX (or IX') are known or can be prepared by methods which are known per se, and are obtained, for example, by the condensation of a compound of the formula VII (or VII'), in which the radicals have the said meanings, and an (if necessary hydroxyl-protected) amine of the formula H 2 N-CH 2 -(CH 2 ) n -OH or a reactive derivative thereof, in which n has the meanings given for compounds of the formula I, under reaction conditions analogous to those described under process a). Compounds of the formula X or Xa are known, are commercially available, or can be prepared by methods which are known per se. Compounds of the formula XVIII and the formula R 2 -CH 2 -W are known or can be prepared by methods which are known per se, or they can be obtained commercially. As an example, mention may be made of the preparation of a compound of the formula XVIII or R 2 -CH 2 -W, in which W is Br or I, by reacting the corresponding precursor, in which W is Cl, with an alkali metal iodide or bromide, such as Nal, for example in ketones, such as a lower-alkanone, for example acetone, at temperatures of between 0 and 50°C, in particular room temperature, or with a phosphorus tri- or penta-iodide or -bromide, such as PBr 3 , for example in hydrocarbons, for example an aromatic hydrocarbon, such as toluene, at preferred temperatures of between 0 and 40°C, for example at room temperature. The precursor (W = Cl) is commercially obtainable, Is known or can be prepared by methods which are known per se. For example, a precursor, in which a hydroxyl group is present in place of the Cl (= W), can be converted into the corresponding chlorinated compound by reaction with PCl 3 , PCl 5 or, in particular, SOCl 2 , in the presence of a tertiary nitrogen base, for example polyhünig base or pyridine, in suitable solvents, for example an ether, such as diethyl ether, or a halohydrocarbon, such as methylene chloride or chloroform, at preferred temperatures of between -10 and 30°C, preferably of between 0 and 25°C. The precursors in which a hydroxyl group is present in place of W are known, can be prepared by methods which are known per se, or are commercially available. The remaining starting compounds are known, are prepared by methods which are known per se, and/or are commercially available. Examples: The following examples serve to illustrate the invention but do not, in any way, restrict its scope. Temperatures are given in degrees centigrade (°C). If no temperature is given, the reactions mentioned below take place at approximately room temperature. The R f values, which indicate the ratio of the distance migrated by the particular substance to the distance migrated by the eluent front, are determined by thin layer chromatography (TLC) on silica gel thin layer plates (Merck, Darmstadt, FRG) using the following solvent systems: TLC eluent systems: TLC eluent systems: A Ethyl acetate B Methylene chloride/methanol 9:1 C Hexane/ethyl acetate 1:1 D Hexane/ethyl acetate 2:1 E Hexane/ethyl acetate 3:1 F Methylene chloride/methanol 12:1 G Hexane/ethyl acetate 6:1 H Methylene chloride/THF 2:1 I Methylene chloride/ether 25:1 J Hexane/ethyl acetate 1:2 K Chloroform/methanol/water/acetic acid 85:13:1.5:0.5 L Methylene chloride/methanol 10:1 M Methylene chloride/methanol 15:1 N Ethyl acetate/methanol 9:1 O Methylene chloride/ethanol 10:1 P Methylene chloride/ethyl acetate/ ethanol 30:20:1 Q Toluene/ethyl acetate 9:1 R Methylene chloride/THF 4:1 The abbreviation "R f (A)" means, for example, that the R f value was determined in the solvent system A. The ratio of the quantities of solvents with respect to each other is always given in parts by volume (v/v). Quantity ratios are also given in parts by volume when defining the mobile solvent systems for the column chromatography. Part of the abovementioned letter code for TLC eluents is also used, for example, for indicating eluents in column chromatography. Medium pressure chromatography: Phase: LiChroprep® Si 60 (Merck, Dietikon/Switzerland); pressure: 10-15 bar. HPLC gradients: I 20 % → 100 % a) Into b) over 35 min II 20 % → 100 % a) into b) over 20 min III 5 % → 40 % a) into b) over 15 min Eluent a): acetonitrile + 0.05 % TFA; eluent b): water + 0.05 % TFA. Column (250 x 4.6 mm) filled with C 18 -Nucleosil® reversed-phase material (silica gel, of 5 µm average particle size, which is covalently derivatized with octadecylsilanes, Macherey & Nagel, Düren, FRG). Detection by UV absorption at 215 nm. The retention times (t Ret ) are given in minutes. Flow speed, 1 ml/min. Mass spectroscopic measurements are as a rule obtained by the fast-atom bombardment method. Unless otherwise indicated, the mass values relate to the protonated molecule ion (M+H) + . The values for IR spectra are given in cm -1 , with the relevant solvent being given in round brackets. The abbreviations which are customary in peptide chemistry are used to designate bivalent radicals of natural α-amino acids. Provided it is known, the configuration at the α-carbon atom is indicated by prefixing with (L)- or (D)-. Glycyl which is bonded to the remainder of the molecule via the amino nitrogen and the carboxyl carbon is indicated by-[(cyclohexyl)Gly]- when it is substituted at the α-carbon atom by a cyclohexyl radical and by -[(phenyl)Gly]- when it is substituted at the α-carbon atom by a phenyl radical. Abbreviations: abs. absolute (indicates that the solvent is anhydrous) anal. calc. calculated value for elementary analysis (theoretical value) anal. found found value for elementary analysis (actual value) atm atmosphere (1 atm corresponds to 1.013 bar) Boc tert-butoxycarbonyl BOP benzotriazol-1-yloxytris(dimethylamino) phosphonium hexafluorophosphate TLC thin layer chromatography DCC dimethoxyethane dicyclohexylcarbodiimide 1,2-dimethoxyethane DIPE diisopropyl ether DMF dimethylformamide DMPU 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)pyrimidinone EDC N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide hydrochloride ether diethyl ether sat. saturated h hour(s) HBTU O-benzotriazol-1-yl-N,N,N',N'-tetra methyluronium hexafluorophosphate HOBT 1-hydroxybenzotriazole HV high vacuum min minute(s) MS mass spectroscopy sodium sulfate indicates disodium sulfate (Na 2 SO 4 ) NMM N-methylmorpholine RT room temperature RE rotary evaporator saline saturated solution of sodium chloride THF tetrahydrofuran TBAF tetrabutylammonium fluoride trihydrate Z benzyloxycarbonyl Example 1: 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 95 mg (0.301 mmol) of TBAF are added, under a N 2 atmosphere, to a solution of 135 mg (0.151 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 1.3 ml of DMF, and the mixture is stirred at RT for 16 h. The reaction mixture is poured onto water and this mixture is extracted with 4 portions of ethyl acetate. The organic phases are washed with sat. NaHCO 3 solution, water and saline, dried with Na 2 SO 4 and evaporated. Digesting twice with DIPE yields the pure title compound: t Ret (II)=18.5 min; FAB-MS (M+H) + =782. The starting material is prepared as follows: 1a) Z-(L)-Val-N-(2-methoxyethyl)amide 19.8 g (78.8 mmol) of Z-(L)-valine in 720 ml 0.25M NMM/CH 3 CN are treated, under protective gas, with 7.5 ml (87.3 mmol) of 2-methoxy-ethylamine (Fluka; Buchs/Switzerland). 32.3 g (85.2 mmol) of HBTU are added to the thick, white suspension, and this mixture is thoroughly stirred at RT for 24 h. The reaction mixture is evaporated under high vacuum and the residue is taken up in ethyl acetate; the solution is extracted with water, 2x 10 % citric acid solution, water, 2x sat NaHCO 3 solution and saline. The aqueous phases are extracted twice more with ethyl acetate, and the organic phases are dried with Na 2 SO 4 and evaporated. Crystallization from ethyl acetate/hexane 1:1 leads to the title compound: TLC R f (G)=0.6; t Ret (II)=11.5 min. 1b) H-(L)-Val-N-(2-methoxyethyl)amide Hydrogenating 22.8 g (74 mmol) of Z-(L)-Val-N-(2-methoxyethyl)amide in 496 ml of methanol, at RT under low pressure and in the presence of 2.3 g of 10 % Pd/C, yields, after filtering off the catalyst, evaporating the filtrate and column chromatography (SiO 2 , methylene chloride using 2.5 → 5 → 7.5 → 10 % methanol), the pure title compound as an oil: TLC R f (B)=0.3; FAB-MS (M+H) + =175; 1 H-NMR (360 MHz, CD 3 OD): 0.90 and 0.95 (2d, J=7 Hz, (H 3 C) 2 C), 1.9 (m, HC-Me 2 ), 3.05 (d, J=6 Hz, HCα), 3.32 (s, H 3 C-O), 3.37 (m, H 2 C), 3.44 (m, H 2 C). 1c) 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Under an N 2 atmosphere, 100 mg (0.135 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyl-dimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid [preparation, see Example 1j)] and 26 mg (0.148 mmol) of H-(L)-Val-N-(2-methoxyethyl)-amide are dissolved in 1.2 ml of 0.25M NMM/CH 3 CN, and the solution is treated with 56.3 mg (0.148 mmol) of HBTU. After 18 h at RT, the reaction mixture is evaporated and the residue is taken up in ethyl acetate; the solution is thoroughly washed with water, 2 portions of 10 % citric acid solution, water, 2 portions of sat. NaHCO 3 solution and, finally, saline. The inorganic phases are extracted two more times with ethyl acetate and the organic phases are dried with Na 2 SO 4 and evaporated to give the title compound: t Ret (II)=24.4 min; FAB-MS (M+H) + =896. 1d) p-Benzyloxybenzyl iodide A solution of 1.0 g (4.3 mmol) of 4-benzyloxybenzyl chloride (Fluka; Buchs/Switzerland) in 8 ml of acetone is stirred at RT with 3.13 g (20.9 mmol) of sodium iodide. After 90 min, a gas chromatogram of the reaction mixture indicates that the reaction is complete; the reaction mixture Is therefore poured onto ether, and this mixture is washed with 10 % sodium thiosulfate solution and saline. Drying the organic phase with Na 2 SO 4 , and evaporating, yields the title compound: 1 H-NMR (200 MHz, CDCl 3 : 4.48 (s, 2 H), 5.06 (s, 2 H), 6.85-6.95 (m, 2 H), 7.25-7.48 (m, 7 H). 1e) (S)-N-Boc-(p-Benzyloxyphenylalaninol) 37.1 g (100 mmol) of Boc-(L)-(p-benzyloxy)phenylalanine (Bachem; Bubendorf/Switzerland) in 116 ml of THF are treated, at from -5°C to -10°C, with 15.33 ml (110 mmol) of triethylamine, and a solution of 14.36 ml (110 mmol) of isobutyl chloroformate in 70 ml of THF is added to this mixture. After stirring at RT for 0.5 h, the precipitate which has formed is filtered off with suction. The filtered reaction mixture is added dropwise to 7.57 g (200 mmol) of sodium borohydride and 44 ml of H 2 O (approximately 10 - 15°C), and this mixture is thoroughly stirred at RT for 3.5 h. The pH of the mixture is adjusted to 2 by adding 10 % citric acid solution, and the mixture is partially evaporated on an RE. The residue is extracted with 3 portions of ethyl acetate, and the organic phases are washed with 2x 2N NaOH, saline, saturated NaHCO 3 solution and saline, dried with Na 2 SO 4 and evaporated; the crude product is digested in hexane to give the title compound: TLC R f (C)=0.50; FAB-MS (M+H) + =358. 1f) (S)-N-Boc-(p-Benzyloxyphenylalaninal) 4.76 g (37.5 mmol) of oxalyl chloride in 33.6 ml of methylene chloride are treated dropwise, at -60°C and under a N 2 atmosphere, with a solution of 3.5 ml (49 mmol) of DMSO in 60 ml of methylene chloride. After the mixture has been stirred for 15 min, 8.94 g (25 mmol) of (S)-N-Boc-(p-benzyloxyphenylalaninol) in 150 ml of methylene chloride are added, and this mixture is subsequently stirred for about 25 min. 14 ml (100 mmol) of triethylamine in 30 ml of methylene chloride are then added and the mixture is stirred for 30 min. 222 ml of a 20 % of a KHSO 4 solution and 187 ml of hexane are added, and the mixture is warmed to 0°C. The aqueous phase is separated off and extracted 2x with ethyl acetate. The organic phases are washed with saturated NaHCO 3 solution and saline, dried with Na 2 SO 4 and evaporated to give the title compound: TLC R t (C)=0.71; 1 H-NMR (200 MHz, CDCl 3 ): 1.44 (s, 9 H), 3.06 (d, J=6 Hz, 2 H), 4.39 (m, 1 H), 5.03 (s + sb, H 2 C-O + HN), 6.86-6.98 and 7.03-7.15 (2m, each 2 H), 7.30-7.48 (m, 5 H), 9.62 (s, 1 H). 1g) 5(S)-[1(S)-(Boc-Amino)-2-(p-benzyloxyphenyl)ethyl]dihydrofuran-2-(3H)-one (see A.E. DeCamp et al., Tetrahedron Lett. 32 , 1867 (1991)) 6.0 g (91.8 mmol) of Zn/Cu (preparation: see R.D. Smith, H.E. Simmons, W.E. Parham, M.D. Bhavsar, Org. Synth., Coll. Vol 5 , 855 (1973)) and 9.69 ml of dimethylacetamide are added, under an N 2 atmosphere, to a solution of 7.7 ml (57.1 mmol) of ethyl 2-iodopropionate (Example 1k)) in 100 ml of toluene, and this mixture is subsequently stirred vigorously at RT for 1 h and at 80°C for 4 h (→ Zn homoenolate solution). In a second apparatus, a solution of 4.17 ml (14.2 mmol) of tetraisopropyl orthotitanate in 12 ml of toluene and 69 ml of methylene chloride is treated, under an N 2 atmosphere and while cooling slightly, with 4.41 ml (40.2 mmol) of TiCl 4 ; this mixture is stirred at RT for 15 min (results in a yellow solution) and cooled down to -40°C, resulting in trichiorotitanium isopropoxide being obtained. The Zn homoenolate solution is decanted off from the metallic solid and transferred by means of a cannula to the trichlorotitanium isopropoxide, which has been cooled down to -40°C, with the temperature being maintained at from -40 to -30°C (deep-red solution). The solution is warmed to -25°C for 5 min and then cooled down once again to -40°C. A solution of 9.7 g (27 mmol) of (S)-N-Boc-(p-benzyloxyphenyl)alaninal in 24.5 ml of methylene chloride is then added dropwise and the mixture is subsequently stirred at approximately -20°C for 15 h and finally at 0°C for 1 h. The reaction mixture is poured onto 0.4 kg of ice-water and 0.5 I of ether, and this mixture is stirred vigorously for 10 min. The aqueous phase is separated off and extracted with 2 portions of ether; the organic phases are washed with water, sat. sodium hydrogen carbonate solution, water and saline, dried with sodium sulfate and evaporated (→ crystalline ethyl 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)hexanoate). The intermediate mentioned immediately above is heated in 220 ml of toluene and 6.73 ml of acetic acid at 100°C for 2.5 h. The cooled reaction mixture is treated with 0.5 I of water, and the aqueous phase is separated off and extracted with 2 portions of ether; the org. phases are washed with sat. sodium hydrogen carbonate solution, water and saline, dried with sodium sulfate and evaporated. Crystallization of the residue from ether/hexane yields the pure title compound: TLC R f (E)=0.28; t Ret (I)=23.5 min; 1 H-NMR (200 MHz, CDCl 3 ): 1.40 (s, 9 H), 2.03-2.2 and 2.44-2.64 and 2.73-2.98 (3m, each 2 H), 3.95 and 4.48 (2m, each 1 H), 4.62 (d, J=9 Hz, 1 H), 6.87-6.97 and 7.09-7.21 (2m, each 2 H), 7.27-7.48 (m, 5 H). 1h) 5(S)-[1(S)-(Boc-Amino)-2-(p-benzyloxyphenyl)ethyl]-3(R)-[(p-benzyloxyphenyl)-methyl]dihydrofuran-2-(3H)-one 2.47 g (6.0 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]dihydrofuran-2-(3H)-one dissolved in 12 ml of THF and 1.2 ml of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone are treated, at -70°C and under a protective gas, with 11.73 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and this mixture is stirred for 15 min; it is then alkylated with 1.946 g (6.0 mmol) of p-benzyloxybenzyl iodide (Example 1d)) in 3 ml of THF (60 min). For hydrolysing, 2.23 ml of propionic acid and 2.23 ml of water are added and the mixture is warmed to 0 °C. The reaction mixture is poured onto 30 ml of 10 % citric acid solution, and this mixture is extracted twice with ethyl acetate; the organic phases are washed twice with saturated NaHCO 3 solution and, finally, with saline. Drying the organic phases with Na 2 SO 4 and evaporating them, and column chromatography (SiO 2 , hexane/ethyl acetate 4:1) of the residue, and subsequent crystallization from ethyl acetate/hexane, affords the pure title compound: TLC R f (D)=0.45; t Ret (I)=19.9 min; FAB-MS (M+H) + =608. 1i) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)-methyl]hexanoic acid 2.7 g (4.43 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]-3(R)-[(p-benzyloxyphenyl)methyl]dihydrofuran-2-(3H)-one in 59 ml of dimethoxyethane and 31.8 ml of water are treated, while excluding air, with 14.8 ml of a 1 M lithium hydroxide solution. The mixture is then stirred at RT for 3 h and partially evaporated. The residue is poured onto a mixture of ice, 181 ml of sat. NH 4 Cl solution, 16.2 ml of 10 % citric acid solution and 400 ml of ethyl acetate, and THF is added until the precipitated solid dissolves. The aqueous phase is separated off and extracted with 2 portions of ethyl acetate, and the organic phases are washed with saline, dried with Na 2 SO 4 , evaporated and digested in hexane: TLC R f (C)=0.07. 1j) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxy-phenyl)-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid 2.44 g (3.90 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoic add in 14 ml of DMF are stirred, under an N 2 atmosphere, together with 2.70 g (17.6 mmol) of tert-butyldimethylchlorosilane and 2.18 g (32 mmol) of imidazole at RT for 18 h. The reaction mixture is poured onto ice-water, and this mixture is extracted with 3 portions of ethyl acetate; the organic phases are washed with 10 % citric acid solution, H 2 O and saline, dried with Na 2 SO 4 and evaporated. The resulting oil is taken up in 30 ml of methanol/THF/H 2 O 3:1:1, and this solution is treated with 3.2 g of K 2 CO 3 and stirred at RT for 1 h. The reaction mixture is partially evaporated, and the aqueous residue is poured onto 10 % citric add solution and ice, and this mixture is extracted 3 x with ethyl acetate; the organic phases are washed twice with H 2 O and, finally, with saline, dried with Na 2 SO 4 and evaporated. Column chromatography (SiO 2 , hexane/ethyl acetate 2:1 → 1:1) of the crude product affords the title compound: TLC R f (C)=0.53; FAB-MS (M+H) + =740. 1k) Ethyl 2-iodopropionate A suspension of 170 ml of ethyl 2-bromopropionate (Fluka; Buchs/Switzerland) and 950 g of sodium iodide in 1.8 I of acetone is stirred at 60°C for 20 h. The reaction mixture is filtered, and the filtrate is partially evaporated, with the residue being poured onto approximately 2.5 I of ether; this mixture is washed with 1.0 I of 1 % sodium thiosulfate solution and, finally, saline, dried with sodium sulfate and evaporated. Distillation (83°C, 20 mbar) affords the pure title compound: MS (M) + =228; 1 H-NMR (200 MHz, CDCl 3 ): 4.17 (q, 7 Hz, 2 H), 3.34 and 2.97 (2t, 7 Hz, 2x 2H), 1.28 (t, 7 Hz, 3 H). Example 2: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-cyanophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1), 2.73 g (3.85 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyl-dimethylsilyloxy)-6-phenyl-2(R)-[(p-cyanophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 90.4 ml of DMF are desilylated with 3.65 g (11.6 mmol) of TBAF, and worked up. Crystallization from methylene chloride/hexane results in the title compound: t Ret (II)=14.0 min; FAB-MS (M+H) + =595. The starting material is prepared as follows: 2a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(p-cyanophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 2.173 g (3.93 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(p-cyanophenyl)methyl]hexanoic acid [preparation, see Example 2e)], 839 mg (4.07mmol) of DCC and 596mg (4.41 mmol) of HOBT are added, while excluding air, to the solution of 753.2 mg (4.32 mmol) of H-(L)-Val-N-(2-methoxy-ethyl)amide (Example 1b) in 47 ml of THF. After 24 h at RT, the reaction mixture is filtered and the filtrate is evaporated. The residue is partitioned between 3 portions of ethyl acetate, 10 % citric acid solution, sat. NaHCO 3 solution and saline. Drying the organic phases with Na 2 SO 4 , evaporating them, and stirring up the residue in DIPE yields the title compound: t Ret (II)=20.8 min. 2b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]dihydrofuran-2-(3H)-one (see, also, A.E. DeCamp, A.T. Kawaguchi, R.P. Volante, and I. Shinkai, Tetrahedron Lett. 32 , 1867 (1991)).8.03 g of Zn/Cu (preparation: R.D. Smith, H.E. Simmons, W.E. Parham, M.D. Bhavsar, Org. Synth., Coll. Vol 5 , 855 (1973)) and 12.96 ml of dimethylacetamide are added, under a N 2 atmosphere, to a solution of 17.4 g of ethyl 2-iodopropionate (Example 1k)) in 130 ml of toluene, and the mixture is subsequently stirred vigorously at RT for 1 h and at 80°C for 4 h (→ Zn homoenolate solution). In a second apparatus (N 2 atmosphere), a solution of 5.58 ml (18.9 mmol) of tetraisopropyl orthotitanate in 16.4 ml of toluene and 91.8 ml of methylene chloride is treated, while cooling slightly, with 5.90 ml (53.8 mmol) of titanium tetrachloride, and this mixture is stirred at RT for 15 min (→ yellow solution) and cooled down to -40°C (→ partial crystallization of the trichlorotatanium isopropoxide). Using a cannula, the Zn homoenolate solution, which has been cooled down to RT, is decanted off from the metallic solid and added dropwise to the trichlorotitanium isopropoxide, with the temperature being maintained at from -40°C to -30°C (→ deep-red solution); the mixture is warmed to -25°C for 5 min and then cooled down once again to -40°C. A solution of 9.0 g of (S)-N-Boc-phenylalaninal (preparation: see D.J. Kempf, J. Org. Chem. 51 , 3921 (1986)) in 32.8 ml of methylene chloride is subsequently added dropwise, and this mixture is stirred at approximately -20°C for 15 h and, finally, at 0°C for 1 h. The reaction mixture Is poured onto 0.5 kg of ice-water and 0.5 I of ether, and this mixture is stirred vigorously for 10 min. The aqueous phase is separated off and extracted with 2 portions of ether, the organic phases are washed with 2 portions of water, saturated sodium hydrogen carbonate solution and saline, dried with sodium sulfate and evaporated. Crystalline ethyl 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl hexanoate Is obtained as an intermediate. This intermediate is heated at 80°C for 2.5 h in 295 ml of toluene and 9 ml of acetic acid. The reaction mixture is treated with 0.51 of water, and the aqueous phase is separated off and extracted with 2 portions of ether; the org. phases are washed with saturated sodium hydrogen carbonate solution, water and saline, and dried with sodium sulfate. Partial evaporation of the organic phases, and treatment with hexane, affords the crystalline title compound, approximately 10 % of which consists, according to analysis, of the (5R) epimer (TLC R f (E)=0.08). Column chromatography (SiO 2 , hexane/ethyl acetate 2:1) yields the pure title compound: TLC R f (E)=0.14; [α] D =17.7° (c=1; ethanol). 2c) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(p-cyano-phenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 1h), 1.5 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one, dissolved in 32 ml of THF, are deprotonated with 9.8 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated with 1.0 g of 4-bromomethylbenzonitrile (Fluka; Buchs/Switzerland) dissolved in 3 ml of THF. Column chromatography (SiO 2 , hexane/ethyl acetate 1:1) affords the pure title compound: TLC R f (D)=0.33. 2d) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-cyanophenyl)methyl]hexanolc acid In analogy with Example 1i), 0.50 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(p-cyanophenyl)methyl]dihydrofuran-2-(3H)-one in 19 ml of dimethoxyethane and 10 ml of water is hydrolysed with 4.8 ml of a 1 M lithium hydroxide solution to form the title compound: TLC R f (B)=0.3. 2e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(p-cyan ophenyl)methyl]hexanoic acid In analogy with Example 1j), 0.62 g of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-cyano-phenyl)methyl]hexanoic acid In 6.2 ml of DMF is silylated with 0.98 g of tert-butyldimethylchlorosilane and 0.79 g of imidazole. Hydrolysis of the silyl ester function with 1.2 g of potassium carbonate in 31 ml of methanol/THF/water, 3:1:1, yields the title compound, after acidifying with citric acid solution and extracting with ethyl acetate: TLC R f (D)=0.29; FAB-MS (M+H) + =553. Example 3: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(o-fluorophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1), 184.9 mg (0.263 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(o-fluorophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 5 ml of DMF are desilylated with 249.3 mg (0.79 mmol) of TBAF, and worked up. Stirring-up with DIPE affords the title compound: t Ret (II)=14.8 min; FAB-MS (M+H) + =588. The starting material is prepared as follows: 3a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(o-fluorophenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 168.9 mg (0.309 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(o-fluorophenyl)methyl]-hexanoic acid [preparation, see Example 3d)], 77.1 mg (0.374 mmol) of DCC and 45.5 mg (0.337 mmol) of HOBT are added, under protective gas, to the solution of 59.3 mg (0.34 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b) in 3.5 ml of THF. After 24 h at RT, the reaction mixture is filtered and the filtrate is evaporated. Partitioning the residue between 3 portions of ethyl acetate, 10 % citric acid solution, sat. NaHCO 3 solution and saline, drying the organic phases with Na 2 SO 4 , and evaporating them, yields the title compound: t Ret (II)=22.3 min. 3b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(o-fluorophenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 1h), 5.0 g (16.37 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one [Example 2b)] dissolved in 75 ml of THF are deprotonated, at-75°C, with 32.7 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated with 2.1 ml (18.0 mmol) of o-fluorobenzyl bromide (Fluka; Buchs/Switzerland) at -75°C initially (heating to a maximum of -60°C over a period of 60 min). Column chromatography (SiO 2 , hexane/ethyl acetate, 3:1) affords the title compound: TLC R f (D)=0.61. 3c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(o-fluorophenyl)methyl]hexanoic acid In analogy with Example 1i), 4.5 g (10.8 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(o-fluorophenyl)methyl]dihydrofuran-2-(3H)-one in 170 ml of dimethoxyethane are hydrolysed with 43.5 ml of a 1 M lithium hydroxide solution. The evaporation residue of the reaction mixture is poured onto a mixture of ice, 120 ml of sat. ammonium chloride solution and 240 ml of 10 % citric acid solution, and this mixture is then extracted with 3 portions of methylene chloride. The organic phases are washed with water and saline, dried over Na 2 SO 4 and evaporated: t Ret (II)=14.5 min. 3d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(o-fluorophenyl)methyl]hexanoic acid In analogy with Example 1j), 1.5 g (3.47 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(o-fluorophenyl)methyl]hexanoic add in 15 ml of DMF are silylated with 2.4 g (16 mmol) of tert-butyldimethylchlorosilane and 1.95 g (28.5 mmol) of imidazole. Hydrolysis of the silyl ester function with 2.8 g of potassium carbonate in 50 ml of methanol/THF/water, 4:1:1, yields the title compound after column chromatography (SiO 2 , hexane/ethyl acetate, 2:1): TLC R f (D)=0.33; t Ret (II)=20.7 min. Example 4: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-difluorophenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1), 197 mg (0.274 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-difluorophenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 5 ml of DMF are desilylated with 173 mg (0.548 mmol) of TBAF, and worked up. Precipitating with DIPE from a concentrated solution in methylene chloride yields the title compound: TLC R f (A)=0.71; t Ret (II)=14.9 min; FAB-MS (M+H) + =606. The starting material is prepared as follows: 4a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-difluorophenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 68 mg (0.39 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b), 80.5 mg (0.39 mmol) of DCC and 57.5 mg (0.426 mmol) of HOBT are added, under an N 2 atmosphere, to 200 mg (0.354 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-difluorophenyl)methyl]hexanoic acid [preparation, see Example 4d)] in 4.6 ml of THF. After 19 h at RT, the mixture is worked up, in analogy with Example 3a) to give the title compound: TLC R f (D)=0.14; t Ret (II)=21.7 min. 4b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(2,4-difluorophenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 1h), 5.0 g (16.37 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one [Example 2b)] dissolved in 100 ml of THF are deprotonated, at-75°C, with 32.7 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated with 2.51 ml (19.6 mmol) of 2,4-difluorobenzyl bromide (Aldrich; Milwaukee/USA) at -75°C initially (heating to a maximum of -60°C over a period of 2 h). Column chromatography (SiO 2 , hexane/ethyl acetate, 2:1) affords the title compound: TLC R f (D)=0.5; t Ret (II)=17.2 min. 4c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-difluorophenyl)methyl]hexanoic acid In analogy with Example 1i), 3.1 g (7.18 mmol) 5(S)-[1(S)-(Boc-amino)-2-phenyl-ethyl]-3(R)-[(2,4-difluorophenyl)methyl]dihydrofuran-2-(3H)-one in 77 ml of dimethoxyethane and 19 ml of water are hydrolysed with 28.7 ml of a 1 M lithium hydroxide solution (19 h at RT) to give the title compound: t Ret (II)=14.7 min. 4d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-difluorophenyl)methyl]hexanoic acid In analogy with Example 1j), 3.2 g (7.12 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-difluorophenyl)methyl]hexanoic acid in 67 ml of DMF are silylated with 4.93 g (32.7 mmol) of tert-butyldimethylchlorosilane and 3.97 g (58.4 mmol) of imidazole. Hydrolysis of the silyl ester function with 5.9 g of potassium carbonate in 77 ml of methanol, 20 ml of THF and 20 ml of water yields the title compound after column chromatography (SiO 2 , hexane/ethyl acetate, 2:1): TLC R f (D)=0.22; t Ret (II)=20.8 min. Example 5: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-{[p-(2-phenyl-ethyl)phenyl]methyl}-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1), 115 mg (0.146 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-{[p-(2-phenylethyl)phenyl]-methyl}-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 2.1 ml of DMF are desilylated with 92 mg (0.292 mmol) of TBAF, and extracted: TLC R f (A)=0.58; t Ret (II)=18.1 min. The starting materials are prepared as follows: 5a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-{[p-(2-phenylethyl)phenyl]methyl}hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Under an N 2 atmosphere, 100 mg (0.158 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-{[p-(2-phenylethyl)phenyl]methyl}hexanoic acid (Example 5f)) and 30 mg (0.174 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b) are dissolved in 1.52 ml of 0.25M NMM/CH 3 CN, and this solution is treated with 66 mg (0.174 mmol) of HBTU. After 18 h at RT, the reaction mixture is poured onto water, and this mixture is extracted with 3 portions of ethyl acetate. The organic phases are washed with 10 % citric acid solution, water, sat. NaHCO 3 solution, water and saline, dried with Na 2 SO 4 and evaporated: t Ret (II)=24.4 min. 5b) p-(2-Phenylethyl)benzyl alcohol Hydrogenating 10 g (48 mmol) of 4-stilbenemethanol (Aldrich; Milwaukee/USA) in 100 ml of THF, in the presence of 0.5 g of 5 % Pd/C under low pressure and at RT, filtering through 'Celite (filtering aid based on kieselguhr; Johns-Manville Corp., obtainable from Fluka, Buchs, Switzerland) and evaporating the filtrate affords the title compound, approximately 15 % of which, according to the 1 H-NMR spectrum, consists of p-(2-phenylethyl)toluene: TLC R f (A)=0.62; 1 H-NMR (200 MHz, CDCl 3 ): 2.92 (s, 4 H), 4.68 (s, 2 H), 7.15-7.35 (m, 9 H). 5c) p-(2-Phenylethyl)benzyl bromide 3.14 ml (33.4 mmol) of phosphorus tribromide in 11 ml of toluene are added dropwise, while cooling and under an N 2 atmosphere, to 8.36 g (85 %; 33.4 mmol) of p-(2-phenylethyl)benzyl alcohol in 100 ml of toluene. After 2 h at RT, the mixture is poured onto ice-water and the organic phase is separated off; it is washed with sat. NaHCO 3 solution, water and saline. The aqueous phases are extracted 2x with ether, and the combined organic phases are dried with Na 2 SO 4 and evaporated: TLC R f (A)=0.77; 1 H-NMR (200 MHz, CDCl 3 ): 2.92 (s, 4 H), 4.50 (s, 2 H), 7.15-7.35 (m, 9 H); additional signals of approximately 20 % p-(2-phenylethyl)toluene. 5d) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-{[p-(2-phenylethyl)phenyl]methyl}dihydrofuran-2-(3H)-one A solution of 4.4 g (14.53 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one [preparation, see Example 2b)] in 21.4 ml of abs. THF and 2.4 ml of DMPU is treated, at -75°C and under an N 2 atmosphere, with 28 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich, Steinheim, FRG), and the mixture is subsequently stirred at this temperature for 15 min. A solution of 6.0 g (approximately 80 %, 17.5 mmol) of p-(2-phenylethyl)benzyl bromide in 5.4 ml of abs. THF is then added dropwise, and this mixture is thoroughly stirred at -70°C for 30 min. 5.4 ml of propionic acid are then added at -75°C, followed by 5.4 ml of water. The mixture is warmed to 0°C and diluted with 150 ml of ethyl acetate; this mixture is then washed with 80 ml of a 10 % solution of citric acid, with sat. sodium bicarbonate solution and with saline. The aqueous phases are reextracted 2x with ethyl acetate, and the organic phases are dried over sodium sulfate and evaporated. Column chromatography (SiO 2 , hexane/ethyl acetate, 3:1) yields the pure title compound: TLC R f (E)=0.27; t Ret (II)=20.8 min; FAB-MS (M-Buten+H) + =444. 5e) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-{[p-(2-phenylethyl)phenyl]methyl}hexanoic acid 5.15 g (10.31 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-{[p-(2-phenylethyl)-phenyl]methyl}dihydrofuran-2-(3H)-one in 166 ml of dimethoxyethane and 85 ml of water are hydrolysed, under protective gas, with 41 ml of a 1 M lithium hydroxide solution. After 3 h, the dimethoxyethane is evaporated off on an RE, and the residue is treated with an ice-cold mixture of 506 ml of sat. NH 4 Cl solution, 42 ml of 10 % citric acid solution and 207 ml of methylene chloride. Methanol is added to dissolve the product completely. The aqueous phase is separated off and extracted 2x with methylene chloride/methanol, 10:1. The organic phases are washed with saline, dried with Na 2 SO 4 and evaporated: t Ret (II)=17.8 min. 5f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-{[p-(2-phenylethyl)phenyl]methyl}hexanoic acid 5.08 g (9.81 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-{[p-(2-phenylethyl)-phenyl]methyl}hexanoic add in 22 ml of DMF are silylated, under a protective gas, with 6.80 g (45.1 mmol) of tert-butyldimethylchlorosilane and 5.48 g (80.4 mmol) of imidazole at RT for 20 h. The reaction mixture is poured onto 500 ml of ice-water, and this mixture is extracted 3x with ethyl acetate. The organic phases are washed with 10 % citric acid solution, 2x water and saline, dried with Na 2 SO 4 and evaporated. The residue is dissolved in 119 ml of methanol and 46 ml of THF, and this solution is treated with 8.1 g of potassium carbonate and 46 ml of water, and then stirred at RT for 17 h. The reaction mixture is subsequently poured onto ice-cold 10 % citric acid solution, and this mixture is extracted 3x with ethyl acetate. The organic phases are washed with 2 portions of water and saline, dried with Na 2 SO 4 and evaporated. Column chromatography (SiO 2 , hexane/ethyl acetate 2:1→1:1 → ethyl acetate) results in the pure title compound: TLC R f (D)=0.22; t Ret (II)=23.3 min. Example 6: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 1.11 g (1.35 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxy-phenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 15 ml DMF are desilylated, under an N 2 atmosphere, with 0.85 g (2.70 mmol) of TBAF. After 18 h at RT, the reaction mixture is poured onto water, and this mixture is extracted with methylene chloride. The organic phases are washed with sat. NaHCO 3 solution and saline, dried with Na 2 SO 4 and evaporated. Stirring-up in DIPE yields the title compound: TLC R f (B)=0.6; t Ret (II)=16.6 min; FAB-MS (M+H) + =706. 6a) 5(S)-[1(S)-(Boc-Amino)-2-(p-benzyloxyphenyl)ethyl]-3(R)-[(p-methoxyphenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 5d), 2.9 g (7.04 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]dihydrofuran-2-(3H)-one [preparation, see Example 1g)], dissolved in 10.3 ml of THF and 1.2 ml of DMPU, are deprotonated, at -70°C, with 14.1 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated (at from -75°C to -50°C), with 2.6 g (10.57 mmol) of p-methoxybenzyl iodide [preparation, see Example 7e)] in 10 ml of THF. Protonation, at -75°C, with 2.6 ml (35.2 mmol) of propionic acid and 2.6 ml of water, extraction and column chromatography (SiO 2 , hexane/ethyl acetate, 2:1) affords the title compound: TLC R f (D)=0.48; t Ret (II)=18.8 min. 6b) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoic acid 2.6 g (4.89 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxy-phenyl)-ethyl]-3(R)-[(p-methoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 50 ml of dimethoxyethane are hydrolysed, under an N 2 atmosphere, with 19.6 ml of a 1 M lithium hydroxide solution in water. After 25 h at RT, the dimethoxyethane is evaporated off on a RE, and the residue is treated with an ice-cold mixture of 150 ml of sat. NH 4 Cl solution, 25 ml of 10 % citric acid solution and methylene chloride. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with saline, dried with Na 2 SO 4 and evaporated to give the title compound: TLC R f (B)=0.28; t Ret (II)=16.4 min. 6c) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoic acid 2.5 g (4.54 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxy-phenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoic acid in 42 ml of DMF are silylated, under a protective gas, with 3.15 g (20.9mmol) of tert-butyldimethylchlorosilane and 2.53g (37.3 mmol) of imidazole at RT for 20 h. The reaction mixture is diluted with ethyl acetate, and this mixture is washed with sat. NaHCO 3 solution, water and saline. The aqueous phases are extracted 2x with ethyl acetate, and the organic phases are dried with Na 2 SO 4 and evaporated. The residue Is dissolved in 50 ml of methanol and 13 ml of THF, and this solution is treated with 3.8 g of potassium carbonate and 13 ml of water, and stirred at RT for 1 h. Subsequently, the reaction mixture is partially evaporated and the residue is diluted with ice-cold 10 % citric acid solution; this mixture is then extracted 3x with ethyl acetate. The organic phases are washed with 2 portions of water and saline, dried with Na 2 SO 4 and evaporated. Column chromatography (SiO 2 , hexane/ethyl acetate, 2:1) results in the pure title compound: TLC R f (C)=0,13; t Ret (II)=21.7 min. 6d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsllyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 960 mg (1.44 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxy-phenyl)methyl]hexanoic acid and 290 mg (1.66 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b) in 14.5 ml of 0.25 M NMM/CH 3 CN are reacted, at RT for 20 h and under an N 2 atmosphere, with 630 mg (1.66 mmol) of HBTU. The mixture is evaporated and the residue is taken up in ethyl acetate; the solution is washed in tum with water, 2x with 10 % citric acid solution, once again with water, 2x with saturated NaHCO 3 solution, water and saline. The aqueous phases are extracted twice more with ethyl acetate, and the organic phases are dried with Na 2 SO 4 and evaporated. Digesting the crude product in hexane results in the title compound: TLC R f (B)=0.70; t Ret (II)=22.5 min. 6e) p-Methoxybenzyl iodide A solution of 1.7 ml (12.8 mmol) of 4-methoxybenzyl chloride (Fluka; Buchs/Switzerland) in 25 ml of acetone is stirred, at RT, together with 9.4 g (62.6 mmol) of sodium iodide. A gas chromatogram of the reaction mixture, carried out after 90 min, indicates that the reaction is complete; the reaction mixture is therefore poured onto ether and this mixture is washed with 10 % sodium thiosulfate solution and saline. Drying the organic phase with Na 2 SO 4 , and evaporating it, affords the title compound: 1 H-NMR (200 MHz, CD 3 OD: 3.78 (s, 3 H), 4.54 (s, 2 H), 6.8-6.95 and 7.2-7.4 (2m, each 2 H). Example 7: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Hydrogenating 500 mg (0.708 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 6) under low pressure in 33 ml of methanol in the presence of 0.11 g of 10 % Pd/C yields the title compound, after filtration, evaporation of the filtrate and digestion with DIPE: TLC R f (B)=0.53; t Ret (II)=12.2 min; FAB-MS (M+H) + =616. Example 8: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 100 mg (0.162 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxy-phenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 7) in 3 ml of DMF/dioxane, 1:1, are treated, at 0°C and under an N 2 atmosphere, with 105mg (0.324mmol) of Cs 2 CO 3 and 10.1 µl (0.162 mmol) of methyl iodide, and the mixture is stirred at RT for 20 h. For the working-up, the reaction mixture is poured onto water, and this mixture is extracted with 3 portions of methylene chloride. The organic phases are washed with water and saline, dried with Na 2 SO 4 and evaporated. Stirring up in DIPE in an ultrasonication bath yields the title compound: TLC R f (B)=0.62; t Ret (II)=14.2 min; FAB-MS (M+H) + =630. Example 9: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-(isobutoxy)-phenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 100 mg (0.162 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 7) in 3 ml of DMF/dioxane, 1:1, are treated, at 0°C and under protective gas, with 105 mg (0.324 mmol) of Cs 2 CO 3 and 18.7 µl (0.162 mmol) of isobutyl iodide, and this mixture is stirred at 50°C for 16 h. Since HPLC indicates that starting material is still present, 5 equivalents of isobutyl iodide and 10 equivalents of Cs 2 CO 3 are added in portions. After each portion, the mixture is stirred at 50°C for 1 day until HPLC indicates that all the 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide has reacted. Working up in analogy with Example 9 affords the title compound: TLC R f (B)=0.76; t Ret (II)=16.8 min; FAB-MS (M+H) + =672. Example 10: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 2.07 g (2.90 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 50 ml of DMF are desilylated, under an N 2 atmosphere, with 1.83 g (5.80 mmol) of TBAF. After 18 h, the reaction mixture is poured onto water, and this mixture is extracted with 4 portions of ethyl acetate. The organic phases are washed with sat. NaHCO 3 solution, water and saline, dried with Na 2 SO 4 and evaporated. Digesting twice with DIPE yields the title compound: t Ret (II)=14.2 min; FAB-MS (M+H) + =600. The starting material is prepared as follows: 10a) 5(S)-[1(S)-(Boc-Amino)-2-(p-methoxyphenyl)ethyl]dihydrofuran-2-(3H)-one A suspension of 4.00 g (12.44 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-hydroxyphenyl)ethyl]-dihydrofuran-2-(3H)-one (Example 10f)) in 240 ml of DMF/dioxane, 1:1, is reacted, under an N 2 atmosphere, with 8.1 g (24.88 mmol) of Cs 2 CO 3 and 0.77 ml (12.44 mmol) of methyl iodide. After 18 h, the reaction mixture is poured onto 190 ml of ice-water, and this mixture is extracted 3x with methylene chloride. The organic phases are washed with water and saline, dried with Na 2 SO 4 and evaporated. Stirring with hexane in an ultrasonication bath affords the title compound: TLC R f (C)=0.43; t Ret (II)=13.5 min; FAB-MS (M+H) + =336. 10b) 5(S)-[1(S)-(Boc-Amino)-2-(p-methoxyphenyl)ethyl]-3(R)-(phenylmethyl)-dihydrofuran-2-(3H)-one In analogy with Example 5d), 4.17 g (12.44 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-methoxyphenyl)ethyl]dihydrofuran-2-(3H)-one, dissolved in 22.4 ml of THF and 2.5 ml of DMPU, are deprotonated, at -70°C, with 24 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated (-75°C, 1 h) with 1.5 ml (12.44 mmol) of benzyl bromide. Protonation, at -75°C, with 4.6 ml of propionic acid and 4.6 ml of water, extraction and column chromatography (SiO 2 , methylene chloride/ether 25:1) yields the title compound: TLC R f (C)=0,74; t Ret (II)=16.6 min; FAB-MS (M+H) + =426. 10c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoi c acid 3.00 g (7.05 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-methoxy-phenyl)-ethyl]-3(R)-(phenylmethyl)dihydrofuran-2-(3H)-one in 112 ml of dimethoxyethane and 57 ml of water are hydrolysed, under protective gas, with 28 ml of 1 M lithium hydroxide solution. After 20 h at RT, the reaction mixture is poured onto an ice-cold mixture of 340 ml of sat. NH 4 Cl solution, 28 ml of 10 % citric acid solution and 140 ml of methylene chloride. Methanol is added in order to dissolve the product completely. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with saline, dried with Na 2 SO 4 and evaporated, with the title compound being obtained: t Ret (II)=14.0 min; FAB-MS (M+H) + =444. 10d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoic acid 2.9 g (6.54 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoic acid in 7 ml of DMF are silylated, at RT for 20 h and under an N 2 atmosphere, with 4.5 g (30 mmol) of tert-butyldimethylchlorosilane and 3.65 g (53.6 mmol) of imidazole. The reaction mixture is poured onto 500 ml of ice-water, and this mixture Is extracted 3x with ethyl acetate. The organic phases are washed with 10 % citric add solution, 2x water and saline, dried with Na 2 SO 4 and evaporated. Hydrolysis of the residue in 80 ml of methanol and 30 ml of THF with 5.4 g of potassium carbonate and 30 ml of water, working up after 3 h in analogy with Example 7c), and column chromatography (SiO 2 , hexane/ethyl acetate, 2:1), affords the title compound: TLC R f (D)=0.13; t Ret (II)=20.3 min. 10e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsllyloxy)-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 1.56 g (2.8 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanolc acid and 538 mg (3.09 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b) in 27 ml of 0.25 M NMM/CH 3 CN are reacted, at RT for 20 h and under an N 2 atmosphere, with 1.17 g (3.09 mmol) of HBTU. Working up in analogy with Example 5a) results in the title compound: t Ret (II)=21.1 min; FAB-MS (M+H) + =714. 10 f) 5(S)-[1(S)-(Boc-Amino)-2-(p-hydroxyphenyl)ethyl]dihydrofuran-2-(3H)-one Hydrogenating 3.0 g (7.29 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]-dihydrofuran-2-(3H)-one [preparation, see Example 1g)] in 100 ml of methanol with 0.6 g of 10 % Pd/C yields the title compound after filtering off the catalyst and evaporating the filtrate: t Ret (II)=10.6 min. Example 11: The following compounds are prepared in analogy with one of the examples given above or below: I) 5(S)-(Boc-Amino)4(S)-hydroxy-6-phenyl-2(R)-[(o-fluoro-p-methoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide II) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-fluoro-p-methoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide III) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(o-hydroxy-p-methoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Example 12: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-(phenylmethyl)hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1, 0.82 g (1.19 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-phenylmethylhexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 12 ml of DMF is reacted with 0.756 g (2.38 mnol) of TBAF trihydrate to give the title compound. After working up, the pure title compound is obtained after stirring up with diethyl ether and filtering. TLC R f (A) = 0.37; t Ret (II)= 14.58 min; FAB-MS (M+H + )= 570. The starting compound is prepared in the following manner: 12a) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]dihydrofuran-2-(3H)-one (see Ex. 2c)) (see, also, A.E. DeCamp, A.T. Kawaguchi, R.P. Volante, and I. Shinkai, Tetrahedron Lett. 32 , 1867 (1991)). 173 g of Zn/Cu (preparation: see R.D. Smith, H.E. Simmons, W.E. Parham, M.D. Bhavsar, Org. Synth., Coll. Vol 5 , 855 (1973)) and 280 ml of dimethylacetamide are added, under an N 2 atmosphere, to a solution of 375 g (1.65 mol) of ethyl 2-iodopropionate (Example 1k)) in 1700 ml of toluene and this mixture is subsequently stirred vigorously at RT for 1 h and at 80°C for 4 h (→ Zn-homoenolate solution). In a second apparatus (N 2 atmosphere), a solution of 122 ml (0.40 mol) of tetraisopropyl orthotitanate in 350 ml of toluene and 1900 ml of methylene chloride is treated, with slight cooling, at an internal temperature of from 15 to 25°C, with 127 ml (1.14 mol) of titanium tetrachloride, and this mixture is stirred at RT for 15 min (→ yellow solution) and cooled down to -40°C (→ partial crystallization of the trichlorotitanium isopropoxide). The Zn-homoenolate solution, which has been cooled down to RT, is filtered, under an argon atmosphere, through a G3 glass frit and added dropwise to the trichlorotitanium isopropoxide, with the temperature being maintained at from -30°C to -25°C (→ deep-red solution), after which the mixture is stirred at -25°C for 5 min and then cooled down to-40°C. A solution of 233 g (0.85 mol) of (S)-N-Boc-phenylalaninal (preparation: see D.J. Kempf, J. Org. Chem. 51, 3921 (1986), then crystallization from hexane (0°C, approximately 18 h), washing with cold hexane, and drying) in 1500 ml of methylene chloride is subsequently added dropwise, and the mixture is then stirred at from -22 to -18°C for 15 h and, finally, at 0°C for 1 h. The reaction mixture is taken up in 10 I of ice-water and 12 I of tert-butyl methyl ether, and this mixture is stirred vigorously for 7-10 min. The aqueous phase is separated off; it is extracted 2x with 10 I of ether, the organic phases are washed with 8 I of water, 8 I of sat. sodium hydrocarbon carbonate solution, 8 I of water and 5 I of saline; they are dried with sodium sulfate and evaporated (→ crystalline ethyl 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenylhexanoate). The above intermediate is heated, in 6500 ml of toluene and 230 ml of acetic acid and under an argon atmosphere, at 100°C for 2.5 h. When it has cooled down, the reaction mixture is poured, with stirring, onto 6 I of ice-water, and the aqueous phase is separated off and extracted 2x with 2000 ml of toluene; the org. phases are washed with 5 I of sat. sodium hydrogen carbonate solution, 5 I of 40 % sodium hydrogen sulfite solution, 4 I of water and 41 of saline, and dried with sodium sulfate. Evaporating the org. phases down to a residue of approximately 300 g, and treating the latter with 800 ml of hexane (thorough stirring for several hours) affords crystalline lactone, which HPLC indicates contains approximately 10 % of the (5R) epimer (TLC R f (E)=0.08; t Ret (II)=18.8 min). This material is employed in the next stage. The pure title compound can be obtained following column chromatography (SiO 2 , hexane/ethyl acetate, 2:1): TLC R f (E)=0.14; t Ret (II)=19.2 min; [α] D =17.7° (c=1; ethanol). 12b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-phenylmethyldihydrofuran-2-(3H)-one (see, also, A.K. Ghosh, S.P. McKee, and W.J. Thompson, J. Org. Chem. 56 , 6500 (1991)). Under an N 2 atmosphere, a solution of 1943 g (6.32 mol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one in 12.01 of THF and 1.9 I of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidlnone is cooled down to -75°C and treated, at an intemal temperature of below -70°C, with 14000 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich), and this mixture is subsequently stirred at -75°C for 20 min. 835 ml (7.00 mol) of benzyl bromide are added dropwise to it over the space of 1 h, during which time the internal temperature is not allowed to exceed -70°C, and the mixture is then thoroughly stirred at -75°C for 30 min. 2320 ml of propionic acid (90 min) and then 2320 ml of water (1 h) are subsequently added to the clear solution, with the temperature being allowed to rise to -10°C. The reaction mixture is poured onto 30 I of ethyl acetate and 35 I of 10 % citric acid solution, and the aqueous phase is separated off and reextracted 2x with 10 I of ethyl acetate. The organic phases are washed with 3x 12 I of sat. sodium bicarbonate solution, 20 I of saline and 2x 20 I of water, and then concentrated. The oily residue is taken up in 10 I of toluene, and this mixture is evaporated down to a residue volume of approximately 5 I. Filtering the evaporation residue through 4 kg of Merck silica gel (0.063-0.200 mm), washing with toluene and crystallizing the crude product from hexane (4 I of hexane/kg of crude product) affords the title compound: TLC R f (D)=0.54; FAB-MS (M+H) + =414. 12c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-phenylmethylhexanoic acid A solution of 17.6 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-phenylmethyldihydrofuran-2-(3H)one in 710 ml of ethylene glycol dimethyl ether and 352 ml of water is treated dropwise, at 20°C and within the space of 10 min, with 176 ml of a 1 M lithium hydroxide solution. After that, the reaction mixture is stirred at RT for 1.5 h, and the solvent is then evaporated off. The residue is poured onto 1 I of cold 10 % citric acid, and this acidic solution is extracted three times with 800 ml of ethyl acetate on each occasion. The combined extracts are washed first with 800 ml of water and then with 800 ml of saline. After the organic solution has been dried over sodium sulfate, the solvent is distilled off. The crude title compound is employed in the next stage without any further purification. FAB-MS (M+H) + =414. 12d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-phenylmethylhexanoic acid A solution of 6.35 g of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-phenylmethylhexanoic add in 90 ml of DMF is treated, while being stirred, with 8 g of imidazole and 10 g of t-butyldimethylchlorosilane. After having been stirred at RT for 18 h, the yellow, clear solution is poured onto ice-water, and this mixture is extracted three times with 250 ml of ethyl acetate on each occasion. The combined extracts are washed, in succession, three times with 10 % citric acid, once with water, three times with aqueous, saturated sodium bicarbonate solution, once with water and, finally, with saline. After drying over sodium sulfate, the solvent is evaporated and the resulting tert-butyl dimethylsilyl ether (13.5 g) is dissolved in 53 ml of THF and treated with 53 ml of acetic acid and 20 ml of water. After having been stirred at RT for 3 h, the mixture is poured onto water, and this mixture is extracted three times with ether. The collected ether extracts are washed twice with water and once with saline and dried over sodium sulfate. After concentrating, the crude product is purified by column chromatography (SiO 2 , hexane/ethyl acetate: 3.5/1.5), and the title compound is obtained. TLC R f (D)= 0.37; FAB-MS (M+H) + = 528. 12e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-(phenylmethyl)hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A solution of 1.25 g (2 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)6-phenyl-2(R)-(phenylmethyl)hexanoic acid, 0.98 g (2.21 mmol) of BOP, 0.3 g (2.21 mmol) of HOBT and 0.55 ml (4.98 mmol) of N-methylmorpholine In 15 ml of DMF is treated, after having been stirred at RT for 30 min, with 0.208 ml (2.42 mmol) of (L)-Val-N-(2-methoxyethyl)amide. After having been stirred at RT for 5.5 h, the mixture is poured onto 300 ml of water, and this mixture is extracted 3 times with ethyl acetate. The combined organic phases are washed with water, saturated sodium bicarbonate solution (twice) and saline, and, after drying over sodium sulfate, are concentrated under reduced pressure. The title compound is purified by column chromatography (SiO 2 ,D to A); TLC R f (C)= 0.23. Example 13: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-benzyloxyphe nyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1, the title compound is obtained by proceeding from 1.29 g (1.63 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsllyloxy)-6-phenyl-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl -(L)-Val-N-(2-methoxyethyl)amide and 1.03 g (3.26 mmol) of TBAF trihydrate. TLC R f (M)= 0.58; t ret (I)= 16.9 min. The starting material is prepared as follows: 13a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 1c), the title compound is obtained as a colourless resin, after chromatographic purification on silica gel using hexane/ethyl acetate (1:1) as eluent, by proceeding from 1.14 g (1.8 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid, 313 mg (1.8 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (preparation, Example 1b)) and 751 mg (1.98 mmol) of HBTU in 18 ml of a 0.25 M solution of NMM in acetonitrile. TLC R f (hexane/ethyl acetate (1:1))= 0.19; t ret (I)= 23.3 min; FAB MS (M+H) + = 790. 13b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(p-benzyloxyphenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 1h), 1.13 g (3.70 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one [Example 2b)], dissolved in 4.8 ml of THF and 0.75 ml of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, are deprotonated, at -75°C, with 7.25 ml of a 1M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated (15 min) with 1.2 g (3.7 mmol) of p-benzyloxybenzyl iodide (Example 1d)) in 2 ml of THF. Column chromatography (SiO 2 , hexane/ethyl acetate, 2:1) affords the pure title compound: TLC R f (D)=0.30; t Ret (I)=28.2 min; FAB-MS (M+H) + =502. 13c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid In analogy with Example 1i), 1.4 g (2.79 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(p-benzyloxyphenyl)methyl]dihydrofuran-2-(3H)-one in 45 ml of dimethoxyethane and 23 ml of water are hydrolysed with 11 ml of a 1 M lithium hydroxide solution. The reaction mixture, which has been partially evaporated, is poured onto a mixture of ice, 137 ml of sat. NH 4 Cl solution, 11 ml of 10 % citric acid solution and 56 ml of methylene chloride, and methanol is added until the precipitated solid dissolves. The aqueous phase is extracted with 2 portions of methylene chloride/methanol, approximately 10:1, and the organic phases are washed with saline, dried with Na 2 SO 4 and evaporated: t Ret (I)=24.0 min; FAB-MS (M+H) + =520. 13d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2 (R)-[(p-benzyloxyphenyl)methyl]hexanoic acid 1.4 g (2.69 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoic acid in 2.9 ml of DMF are stirred, at RT for 18 h, together with 1.87 g (12.4 mmol) of tert-butyldimethylchlorosilane and 1.5 g (22 mmol) of imidazole. The reaction mixture is then poured onto ice water, and this mixture is extracted with 3 portions of ethyl acetate; the combined organic phases are washed with 10 % citric acid solution, water and saline, dried with sodium sulfate and evaporated. An oil is obtained. This is followed by hydrolysis of the silyl ester function of the oil, at RT, using 2.2 g of potassium carbonate in 63 ml of methanol/water/THF, 3:1:1, and partial evaporation at RT. The aqueous residue is poured onto 10 % citric acid solution and ice, and this mixture is extracted 3 times with ethyl acetate; the organic phases are washed twice with water and saline, dried with sodium sulfate and evaporated. Column chromatography (SiO 2 , D) of the crude product yields the title compound: TLC R f (D)=0,17; t Ret (I)=33,7 min; FAB-NS (M+H) + =634. Example 14: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-hydroxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A solution of 718 mg (1.06 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide from Example 13 in 50 ml of methanol is hydrogenated, at RT for 3 h, in the presence of 150 mg of 10 % palladium on charcoal and under 1 atm hydrogen pressure. The title compound is obtained as an amorphous solid after the catalyst has been filtered off and the filtrate has been evaporated. TLC R f (hexane/ethyl acetate (2:1))= 0.29; t ret (I)= 12.8 min; FAB MS (M+H) + = 586. Example 15: (S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-isobutoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A suspension consisting of 585 mg (1 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide from Example 14 and 1.22 g of caesium carbonate in 50 ml of dioxane is stirred at RT for 16 h under a nitrogen atmosphere; it is then treated with 2.7 ml of isobutyl iodide (Fluka, Buchs, Switzerland) and heated at 80°C for 3 h until TLC monitoring can no longer detect any starting materials. Finally, the mixture is diluted with methylene chloride and the precipitate is filtered off. The filtrate is evaporated and yields the title compound after chromatographic purification on silica gel using methylene chloride/methanol (95:5) as the eluent and crystallization from ethyl acetate/hexane. TLC R f (L)= 0.5; t ret (I)= 17.1 min; FAB MS (M+H) + = 642. Example 16: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-(2-pyridylmet hoxy)phenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 15, the title compound is obtained, after chromatographic purification on silica gel using methylene chloride/methanol (97:3) as eluent and crystallization from ethyl acetate, by proceeding from 65 mg of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide from Example 39, 137 mg of caesium carbonate and 3 ml of 2-picolyl chloride (liberated from the HCI salt (Fluka, Buchs, Switzerland) with NaHCO 3 solution). TLC R f (L)= 0.4; t ret (I)= 11.7 min; FAB MS (M+H) + = 677. Example 17: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-(3-pyridylmet hoxy)phenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A suspension consisting of 585 mg (1 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide from Example 14 and 1.22 g caesium carbonate is stirred overnight, at RT and under a nitrogen atmosphere; it is then treated with 4.0 g of 3-picolyl chloride (liberated from the HCI salt (Fluka, Buchs, Switzerland) with NaHCO 3 solution) and heated at 85°C for 6 h. After the addition of 100 mg of sodium iodide and 500 mg of caesium carbonate, it is heated for a further 18 h. For the working-up, the mixture is eluted with methylene chloride and the precipitate is filtered off. The filtrate is evaporated and yields the title compound, as an amorphous solid, after chromatographic purification using methylene chloride/THF (2:1) and lyophilization from dioxane. TLC R f (L)= 0.5; t ret (I)= 11.5 min; FAB MS (M+H) + = 677. Example 18: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A solution of 90 mg (0.154 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide from Example 14 in 5 ml of dioxane/DMF (1:1) is treated, at 0 °C, with 100 mg (0.31 mmol) of caesium carbonate and then with 0.01 ml (0.15 mmol) of methyl iodide. After having been stirred at RT for 14 h under a nitrogen atmosphere, the reaction mixture is poured onto ice-water, and this mixture is extracted with methylene chloride. The organic extracts are washed with sat. sodium bicarbonate solution and saline, filtered through wadding and evaporated. The title compound is obtained after chromatographic purification on silica gel using methylene chloride/methanol (19:1) and lyophilization from dioxane. TLC R f (methylene chloride/methanol (19:1))= 0.27; t ret (I)= 14.6 min; FAB MS (M+H) + = 600. Example 19: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A solution of 165 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 4.04 ml of abs. DMF Is treated with 127.4 mg of TBAF, and the reaction mixture is stirred at RT for 21 h. The slightly turbid, yellowish solution is poured onto 30 ml of water, and this mixture is extracted with ethyl acetate. The organic phase is washed, so that it becomes neutral, in succession, with sat. sodium bicarbonate solution and saline, and dried over sodium sulfate. The title compound is dissolved in methylene chloride and precipitated with hexane. TLC R f (A)=0.42; FAB-MS (M+H) + =614. The starting material is prepared as follows: 19a) 3,4-Methylenedioxybenzyl chloride 15.04 ml of thionyl chloride are added dropwise, at 0°C, over the space of 25 min and under argon, to 10.82 g of 3,4-methylenedioxybenzyl alcohol (Fluka, Buchs, Switzerland) and 48 g of diisopropylaminomethylpolystyrene (polyhünig base: polystyrene crosslinked with 2 % divinylbenzene, diisopropylaminomethylated; Fluka, Buchs, Switzerland) in 200 ml of abs. ether. After having been stirred at 0°C for a further 1.5 h, the mixture is filtered with suction and the filtrate is concentrated on a RE and then under HV. The residue is purified by chromatography on silica gel (eluent C), and the title compound thus obtained. TLC R f (hexane:ethyl acetate, 4:1)=0.47; 1 H-NMR (200 MHz, CDCl 3 ): 6.95-6.7(m, 3H), 5.97(s, 2H), 4.53(s, 2H). 19b) 3,4-Methylenedioxybenzyl iodide 11.65 g 3,4-methylenedioxybenzyl chloride in 128 ml of abs. acetone are treated with 49.7 g of sodium iodide, and this mixture is stirrred at RT for 2.5 h under argon and while excluding light. The reaction mixture is diluted with 1.5 I of ether, and this mixture is washed with 10 % sodium thiosulfate solution (600 ml) and saline. The title compound is obtained after drying over sodium sulfate and removing the solvent. It is recrystallized from ether/hexane. m.p.: 51°C. TLC R f (hexane:ethyl acetate, 4:1)=0.43. 1 H-NMR (360 MHz, CDCl 3 ): 6.93-6.77(m, 2H), 6.77-6.64(m,1H), 5.95(s, 2H), 4.44 (s,2H). 19c) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(3,4-methylenedioxyphenyl)methyl]dihydrofuran-2-(3H)-one Under an N 2 atmosphere, a solution of 500 mg of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one [Example 2b)] in 2 ml of abs. THF and 0.33 ml of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidone (DMPU) is cooled down to -75°C and treated, at an internal temperature of below -70°C, with 3.21 ml of a 1M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich, Steinheim, FRG), and this mixture is then stirred at-75°C for 20 min. 429 mg of 3,4-methylenedioxybenzyl iodide in 1 ml of abs. THF are added dropwise to the reaction solution within the space of 10 min using a syringe, during which period the internal temperature is not allowed to exceed -70°C, and this mixture is then thoroughly stirred at -75°C for 1 h. 0.611 ml of propionic acid are then added to the clear solution, at from -75°C to -70°C, using a syringe, and this is followed by 0.611 ml of water. During this procedure, the temperature rises to -30°C. After that, the reaction mixture is diluted with 35 ml of ethyl acetate, and the whole is stirred up with 10 ml of 10 % citric acid solution for 5 min in the cold (ice/water cooling). The aqueous phase is separated off and the organic phase is washed, in succession, with saline, sat. sodium bicarbonate solution, and once again with saline. The combined aqueous phases are reextracted 2 times with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated. The title compound is obtained as a brownish oil. Purification is effected by chromatography on silica gel (eluent D). TLC R f (D)=0.38; FAB-MS (M+H) + =440. 19d) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoic acid A solution of 278 mg of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(3,4-methylenedioxyphenyl)methyl]dihydrofuran-2-(3H)-one in 10.25 ml of ethylene glycol dimethyl ether and 5.15 ml of water is treated dropwise, at RT, with 2,53 ml of a 1M lithium hydroxide solution. After that, the reaction mixture is stirred at RT for 3 h, diluted with ethyl acetate and THF, and washed in a separating funnel until neutral with a mixture consisting of 31 ml of sat. ammonium chloride solution and 2.6 ml of 10 % citric acid solution, followed by saline and water. The title compound, which is subjected to further processing without any further purification, is obtained after drying over sodium sulfate and removing the solvent. FAB-MS (M+H) + =458. 19e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoic acid A solution of 271 mg of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoic acid in 2.13 ml of DMF is treated, while being stirred, with 338 mg of imidazole and 415 mg of tert-butyldimethylchlorosilane. After having been stirred at RT for 20 h, the reaction solution is poured onto ice-water, and this mixture is extracted with ethyl acetate. The organic phase Is washed with 10 % citric acid solution and saline. A crude product is obtained which is dissolved in 7.13 ml of methanol and 2.75 ml of THF, with this solution then being treated, at RT, with a solution of 485 mg of potassium carbonate in 2.75 ml of water. The reaction mixture is stirred at RT for 2 h, concentrated down to approximately half its volume and poured onto 10 % citric add solution and ice; this mixture is then extracted with ethyl acetate. The organic phase is washed with (cold) saline. After drying over sodium sulfate, the solvent is evaporated and the residue is chromatographed on silica gel (eluent C), and the title compound is obtained. TLC R f (C)=0.27. FAB-MS (M+H) + =572. 19f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A mixture of 120 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoic acid, 87.6 mg of HBTU and 40.2 mg of H-(L)-Val-N-(2-methoxyethyl)amide [preparation, see Example 1b)] in 1.97 ml of a 0.25 M solution of NMM in acetonitrile is stirred at RT for 19 h under argon. The solution is concentrated down to half its volume on a RE, diluted with cold ethyl acetate, and washed, in succession, with 10 % citric acid, water, sat. sodium bicarbonate solution and saline. The title compound, which is subjected to further processing without being purified, is obtained after drying over sodium sulfate and removing the solvent. TLC R f (D)=0.21. FAB-MS (M+H) + =728. Example 20: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19,136 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 3.38 ml of abs. DMF are desilylated with 113.6 mg of TBAF to give the title compound. Purification is effected by chromatographing twice on silica gel (eluent A, THF and methanol). The title compound is recrystallized from methylene chloride/hexane. TLC R f (A)=0.37. FAB-MS (M+H) + =630. 20a) 3,4-Dimethoxybenzyl chloride In analogy with Example 19a), the title compound is obtained from 10 g of 3,4-dimethoxybenzyl alcohol (Fluka, Buchs, Switzerland), 46.2 g of diisopropylaminomethylpolystyrene (polyhünig base) and 4.62 ml of thionyl chloride in 200 ml of abs. ether. TLC R f (hexane:ethyl acetate 4:1)=0.31. 1 H-NMR (200 MHz, CDCl 3 ): 7.0-6.87 (m, 2H); 6.82 (d, 1H); 4.56 (s, 2H); 3.9 (s, 3H); 3.87 (s, 3H). 20b) 3,4-Dimethoxybenzyl Iodide In analogy with Example 19b), the title compound is obtained from 6.185 g of 3,4-dimethoxybenzyl chloride and 24.19 g of sodium iodide in 62 ml of abs. acetone. TLC R f (hexane:ethyl acetate 4:1)=0.40. 1 H-NMR (200 MHz, CDCl 3 ): 6.95 (dxd, 1H); 6.88 (d, 1H); 6.75 (d, 1H); 4.47 (s, 2H); 3.87 (s, 3H); 3.86 (s, 3H). 20c) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(3,4-dimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 19c), 1 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one [Example 2b)] in 4 ml of abs. THF is deprotonated (-75°C) with 6.42 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, with the addition of 0.66 ml of DMPU, and alkylated with 911 mg of 3,4-dimethoxybenzyl iodide. Chromatography on silica gel (eluents D, C and J) gives the pure title compound. TLC R f (C)=0.42. MS M + =455. 20d) 5 (S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoic acid In analogy with Example 19d), 778 mg of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(3,4-dimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 27.67 ml of dimethoxyethane and 13.91 ml of water are hydrolysed with 6.83 ml of 1 M lithium hydroxide solution to give the title compound, which is subjected directly to further processing. TLC R f (C)=0.07. 20e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoic acid In analogy with Example 19e), 804 mg of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoic acid in 5.94 ml of DMF are silylated wth 1.162 g of tert-butyldimethylchlorosilane and 946.6 mg of imidazole. The silyl ester in the crude product is cleaved at RT in 2 h in a mixture consisting of 19.61 ml of methanol, 7.56 ml of THF, 7.56 ml of water and 1.334 g of potassium carbonate. The title compound is purified by being chromatographed twice on silica gel (eluents: D, C, J and B). TLC R f (C)=0.27. MS M + =557. 20f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19f), 109.9 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]hexanoic acid, 78.1 mg of HBTU and 35.9 mg of H-(L)-Val-N-(2-methoxyethyl)amide [Example 1b)] in 1.75 ml of 0.25 M NMM/CH 3 CN are reacted to yield the title compound. TLC R f (A)=0.39. FAB-MS (M+H) + =744. Example 21: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19, 300 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 6.63 ml of abs. DMF are desilylated with 217.7 mg of TBAF to give the title compound. Purification is effected by chromatography on silica gel (eluent A and methanol), or by precipitating the substance from cold ethyl acetate. TLC R f (A)=0.32. FAB-MS (M+H) + =600. 21a) 3-Methoxybenzyl iodide In analogy with Example 19b), the title compound is obtained from 2 ml of 3-methoxybenzyl chloride (Fluka, Buchs, Switzerland) and 9.72 g of sodium iodide in 23 ml of abs. acetone. TLC R f (hexane/ethyl acetate, 2.5:1)=0.71. 1 H-NMR (200 MHz, CDCl 3 ): 7.20 (m, 1H); 7.0-6.87 (m, 2H); 6.78 (dxd, 1H); 4.42 (s, 2H); 3.8 (s, 3H). 21b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(3-methoxyphenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 19c), 1.5 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one [Example 2b)] in 3 ml of abs. THF are deprotonated (-75°C) with 9.62 ml of a 1M solution of lithium bis(trlmethylsilyl)amide in THF, and with the addition of 0.998 ml of DMPU and alkylated with 1.22 g of 3-methoxybenzyl iodide. Chromatography on silica gel (eluent E) affords the pure title compound. TLC R f (hexane/ethyl acetate, 2.5:1)=0.32. FAB-MS (M+H) + =426. 21c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoic acid In analogy with Example 19d), 1.315 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(3-methoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 49.9 ml of dimethoxyethane and 25.16 ml of water are hydrolysed with 12.36 ml of a 1M lithium hydroxide solution to give the title compound, which is directly subjected to further processing. TLC R f (C)=0.09. FAB-MS (M+H) + =444. 21d) 5(S)-(Boc-Amino)-4(S)-(tert-butyidimethylsilyloxy)-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoic acid In analogy with Example 19e), 1.3 g of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoic acid in 13 ml of DMF are silylated with 1.987 g of tert-butyldimethylchlorosilane and 1.646 g of imidazole. The silyl ester group in the crude product is detached at RT in 2 h in a mixture consisting of 38.94 ml of methanol, 13.34 ml of THF, 13.34 ml of water and 2.35 g of potassium carbonate, Chromatography on silica gel (eluents: E, D and C) yields the pure title compound. TLC R f (D)=0.06. FAB-MS (M+H) + =558. 21e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19f), 200 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]hexanoic add and 68.6 mg of H-(L)-Val-N-(2-methoxyethyl)amide [Example 1b)] in 3.36 ml of 0.25 M NMM/CH 3 CN are reacted with 149.4 mg of HBTU to give the title compound. TLC R f (C)=0.20. FAB-MS (M+H) + =714. Example 22: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 337 mg (0.379 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 7.28ml of abs. DMF are treated with 244 mg (0.758 mmol) of TBAF, and this mixture is stirred at RT for 20 h under argon. The reaction mixture is diluted with approximately 50 ml of ethyl acetate, and this mixture is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated at approximately 30°C. The residue is dissolved in a little ethyl acetate. Adding hexane results in the desired title compound being crystallized. Additional product is obtained by purifying the mother liquor on silica gel (eluent, ethyl acetate:methanol, 9:1). m.p.: 141-143°C. TLC R f (ethyl acetate)=0.16. FAB-MS (M+H) + =660. HPLC t Ret =14.59 min (gradient II). IR (KBr) = inter alia, 1687, 1651, 1622, 1525, 1495 and 1172 cm -1 . 1 H-NMR(CD 3 OD) = inter alia, 7.30-7.10/m (5H); 6.78 and 6.63/each d (each 1 H); 4.03/d (1H); 3.85, 3.81 and 3.80/each s (each 3 H); 1,32 and 1.26/each s (in all, 9H from Boc); 0.82/pseudo t (6H). The starting material is prepared as follows: 22a) 2,3,4-Trimethoxybenzyl chloride 5 g (24.47 mmol) of 2,3,4-trimethoxybenzyl alcohol (Aldrich, Steinheim, FRG) are dissolved, under argon, in 13.9 ml of abs. methylene chloride, and this solution is treated with 0.278 ml of pyridine. 3.05 ml of thionyl chloride in 6.94 ml of abs. methylene chloride are added dropwise to this solution, while cooling slightly (ice/water), within the period of 20 min. During this procedure, the internal temperature rises to approximately 18-23°C. The mixture is left to react subsequently for 45 min and the slightly yellow solution is then poured onto ice/water. After the phases have been separated, the organic phase is washed once each with 1N sulfuric acid and water. After drying over Na 2 SO 4 , and removing the solvent, the oily residue is distilled under HV (b.p.: 93-95 °C/0.07 Torr), and the title compound is obtained. 1 H-NMR (220 MHz, CDCl 3 ): 7.05 (d, 1H); 6.65 (d, 1H); 4.61 (s, 2H); 3.97 (s, 3H); 3.85 (s, 3H). HPLC: t Ret = 8.1 min (gradient II). 22b) 2,3,4-Trimethoxybenzyl iodide 46.64 g (215.2 mmol) of 2,3,4-trimethoxybenzyl chloride in 466 ml of abs. acetone are treated with 156.7 g (4.86 equivalents) of sodium iodide, and this mixture is stirred at RT for 2.75 h while excluding light. The reaction mixture is treated with approximately 3 l of (cold) ether, and the organic phase is washed once with 10 % sodium thiophosphate solution and twice with saline (both kinds of solutions being cold). The combined aqueous phases are reextracted with ether. The combined organic phases are dried over Na 2 SO 4 and evaporated on a RE at approximately 30°C. The residue, which is the desired title compound, is dried again under HV and subjected to further processing as a crude product. 1 H-NMR (200 MHz, CDCl 3 ): 7.03 and 6.59 (each d; each 1H); 4.47 (s, 2H); 4.05, 3.85 and 3.84 (each s, each 3H). 22c) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(2,3,4-trimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one A solution of 1.368 g (4.48 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one [Example 2b)] in 5 ml of abs. THF and 0.91 ml (1.67 equivalents) of DMPU is cooled down to -75°C, under argon, and treated dropwise, at an internal temperature of below -70°C and over the period of approximately 20 min, with 8.78 ml of a 1M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich). After a further 15 min, a solution of 1.38 g (1 equivalent) of 2,3,4-trimethoxybenzyl iodide in 2.5 ml of abs. THF is added dropwise to this mixture, within the period of approximately 15 min, and the mixture is allowed to react at-75°C for a further 2.25 h. For the working-up, the reaction mixture is treated with 1.67 ml of propionic acid and 1.67 ml of water, and the temperature is allowed to rise to 0°C. The mixture is poured onto 20 ml of (cold) 10 % citric acid, and approximately 50 ml of (cold) ethyl acetate is added to this mixture. After stirring for a further 5 min, the phases are separated. The organic phase is washed, in succession, with saline, sat. sodium bicarbonate solution and saline once again. The combined aqueous phases are reextracted twice with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and concentrated. The residue which remains after removing the solvent is chromatographed on silica gel (hexane:ethyl acetate, 3:1), and the title compound thereby obtained. HPLC t Ret = 16.49 min (gradient II). FAB-MS (M+H) + =486 and M + =485. IR(KBr) = inter alia, 3312, 1759, 1686, 1603, 1537, 1165 and 1104 cm -1 . 1 H-NMR(CD 3 OD) = inter alia, 7.30-7.10 (m, 5H); 6.84 and 6.66 (each d, each 1H); 3.85, 3.82 and 3.87 (each s, each 3H); 1.30 (s, 9H). 22d) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid A solution of 1.354 g (2.685 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(2,3,4-trimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 43.36 ml of dimethoxyethane and 21.86 ml of water is treated, at RT, with 10.74 ml of a 1M solution of lithium hydroxide in water, and this reaction mixture is stirred for 2 h. It is then transferred to a separating funnel, diluted with 132 ml of sat. ammonium chloride solution and 11 ml of a 10 % citric acid solution (both cold), and this mixture is then extracted with ethyl acetate and a little THF. The title compound, which is dried under HV and subjected to further processing without being purified, is obtained after washing the organic phase with (cold) saline and drying it over sodium sulfate. TLC R f (C)=0.03. MS (M-H 2 O) + = 485. 22e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid A solution of 1.308 g (2.597 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanolc acid, 1.443 g (20.776 mmol) of imidazole and 1.816 g (11.686 mmol) of tert-butyldimethylchlorosilane in 13 ml of abs. DMF is stirred at RT for 17 h under argon. After that, the reaction mixture is poured onto ice-water and this mixture is extracted with ethyl acetate. The organic phase is washed with cold 10 % citric acid solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and evaporated on a RE at approximately 30°C. The resulting product is dissolved in 34.51 ml of methanol and 11.82 ml of THF, and this solution is treated, at RT, with 2.08 g of potassium carbonate in 11.82 ml of water. After it has been stirred for 2.5 h, the reaction mixture is concentrated down, at approximately 30°C, to half its volume and treated with ethyl acetate and 10 % citric acid solution (cold), and the phases are separated. The organic phase is washed a further two times with (cold) saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and concentrated. The residue is purified by chromatography on silica gel (hexane:ethyl acetate, 1:1, and then 1:1.5), and the title compound is obtained. TLC R f (J)=0.02. FAB-MS (M+H) + =618 IR(KBr) inter alia: 1712, 1495, 1366, 1101 and 836 cm -1 . 1 H-NMR(CD 3 OD) inter alia: 7.30-7.10 (m, 5H); 6.84 and 6.67 (each d, each 1H); 6.23 and 5.55 (each d, in all 1H from NH); 3.86, 3.81 and 3.80 (each s, each 3H); 1.31 and 1.20 (each s, in all 9H from Boc); 0.93 (s, 9H); 0.14 and 0.11 (each s, each 3H). 22f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A mixture of 250 mg (0.405 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid, 168.8 mg (0.445 mmol) of HBTU and 77.55 mg (0.445 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide [Example 1b)] in 3.8 ml of a 0.25 M solution of NMM in acetonitrile (2.35 equivalents) is stirred for 21 h under argon and at RT. After that, the reaction mixture is concentrated on a RE at approximately 30°C, and the residue is taken up in ethyl acetate; this solution is washed, in succession, with 10 % citric acid solution, water, sat. sodium bicarbonate solution and saline (all being cold). The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and concentrated. The crude product (title compound) is subjected to further processing without purification. TLC R f (A)=0.57. FAB-MS (M+H) + =774. HPLC t Ret = 21.68 min (gradient II). IR(KBr)= inter alia 1711, 1653, 1495, 1468, 1100 and 836 cm -1 . 1 H-NMR(CD 3 OD)=inter alia, 7.3-7.1 (m, 5H); 6.79 and 6.65 (each d, each 1H); 5.93 and 5.57 (each d, in all 1H from NH); 3.87, 3.83 and 3.80 (each s, each 3H); 3.35 (s, 2H); 1.30 and 1.20 (each s, in all 9H from Boc); 0.96 (s, 9H); 0.90 and 0.87 (each 3H); 0.18 and 0.16 (each s, each 3H).Altematively, the compound described in Example 22 can also be readily obtained in the following manner [see, in this context, J. Med. Chem. 37 , 2991 (1994)]: 22g) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 1 g (2.06 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(2,3,4-trimethoxyphenyl)-methyl]dihydrofuran-2-(3H)-one [prepared in accordance with Example 22c)] and 2.51 g (7 equivalents) of H-(L)-Val-N-(2-methoxyethyl)amide [prepared in accordance with Example 1b)] are reacted, at 70°C for 18 h, with 0.354 ml (3 equivalents) of acetic acid in a bomb tube. The mixture is allowed to cool down and the residue is taken up in ethyl acetate, and the organic phase is washed, in succession, with 1N hydrochloric acid, water and saline. After drying over sodium sulfate and removal of the solvent, the residue is recrystallized from ethanol/water. The resulting compound is identical to the title compound described In Example 22.Another alternative method for preparing the title compound from Example 22: 22h) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 500 mg (1.03 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(2,3,4-trimethoxy phenyl)methyl]dihydrofuran-2-(3H)-one [prepared in accordance with Example 22c)] and 538.5 mg (3 equivalents) of H-(L)-Val-N-(2-methoxyethyl)amide [prepared in accordance with Example 1b)] are reacted, at 90°C for 40 h, with 101 mg (1 equivalent) of 2-hydroxypyridine in a bomb tube. The residue is taken up in 4 ml of ethanol and poured onto 50 ml of water, and this mixture is stirred for 2 h. The crystalline precipitate is filtered off with suction, washed with water and dried. The resulting compound is identical to the title compound described in Example 22.Alternatively, and in a manner analogous to that indicated in Example 22c), the title compound described in that example can also be prepared using 2,3,4-trimethoxybenzyl bromide (instead of 2,3,4-trimethoxybenzyl iodide). The 2,3,4-trimethoxybenzyl bromide is prepared in the following manner 22i) 2,3,4-Trimethoxybenzyl bromide 2.04 g (10 mmol) of 2,3,4-trimethoxybenzyl alcohol in 30 ml of abs. toluene are treated with 0.258 ml (0.32 equivalents) of pyridine, and the solution is cooled down to approximately 4°C using ice-water. 0.951 ml of phosphorus tribromide in 5 ml of abs. toluene is added dropwise, at this temperature and over the period of 30 min, to this solution, which is left to stir at this temperature for a further 45 min. The reaction mixture is diluted with ether and the whole is poured onto ice-water, with this mixture then being stirred for 5 min. After the phases have been separated, the organic phase is washed, in succession, with water, saline, sat. sodium bicarbonate solution and once again with saline (all being cold). After the organic phase has been dried over sodium sulfate, it is concentrated, and residual solvents are removed from the residue under high vacuum for 1 h. The resulting title compound is subjected, without purification, to further processing. 1 H-NMR (200 MHz; CDCl 3 ) = 7.05/d (1 H); 6.65/d (1 H); 4.55/s (2H); 4.07, 3.88 and 3.85/each s (each 3H). Example 23: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19, 191 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxy-ethyl)amide in 4.6 ml of abs. DMF are desilylated with 159 mg of TBAF to give the title compound. The crude product is purified by chromatography on silica gel (eluent A), dissolved in dioxane and lyophilized. TLC R f (A)=0,26. FAB-MS (M+H) + =660. The starting material is prepared as follows: 23a) 3,4,5-Trimethoxybenzyl iodide In analogy with Example 19b), the title compound is obtained from 5 g of 3,4,5-trimethoxybenzyl chloride (Fluka, Buchs, Switzerland) and 16.89 g of sodium iodide in 40 ml of abs. acetone. TLC R f (hexane:ethyl acetate, 4:1)=0.27. 1 H-NMR (360 MHz, CDCl 3 ): 6.60 (s, 2H); 4.44 (s, 2H); 3.86 (s, 6H); 3.83 (s, 3H). 23b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(3,4,5-trimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 19c), 1 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one [Example 2b)] in 4 ml of abs. THF is deprotonated (-75°C) with 6.42 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and with the addition of 0.66 ml of DMPU and alkylated with 1.008 g 3,4,5-trimethoxybenzyl iodide. Chromatography on silica gel (eluent, hexane/acetone 3:1) affords the title compound. TLC R f (hexane/acetone, 3:1)=0.22. FAB-MS M + =485. 23c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoic acid In analogy with Example 19d), 1.097 g of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(3,4,5-trimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 36.48 ml of dimethoxyethane and 18.39 ml of water are hydrolysed with 9.03 ml of 1M lithium hydroxide solution to give the title compound, which is subjected, without purification, to further processing. 23d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoic acid In analogy with Example 19e), 1.526 g of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoic acid in 15.16 ml of DMF are silylated with 2.11 g of tert-butyldimethylchlorosilane and 1.683 g of imidazole. The silyl ester group in the crude product is detached, at RT in 2.5 h, in a mixture consisting of 40.3 ml of methanol, 13.8 ml of THF, 13.8 ml of water and 2.42 g of potassium carbonate. The title compound is purified by being chromatographed twice on silica gel (solvents: hexane, C and J). TLC R f (A)=0.39. FAB-MS (M+H) + =618. 23e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19f), 202 mg of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]hexanoic acid and 62.6 mg of H-(L)-Val-N-(2-methoxyethyl)amide [prepared in accordance with Example 1b)] in 3.07 ml of 0.25 M NMM/CH 3 CN are reacted with 136.4 mg of HBTU, and with a further 24.8 mg of HBTU, to form the title compound, which is subjected, without purification, to further processing, after a reaction time of 20 h. TLC R f (A)=0.32. FAB-MS (M+H) + =774. Example 24: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 599 mg (0.805 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 15.5 ml of abs. DMF are treated with 508 mg (1.61 mmol) of TBAF and the reaction mixture is stirred at RT for 20 h under argon. It is then diluted with approximately 80 ml of ethyl acetate, and the whole is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and concentrated down to approximately 30 ml on a RE. During this procedure, the title compound precipitates in pure form. The latter is filtered off with suction, washed with hexane and dried to constant weight. TLC R f (A) = 0.28.- FAB-MS (M+H) + =630.- HPLC t Ret = 14.79 min (gradient II).- IR(KBr) = inter alia 3463, 3340, 3305, 1685, 1648, 1620 und 1524 cm -1 .- 1 H-NMR(CD 3 OD) = inter alia 7.29-7.09/m (5H); 6.90/d (1H); 6.46/d (1H); 6.35/dxd (1H); 4.01/d (1H); 3.80 and 3.75/each s (each 3H); 3.30/s (3H); 1.35/s (9H); 0.83/pseudo t (6H).- The starting material is prepared as follows: 24a) 2,4-Dimethoxybenzyl bromide 2 g (11.77 mmol) of 2,4-dimethoxybenzyl alcohol (Aldrich, Steinheim, FRG) are dissolved in 30ml of abs. toluene, and this solution is treated with 0.3 ml of pyridine. The dear solution is cooled down to approximately 4°C and 1.12 ml (0.992 equivalents) of PBr 3 in 6 ml of abs. toluene are added dropwise to it over the space of 30 min. After a further 45 min, the reaction solution is poured onto ice-water and the whole is extracted with ether. The organic phase is washed, in succession, with water, sat. sodium bicarbonate soluton and saline (all being cold). The combined aqueous phases are reextracted with ether. The combined organic phases are dried over Na 2 SO 4 and the ether is removed on a RE at about 30°C. The toluene solution which remains, and which contains the title compound, is immediately subjected to further use. TLC (hexane:ethyl acetate, 1:1): decomposition. 24b) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(2,4-dimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one A solution of 3.57 g (11.7 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one [Example 2b)] in 12 ml of abs. THF and 2.35 ml of DMPU (1.65 equivalents) is cooled down to -75°C, under argon, and is treated dropwise, at an intemal temperature of less than -70°C and over a period of 30 min, with 22.9 ml (1.96 equivalents) of a 1 M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich, Steinheim, FRG). After a further 15 min, 25 ml of a toluene solution containing approximately 1 equivalent of 2,4-dimethoxybenzyl bromide is added dropwise to this mixture, over the space of 20 min, and this mixture is allowed to react at -70°C for 2 h. 4.36 ml of propionic acid and 4.36 ml of water are then added to this solution and the temperature is allowed to rise to 0°C. The reaction mixture is diluted with 200 ml of (cold) ethyl acetate and stirred up for 5 min with 60 ml of (cold) 10 % citric acid. After that, the phases are separated. The organic phase is washed, in succession, with saline, sat. sodium bicarbonate solution and with saline once again, dried over Na 2 SO 4 and concentrated. The title compound is isolated by flash chromatography on silica gel (E). TLC R f (E) = 0.24.- FAB-MS (M+H) + = 455. - HPLC t Ret = 16.85 min (gradient II). IR(CH 2 Cl 2 ) = inter alia 3429, 1769, 1712, 1613 and 1506 cm -1 .- 1 H-NMR(CDCl 3 ) = inter alia 7.34-7.10/m (5H); 6.98/d (1H); 6.45-6.29/m (2H); 4.31/txd (1H); 3.78 and 3.71/each s (each 3 H); 3.08 and 2.66/each dxd (each 1H); 1.35/s (9H). 24c) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoic acid A solution of 1.58 g (3.47 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(2,4-dimethoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 56 ml of ethylene glycol dimethyl ether and 28.2 ml of water is treated, at RT, with 13.87 ml of a 1M solution of LiOH in water, and this mixture is stirred for 1.75 h. After that, the reaction mixture is diluted with ethyl acetate and a little THF and the whole is washed firstly with a mixture consisting of 170.6 ml of sat. ammonium chloride solution and 14.25 ml of 10 % citric acid solution (both being cold) and then with saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and evaporated on a RE at about 30°C. The residue, which is the title compound, is triturated with hexane and filtered off with suction. M.p.: 144-145 C.- TLC Rf (D) = at the start.- FAB-MS (M+H) + = 474.- HPLC t Ret = 14.34 min (gradient II).- IR(KBr) = u.a. 3420, 3350, 2818, 1686, 1518 and 1508 cm -1 .- 1 H-NMR(CD 3 OD) = inter alia 7.30-7.09/m (5H); 6.94/d (1H); 6.47/d (1H); 6.37/dxd (1H); 3,78 and 3.75/each s (each 3 H); 1.33/s (9H).- 24d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoic acid A solution of 1.5 g (3.17 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoic add, 1.76 g (25.36 mmol) of imidazole and 2.22 g (14.26 mmol) of tert-butyldimethylchlorosilane in 16 ml of abs. DMF is stirred at RT for 20 h under argon. After that, the reaction mixture is poured onto ice-water and the whole is extracted with ethyl acetate. The organic phase is washed with cold 10 % citric acid solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 , and the solvent is removed on a RE at about 30°C. An oil is obtained which is dissolved in 42.1 ml of methanol and 14.4 ml of THF, and this solution is then treated, at RT, with 2.5 g of potassium carbonate in 14.4 ml of water. After it has been stirred at RT for 2 h, the reaction mixture is concentrated down to half its volume at approximately 30°C and the residue is diluted with ethyl acetate; the whole is then washed with 10 % citric add solution and with saline (both being cold). The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and evaporated. Chromatography on silica gel (D) affords the pure title compound. TLC R f (C) = 0.34.- FAB-MS (M+H) + = 588.- HPLC t Ret = 20.24 min (gradient II).-IR(KBr) = inter alia 1712, 1654, 1614, 1588 und 1507 cm -1 .- 1 H-NMR(CD 3 OD) = inter alia 7.30-7.10/m (5H); 6.98/d (1H); 6.50/d (1H); 6.40/dxd (1H); 3.80 and 3.76/each s (each 3 H); 1.31/s (9H); 0.93/s (9H); 0.14 and 0.11/each s (each 3H).- 24e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A mixture of 497 mg (0.845 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl]hexanoic acid, 352 mg (0.929 mmol) of HBTU and 162 mg (0.929 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide [Example 1b)] in 7.94 ml of a 0.25 M solution of NMM in acetonitrile (2.35 equivalents) is stirred at RT for 20 h under argon. After that, the reaction mixture is concentrated on a RE at about 30°C and the residue is taken up in ethyl acetate, with this solution being washed with sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 , and the solvent is removed on a RE. The residue consists of the title compound in virtually pure form. TLC R f (J) = 0.25.- FAB-MS (M+H) + = 744.- HPLC t Ret = 21.55 min (gradient II).- IR(CH 2 Cl 2 ) = inter alia 3434, 1703, 1667, 1506 and 838 cm -1 .- 1 H-NMR(CD 3 OD) = inter alia 7.31-7.11/m (5H); 6.91/d (1H); 6.50/d (1H); 6.37/dxd (1H); 3.84 and 3.76/each s (each 3H); 3.31/s (3H); 1.30/s (9H); 0.94/s (9H); 0.85 and 0.83/each d (each 3H); 0.16 and 0.15/each s (each 3H).- Example 25: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 311 mg (0.436 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 8.4 ml of abs. DMF are treated with 275 mg (0.871 mmol) of TBAF, and this reaction mixture is stirred at RT for 21 h under argon. It Is then diluted with approximately 60 ml of ethyl acetate, and the whole is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and concentrated down to 10 ml on a RE at approximately 30°C. During this procedure, the title compound is precipitated in pure form. It is filtered off with suction, washed with hexane and dried overnight under HV. TLC R f (ethyl acetate) = 0.38.- FAB-MS (M+H) + = 600.- HPLC t Ret = 14.78 min (gradient II).- IR(KBr) = inter alia 3335, 1685, 1653, 1619, and 1526 cm -1 .- 1 H-NMR(CD 3 OD) = inter alia 7.28-7.06/m (6H); 7.00/d (1H); 6.88/d (1H); 6.76/t (1H); 3.81/s (3 H); 3.48/s (3H); 1.33/s (9H); 0.81/pseudo t (6H).- The starting material is prepared as follows: 25a) 2-Methoxybenzyl chloride 16.8 ml of thionyl chloride are added dropwise, over the space of approximately 30 min, to 10 ml of 2-methoxybenzyl alcohol (Fluka, Buchs, Switzerland) and 53.76 g of diisopropylaminomethylpolystyrene (polyhünig base, see Ex. 19a)) in 200 ml of abs. ether. After the mixture has been stirred at 0°C for a further 1.5 h, it is filtered with suction and the filtrate is concentrated on a RE and under HV. The residue is purified by chromatography on silica gel (eluent: hexane/ethyl acetate, 6:1). TLC R f (hexane:ethyl acetate = 4:1)=0.5. 1 H-NMR (200 MHz, CDCl 3 ): 7.42-7.24 (m, 2H); 7.0-6.84 (m, 2H); 4.68 (s, 2H); 3.9 (s, 3H). 25b) 2-Methoxybenzyl iodide 2 g of 2-methoxybenzyl chloride in 22 ml of abs. acetone are treated with 9.3 g of sodium iodide and the reaction mixture is stirred at RT overnight. It is then diluted with 250 ml of ether and the whole is washed with 10 % sodium thiosulfate solution and saline. After drying over sodium sulfate, and removing the solvent, the title compound, which is subjected, without purification, to further processing, is obtained. TLC R f (hexane:ethyl acetate = 4:1)=0.46. 1 H-NMR (200 MHz, CDCl 3 ): 7.36-7.2 (m, 2H); 6.92-6.8 (m, 2H); 4.48 (s, 2H); 3.91 (s, 3H). 25c) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(2-methoxyphenyl)methyl]dihydrofuran-2-(3H)-one A solution of 1 g (3.275 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one [Example 2b)] in 4 ml of abs. THF and 0.66 ml of DMPU (1.67 equivalents) is cooled down to -75°C, under argon, and treated dropwise, at an internal temperature of below-70°C and over the space of 30 min, with 6.42 ml (1.96 equivalents) of a 1 M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich, Steinheim, FRG). After a further 15 min, 812 mg (3.275 mmol) of 2-methoxybenzyl iodide, dissolved in 2 ml of THF, are added dropwise to this mixture within the space of 10 min, and the whole is allowed to react at -70°C for 2 h. 1.22 ml of propionic acid and 1.22 ml of water are subsequently added to this solution, and the temperature is allowed to rise to 0°C. The reaction mixture is diluted with 50 ml of (cold) ethyl acetate and stirred, for 5 min, with 20 ml of (cold) 10 % citric acid, and, after that, the phases are separated. The organic phase is washed, in succession, with saline, sat. sodium bicarbonate solution and once again with saline, dried over Na 2 SO 4 and concentrated. The title compound is isolated by means of flash chromatography on silica gel (hexane:ethyl acetate = 3:1). TLC R f (hexane:ethyl acetate = 3:1) = 0.54.- MS M + = 455.- HPLC t Ret = 17.09 min (gradient II).- IR(CH 2 Cl 2 ) = inter alia 3429, 1769, 1712, and 1495 cm -1 .- 1 H-NMR(CDCl 3 ) = inter alia 7.38-7.13/m (5H); 7.20/d (1H); 7.08/d (1H); 6.87/t (1H); 6.81/d (1H); 3.74/s (3 H); 1.34/s (9H).- 25d) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]hexanoic acid A solution of 474 mg of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(2-methoxyphenyl)-methyl]dihydrofuran-2-(3H)-one in 18 ml of dimethoxyethane and 9.07 ml of water is treated dropwise, at RT, with 4.45 ml of a 1M lithium hydroxide solution. After that, the reaction mixture is stirred at RT for 3 h and diluted with ethyl acetate and THF, and the whole is washed in a separating funnel until neutral with a mixture consisting of 54.78 ml of sat. ammonium chloride solution and 4.58 ml of 10 % citric acid solution, followed by saline and water. The title compound, which is subjected to further processing without any further purification, is obtained after drying over sodium sulfate and removing the solvent. TLC R f (hexane/ethyl acetate 2.5:1)=0.15. 25e) 5 (S)-(Boc-Amino)-4(S)-(tert-butyldimethyls ilyloxy)-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]hexanoic acid A solution of 500 mg of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2-methoxyphenyl)-methyl]hexanoic acid in 5 ml of DMF is treated, while being stirred, with 614 mg of imidazole and 796 mg of tert-butyldimethylchlorosilane. After it has been stirred at RT for 20 h, the reaction solution is poured onto ice-water and the whole is extracted with ethyl acetate. The organic phase is washed with 10 % citric acid solution and saline. The silyl ester group in the crude product is detached, at RT in 2 h, In a mixture consisting of 13.29 ml of methanol, 5.13 ml of THF, 5.13 ml of water and 904 mg of potassium carbonate. The mixture is concentrated down to half its volume on a RE at approximately 30°C, and the residue is diluted with ethyl acetate, and the organic phase is washed with 10 % citric acid and saline (all being cold). The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and the residue is chromatographed on silica gel (eluent, hexane:ethyl acetate, 3:1 and 1:1), and the title compound is obtained. TLC R f (hexane/ethyl acetate 2.5:1)=0.12. FAB-MS (M+H) + =558. 25f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A mixture of 250 mg (0.448 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]hexanoic add, 187 mg (0.493 mmol) of HBTU and 86 mg (0.493 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide [Example 1b)] in 4.2 ml of a 0.25 M solution of NMM in acetonitrile (2.35 equivalents) is stirred at RT for 20 h under argon. After that, the reaction mixture is concentrated on a RE at approximately 30°C and residue is taken up in ethyl acetate, and the whole is washed, in succession, with 10 % citric acid solution, sat. sodium bicarbonate solution and saline (all being cold). The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and the solvent is removed on a RE. The residue consists of the title compound in virtually pure form. TLC R f (hexane:ethyl acetate 1:2) = 0.29.- FAB-MS (M+H) + = 714.- HPLC t Ret = 21.66 min (gradient II).- IR(CH 2 Cl 2 ) = inter alia 3435, 1704, 1667, 1495 and 836 cm -1 .- 1 H-NMR(CD 3 OD) = inter alia 7.29-7.10/m (6H); 7.02/d (1H); 6.91/d (1H); 6.80/t (1H); 3.86/s (3 H); 3.30/s (3H); 1.31/s (9H); 0.93/s (9H); 0.85/d (6H); 0.16 and 0.15/each s (each 3H).- Example 26: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 323.5 mg (0.436 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 8.4 ml of abs. DMF are treated with 280.7 mg (0.872 mmol) of TBAF, and this reaction mixture is stirred at RT for 20 h under argon. It is then diluted with approximately 80 ml of ethyl acetate and the whole is washed, in succession, with water, sat. sodium carbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated. The resulting gel-like product is chromatographed on silica gel (hexane:ethyl acetate, 1:2). The product-containing fractions are pooled and concentrated. The residue is dissolved in dioxane and lyophilized, with the title compound being obtained. TLC R f (hexane:ethyl acetate 1:2)=0.18. FAB-MS (M+H) + =628. HPLC t Ret = 15.52 min (gradient II). IR(KBr)= inter alia 1688, 1650, 1619, 1519 and 1261 cm -1 . 1 H-NMR(CD 3 OD)= inter alia 7.31-7.10 (m, 5H); 6.87 and 6.63 (each d, each 1H); 4.03 (d, 1H); 3.75, 2.20 and 2.11 (each s, each 3H); 1.35 (s, 3H); 0.83 (pseudo t, 6H). The starting material is prepared as follows: 26a) 2,3-Dimethyl-4-methoxybenzyl chloride 1 g (6.016 mmol) of 2,3-dimethyl-4-methoxybenzyl alcohol (Aldrich, Steinheim, FRG) and 4.8 g of diisopropylaminomethylpolystyrene (polyhünig base, see Ex. 19a) in 21 ml of abs. ether are treated dropwise, at from 0°C to 5°C and over the space of approximately 25 min, with 0.482 ml of thionyl chloride. After the reaction has ended, the mixture is filtered with suction and the solvent and the excess reagent are removed. The residue, which is the desired title compound, is subjected, without purification, to further processing. TLC R f (hexane:ethyl acetate 4:1)=0.59. IR(CH 2 Cl 2 ) inter alia: 1599, 1485, 1466 und 1107 cm -1 . 1 H-NMR (200 MHz, CDCl 3 ): 7.14 (d, 1H); 6.69 (d, 1H); 4.64 (s, 2H); 3.82, 2.34 and 2.18 (each s, each 3H). 26 b) 2,3-Dimethyl-4-methoxybenzyl iodide 838.6 mg (4.54 mmol) of 2,3-dimethyl-4-methoxybenzyl chloride in 8.5 ml abs. acetone are treated with 3.328 g (22.1 mmol) of sodium Iodide, and this mixture is stirred at RT for 15 h while excluding light. A dark-brown suspension is obtained which is taken up, for working-up, in 100 ml of diethyl ether with this solution then being washed with 10 % sodium thiosulfate solution. After drying with sodium sulfate and removing the solvent, the desired title compound is obtained as a yellowish solid which is subjected, without purification, to further processing. TLC R f (hexane:ethyl acetate 4:1)=0.63. IR (CH 2 Cl 2 ) inter alia: 1610, 1495, 1120 and 820 cm -1 . 1 H-NMR (200 MHz, CDCl 3 ): 7.17 and 6.65 (each d, each 1H); 4.52 (s, 2H); 3.82, 2.23 and 2.18 (each s, each 3H). 26c) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]dihydrofuran-2(3H)-one A solution of 1.248 g (4.087 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one (Example 2b)) in 5 ml of abs. THF and 0.823 ml (6.825 mmol) of DMPU is cooled down to -75°C, under argon, and treated dropwise, at an internal temperature of below-70°C and over the space of approximately 17 min, with 8 ml of a 1M solution of lithium bis(trimethylsiiyl)amide in THF (Aldrich). After a further 15 min, a solution of 1.128 g (4.087 mmol) of 2,3-dimethyl-4-methoxybenzyl iodide in 3 ml of abs. THF is added dropwise to this mixture within the space of 10 min, and the whole is allowed to react at -75°C for a further 2 h. For the working-up, the reaction mixture is treated with 1.5 ml of propionic acid and 1.5 ml of water and the temperature is allowed to rise to 0°C. The mixture is poured onto 35 ml of (cold) 10 % citric acid solution, and approximately 70 ml of (cold) ethyl acetate is added to this mixture. After stirring for a further 5 min, the phases are separated. The organic phase is washed, in succession, with saline, sat. sodium bicarbonate solution and with saline once again, dried over Na 2 SO 4 and concentrated. The residue which remains after removing the solvent is chromatographed on silica gel (hexane:ethyl acetate, 2:1). The title compound is obtained as a colourless foam. TLC R f (hexane:ethyl acetate 2:1)=0.37. HPLC t Ret =17.83 min (gradient II). FAB-MS (M+H) + _453. IR(CH 2 Cl 2 )= inter alia 3428, 1769, 1712 and 1495 cm -1 . 1 H-NMR(CDCl 3 )= inter alia 7.38-7,08 (m, 5H); 6.86 and 6.62 (each d, each 1H); 3.78 (3H); 3.21 and 2.16 (each dxd, each 1H); 2.19 and 2.13 (each s, each 3H); and 1.35(s,9H). 26d) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)-methyl]hexanoic acid A solution of 1.001 g (2.2 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]dihydrofuran-2-(3H)-one in 35.8 ml of dimethoxyethane and 18 ml of water is treated, at RT, with 8.8 ml of a 1M solution of lithium hydroxide in water, and this reaction mixture is stirred for 2.5 h. It is then transferred to a separating funnel and diluted with 108.5 ml of sat. ammonium chloride solution and 9 ml of a 10 % citric add solution (both being cold); the whole is then extracted with ethyl acetate and a little THF. The title compound, which is subjected to further processing without being purified, is obtained after washing the organic phase with (cold) saline and drying it over sodium sulfate. TLC R f (hexane:ethyl acetate 1:1)=at the start. FAB-MS (M+H) + =472; IR(KBr) inter alia: 1724, 1666, 1527 and 1169 cm -1 . 1 H-NMR(CD 3 OD) inter alia: 7.31-7.11 (m, 5H); 6.93 and 6.68 (each d, each 1H); 3.76 (s, 3H); 3.23 and 2.59 (each dxd, each 1H); 2.21 and 2.12 (each s, each 3H); 1.27 (s, 9H). 26e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]hexanoic acid A solution of 1.153 g (2.445 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]hexanoic acid, 1.372 g (20.05 mmol) of imidazole and 1.709 g (11.0 mmol) of tert-butyldimethylchlorosilane in 8.7 ml of abs. DMF is stirred at RT for 18 h under argon. After that, the reaction mixture is poured onto ice-water and the whole is extracted with ethyl acetate. The organic phase is washed with cold 10 % citric acid solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and evaporated on a RE at approximately 30°C. The resulting product is dissolved in 28.8 ml of methanol and 11.2 ml of THF, and this solution is treated, at RT, with 1.962 g of potassium carbonate in 11.2 ml of water. After having been stirred for 2.25 h, the reaction mixture is concentrated down to half its volume at approximately 30°C and the residue is treated with ethyl acetate and (cold) 10 % citric acid solution, and the phases are separated. The organic phase is washed a further two times with saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated. The residue is purified by being chromatographed twice on silica gel (hexane:ethyl acetate, 1:1 and then 3:1), and the title compound is obtained. TLC R f (hexane:ethyl acetate. 1:1)=0.42. FAB-MS (M+H) + =586. IR (KBr) inter alia: 1711, 1485, 1260 and 1107 cm -1 . 1 H-NMR (CD 3 OD) inter alia: 7.30-7.06 (m, 5H); 6.91 and 6.65 (each d, each 1H); 6.00 and 5.41 (each d, in all 1 H from NH); 3.75 (s, 3H); 2.21 and 2.12 (each s, each 3H); 1.31 and 1.21 (each s, in all 9H from Boc); 0.89 (s, 9H); 0.12 and 0.08 (each s, each 3H). 26f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxylethyl)amide A mixture of 319.6 mg (0.546 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]hexanoic acid, 232.5 mg (0.613 mmol) of HBTU and 106.8 mg (0.613 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (preparation, see Example 1b)) in 5.3 ml of a 0.25 M solution of NMM in acetonitrile (2.4 equivalents) is stirred at RT for 2.25 h under argon. After that, the reaction mixture is concentrated on a RE at approximately 30°C and the residue is taken up in ethyl acetate; this solution is then washed, in succession, with 10 % citric acid, sat. sodium bicarbonate solution and saline (all being cold). The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over Na 2 SO 4 and concentrated. The crude product is chromatographed twice on silica gel (hexane:ethyl acetate, 1:2 and 1:1), and the title compound is obtained. TLC R f (hexane:ethyl acetate, 1:1)= 0.16. FAB-MS (M+H) + = 742. HPLC t Ret =22.41 min (gradient II). IR(CH 2 Cl 2 )= inter alia 3434, 1701, 1667, 1499 and 1165 cm -1 . 1 H-NMR(CD 3 OD) = inter alia 7.3-7.1 (m, 5H); 6.85 and 6.64 (each d, each 1H); 5.59 and 5.61 (each d, in all 1H from NH); 3.75 (s, 3H); 2.16 and 2.02 (each s, each 3H); 1.31 and 1.20 (each s, in all 9H from Boc); 0.95 (s, 9H); 0.68 and 0.66 (each d, each 3H); 0.17 and 0.16 (each s, each 3H). Example 27: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4,5-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19, the title compound is obtained from 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4,5-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in abs. DMF using TBAF. [The starting compound for the 2,4,5-trimethoxybenzyl substituent can be bought from Fluka, Buchs, Switzerland, as 2,4,5-trimethoxybenzaldehyde, from which the corresponding alcohol is obtained as an intermediate by reducing with sodium borohydride]. Example 28: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4,6-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19, the title compound is obtained from 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,4,6-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in abs. DMF using TBAF. [The starting compound for the 2,4,6-trimethoxybenzyl substituent can be bought from Fluka, Buchs, Switzerland, as 2,4,6-trimethoxybenzaldehyde, from which the corresponding alcohol is obtained as an intermediate by reducing with sodium borohydride]. Example 29: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,5-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19, the title compound is obtained from 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,5-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in abs. DMF using TBAF. [The starting compound for the 2,5-dimethoxybenzyl substituent can be bought from Fluka, Buchs, Switzerland as 2,5-dimethoxybenzyl alcohol]. Example 30: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,6-dimethoxyph enyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide In analogy with Example 19, the title compound is obtained from 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,6-dimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in abs. DMF using TBAF. [The starting compound for the 2,6-dimethoxybenzyl substituent, 2,6-dimethoxybenzyl alcohol, is prepared from methyl 2,6-dimethoxybenzoate by reduction with lithium aluminium hydride in abs. THF. Methyl 2,6-dimethoxybenzoate is obtained from 2,6-dimethoxybenzoic acid (Fluka, Buchs, Switzerland) by reaction with dimethyl sulfate in acetone and in the presence of potassium carbonate (see instructions in Chem. Letters, 1990, 389)]. Example 31: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 1.21 g (1.41 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 31f)) in 31 ml of DMF are desilylated with 890 mg (2.82 mmol) of TBAF under an N 2 atmosphere. After 18 h at RT, the mixture is poured onto 430 ml of water and the whole is extracted with 3 portions of ethyl acetate/methanol, -10:1. The organic phases are washed 2 times with sat. NaHCO 3 solution and with saline, dried with Na 2 SO 4 and evaporated to give the title compound: TLC R f (F)=0.38; t Ret (II)=16.4 min; FAB-MS (M+H) + =750. The starting material is prepared as follows: 31a) 5(S)-[1(S)-(Boc-Amino)-2-(p-hydroxyphenyl)ethyl]-dihydrofuran-2-(3H)-one Hydrogenating 3.0 g (7.29 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]-dihydrofuran-2-(3H)-one [preparation, see Example 1g)] in 100 ml of methanol with 0.6 g of 10 % Pd/C results in the title compound, after filtering off the catalyst and evaporating the filtrate: t Ret (II)=10.6 min. 31b) 5(S)-[1(S)-(Boc-Amino)-2-[p-(2-methoxyethoxy)phenyl]ethyl]dihydrofuran-2-(3H)-one 3.17 g (9.86 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-hydroxyphenyl)ethyl]dihydrofuran-2-(3H)-one in 190 ml of DMF/dioxane, 1:1, are treated, under an N 2 atmosphere, with 6.4 g (19.7 mmol) of Cs 2 CO 3 and 2.0 g (9.86 mmol) of 2-methoxyethyl iodide. Since HPLC indicates that unreacted 5(S)-[1(S)-(Boc-amino)-2-(p-hydroxyphenyl)ethyl]dihydrofuran-2-(3H)-one is still present after 18 h at RT, a further 1.2 g of 2-methoxyethyl iodide are added in portions. As soon as HPLC indicates that the reaction Is complete, the reaction mixture is poured onto 190 ml of ice-water, and the whole is extracted 3x with methylene chloride. The organic phases are washed with water and saline, dried with Na 2 SO 4 and evaporated. Stirring up the residue with hexane in an ultrasonication bath affords the title compound: TLC R f (D)=0.08; FAB-MS (M+H) + =380. 31b') 2-Methoxyethyl iodide A solution of 10 ml (109 mmol) of 2-chloroethyl methyl ether in 205 ml of acetone is treated in portions with 80.1 g (534 mmol) of Nal, and the mixture is boiled under reflux for 20 h. Partitioning the reaction mixture between 2 portions of ether and saline, drying the organic phases with Na 2 SO 4 and evaporating them (RT, 300 mbar) affords the title compound: 1 H--NMR (200 MHz, CDCl 3 ): 3.25 (t, J=7 Hz, 2 H), 3.39 (s, 3 H), 3.65 (t, J= 7 Hz, 2 H). 31c) 5(S)-[1(S)-(Boc-Amino)-2-[p-(2-methoxyethoxy)phenyl]ethyl]-3(R)-[(p-benzyloxyphenyl)methyl]dihydrofuran-2-(3H)-one Under an N 2 atmosphere, 3,6 g (9,48 mmol) of 5(S)-[1(S)-(Boc-amino)-2-[p-(2-methoxyethoxy)phenyl]ethyl]dihydrofuran-2-(3H)-one, dissolved In 17.3 ml of THF and 1.9 ml of DMPU, are deprotonated, at -70°C, with 18.58 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and, after 15 min, alkylated with 3.07 g (9.48 mmol) of p-benzyloxybenzyl iodide (Example 1d)) in 6 ml of THF. After 30 min at -75°C, the mixture is protonated with 3.53 ml (47.4 mmol) of propionic acid and 3.53 ml of water and warmed to 0°C. The reaction mixture is diluted with 95 ml of ethyl acetate and the whole is washed with 10 % citric acid solution, sat. NaHCO 3 solution and saline. The aqueous phases are extracted with 2 portions of ethyl acetate. The organic phases are dried with Na 2 SO 4 and evaporated. Column chromatography (SiO 2 , hexane/ethyl acetate, 1:1) and crystallization from ethyl acetate/hexane yields the pure title compound: TLC R f (C)=0.38; t Ret (II)=18.0 min; FAB-MS (M+H) + =576. 31d) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid 3.85 g (6.68 mmol) of 5(S)-[1(S)-(Boc-amino)-2-[p-(2-methoxyethoxy)phenyl]ethyl]-3(R)-[(p-benzyloxyphenyl)methyl]dihydrofuran-2-(3H)-one in 107 ml of dimethoxyethane and 54 ml of water are hydrolysed, under a protective gas, with 26.5 ml of a 1 M lithium hydroxide solution. After 17 h at RT, the reaction mixture is treated with an ice-cold mixture of 324 ml of sat. NH 4 Cl solution, 27 ml of 10 % citric acid solution and 134 ml of methylene chloride. Methanol is added in order to dissolve the product completely. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with saline, dried with Na 2 SO 4 and evaporated: t Ret (II)=15.8 min; FAB-MS (M+H) + =594. 31e) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-[p-(2-methoxyethoxy) phenyl]-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid 3.85 g (6.48 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)--[(p-benzyloxyphenyl)methyl]hexanoic acid in 11 ml of DMF are silylated, at RT for 16 h and under a protective gas, with 4.49 g (29.8 mmol) of tert-butyldimethylchlorosilane and 3.6 g (53.1 mmol) of imidazole. The reaction mixture is poured onto ice-water and the whole is extracted 3 times with ethyl acetate. The organic phases are washed with 10 % citric acid solution, 2 times with water and with saline, dried with Na 2 SO 4 and evaporated. The residue is dissolved in 79 ml of methanol and 30 ml of THF, and this solution is treated with 5.37 g of potassium carbonate and 30 ml of water and stirred at RT for 3 h. The reaction mixture is subsequently poured onto an ice-cold 10 % citric acid solution, and this mixture is extracted 3 times with ethyl acetate. The organic phases are washed with 2 portions of H 2 O and saline, dried with Na 2 SO 4 and evaporated. Column chromatography (SiO 2 , hexane/ethyl acetate, 1:1) affords the title compound: TLC R f (C)=0,28; t Ret (II)=20.9 min. 31f) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-[p-(2-methoxyethoxylphenyl]-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 1.00 g (1.41 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid and 270 mg (1.55 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b)) in 13.5 ml of 0.25 M NMM/CH 3 CN are reacted, under a protective gas, with 588 mg (1.55 mmol) of HBTU. After 18 h at RT, the mixture is finally evaporated. The residue is taken up in ethyl acetate, and the solution is washed with water, 2x with 10 % citric acid solution, water, 2x with sat. NaHCO 3 solution, 1x with water and 1x with saline. The aqueous phases are extracted a further 2 x with ethyl acetate, and the organic phases are dried with sodium sulfate and evaporated. The title compound is obtained: t Ret (II)=22.7 min; FAB-MS (M+H) + =864. Example 32: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Hydrogenating a solution of 600 mg (0.80 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-benzyloxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 31) in 20 ml of methanol in the presence of 200 mg of 10 % Pd/C, filtering the mixture and evaporating it, results in the title compound: TLC R f (F)=0,19; t Ret (II)=12.3 min; FAB-MS (M+H) + =660. Example 33: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Under an N 2 atmosphere, 100 mg (0.152 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 32) in 3 ml of DMF/dioxane, 1:1, are treated, at 0°C, with 98.7 mg (0.303 mmol) of Cs 2 CO 3 and 9.4 µl (0.152 mmol) of methyl iodide, and the mixture is stirred at RT for 24 h. Since HPLC indicates that the starting material is still present, a further 6 µl of methyl iodide are added. After a further 20 h at RT, the reaction mixture is poured onto water and the whole is extracted with 3 portions of methylene chloride. The organic phases are washed with water and saline, dried with Na 2 SO 4 and evaporated. Recrystallizing from methylene chloride, a little methanol and DIPE yields the title compound: TLC R f (H)=0.47; t Ret (II)=14.0 min; FAB-MS (M+H) + =674. Example 34: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-{[p-(2-methoxyethoxy)phenyl]methyl}-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Under an N 2 atmosphere, 100 mg (0.152 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-hydroxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 32) in 3 ml of DMF/dioxane, 1:1, are treated, at 0°C, with 98.7 mg (0.303 mmol) of Cs 2 CO 3 and 40 mg (0.152 mmol) of 2-methoxyethyl iodide (Example 62b'), and the mixture is stirred at RT for 24 h. Since HPLC indicates that starting material is still present, a further 60 mg of 2-methoxyethyl iodide are added in 3 portions, with the mixture being stirred at RT for a few hours on each occasion. Precipitating out of the reaction mixture with 4 ml of ice-water, filtering, column chromatography (SiO 2 , methylene chloride/THF, 3:1), and digesting in hexane, yields the pure title compound: TLC R f (H)=0.59; t Ret (II)=13.9 min; FAB-MS (M+H) + =718. Example 35: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 0.21 g (0.276 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 4 ml of DMF is desilylated, under an N 2 atmosphere, with 0.174 g (0.55 mmol) of TBAF. After 18 h at RT, the reaction mixture is poured onto water and the whole is extracted with 3 portions of ethyl acetate. The organic phases are washed with sat. NaHCO 3 solution and saline, dried with Na 2 SO 4 and evaporated. Stirring up in DIPE affords the title compound: TLC R f (B)=0.55; t Ret (II)=16.5 min; FAB-MS (M+H) + =646. The starting material is prepared in the following manner: 35a) 5(S)-[1(S)-(Boc-Amino)-2-phenylethyl]-3(R)-[(4-biphenyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 5d), 5.0 g (16.37 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-dihydrofuran-2-(3H)-one dissolved in 24 ml of THF and 2.8 ml of DMPU are deprotonated, at -70°C, with 32.7 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated (from -75°C to -50°C) with 6.07 g (24.6 mmol) of 4-biphenylylmethyl bromide (Salor; Milwaukee/USA) In 20 ml of THF. Protonating with 6.1 ml (81.9 mmol) of propionic acid and 6.1 ml of water, at -75°C, extracting and medium pressure chromatography (gradient: 0-1 % ethyl acetate in toluene) affords the title compound: TLC R f (D)=0.57; t Ret (II)=18.8 min. 35b) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(4-biphenylyl)methyl]hexanoic acid 1.3 g (2.76 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]-3(R)-[(4-biphenylyl)methyl]-dihydrofuran-2-(3H)-one are hydrolysed, in 28 ml of dimethoxyethane, with 11 ml of a 1 M solution of lithium hydroxide in water. After 16 h at RT, the dimethoxyethane is evaporated off on a RE and the residue is treated with an ice-cold mixture of 15 ml of sat. NH 4 Cl solution, 80 ml of 10 % citric acid solution and methylene chloride. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with saline, dried with Na 2 SO 4 and evaporated to give the title compound: TLC R f (B)=0.4; t Ret (II)=16.4 min. 35c) 5 (S)-(Boc-Amino-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(4-biphenylyl)methyl]hexanoic acid Under a protective gas, 1.23 g (2.51 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl)-2(R)-[(4-biphenylyl)methyl]hexanoic acid in 25 ml of DMF are silylated, at RT and for 20 h, with 1.74g (11.5mmol) of tert-butyldimethylchlorosilane and 1.40 g (20.6 mmol) of imidazole. The reaction mixture is evaporated and the residue is taken up in ethyl acetate, with this solution being washed with sat. NaHCO 3 solution, water and saline. The aqueous phases are extracted 2x with ethyl acetate and the organic phases are dried with Na 2 SO 4 and evaporated. The residue is dissolved in 30 ml of methanol and 7 ml of THF, and this solution is treated with 2.0 g of potassium carbonate and 7 ml of water and stirred at RT for 1 h. The reaction mixture is then partially evaporated and the residue is diluted with ice-cold 10 % citric acid solution and the whole extracted 3x with ethyl acetate. The organic phases are washed with 2 portions of water and saline, dried with Na 2 SO 4 and evaporated. Medium pressure chromatography (gradient: 0-50 % ethyl acetate in hexane) results in the title compound: TLC R f (C)=0.56; t Ret (II)=22.1 min. 35d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 280 mg (0.46 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(4-biphenylyl)methyl]hexanoic acid in 4.44 ml of 0.25 M NMM/CH 3 CN are activated, under an N 2 atmosphere, with 193 mg (0.51 mmol) of HBTU. After 5 min. 90 mg (0.51 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b)) are added and the mixture is thoroughly stirred at RT for 20 h. Working up in an analogy with Example 1c), and digestion of the crude product in hexane, results in the title compound: TLC R f (D)=0.2; t Ret (II)=22.7 min. Example 36: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Under a protective gas, 1.4 g (1.6 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 30 ml of DMF are desilylated with 1.0 g (3.2 mmol) of TBAF and, after 20 h, are worked up in analogy with Example 35. Column chromatography (silica gel, methylene chloride → methylene chloride/methanol 9:1) and stirring up in DIPE affords the title compound: t Ret (II)=18.0 min; FAB-MS (M+H) + =752. The starting material is prepared in the following manner: 36a) 5(S)-[1(S)-(Boc-Amino)-2-(p-benzyloxyphenyl)-ethyl]-3(R)-[(4-biphenylyl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 5d), 5.55 g (13.5 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]dihydrofuran-2-(3H)-one [preparation, see Example 1g)], dissolved in 20 ml of THF and 2.3 ml of DMPU, are deprotonated, at -70°C, with 27 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated (1 h) with 5.0 g (20.2 mmol) of 4-biphenylylmethyl bromide (Salor; Milwaukee, USA) in 16 ml of THF. Protonating with 5 ml (67.4 mmol) of propionic acid and 5 ml of water, at -75°C, extracting and medium pressure chromatography (gradient: 30-50 % ethyl acetate in toluene) results in the title compound: TLC R f (Q)=0.15; t Ret (II)=20.0 min. 35b) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylylmethyl] hexanoic acid 4.56 g (7.9 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]-3(R)-[(4-biphenylyl)methyl]dihydrofuran-2-(3H)-one are hydrolysed, in 80 ml of dimethoxyethane, with 31.6 ml of a 1 M solution of lithium hydroxide in water. After 18 h at RT, the dimethoxyethane is evaporated off on a RE and the residue Is treated with an ice-cold mixture of 43 ml of sat. NH 4 Cl solution, 229 ml of 10 % citric acid solution and methylene chloride. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with saline, dried with Na 2 SO 4 and evaporated. Crystallization from DIPE yields the title compound: t Ret (II)=17.9 min. 35c) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoic acid 3.19 g (5.4 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoic acid in 55 ml of DMF are silylated, at RT for 20 h and under a protective gas, with 3.71 g (24.6 mmol) of tert-butyldimethylchlorosilane and 3.0 g (44 mmol) of imidazole. The reaction mixture is evaporated and the residue is taken up in ethyl acetate; this solution is then washed with sat. NaHCO 3 solution, water and saline. The aqueous phases are extracted 2x with ethyl acetate and the organic phases are dried with Na 2 SO 4 and evaporated. The residue is dissolved in 64 ml of methanol and 15 ml of THF, and this solution is treated with 4.5 g of potassium carbonate and 15 ml of water and stirred at RT for 1 h. Working up in analogy with Example 88c), and medium pressure chromatography (gradient: 0-10 % methanol in methylene chloride), results in the title compound: TLC R f (B)=0.7; t Ret (II)=22.7 min. 35d) 5 (S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 1000 mg (1.44 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoic add in 13.8 ml of 0.25 M NMM/CH 3 CN are activated, under an N 2 atmosphere, with 601 mg (1.58 mmol) of HBTU. After 5 min, a quantity of 276 mg (1.58 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b) is added and the mixture is thoroughly stirred at RT for 20 h. Working up in analogy with Example 1c), and medium pressure chromatography (gradient: 40-60 % ethyl acetate in hexane), results in the title compound: TLC R f (C)=0.33; t Ret (II)=23.5 min. Example 37: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Hydrogenating 200 mg (0.265 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxy-ethyl)amide (Example 36) in 20 ml of methanol/methylene chloride, 1:1, in the presence of 0.1 g of 10 % Pd/C, filtering off the catalyst and evaporating, affords the title compound: t Ret (II)=14.5 min; FAB-MS (M+H) + =662. Example 38: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-[(4-biphenyly l)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A solution of 173 mg (0.26 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[(4-biphenylyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 37) in 5 ml of DMF/dioxane, 1:1, is treated, under an N 2 atmosphere and while cooling with ice, with 170 mg (0.52 mmol) of Cs 2 CO 3 and 16 µl (0.26 mmol) of methyl iodide. After the mixture has been stirred at RT for 20 h, 4.5 ml of ice-water are added and the mixture is finally diluted with water and methylene chloride. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with water and saline, dried with Na 2 SO 4 and evaporated. Stirring up the residue in hexane affords the title compound: t Ret (II)=16.2 min; FAB-MS (M+H) + =676. Example 39: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Under an N 2 atmosphere, 2.11 g (2.36 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyt)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide in 49 ml of DMF are desilylated with 1.49 g (4.7 mmol) of TBAF and, after 20 h, worked up in analogy with Example 88). Stirring up in hexane affords the title compound: t Ret (II)=17.4 min; FAB-MS (M+H) + =777. The starting material is prepared in the following manner: 39a) 5(S)-[1(S)-(Boc-Amino)-2-(p-benzyloxyphenyl)ethyl]-3(R)-[({2'-cyanobiphenyl}-4-yl)methyl]dihydrofuran-2-(3H)-one In analogy with Example 5d), 5.00 g (12.1 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]dihydrofuran-2-(3H)-one [preparation, see Example 1g)], dissolved in 22 ml of THF and 2.4 ml of DMPU, are deprotonated, at -70°C, with 23.5 ml of a 1 M solution of lithium bis(trimethylsilyl)amide in THF, and alkylated (2 h) with 3.43 g (12.1 mmol) of 4-(bromomethyl)-2'-cyanobiphenyl [96 %; for preparation, see for example: J. Med. Chem. 34 , 2525 (1991)]. Protonating with 4.5 ml of propionic acid and 4.5 ml of water, at -75°C, extracting, column chromatography (silica gel, hexane/ethyl acetate, 2:1) and recrystallization from hot ethyl acetate/hexane, results in the title compound: TLC R f (D)=0.3; t Ret (II)=19.0 min; FAB-MS (M+H) + =603. 39b) 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoic acid (lithium salt) 4.59 g (7.6 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-benzyloxyphenyl)ethyl]-3(R)-[({2'-cyanobiphenyl}-4-yl)methyl]dihydrofuran-2-(3H)-one in 120 ml of dimethoxyethane and 61 ml of water are stirred together with 30 ml of a 1 M solution of lithium hydroxide in water, with a white suspension being formed. After 16 h at RT, the crystals are filtered off with suction and washed with dimethoxethane (→ lithium salt of the title compound): anal. calc. for C 38 H 39 N 2 O 6 Li x 2 H 2 O: C 68.87 %, H 6.54 %, N 4.23 %, H 2 O 5.44; found:C 68.4 %, H 6.5 %, N 4.2 %, H 2 O 5.23; t Ret (II)=17.2 min; FAB-MS (M+H) + =627. The mother liquor is partially evaporated and the residue is treated with an ice-cold mixture of 340 ml of sat. NH 4 Cl solution, 30 ml of 10 % citric acid solution and methylene chloride. The aqueous phase is separated off and extracted 2x with methylene chloride. Washing the organic phases with saline, drying them with Na 2 SO 4 and evaporating them yields the title compound as a free acid. 39c) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoic acid 4.7 g (7.5 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoic acid (lithium salt) in 8.1 ml of DMF is stirred, at RT for 20 h, together with 5.2 g (34.6 mmol) of tert-butyldimethylchlorosilane and 4.18 g (61.4 mmol) of imidazole while excluding moisture. Since HPLC indicates that starting material is still present, a further 1.02 g of imidazole and 1.13 g of tert-butyldimethylchlorosilane are added. After 2 days, the reaction mixture is poured onto ice-water and the whole is extracted 3x with ethyl acetate. The organic phases are washed with 10 % citric acid solution, water and saline, dried with Na 2 SO 4 and evaporated. The residue is taken up in 91 ml of methanol and 34 ml of THF, and this solution is treated with 6.2 g of potassium carbonate and 34 ml of water, and stirred at RT for 1.5 h. The reaction mixture is subsequently partially evaporated and the residue is diluted with ice-cold 10 % citric acid solution with the whole then being extracted with 3x ethyl acetate. The organic phases are washed with 2 portions of water and saline, dried with Na 2 SO 4 and evaporated. Column chromatography (silica gel, hexane/ethyl acetate, 1:1) results in the title compound: TLC R f (C)=0.21; t Ret (II)=22.0 min. 39d) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide 2.00 g (2.72 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoic add, 652 mg (4.83 mmol) of HOBT, 1.54 g (8.05 mmol) of EDC and 1.17 ml (8.37 mmol) of triethylamine are initially introduced in 24 ml of DMF under an N 2 atmosphere. 674 mg (3.87 mmol) of H-(L)-Val-N-(2-methoxyethyl)amide (Example 1b) are added to this mixture, and the whole is thoroughly stirred at RT overnight. The reaction mixture is evaporated under HV. The residue is partitioned between 3 portions of methylene chloride, 10 % citric acid solution, sat. NaHCO 3 solution and saline. Drying the organic phases with Na 2 SO 4 , evaporating them, and recrystallizing the residue from hot ethyl acetate/hexane, affords the title compound: t Ret (II)=22.7 min; FAB-MS (M+H) + =891. Example 40: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide Hydrating 1.20 g (1.54 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 39) in 40 ml of methanol and 15 ml of THF in the presence of 0.24 g of 10 % Pd/C, filtering off the catalyst, evaporating, and precipitating with DIPE from a concentrated solution in methanol, affords the title compound: t Ret (II)=13.7 min; FAB-MS (M+H) + =687. Example 41: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide A solution of 100 mg (0.145 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[({2'-cyanobiphenyl}-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (Example 40) in 3 ml of DMF/dioxane, 1:1 is treated, under an N 2 atmosphere and while being cooled with ice, with 94.6 mg (0.29 mmol) of Cs 2 CO 3 and 9 µl (0.145 mmol) of methyl iodide. After the mixture has been stirred at RT for 20 h, HPLC indicates that starting material is still present; the same quantities of Cs 2 CO 3 and methyl iodide are therefore added once again and the mixture is stirred over a further night. 2.5 ml of ice-water are added to the reaction mixture and the suspension is diluted with water and methylene chloride. The aqueous phase is separated off and extracted 2x with methylene chloride. The organic phases are washed with water and saline, dried with Na 2 SO 4 and evaporated. Column chromatography (silica gel, methylene chloride/THF 15:1 → 4:1) and stirring up the residue in hexane affords the title compound: TLC R f (R)=0.1; t Ret (II)= 15.5 min; FAB-MS (M+H) + =701. Example 42: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-ethoxyethyl)amide 1120 mg (1.42 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-ethoxyethyl)amide in 14 ml of abs. DMF are treated with 920 mg (2.84 mmol) of TBAF, and the reaction mixture is stirred at RT for 21 h under argon. It is then poured onto cold saline and the solid is filtered. This solid is dissolved in ethyl acetate and the solution is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated at approximately 30°C. The residue is digested in diisopropyl ether and filtered off. After having been filtered off, the title compound is washed with hexane and subsequently dried under reduced pressure. m.p.: 117°C. TLC R f (A)=0.28. FAB-MS (M+H) + =674. HPLC t Ret =15.19 min (gradient II); IR (methylene chloride) = inter alia 3431, 2967, 1680, 1494, 1467, 1367, 1275 and 1166 cm -1 ; 1 H-NMR (CD 3 OD) = inter alia 7.30-7.10/m (5H); 6.78 and 6.61/each d (each 1 H); 4.03/d (1H); 3.85, 3.81 and 3.80/each s (each 3 H); 3.46/q (2H), 1.32 and 1.26/each s (in all 9H from Boc), 1.15/t (3H); 0.82/pseudo t (6H). The starting material Is prepared in the following manner: 42a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl]methyl)hexanoyl-(L)-Val-N-(2-ethoxyethyl)amide In analogy with Example 1c), 1.27 g (2.05 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid (Example 47e)) and 460 mg of H-(L)-Val-N-(2-ethoxyethyl)amide In 19.2 ml of 0.25 M NMM/CH 3 CN are reacted with 860 mg of HBTU, within a reaction time of 20 h, to form the title compound. The latter is dissolved in ethyl acetate and this solution is washed, in succession, with 10 % cold citric acid, water, saturated sodium bicarbonate solution and saline (2x). After the organic phase has been dried over sodium sulfate, it is filtered and concentrated under reduced pressure. The title compound is purified by medium pressure column chromatography (8 bar, methylene chloride/methanol). TLC R f (A)=0.5; FAB-MS (M+H) + =788; IR (methylene chloride) = inter alia 3436, 2932, 1666, 1602, 1495, 1467, 1367 1249 and 1164 cm -1 . 42b) H-(L)-Val-N-(2-ethoxyethyl)amide In analogy with Example 1b), the pure title compound is obtained as an oil, after filtering off the catalyst and evaporating the filtrate, by hydrogenating 6.12 g (19.59 mmol) of Z-(L)-Val-N-(2-ethoxyethyl)amide in 120 ml of methanol at RT, under low pressure and in the presence of 0.61 g of 10 % Pd/C: 1 H-NMR (200 MHz, CDCl 3 ): 0.80 and 0.95 (2d, 6H), 1.2 (t, 3H), 1.35 (b, 2H), 2.25 (m, 1H), 3.2 (d, 1H), 3.45 (t, 2H), 3.47 (m, 4H), 7.5 (b, 1H). 42c) Z-(L)-Val-N-(2-ethoxyethyl)amide 5.025 g (20 mmol) of Z-(L)-valine are dissolved in 20 ml of methylene chloride and this solution is treated, at from -10 to -15°C, with 2.68 ml (20.4 mmol) of isobutyl chloroformate (Fluka, Buchs, Switzerland) and 22.2 ml (20 mmol) of NMM. After the mixture has been stirred for 15 minutes, 2.064 g (23.2 mmol) of 2-ethoxyethylamine (Pfaltz & Bauer, Waterbury, USA) are added under a protective gas. The beige suspension is warmed to RT and treated with 100 ml of ethyl acetate and 40 ml of water. After the organic phase has been separated off, it is washed with 40 ml of 1 N sodium hydroxide solution and with saline (3x). The solution is dried over sodium sulfate and subsequently evaporated under HV. The residue is digested in hexane and filtered off with suction. The title compound, which has thus been obtained, is subjected to further reaction without any additional purification. TLC R f (A)=0.4; 1 H-NMR (200 MHz, CDCl 3 ): 0.95 (2d, 6H), 1.2 (t, 3H), 2.1 (m, 1H), 3.4-3.55 (m, 6H), 3.97 (dd, 1H), 5.2 (s, 2H), 5.4 (b, 1H), 6.2 (b, 1H), 7.35 (s, 5H). Example 43: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(3-methoxypropyl)amide 1.19 g (1.51 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(3-methoxypropyl)amide in 14.5 ml of abs. DMF are treated with 980 mg (3.02 mmol) of TBAF, and the reaction mixture is stirred at RT for 22 h under argon. It is then poured onto cold saline and the solid is filtered off. This solid is dissolved in ethyl acetate and the solution is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated at approximately 30°C. The residue is digested in diisopropyl ether and filtered off. After having been filtered off, the title compound is dried under reduced pressure. m.p.: 131-132°C; TLC R f (A)=0.23; FAB-MS (M+H) + =674. HPLC t Ret =14.88 min (gradient II). IR (methylene chloride) = inter alia 3430, 2966, 1665, 1494, 1467, 1367, 1275 and 1167 cm -1 ; 1 H-NMR (CD 3 OD) = inter alia 7.30-7.20/m (5H); 6.78 and 6.61/each d (each 1H); 4.03/d (1H); 3.85, 3.81 and 3.80/each s (each 3H); 3.7 (m, 1H), 3.53 (m, 1H), 3.39 (t, 2H), 3.29 (s, 3H), 1.32 and 1.26/each s (in all 9H from Boc), 0.85/pseudo t (6H). The starting material is prepared in the following manner: 43a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-methoxypropyl)amide In analogy with Example 1c), 2.47 g (4 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid (Example 47e)) and 830 mg (4.4 mmol) of H-(L)-Val-N-(3-methoxypropyl)amide in 37.6 ml of 0.25 M NMM/CH 3 CN are reacted with 1.67 g HBTU, within a reaction time of 22 h, to form the title compound. The latter is dissolved in ethyl acetate and this solution is washed, in succession, with 10 % cold citric add, water, saturated sodium bicarbonate solution and saline (2x). After the organic phase has been dried over sodium sulfate, it is filtered and concentrated under reduced pressure. The title compound is purified by medium pressure column chromatography (8 bar, methylene chloride/methanol). TLC R f (A)=0.35; FAB-MS (M+H) + =788; IR (methylene chloride) = inter alia 3436, 2932, 1665, 1602, 1494, 1468, 1390, 1367, 1250 and 1165 cm -1 . 43b) H-(L)-Val-N-(3-methoxypropyl)amide In analogy with Example 1b), the pure title compound is obtained as an oil, after filtering off the catalyst and evaporating the filtrate, by hydrogenating 22.26 g (69.044 mmol) of Z-(L)-Val-N-(3-methoxypropyl)amide in 463.3 ml of methanol at RT, under low pressure and in the presence of 2.226 g of 10 % Pd/C: FAB-MS (M+H) + =189; 1 H-NMR (360 MHz, DMSO-D 6 ): 0.76 and 0.87 (2d, 6H), 1.6 (b, 2H), 1.63 (m, 2H), 1.84 (m, 1H), 2.9 (m, 1H), 3.1 (m, 2H), 3.22 (s, 3H), 3.31 (m, 2H), 7.82 (b, 1H). 43c) Z-(L)-Val-N-(3-methoxypropyl)amide In analogy with Example 1a), 20 g (79.6 mmol) of Z-(L)-valine in 250 ml of CH 3 CN and 20.5 ml of 95 % NMM (175.1 mmol) are treated with 9 ml (87.55 mmol) of 3-methoxypropylamine (Fluka, Buchs, Switzerland). 33.2 g (87.55 mmol) of HBTU are added to the thick suspension and the whole is thoroughly stirred at RT for 22 h. The reaction mixture is evaporated under HV and the residue is taken up in ethyl acetate, with this solution being extracted with water, 2x 10 % citric acid solution, water, 2x sat. NaHCO 3 solution and saline. The aqueous phases are extracted a further 2x with ethyl acetate and the organic phases are dried with Na 2 SO 4 and evaporated. Crystallization from ethyl acetate/hexane results in the title compound: TLC R f (G)=0.41; t Ret (II)=11.86 min; FAB-MS (M+H) + =323. Example 44: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-ethoxypropyl)amide 0.97 g (1.57 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-ethoxypropyl)amide in 11 ml of abs. DMF is treated with 814 mg of TBAF and the reaction mixture is stirred at RT for 18 h under argon. It is then dissolved in ethyl acetate and this solution is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated at approximately 30°C. The residue is purified by column chromatography (silica gel, C). TLC R f (A)=0.44; FAB-MS (M+H) + =688; HPLC t Ret =15.43 min (gradient II); 1 H-NMR (CD 3 OD) = inter alia 7.30-7.10/m (5H); 6.78 and 6.61/each d (each 1H); 4.0 (d, 1H); 3.85, 3.81 and 3.80/each s (each 3H); 3.7 (m, 1H), 3.53 (m, 1H), 3.45 (q, 2H) and (m, 2H), 3.17 (m, 2H), 2.85-2.7 (2m, 5H), 1.93-1.6 (m, 5H), 1.32 and 1.26/each s (in all 9H from Boc), 0.85/pseudo-t (6H). The starting material is prepared in the following manner: 44a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-ethoxypropyl)amide In analogy with Example 1c), 1.235 g (2 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-bulyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid (Example 47e)) and 445 mg (2.2 mmol) of H-(L)-Val-N-(3-ethoxypropyl)amide in 18.8 ml of 0.25 M NMM/CH 3 CN are reacted with 0.835 g of HBTU, within a reaction time of 22 h to form the title compound. After the suspension has been concentrated, it is dissolved in ethyl acetate and this solution is washed, in succession, with 10 % cold citric acid, water, saturated sodium bicarbonate solution and saline (2x). After the organic phase has been dried over sodium sulfate, it is filtered and concentrated under reduced pressure. The title compound is purified by column chromatography (silica gel, methylene chloride/methanol: 99/1). TLC R f (C)=0.32; t Ret (II)=22.58 min; FAB-MS (M+H) + =802. 44b) H-(L)-Val-N-(3-ethoxypropyl)amide In analogy with example 1b), the pure title compound is obtained as an oil, after filtering off the catalyst and evaporating the filtrate, by hydrogenating 6.2 g (18.4 mmol) of Z-(L)-Val-N-(3-ethoxypropyl)amide in 120 ml of methanol at RT, under low pressure and in the presence of 0.62 g of 10 % Pd/C: 1 H-NMR (200 MHz, CDCl 3 ): 0.8 and 0.97 (2d; 6H), 1.2 (t, 3H), 1.3 (b, 2H), 1.8 (m, 2H), 2.25 (m, 1H), 3.2 (d, 1H), 3.38 (m, 2H), 3.45 (m, 4H), 7.55 (b, 1H). 44c) Z-(L)-Val-N-(3-ethoxypropyl)amide 5.025 g (20 mmol) of Z-(L)-valine are dissolved in 20 ml of methylene chloride and this solution is treated, at from -10 to -15°C, with 2.68 ml (20.4 mmol) of isobutyl chloroformate and 2.2 ml (20 mmol) of NMM. After the mixture has been stirred for 15 minutes, 2.78 ml (23.2 mmol) of 3-ethoxypropylamine are added under a protective gas. The beige suspension is warmed to RT and treated with 100 ml of ethyl acetate and 40 ml of water. After the organic phase has been separated off, it is washed with 40 ml of 1 N sodium hydroxide solution and with saline (3x). The solution is dried over sodium sulfate and then evaporated under HV. The residue is digested in hexane and filtered off with suction. The title compound which is thus obtained is subjected to further reaction without any additional purification. TLC R f (C)=0.35; 1 H-NMR (200 MHz, CDCl 3 ): 0.95 (2d, 6H), 1.2 (t, 3H), 1.75 (m, 2H), 2.1 (m, 1H), 3.3-3.55 (m, 7H), 3.93 (dd, 1H), 5.1 (s, 2H), 5.4 (b, 1H), 6.55 (b, 1H), 7.35 (s, 5H). Example 45: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-(n-propyloxy)propyl)amide 1.4 g (1.71 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-(n-propyloxy)propyl)amide in 16 ml of abs. DMF are treated with 1.17 g of TBAF and the reaction mixture is stirred at RT for 18 h under argon. It Is then poured onto saline/ice, and insoluble material is filtered off. The residue is dissolved in ethyl acetate and this solution is washed, in succession, with water, sat. sodium bicarbonate solution and saline. The combined aqueous phases are reextracted with ethyl acetate. The combined organic phases are dried over sodium sulfate and concentrated at approximately 30°C. The residue Is crystallized from dlisopropyl ether, a little ethyl acetate and hexane. TLC R f (A)=0.53; FAB-MS (M+H) + =702; HPLC T Ret =16.31 min (gradient II); 1 H-NMR (CD 3 OD)= inter alia 7.30-7.10/ (m, 5H); 6.78 and 6.61/each d (each 1H); 4.0 (d, 1H); 3.85,3.81 and 3.80 (each s, each 3H); 3.7 (m, 1H), 3.54 (m, 1H), 3.43 (t, 2H) 3.37 (t, 2H), 3.15 (m, 2H), 2.9-2.63 (2m, 5H), 1.93 (m, 1H), 1.82-1.5 (m, 6H), 1.32 and 1.26/each s (in all 9H from Boc), 0.85/pseudo t (6H). The starting material is prepared in the following manner 45a) 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-(n-propyloxy)propyl)amide In analogy with Example 1c), 1.235 g (2 mmol) of 5(S)-(Boc-amino)-4(S)-(tert-butyldimethylsilyloxy)-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoic acid (Example 47e)) and 497 mg (2.3 mmol) of H-(L)-Val-N-(3-(n-propyloxy)propyl)amide In 18.8 ml of 0.25 M NMM/CH 3 CN are reacted with 0.835 g of HBTU, within a reaction time of 22 h, to form the title compound. After the suspension has been concentrated, it is dissolved in cold ethyl acetate and this solution is washed, in succession, with 10 % cold citric acid, water, saturated sodium bicarbonate solution and saline (2x). After the organic phase has been dried over sodium sulfate, it is filtered and concentrated under reduced pressure. The title compound is purified by column chromatography (silica gel, methylene chloride/methanol: 99/1). TLC R f (C)=0.27; t Ret (II)=23.09 min; FAB-MS (M+H) + =816. 45b) H-(L)-Val-N-(3-(n-propyloxy)propyl)amide In analogy with Example 1b), the pure title compound is obtained as an oil, after filtering off the catalyst and evaporating the filtrate, by hydrogenating 6.3 g (17.48 mmol) of Z-(L)-Val-N-(3-(n-propyloxy)propyl)amide in 120 ml of methanol at RT, under low pressure and in the presence of 0.63 g of 10 % Pd/C: 1 H-NMR (200 MHz, CDCl 3 ): 0.8 (d, 3H), 0.9 and 0.97 (2d, 6H), 1.25 (b, 2H), 1.4 (m, 2H), 1.78 (m, 2H), 2.25 (m, 1H), 3.2 (d, 1H), 3.38 (m, 4H), 3.5 (m, 2H), 7.5 (b, 1H). 45c) Z-(L)-Val-N-(3-(n-propyloxy)propyl)amide 5.025 g (20 mmol) of Z-(L)-valine are dissolved in 20 ml of methylene chloride and this solution is treated, at from -10 to -15°C, with 2.68 ml (20.4 mmol) of isobutyl chloroformate and 2.2 ml (20 mmol) of NMM. After the mixture has been stirred for 15 min, 2.72 ml (23.2 mmol) of 3-(n-propyloxy)propylamine (Tokyo Kasei Organic Chemicals, Tokyo, Japan) are added under a protective gas. The beige suspension is warmed to RT and treated with 100 ml of ethyl acetate and 40 ml of water. After the organic phase has been separated off, it is washed with 40 ml of 1N sodium hydroxide solution and with saline (3x). The solution is dried over sodium sulfate and then evaporated under HV. The residue is digested in hexane and filtered off with suction. The title compound which is thereby obtained is subjected to further reaction without any additional purification. TLC R f (C)=0.6; 1 H-NMR (200 MHz, CDCl 3 ): 0.92 (m, 9H), 1.6 (m, 2H), 1.75 (m, 2H), 2.1 (m, 1H), 3.35 (m, 4H), 3.5 (m, 2H), 3.93 (dd, 1H), 5.1 (s, 2H), 5.4 (b, 1H), 6.5 (b, 1H), 7.35 (s, 5H). Example 46: 5(S)-(Boc-Amino)-4(S)-hydroxy-6-phenyl-2(R)-[({2'-cyanobiphenyl)-4-yl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide The title compound is prepared in analogy with one of the methods described in the abovementioned examples. Example 47: Capsules (I) Crystalline 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-(2,3,4-trimethoxyphenylmethyl)-hexanoyl-(L)-Val-N-(2-methoxy-ethyl)amide (active substance) is micronized (particle size, from approximately 1 to 100 µm) with a customary knife mixer (for example Turmix). 'Pluronic F 68 (block polymer consisting of polyethylene and polypropylene glycol; Wyandotte Chem. Corp., Michigan, USA; also obtainable from Emkalyx, France; BASF trademark) is likewise micronized with a customary mixer, and the fine fraction is separated by screening using a sieve (0.5 mm) and subjected to further use as described below. 16.00 g of sesame oil are initially introduced in a beaker, and 1.20 g of the micronized active substance, 1.20 g of the fine fraction of 'Pluronic F 68 and 1,20 g of hydroxypropyl methyl cellulose (HP-M-603 cellulose from Shin-Etsu Chemicals Ltd., Tokyo, Japan) are added while stirring with an agitator (IKA-Werk, FRG) which is combined with a cogged stirrer (diameter: 46 mm) (stirring speed: 2000 rpm). 20 min of stirring at the given stirring speed produces a suspension of a pasty consistency which is used to fill hard gelatin capsules (20 x 40 mm; R. P. Scherer AG, Eberbach, FRG). Example 48: Capsules (II): The following constituents are processed as follows in order to prepare 10,000 capsules containing 100 mg of active compound (for example 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-(2,3,4-trimethoxyphenylmethyl)-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide) per capsule: Active compound 1000 g 'Pluronic F 68 1000 g Hydroxypropyl methyl cellulose 1000 g Sesame oil 1000 g (origin of the constituents: see Example 47) The sesame oil is initially introduced in a heatable vessel (Fryma), and the Pluronic F 68 is sprinkled in. The vessel is heated to 60°C and the Pluronic F 68 is distributed by stirring the mixture (duration approximately 2 h). The mixture is cooled down to approximately 30°C while being stirred and homogenized. The hydroxypropyl methyl cellulose and the active compound are sprinkled in and distributed in the oily mass while stirring and homogenizing (approximately 1 h). The suspension, which is of a pasty consistency, is used to fill hard gelatin capsules (size 0; obtainable, for example, from Elanco or Parke-Davies (Caprogel)) or soft gelatin capsules (20 mm oblong; R.P. Scherer AG, Eberbach, FRG) with the aid of the customary equipment. Example 49: Gelatin solution: An aqueous solution, which has been sterilized by filtration and which contains, as active compound, one of the compounds of the formula I mentioned in the preceding examples, together with 20 % cyclodextrins as solubilizers, is mixed, under aseptic conditions and while heating, with a sterile gelatin solution, which contains phenol as preservative, such that 1.0 ml of solution has the following composition: Active compound 3 mg Gelatin 150.0 mg Phenol 4.7 mg Dist. water containing 20 % cyclodextrins as solubilizers 1.0 ml Example 50: Sterile dry substance for injection: 5 mg of one of the compounds of the formula I mentioned in the preceding examples, as active compound, are dissolved in 1 ml of an aqueous solution containing 20 mg of mannitol and 20 % cyclodextrins as solubilizers. The solution is sterilized by filtration and used, under aseptic conditions, to fill a 2 ml ampoule, after which it is frozen and lyophilized. Before use, the lyophilisate is dissolved in 1 ml of distilled water or 1 ml of physiological sodium chloride solution. The solution is used for intramuscular or intravenous administration. This formulation can also be used to fill double-chambered disposable syringes. Example 51: Nasal spray: 500 mg of a finely ground (<5.0 µm) powder of one of the compounds of the formula I mentioned in the preceding examples, as active compound, are suspended in a mixture of 3.5 ml of Myglyol 812' and 0.08 g of benzyl alcohol. This suspension is introduced into a container possessing a dosing valve. 5.0 g of Freon 12', which is under pressure due to the valve, are introduced into the container. The "Freon" is dissolved in the Myglyol/benzyl alcohol mixture by shaking. This spray container contains approximately 100 individual doses which can be administered individually. Example 52: Lacquered tablets The following constituents are processed for preparing 10,000 tablets each containing 100 mg of active compound: Active compound 1000 g Corn starch 680 g Colloidal silicic acid 200 g Magnesium stearate 20 g Stearic acid 50 g Sodium carboxymethyl starch 250 g Water quantum satis A mixture of one of the compounds of the formula I mentioned in the preceding examples, as active compound, 50 g of com starch and the colloidal silicic acid is processed together with starch paste consisting of 250 g of com starch and 2.2 kg of demineralized water to form a moist mass. This is forced through a sieve of 3 mm mesh size and dried in a fluidized-bed dryer at 45° for 30 min. The dried granulate is pressed through a sieve of 1 mm mesh size, mixed with a previously screened mixture (1 mm sieve) of 330 g of com starch, the magnesium stearate, the stearic acid and the sodium carboxymethyl starch, and pressed into slightly domed tablets. Example 53: Pharmacokinetics in the dog Formulation: Capsules from Example 47 Conduct of the experiment: 2 female beagle breeding dogs (Ciba Geigy, Sisseln) are used. During the experiment, the bitches have free access to water and are given their last meal approximately 16 h before the beginning of the experiment. Feed is proffered once again at 8 h after the beginning of the experiment. Each bitch is given 2 capsules of the specified formulation, which capsules together contain 1.2 g of 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-(2,3,4-trimethoxyphenylmethyl)hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (active substance), corresponding to an average dose of approximately 100 mg/kg of body weight. Blood from the saphenous vein is collected in heparinized tubes at different times after the administration. In order to analyse the plasma concentration, the heparinized blood is centrifuged (4000 x g, 20 min) and the plasma is removed and mixed with an equal volume of acetonitrile. The mixture is kept on ice for 30 min. The protein precipitate is removed by centrifugation (10,000 x g, 5 min) and the supematant is centrifuged once again. The concentration of the active substance in the final supernatant which is obtained is determined by means of reversed-phase HPLC: the HPLC analysis is carried out on an analytical 125 x 4.6 mm Nucleosil C18 (5 µm) column (Macherey & Nagel, Düren, FRG), which is equilibrated with a mobile phase of 50 % acetonitrile and 0.1 % trifluoroacetic acid in water. The flow rate is 1 ml/min. Under these conditions, the detection limit is 0.1 µM. The active substance is detected by UV absorption at 215 nm. The concentrations are determined by the external standard method; the heights of the peaks are used to determine the concentrations by comparison with standard curves. The standard curves are obtained by HPLC analysis of dog plasmas containing known added concentrations of the active substance, which plasmas are themselves worked up in a manner analogous to that for the samples, by means of the abovementioned steps. Results: The values are given in ng/ml Time (h) Bitch 1 Bitch 2 2 7592 13947 4 4688 4570 6 616 192 8 44 18 12 11 <0.1 24 14 <0.1 Area under the curve (AUC) for the period from 0 to 24 h (ng x h/ml) 26101 37473 Example 54: Synergistic effect produced by combining 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (compound from Example 22) with indinavir or saquinavir in the experiment using cell lines: The activities of the individual compounds, and the combinations, mentioned in the title, in the coculture of the CEM-SS cell line and the permanently infected cell line H9/HIV-1/IIIB are determined using the method described above in association with the description of the pharmacological properties. The measurement result is expressed as % reduction of the reverse transcriptase (RT) activity. The results are presented in the following table; measurement results which confirm the occurrence of synergism are emphasized by underlining: a) Combination with saquinavir: Concentration of the active compound % Inhibition of the RT activity by Example 22 title compound (nM) Saquinavir (nM) Example 22 title compound alone Saquinavir alone Combination of Example 22 and Saquinavir 3.125 0.78 2.7% 6.6% 24.2 % 1.56 - 14.7% 23.7 % 3.125 - 39.3% 83.7% 6.25 1.56 1.3% 14.7% 58.0% 3.125 - 39.3% 90.5% 6.26 - 93.8% 96.6% b) Combination with indinavir: Concentration of the active compound % Inhibition of the RT activity by Example 22 title compound (nM) Indinavir (nM) Example 22 title compound alone Indinavir alone Combination of Example 22 and Indinavir 6.25 12.5 1.3% 3.2% 39.1% 12.5 12.5 52.0% 3.2% 76.6% 25 - 59.7% 90.7% Consequently, an additive to synergistic effect can be seen in coculture. Example 54: Synergistic effect produced by combining 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide (compound from Example 22) with indinavir or saquinavir in the experiment using peripheral mononuclear blood cells: The activities of the individual compounds, and the combinations, specified in the title, in the peripheral mononuclear blood cell culture are determined using the method described above in association with the description of the pharmacological properties. The measurement result is expressed as the cumulative activity of the reverse transcriptase (RT), in cpm/1.25 µl (number of measured 32 P disintegrations per 1.25 µl of test mixture and minute) on day 17 after the infection. The results are presented in the following table; measurement results which confirm the occurrence of synergism are emphasized by underlining. The test compound(s) is/are re-added in associated with each change of the medium (on days 0, 3, 6, 10 and 13): Cumulative RT activity (cpm/µl) on day 17 after the infection Concentration of saquinavir (nM) Concentration of the title compound from Example 22 0 7.5 15 30 60 120 0 7505 9411 10299 111 64 47 7.5 7909 8724 541 57 64 57 15 9132 5381 120 61 58 50 30 8457 255 63 51 59 53 60 1823 91 59 45 57 43 120 49 60 50 70 63 63 Consequently, a synergistic effect can also be detected in the experiment using human peripheral mononuclear blood cells.

Claims: A compound of the formula I, in which R 1 is lower alkoxy-lower alkanoyl (including lower alkoxycarbonyl); R 2 and R 3 are, independently of each other, phenyl, which is unsubstituted or is substituted by one or more radicals selected, independently of each other, from lower alkyl, phenyl, cyanophenyl, phenyl-lower-alkyl, halogen, halo-lower-alkyl, cyano, hydroxyl, lower alkoxy, phenyl-lower-alkoxyl, pyridyl-lower-alkoxy, in which pyridyl is bonded via a ring carbon atom, lower-alkoxy-lower-alkoxy, lower-alkoxycarbonyl-lower-alkoxy, carboxyl-lower- alkoxy, hydroxyl-lower-alkoxy having at least two carbon atoms, in which hydroxyl is not bonded in the 1 position, carbamoyl-lower-alkoxy, cyano-lower-alkoxy and lower alkylenedioxy, R 4 is lower alkyl; R 5 is lower alkyl, n is 1 or 2, and "lower" denotes a radical having not more than 7 carbon atoms, or salts thereof, provided at least one salt-forming group is present. A compound of the formula I according to claim 1, in which R 1 , R 4 , R 5 and n are as defined in claim 1, and R 2 and R 3 are, independently of each other, selected from phenyl, phenyl-lower-alkoxyphenyl, difluorophenyl, cyanophenyl, lower-alkoxyphenyl, tri-lower-alkoxyphenyl, lower-alkoxy-lower-alkoxyphenyl, lower-alkylenedioxyphenyl in which the lower-alkylenedioxy radical is bonded via its two oxygen atoms to two adjacent carbon atoms of the phenyl ring, pyridyl-lower-alkoxyphenyl in which pyridyl is bonded via a ring carbon atom, 4-lower-alkoxy-2-fluorophenyl, 4-fluoro-2-lower-alkoxyphenyl, 4-lower-alkoxy-2-hydroxyphenyl, phenyl which is substituted up to three times by lower-alkyl and lower-alkoxy, phenyl-lower-alkylphenyl, fluorophenyl, hydroxyphenyl and di-lower-alkoxyphenyl; or a salt thereof, provided at least one salt-forming group is present. A compound of the formula I according to claims 1 or 2, in which R 1 , R 2 , R 4 , R 5 , R 6 and n have the meanings specified in claim 1 or 2 and R 3 is 2,3,4-lower-alkoxyphenyl, or a salt thereof, provided at least one salt-forming group is present. A compound of the formula I according to claim 1, in which R 1 is lower-alkoxycarbonyl, R 2 and R 3 appear in the following combinations: R 2 = phenyl and R 3 = cyanophenyl; R 2 = phenyl and R 3 = difluorophenyl; R 2 = phenyl and R 3 = 4-lower-alkoxyphenyl; R 2 = 4-(lower-alkoxy-lower-alkoxy)phenyl and R 3 = 4-phenyl-lower-alkoxyphenyl; R 2 = phenyl and R 3 = phenyl; R 2 = phenyl and R 3 = 4-phenyl-lower-alkoxyphenyl; R 2 = phenyl and R 3 = 4-(pyridin-3-yl-lower-alkoxy)phenyl; R 2 = phenyl and R 3 = 3,4-lower-alkylenedioxyphenyl; R 2 = phenyl and R 3 = 2,3,4-tri-lower-alkoxyphenyl; or R 4 is isopropyl; R 5 is methyl; and n is 1. A compound of the formula I according to claim 1, in which R 1 is tert-butoxycarbonyl; R 2 and R 3 are present in the following combinations: R 2 = phenyl and R 3 = 2,3,4-trimethoxyphenyl; or R 2 = phenyl and R 3 = 4-methoxyphenyl; R 4 is isopropyl; R 5 is ethyl or methyl; and n is 2 or is 1; or a salt thereof, provided at least one salt-forming group is present. A compound according to any one of claims 1 to 5, which is of the formula I', which comes under formula I, in which the radicals have the meanings specified in each case for compounds of the formula I. A compound of the formula l'according to claim 6, in which R 1 is lower-alkoxycarbonyl; R 2 is phenyl and R 3 is 4-lower-alkoxyphenyl or 2,3,4-tri-lower-alkoxyphenyl; R 4 is isopropyl; R 5 is methyl; and n is 1. A compound of the formula I according to claim 1, said compound being selected from the compounds with the following names: 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-cyanoyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-difluoro-phenyl)methyl]-hexanoyl-(L)-Val-N-(2-m ethoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-(phenylmethyl)-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)- [(p-(3-pyridylmethoxy)phenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[p-(methoxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-m ethoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-methylenedioxyphenyl)methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-benzyloxyphenyl) methyl]-hexanoyl-(L)-Val-N-(2-m ethoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-ethoxyethyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)methyl]hexanoyl-(L)-Val-N-(3-m ethoxypropyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(3-ethoxypropyl)amide; 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3,4-trimethoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(3-(n-propyloxy)propyl)amide; or a salt thereof where a salt-forming group is present. A compound of the formula I according to claim 1 which is selected from the following compounds: 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-cyanophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(o-fluorophenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-{[p-(2-phenylethyl)phenyl]methyl}hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-methoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[((p-methoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-[(p-methoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-(isobutoxy)phenyl)-2(R)-[(p-methoxyphenyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-benzyloxyphenyl)-methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-hydroxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(p-isobutoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[p-(2-pyridylmethoxy)phenyl)-methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4-dimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3-methoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(3,4,5-trimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4-dimethoxyphenyl)methyl)-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2-methoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,3-dimethyl-4-methoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4,5-trimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,4,6-trimethoxy-phenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,5-dimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(2,6-dimethoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-hydroxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-[(p-methoxyphenyl)methyl]-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide and 5(S)-(Boc-amino)-4(S)-hydroxy-6-[p-(2-methoxyethoxy)phenyl]-2(R)-{[p-2-methoxyethoxy)phenyl]methyl}-hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, or a salt thereof, provided at least one salt-forming group is present. A compound of the formula I according to claim 1 which is selected from the following compounds: 5(S)-(Boc-amino)-4(S)-hydroxy-6-phenyl-2(R)-[(4-biphenylyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(4-biphenylyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[(4-biphenylyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-[(4-biphenylyl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyi)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[({2'-cyanobiphenyl)-4-yl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-hydroxyphenyl)-2(R)-[({2'-cyanobiphenyl)-4-yl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, and 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-[({2'-cyanobiphenyl)-4-yl)-methyl]hexanoyl-(L)-Val-N-(2-methoxyethyl)amide, or a salt thereof, provide at least one salt-forming group is present. A compound of the formula I according to any one of claims 1 to 10, for use in a process for the diagnostic or therapeutic treatment of the human or animal body. A pharmaceutical preparation containing a compound of the formula 1, or a pharmaceutically utilizable salt thereof, according to any one of claims 1 to 10, together with a pharmaceutically utilizable carrier material. Use of a compound of the formula I, or of a pharmaceutically utilizable salt thereof, according to any one of claims 1 to 10, for preparing a pharmaceutical preparation for the prophylaxis or treatment of a retroviral disease. A product which comprises a) at least one compound of the formula I according to any one of claims 1 to 10, or a pharmaceutically acceptable salt thereof, provided a salt-forming group is present, and b) one, two or more other active compounds, which are effective against retroviruses, in the presence or absence of one or more pharmaceutically acceptable carrier materials, as a combination preparation for simultaneous or chronologically staggered use within a period of time which is small enough for the active compounds both of component a) and of component b) to be present simultaneously in the patient, for treating a retroviral disease which responds to such active compounds. A product according to claim 14 for use in a process for the therapeutic treatment of the human or animal body. A process for preparing a compound of the formula I according to claim 1, which comprises a) condensing an acid of the formula R 1 -OH or a reactive acid derivative thereof, in which R 1 has the same meanings as R 1 in compounds of the formula I, with an amino compound of the formula or a reactive derivative thereof, in which n and the radicals have the meanings specified for compounds of the formula I, with free functional groups, with the exception of those participating in the reaction, being present, if necessary, in protected form in the starting materials of the formulae II and III, and eliminating protective groups which are present, or b) condensing a carboxylic acid of the formula or a reactive derivative thereof, in which the radicals have the meanings specified for compounds of the formula I, with an amino compound of the formula or a reactive derivative thereof, in which n and the radicals have the meanings specified for compounds of the formula I, with free functional groups, with the exception of those participating in the reaction, being present, if necessary, in protected form in the starting materials of the formulae V and VI, and protective groups which are present being eliminated, or c) condensing a carboxylic acid of the formula or a reactive derivative thereof, in which the radicals have the meanings specified for compounds of the formula I, with an amino compound of the formula or a reactive derivative thereof, in which n and R 5 have the meanings specified for compounds of the formula I, with free functional groups, with the exception of those participating in the reaction, being present, if required, in protective form in the starting materials of the formulae VII and VIII, and protective groups which are present being eliminated if desired, or d) either (i) etherifying a hydroxy compound of the formula or its alcoholate salt, in which n and the radicals have the meanings specified for compounds of the formula I, with a compound of the formula W 1 -R 5 in which R 5 has the meanings specified for compounds of the formula I and W 1 is a leaving group, which is a nucleofugic group selected from hydroxyl which is esterified with a strong organic or inorganic acid, or (ii) etherifying a reactive derivative of the hydroxy compound of the formula IX with a compound of the formula HO-R 5 or its alcoholate salt, in which R 5 is defined as immediately above, with free functional groups, with the exception of those participating in the reaction, being present, if necessary, in protected form in the starting materials of the formulae IX, X and Xa and protective groups which are present being eliminated, or e) eliminating protective groups which are present in a compound of the formula I, in which the substituents are as defined above, with the proviso that in the compound of the formula I concerned at least one functional group is protected by protective groups, with it being possible, in the specified process steps a) to e), if not already specifically mentioned, for starting materials also to be employed in the form of salts, provided salt-forming groups are present, and/or converting if desired, a compound of the formula I, which is obtained by one of the abovementioned processes a) to e) and which has at least one salt-forming group, into its salt, and/or converting an obtainable salt into the free compound or into another salt, andlor resolving isomeric mixtures, which may be obtainable, of compounds of the formula I, and/or transforming a novel compound of the formula I into another novel compound of the formula I.

Inventors: BHAGWAT SHRIPAD SUBRAY DR, BOLD GUIDO DR, CAPRARO HANS-GEORG DR, FAESSLER ALEXANDER DR, KHANNA SATISH CHANDRA DR, LANG MARC DR, LAZDINS JANIS KARLIS DR, MESTAN JUERGEN DR, BHAGWAT, SHRIPAD SUBRAY, DR., BOLD, GUIDO, DR., CAPRARO, HANS-GEORG, DR., FAESSLER, ALEXANDER, DR., KHANNA, SATISH CHANDRA, DR., LANG, MARC, DR., LAZDINS, JANIS KARLIS, DR., MESTAN, JUERGEN, DR., Fässler, Alexander, Dr., Mestan, Jürgen, Dr.
Applicants: NOVARTIS AG, NOVARTIS ERFIND VERWALT GMBH, NOVARTIS-ERFINDUNGEN VERWALTUNGSGESELLSCHAFT M.B.H.
Application year: 1995
Main classification: C07C271
IPC codes: C07D213, C07D211, A61K31, C07C311, C07D207, C07D277, C07D317, A61K38, C07D309, C07C255, C07D295, C07D307, A61P31, C07D311, C07D401, C07C271, C07K5, C07C237, C07C317, C07D209