PRODRUGS

Abstract: A pharmaceutical compound or an intermediate therefor, having the formula: D*-Linker*(R2')k-R2, where R2 and R2' (if present) is the amide or ester residue of an aliphatic amino acid, k is 0 or 1, D* is a Drug residue bearing an accessible function selected from amine, hydroxy and carboxy, or a group amenable to attachment to said accessible function, Linker* is an at least bifunctional linker comprising a first function bound to said accessible function spaced from a second function forming an amide or acyl bond with the aliphatic amino acid; wherein the compound is free from long chain fatty acid esters; and with the provisos that Linker* does not consist solely of alkoxy when the Drug comprises a lactamcarboxy or enolic hydroxy function and that the Drug is not a monohydric nucleoside.

Description: PRODRUGS Technical Field This invention relates to the field of prodrugs, that is novel derivatives of otherwise known and proven drugs which release that drug in active or pro-active form in vivo. The enzymatic and/or chemical cleavage of the compounds of the present invention occurs in such a manner that the parent drug is released and the moiety or moieties split off remain non-toxic or are metabolized so that non-toxic or acceptable amounts of metabolic products are produced. The present compounds thus modify the in vivo availability of the parent compound compared to what would be the case if the parent compound was to be administered itself. For instance the prodrugs of the invention may give higher bioavailabilities, varied bioavailability kinetics or bioavailabilities with a decreased interpersonal spread. Background to the invention WO97/30051 and WO 98/21223 describe prodrugs of nucleoside analogues comprising a fatty acid ester and an amino acid ester, optionally combined on a linker structure which is in turn bonded to the nucleoside. As shown in the examples of WO 97/30051 , the presence of the fatty acid component was essential to good bioavailability. J Med Chem 39 (1) 10-18 1996 describes a number of acyloxymethyl ethers of the enolic drug oxindole and indicate that the amino acyl variants have poorer bioaviailability that the mother substance. J Med Chem 22 657-661 (1979) and DE 2112057 describe valyloxymethyl esters of lactamcarboxy functions of various penicillins although to our knowledge none have shown clinical promise. 2 Brief description of the invention In a ccordance with a first aspect of the invention there are provided pharmaceutical compounds of the formula: D*-Linker* (R 2 ') k -R, where R : and R 2 ' (if present) is the amide or ester residue of an aliphatic amino acid, k is 0 or 1, D* is a Drug residue bearing an accessible function selected from amine, hydroxy and carboxy, Linker* is an at least bifunctional linker comprising a first function bound to said accessible function spaced from a second function forming an amide or acyl bond with the aliphatic amino acid; wherein the compound is free from long chain fatty acid esters; and with the provisos that Linker* does not consist solely of alkoxy when the Drug comprises a lactamcarboxy or enolic hydroxy function and that the Drug is not a monohydric nucleoside. The invention further provides novel intermediates useful for derivatising accessible hydroxy, carboxy or amino functions of Drugs to prepare prodrugs as described in the foregoing paragraph. Certain of these novel intermediates are also useful for derivatising other functions on drugs, as described and claimed in our co-pending international application filed 30 March 1999 and claiming priority from SE 9801216-4. A further aspect of the invention provides the use of a structure of the formula -Linker* (R 2 ') k -R 2 as a prodrug moiety for a drug bearing an accesible hydroxy, carboxy or amino function. By the use of the invention the pharmacokinetics of a broad range of orally administered drugs are enhanced, for instance by improving absolute bioavailability or by providing a more even release of the mother compound or by providing for a reduced interpersonal spread in pharmacokinetic performance. However the compounds of the invention are not limited to those based on orally administered 3 drugs as the prodrugs of the invention, when parenterally administered, provide enhanced pharmacokinetic performance, for instance by improving solubility, while still allowing for efficient release of the mother compound. Drug residue as used in its conventional significance, that is implying that during linkage a hydrogen or hydroxy has been eliminated from an accessible amino, carboxy or hydroxy function on the Drug. The amine function on the Drug can be a primary amine (-NH 2 ) or a secondary amine (-NH-). The expression difunctional in the context of the linker group means that the linker has at least one hydroxy or amine function available for esterification or amide bonding with R 2 , or a carboxyl function available for amide bonding with the free α- amine function of R 2 . Spaced therefrom on the difunctional linker is a further functional group for linkage to a cooperating function on the Drug such as hydroxy, carboxy or amino. The linker may in fact be trifunctional, that is the linker has at least three functions including two independently selected from hydroxy, amine or carboxy, the amine and hydroxy function(s) being available for esterification/amide bonding with the carboxyl functions of a pair of R 2 , or the carboxy function(s) on the linker being available for amide bonding with the free α-amine function of R 2 . These hydroxy/amine/carboxy functions are spaced from a further functional group for linkage with a cooperating hydroxy, carboxy or amine function on the drug. Other trifunctional linker groups may comprise a first hydroxy, amine or carboxy function cooperating with R 2 , a function cooperating with the drug and a further functional group either underivatised such as hydroxy, carboxy, amine etc or alternatively protected with conventional pharmaceutically acceptable protecting groups. The invention further provides pharmaceutical compositions comprising the pharmaceutical compounds of the invention and pharmaceutically acceptable carriers or diluents therefor. Additional aspects of the invention provide methods of medical treatment or prophylaxis comprising the administration of the pharmaceutical compounds of the invention to a human or animal suffering from or prone to the ailment to which the respective Drug is applicable. Convenient linker groups, for instance when the Drug comprises an amine or hydroxy function, include those of the Formulae Ila A — On. O ,Q — Alk T V ( — A { )r ) llaa where A and A' are independently an ester linkage between an hydroxy on the linker and the carboxy on R 2 , or an amide linkage between an amine on the linker and a carboxy on R 2 Q is a structure: 7 ■ 4 7 " 4 \ or (/ )k R. or Q is a monocyclic, saturated or unsaturated carbo- or heterocycle with 4, 5 or 6 ring atoms; Alk is absent, C,-C 4 alkylene or C 2 -C 4 alkenylene; T is a bond, -O- or -N(R 4 )-, V is a bond or a structure of the formula Ilbb or lice: R4 R4 O — O or — O O * R ■ 4' Ilbb R4' llcc R 4 and R 4 ' are independently hydrogen or C,-C 3 alkyl; and m and n are independently 0, 1 or 2; k is 0 (that is the branch is absent )or 1 5 A number of useful hetero or carbocycles for Q as a ring are defined below which is preferably an aromatic group such as pyridine, furyl, imidazol etc or especially phenyl, such as aromatic moieties wherein the arm(s) bearing the or each R 2 group are respectively para and meta or both meta to the remainder of the linker. Where the Drug comprises a carboxyl function, the linker may comprise a structure of the formulae VIII: A ( )rκ Q Alk (— A' — ( )^ k VIII where A, A', Q, Alk, k m, and n are as defined for Formula Ila. Preferably, however, when the Drug comprises a carboxy function, the di- or trifunctional linker group is a structure of Formulae lid (that is a compound of Formulae Ila, wherein T is O and V is a structure of the formula Ilbb): A — On R4 O — Alk — O-U-O * (— A— Om k R4 , lldd In structure lid, R 4 ' is preferably hydrogen and R 4 is ethyl, phenyl, but especially methyl or hydrogen, or R 4 and R 4 . together define isopropyl. Particularly convenient structures when the drug comprises an hydroxy function include the corresponding structures to: formula II e*, that is 6 O O R 0 - !!- Op—^Oq- r ~ ( )r — L °- Drug O o I R 2 He * formula II f*, that is R 2 O O R— y O * Oo ■ ()c O — Drug o I If Formula Id*, that is O R,2 — O — Alk — U- O — Drug Id* A favoured structure within formula Ila has the formula: O R 2 -O- R 2 — O which breaks down in vivo to the nature identical glyceric acid. Particularly preferred are compounds derived from D-glyceric acid. Thus preferred pharmaceutical compounds of the invention will comprise a [(R) 2,3-bis-(L-valyloxy)-propionyl] or [(R) 2,3-bis-(L-isoleucyloxy)-propionyl] moiety. A preferred group of linker(R 2 ')-R 2 structures comprise glycerol derivatives of the formula lie A — O- \-0— D A'— O- llc or the corresponding 2,3 enantiomer, where A is hydrogen or the acyl residue of an aliphatic L-amino acid ester, A' is the acyl residue of an aliphatic amino acid residue and D is a C 2 -C 6 saturated or unsaturated dicarboxylic acid residue. Trifunctional linkers of the formula lie are hydro lysed or otherwise break down in vivo to release the nature identical compounds glycerol, the L-amino acid, the fatty acid (if present) and the dicarboxylic acid, each of which are generally safely metabolised and/or excreted by the body. Preferably A and A' are both the same residue, particularly residues of L-valine or L-isoleucine. Particularly preferred dicarboxylic acid residues include those derived from oxalic, malonic, tartronic, succinic, maleic, fumaric, malic, tartaric, glutaric, glutaconic, citraconic, itaconic, ethidine-malonic, mesaconic, adipic, allylmalonic, propylidenemalonic, hydromuconic, pyrocinchonic and muconic acids and the like. The dicarboxylic acid residue may be optionally substituted. Several of the abovementioned dicarboxylic acids can themselves define a trifunctional linker. For instance hydroxy-substituted dicarboxylic acids such as tartaric acid or malic acid offer a number of configurations within the scope of the invention. Taking tartaric acid as an example a carboxyl function is available for esterification with an hydroxy function on the drug (optionally via a difunctional linker). The hydroxy function(s) are available for esterification with the respective carboxyl functions of the R 2 amino acid while the remaining carboxy group can be free, or optionally protected, for instance with a conventional pharmaceutically acceptable ester such as the methyl or ethyl ester. 8 R 2 I O O R, — O — - O — Drug O O R Favoured linkers of the tartaric acid series above can be generically depicted as Formula He: R 2 O O R y ° iri O / D P— ^O / Oq - r- () r - L~ O O I R 2 lie where R 2 is as shown above, p, q and r are each independently 0 to 5, preferably 0 or 1 and R y is the free acid, or a conventional pharmaceutically acceptable carboxy protecting group, such as the methyl, benzyl or especially the ethyl ester. Favoured linkers of the malic series have the formula Ilf: Q O R °ιr Op-^Op-^ O Ilf where Ry, p,q and R 2 are as defined above, preferably those where p and q are zero. Preferred pharmaceutical compounds of this aspect of the invention will hus comprise a moity selected from: [3 -methoxycarbonyl-2-valyloxy-propionyl] , [3-benzyloxycarbonyl-2-valyloxy-propionyl], [3-methoxycarbonyl-2-isoleucloxy-propionyl], [3-benzyloxycarbonyl-2-isoleucyloxy-propionyl], 9 [4-methoxycarbonyl-2,3-bis-valyloxy-butyryl], [4-benzyloxycarbonyl-2,3-bis-valyloxy-butyryl], [4-methoxycarbonyl-2,3-bis-isoleucyloxy-butyryl], [4-benzyloxycarbonyl-2,3-bis-isoleucyloxy-butyryl], And especially: [3-ethoxycarbonyl-2-valyloxy-propionyl], [3-ethoxycarbonyl-2-isoleucyloxy-propionyl] [4-ethoxycarbonyl-2,3-bis-valyloxy-butyryl] [4-ethoxycarbonyl-2 ,3 -bis-isoleucyloxy-butyryl] , particularly those derived from L-malic acid and L-tartaric acid; and corresponding derivatives employing conventional pharmaceutically acceptable esters on the terminal carboxy function. A further prefeπed prodrug moiety, especially for Drugs containing hydroxy groups which are not prone to electron withdrawal include α-co hydroxyalkanoic acid derivatives where R 2 is esterified to the terminal hydroxy group. In these compounds hydrolysis and removal of the R 2 group in vivo leaves a reactive terminal radical which will tend to cyclize and prompt the effective release of the mother drug.Linkers of this aspect of the invention are conveniently prepared from α- hydroxy ω-carboxylic acids such as carbonic acid, glycollic acid, hydroxypropanoic acid, hydroxybutyric acid, hydroxyvaleric acid or hydroxycaproic acid. Preferred pharmaceutical compounds will thus comprise a moiety selected from: [3-(L-valyloxy)-propionyl] [5-(L-valyloxy)-pentanoyl] [5-(L-valyloxy)-cis-pent-2-enoyl] [5-(L-valyloxy)-cis-pent-3enoyl] [6-(L-valyloxy)-hexanoyl] [3-(L-isoleuclyoxy)-propionyl] [5-(L-isoleucyloxy)-pentanoyl] [5-(L-isoleucyloxy)-cis-pent-2-enoyl] 10 [5-(L-isoleucyloxy)-cis-pent-2-enoyl] [6-(L-isoleucyloxy)-hexanoyl]; and especially [4-(L- valy loxy)-butyryl] ; [4-(L-valyloxy)-cis-but-2-enoyl] [4-(L-isoleucyloxy)-butyryl] [4-(L-isoleucyloxy)-cis-but-2-enoyl]. A convenient linker (R 2 ') k (R 2 ) structure has the formula: O T 2 O H 3 C- Op " L () q - JL - I lei where R 2 is the residue of an aliphatic L-amino acid and, p is 0, 1 or 2-20 (optionally including a double bond) and q is 0-5, preferably 0. Preferred pharmaceutical compound will thus comprise a moiety selected from: [2-(L-valyloxy)-butyryl], [2-(L-isoleucyloxy)-butyryl], [2-(L-valyloxy)-pentanoyl], [2-(L-isoleucyloxy)-pentanoyl], [2-(L-valyloxy)-hexanoyl], [2-(L-isoleucyloxy)-hexanoyl], etc. In formula lid, however, p and q are preferably 0, thus defining lactic acid derivatives, preferably L-lactic acid derivatives, such as the [2-(L-valyloxy)-propionyl] and [2-(L-isoleucyloxy)-propionyl] moieties, as the breakdown products, lactic acid and the amino aicd are both well accepted physiologically. A convenient linker (R 2 ') k (R 2 ) structure, for instance with drugs comprising an hydroxy group prone to electron withdrawal has the formula: Illb: 11 R„ O R2 — O * 0 _lL 0 _ Drug R, lllb where R 4 and R 4 'are independently H or C,-C 4 alkyl. A convenient linker (R, (R 2 ) structure for instance with hydroxy groups prone to electron withdrawing effects has the structure IIIc: R4 R2 — O * O — Drug R4' IIIc where R • ~„2> R, and R,. are as discussed above. A preferred group of prodrugs of the invention have the formula: R. 4L o PG-R ? — O — ()ql- ()qr-T X Rm wherein PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected, R 4L is H, C,. 3 alkyl or phenyl, Rm is H, C,_ 3 alkyl, phenyl or -() m -O-R 2 ql is 0-3, qr is 0-3, m is 0-2 T is a bond, -NR 4 - or -O- R 4 is H or C, .3 alkyl; X is an ester linkage to a Drug bearing an accessible hydroxy function, an amide linkage to a Drug bearing an accessible amine function or a structure of the formula: 12 FL • 4,R O * ■ X' R 4R' where R 4R and R 4R ' are independently H, C,. 3 alkyl or phenyl; and X' is an ether linkage to a drug bearing an accessible hydroxy function or an ester linkage to a Drug bearing an accessible carboxy function; and pharmaceutically acceptable salts thereof. A further preferred group of compounds of the invention comprises those wherein Linker* (R 2 ' ) k -R 2 comprises a structure of the formula O PG-R 2 -O- ()ql Ring ()qr-T — L χ wherein PG-R, is the acyl residue of an aliphatic amino acid, optionally N-protected, ql is 0-3, qr is 0-3, T is a bond, -NR 4 - or -O- R 4 is H or C,. 3 alkyl; ring is an optionally substituted hetero- or carbocyclic ring structure, X is an ester linkage to a Drug bearing an accessible hydroxy function, an amide linkage to a Drug bearing an accessible amine function or a structure of the formula: Ft -4,R — O * X * R 4R' where R 4R and R 4R ' are independently H, C,. 3 alkyl or phenyl; and X' is an ether linkage to a drug bearing an accessible hydroxy function or an ester linkage to a Drug bearing an accessible carboxy function; and pharmaceutically acceptable salts thereof. Preferably, the difunctional linker comprises a structure of the formula II"b: 13 R R 41 0 4r 0 qr -τ— N-o- ' 0 ql R 41 R 4r ll"b where T is a bond, -O- or -NH-, R 41 R 4r and R 41 ' and R 4r ' are independently H or C,-C 3 alkyl and A is as defined above (or wherein A is a further difunctional linker to which one or more R 2 depend). Examples of structures belonging to the latter possibility for A include those of Formula Va and Vb: Ro — O- O O R 41 o r -o- 0l-5 -o- O. -o- ql ■ Oqr-T- R — O- 1 R Va 41 R 4r O R 31 o 3r R. ■ O - 01-5 ^ " OqT qr-^ O- R Vb 31 R 3r where T, q, R 2 , R 41 R 4I ' R 4r and R 4r ' are as defined above. Although formulae Va and Vb depict the dicarboxylate moiety as unbranched, it will be apparent that a wide variety of dicarboxylates will be suitable here, including branched and/or unsaturated and/or substituted dicarboxylic acid derivatives or various lengths, as described in more detail above. Amongst the preferred configurations for formulae II"b, Va and Vb, are those wherein T is absent. 14 Convenient values for the rightmost R 4 and R 4 , are hydrogen and for the left most R 4 and R 4 . both methyl. Other preferred embodiments comprise structures of the formulae II"b, Va or Vb wherein the rightmost R 4 is H and the rightmost R 4 is isopropyl, cycloC,. 6 alkyl, phenyl or benzyl. Convenient values of the leftmost q and rightmostq are as follows: 1,0; 2,0 3,0 and 4,0 Other convenient values include 1,1 ; 2,1 3,1 4,1; or 2,2. Especially 1,0; 2,0; 3,0; 1,1; 0,1; 2,2; 0,3; 3,1 Still further prefeπed embodiments comprise structures of the formula II"b, Va or Vb wherein T is -NH- or -O-. Intermediates: A further aspect of the invention provides novel intermediates for linking to Drugs having accessible amine, hydroxy or carboxy functions, but also including those drugs in our copending international application discussed above. However it should be appreciated that the pharmaceutical compounds of the invention are not limited to those prepared from the intermediates defined below, as many pharmaceutical compounds within the scope of the invention maybe synthesised by a stepwise process, for instance by first attaching an optionally protected di- or trifunctional linker to the drug, followed by attachment of the R 2 group(s). A number of such stepwise syntheses are exemplified below. 15 Prefeπed linkers in accordance with this aspect of the invention include compounds of the Formulae IVa: R 2— A — () o Q — Alk T — L x ( R 2 — A' — °- )k v ' IVa where R 2 , A, A', n, m, Q, Alk, k and T are as defined above and X is hydroxy or an activating group such as an acid derivatives including the acid halide, such as the chloride, anhydrides derived from alkoxycarbonyl halides such as isobutyloxycarbonylchloride and the like, N-hydroxysuccinamide derived esters, N-hydroxyphthalimide derived esters, N-hydroxy-5-norbornene- 2,3-dicarboxamide derived esters, 2,4,5-trichlorophenol derived esters and the like. Compounds of Formula IVa will be particularly useful for Drugs bearing hydroxy or amine functions. Further preferred linkers in accordance with this aspect of the invention include compounds of the formulae IVe: R2 — A ()n O F MR Q Alk T - II 0 - X' ( R2- A' ()m ) k F MR IVe where R 2 , A, A', n, m, Q, Alk and T are as defined above, and R 4 an activating group such as a halide, including bromo, chloro and iodo. Compounds of Formula IVe will be especially useful for Drugs bearing carboxy functions (especially those where T is O, R 3 is Me and R 3 ' is H) Alternative prefeπed di- or trifunctional linker compounds of this aspect of the invention include compounds of the Formulae Ilia: 16 R A On Q Alk X' ( R 2 A" o m ) k where R 2 , A, A', n, m, Q and Alk are as defined above and R 4 is hydroxy or an activating moiety such as halo, including chloro, iodo and bromo. A prefeπed group of novel intermediates useful in applying structures of the formulae IF'b to a drug and having the formula N-l : R R 41 o 4r A * Oql ■ Oqr "1" - -o- " halo R 41 R 4r' N-1 where A, q, R 4 , R 4 ' and T are as defined for formula IF'b. A prefeπed group of intermediates have the formula: R '4L o PG-R 2 — O — ()ql- ()qr-T X Rm wherein PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected, R 4L is H, C,. 3 alkyl or phenyl, Rm is H, C,. 3 alkyl, phenyl or -() m -O-R 2 ql is 0-3, qr is 0-3, m is 0-2 T is a bond, -NR 4 - or -O- R 4 is H or C,. 3 alkyl; X is OH or an activating group or a structure of the formula: 17 R 4R — O * X' R 4R' where R R and R 4R ' are independently H, C,. 3 alkyl or phenyl; and X' is halo. An alternative group of intermediates of the invention comprise a structure of the formula O PG-R 2 — O — ()ql Ring ()qr -T — U — X wherein PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected, ql is 0-3, qr is 0-3, T is a bond, -NR 4 - or -O- R 4 is H or C,_ 3 alkyl; ring is an optionally substituted hetero- or carbocyclic ring structure, X is OH or an activating group, such as halo, or a structure of the formula: Ft '4,R — O * X' R • 4. R where R 4R and R 4R ' are independently H, C,_ 3 alkyl or phenyl; and X' is halo. Halo for X or X' is bromo, chloro and especially iodo. Representative intermediates of the invention include: 2,2-dimethyl-3-(N-Boc-L-valyloxy)propionic acid iodomethyl ester 3,3- bis (N-CBz-L-valyloxymethyl)-propionic acid iodomethyl ester, 2-(N-CBz-L-valyloxy)ethoxycarbonyloxymethyl iodide 18 Iodomethyl 1 ,3-bis(N-benzyloxycarbonyl-L-valyloxy)-2-propyl carbonate, Iodomethyl 2-methyl-2-(N-benzyloxycarbonyl-L-valyloxymethyl) propionate, Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-DL-propionate. Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)isobutyrate. Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)-(+)-butyrate. Iodomethyl 2-O-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetate Iodomethyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate. Iodomethyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate 2-(N-CBz-L-valyloxy)-ethyl iodomethyl carbonate 4-(N-CBz-L-valyloxy) butyric acid iodomethyl ester Iodomethyl-3-(N-benzyloxycarbonyl-L-valyloxy)-benzoate Iodomethyl-3-(N-benzyloxycarbonyl-L-valyloxy)-propionate 1 ,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propyl 1 -iodoethyl carbonate 3-(N-benzyloxycarbonyl-L-valyloxy)-2,2-dimethylpropyl iodomethyl carbonate Iodomethyl 3,4-di-(Ν-CBZ-L-valyloxy)hydrocinnamate 3-(N-CBZ-L-valyloxy)phenyl iodomethyl carbonate Iodomethyl 2-(N-CBZ-L-valyloxy)phenylacetate Iodomethyl 4-(N-CBZ-L-valyloxyxy)phenylacetate Iodomethyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl) benzoate Iodomethyl 4-(N-benzyloxycarbonyl-L-valyloxy)cyclohexanoate. Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2-ethyl butyrate 2-(N-(iodomethoxycarbonyl)-amino)-2-methyl-l-(N-benzyloxycarbonyl- L-valyloxy)-propane 1 -(2 -N-CBz-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3 -carboxylic acid iodomethyl ester Iodomethyl 5-[(N-benzyloxycarbonyl-L-valyloxy)methyl]-2-furoate Iodomethyl 4-(2-Ν-benzyloxycarbonyl-L-valyloxyethoxy)-benzoic acid 2,2-dimethyl-3-(N-Boc-L-isoleucyloxy)propionic acid iodomethyl ester 3,3- bis (N-CBz-L-isoleucyloxymethyl)-propionic acid iodomethyl ester, 2-(N-CBz-L-isoleucyloxy)ethoxycarbonyloxymethyl iodide Iodomethyl 1 ,3-bis(N-benzyloxycarbonyl-L-isoleucyloxy)-2-propyl carbonate, 19 Iodomethyl 2-methyl-2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl) propionate, Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxy)-DL-propionate. Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxy)isobutyrate. Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxy)-3-methyl-(S)-(+)-butyrate. Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxy)-2-phenyl-DL-acetate Iodomethyl 4-(N-benzyloxycarbonyl-L-isoleucyloxy) benzoate. Iodomethyl 5-(N-CBz-L-isoleucyloxy)-2,2-dimethylvalerate 2-(N-CBz-L-isoleucyloxy)-ethyl iodomethyl carbonate 4-(N-CBz-L-isoleucyloxy) butyric acid iodomethyl ester Iodomethyl-3-(N-benzyloxycarbonyl-L-isoleuclyloxy)-benzoate Iodomethyl-3-(N-benzyloxycarbonyl-L-isoleucyloxy)-propionate 1 ,3-bis(N-tert-butoxycarbonyl-L-isoleucyloxy)-2-propyl 1-iodoethyl carbonate 3-(N-benzyloxycarbonyl-L-isoleucyloxy)-2,2-dimethylpropyl iodomethyl carbonate Iodomethyl 3 ,4-di-(Ν-CBz-L-isoleucyloxy)hydrocinnamate 3-(N-CBz-L-isoleucyloxy)phenyl iodomethyl carbonate Iodomethyl 2-(N-CBz-L-isoleucyloxy)phenylacetate Iodomethyl 4-(N-CBz-L-isoleucyloxy)phenylacetate Iodomethyl 4-(2-N-benzyloxycarbonyl-L-isoleucyloxyethyl) benzoate Iodomethyl 4-(N-benzyloxycarbonyl-L-isoleucyloxy)cyclohexanoate, Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl)-2-ethyl butyrate, 2-(N-(iodomethoxycarbonyl)-amino)-2-methyl-l-(N-benzyloxycarbonyl- L-isoleucyloxy)-propane, l-(2-N-CBz-L-isoleucyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid iodomethyl ester iodomethyl 5-[(N-benzyloxycarbonyl-L-isoleucyloxy)methyl]-2-furoate iodomethyl 4-(2-Ν-benzyloxycarbonyl-L-isoleucyloxyethoxy)-benzoic acid and the coπesponding chloro analogues. Other prefeπed intermediates include: 2,2-dimethyl-3-(N-PG-L-valyloxy)propionic acid 3,3- bis (N-PG-L-valyloxymethyl)-propionic acid, 2-methyl-2-(N-PG-L-valyloxymethyl) propionate, 2-(N-PG-L-valyloxy)-DL-propionate. 20 2-(N-PG-L-valyloxy)isobutyrate. 2-(N-PG-L-valyloxy)-3-methyl-(S)-(+)-butyrate. 2-O-(N-PG-L-valyloxy)-2-phenyl-DL-acetate 5-(N-PG-L-valyloxy)-2,2-dimethylvalerate 4-(N-PG-L-valyloxy) butyric acid 3-(N-PG-L-valyloxy)-propionate 2-(N-PG-L-valyloxymethyl)-2-ethyl butyrate 2,2-dimethyl-3-(N-PG-L-isoleucyloxy)propionic acid 3,3- bis (N-PG-L-isoleucyloxymethyl)-propionic acid 2-methyl-2-(N-PG-L-isoleucyloxymethyl) propionate, 2-(N-PG-L-isoleucyloxy)-DL-propionate. 2-(N-PG-L-isoleucyloxy)isobutyrate. 2-(N-PG-L-isoleucyloxy)-3-methyl-(S)-(+)-butyrate. 2-(N-PG-L-isoleucyloxy)-2-phenyl-DL-acetate 5-(N-PG-L-isoleucyloxy)-2,2-dimethylvalerate 4-(N-PG-L-isoleucyloxy) butyric acid 3-(N-PG-L-isoleucyloxy)-propionate and the coπesponding activated acid halides where PG is an N-protecting group. Exemplary Linker groups also include an alkoxy moiety such as -CH 3 O-, - CH(CH 3 )O-, C(CH 3 ) 2 O- and the like. Other exemplary L groups include an alkoxyalkoxy moiety such as -CH 3 O-Alk-O-, -CH(CH 3 )O-Alk-O-, C(CH 3 ) 2 O-Alk-O, where Alk is a C,-C 6 branched or straight chain saturated or unsaturated alkylene group, such as methylene, ethylene, l,lbismethylethylene and the like. Other exemplary L groups include derivatives of hydroxyalkanoic acids, where the carboxy function is acylated to the hydroxy function at the 3 or 4 position of the backbone of the structure of formula III', while the hydroxy function is available for acylation with the carboxy function of the amino acid group R 2 . Convenient hydroxyalkanoic acids include those derived from α-hydroxy ω-carboxylic acids such as carbonic acid, glycollic acid, hydroxypropanoic acid, hydroxybutyric acid, hydroxyvaleric acid or hydroxycaproic acid. 21 Linkers prepared from ω -hydroxybutyric derivatives are convenient as with these compounds hydrolysis and removal of the R 2 group in vivo leaves a reactive terminal radical which will tend to cyclize and prompt the effective release of the mother compound. Similarly, linkers of the formula L a : o R 2 - 0 R 2 -0 La are convenient as enzymatic or spontaneous hydrolysis of a first of the R 2 groups will result in an active terminus able to curl back and attack the acyl linkage to the mother compound thus promoting spontaneous release of the linker fragment. Other convenient linkers along the same principle have the formula 1^ or L c : o R 2 — O or L b c Prefeπed novel intermediates thus include the free or activated acid precursors of compounds such as : 3-N-Boc-L-valyloxypropanoic acid, 3-N-Fmoc-L-valyloxypropanoic acid, 3-N-CBZ- L-valyloxypropanoic acid, 3-N-Boc-L-isoleucyloxypropanoic acid, 3-N-Fmoc-L- isoleucyloxypropanoic acid, 3-N-CBZ-L-isoleucyloxypropanoic acid, 4-N-Boc-L- valyloxybutyric acid, 4-N-Fmoc-L-valyloxybutyric acid, 4-N-CBZ-L- valyloxybutyric acid, 4-N-Boc-L-isoleucyloxybutyric acid, 4-N-Fmoc-L- isoleucyloxybutyric acid, 4-N-CBZ-L-isoleucyloxybutyric acid and the like; and the activated derivatives, such as the acid halides Further useful intermediates comprise compounds such as 2-(L-valyloxy)propanoic acid, 2-(N-Boc-L-valyloxy)propanoic acid, 2-(N- Fmoc-L-valyloxy)propanoic acid, 2-(N-CBZ-L-valyloxy)propanoic acid, 2-(L- 22 isoleucyloxy)propanoic acid, 2-(N-Boc-L-isoleucyloxy)propanoic acid, N- (Fmoc-L-isoleucyloxy)propanoic acid, N-(CBZ-L-isoleucyloxy)propanoic acid, 2-(L-valyloxy)butyric acid, 2-(N-Boc-L-valyloxy)butyric acid, 2-(N-Fmoc-L- valyloxy)butyric acid, 2-(N-CBZ-L-valyloxy)butyric acid, 2-(L- isoleucyloxy)butyric acid, 2-(N-Boc-L-isoleucyloxy)butyric acid, N-(Fmoc-L- isoleucyloxy)butyric acid, N-(CBZ-L-isoleucyloxy)butyric acid, and the like; and activated derivatives therof, such as the acid halides. Further novel intermediates include precursors of compounds of the formula He and Ilf above, especially those derived from "natural" configurations such as L- malic and L-tartaric acid; for instance: 3-ethoxycarbonyl-2-valyloxy-propionic acid 3-ethoxycarbonyl-2-isoleucyloxy-propionic acid 4-ethoxycarbonyl-2,3-bis-valyloxy-butyric acid 4-ethoxycarbonyl-2,3-bis-isoleucyloxy-butyric acid 3 -t-butoxycarbonyl-2-valyloxy-propionic acid 3-t-butoxycarbonyl-2-isoleucyloxy-propionic acid 4-t-butoxycarbonyl-2,3-bis-valyloxy-butyric acid 4-t-butoxycarbonyl-2,3-bis-isoleucyloxy-butyric acid 3 -benzyloxycarbonyl-2-valyloxy-propionic acid 3 -benzyloxycarbonyl-2-isoleucyloxy-propionic acid 4-benzyloxycarbonyl-2,3-bis-valyloxy-butyric acid 4-benzyloxycarbonyl-2,3-bis-isoleucyloxy-butyric acid, and the like; especially the coπesponding compounds wherein the amino acid is N- protected, particularly with a protecting group allowing selective deprotection of the N-protective group without removal of the carboxy protecting group; and the coπesponding activated derivatives such as the acid halides. Further useful intermediates include: Still further novel intermediates include precursors coπesponding to structure lid, such as; 23 2-(L-valyloxy)propanoic acid, 2-(N-Boc-L-valyloxy)propanoic acid, 2-(N- Fmoc-L-valyloxy)propanoic acid, 2-(N-CBZ-L-valyloxy)propanoic acid, 2-(L- isoleucyloxy)propanoic acid, 2-(N-Boc-L-isoleucyloxy)propanoic acid, N- (Fmoc-L-isoleucyloxy)propanoic acid, N-(CBZ-L-isoleucyloxy)propanoic acid, 2-(L-valyloxy)butyric acid, 2-(N-Boc-L-valyloxy)butyric acid, 2-(N- Fmoc-L-valyloxy)butyric acid, 2-(N-CBZ-L-valyloxy)butyric acid, 2-(L- isoleucyloxy)butyric acid, 2-(N-Boc-L-isoleucyloxy)butyric acid, N-(Fmoc-L- isoleucyloxy)butyric acid, N-(CBZ-L-isoleucyloxy)butyric acid, and the like; and activated derivatives therof, such as the acid halides. Alkylation of the mother compound, for instance when group linker-(R 2 ') k -R 2 such as L-R y is derived from an alkoxyamino acid ester, is conveniently done with the coπesponding N-protected haloalkoxyamino acid ester. Convenient alkylation intermediates thus include iodomethyloxy-N-CBz-valyl, iodomethyloxy-N-Boc-valyl, iodomethyloxy-N-Fmoc-valyl iodomethyloxy-N-CBz-isoeucyl, iodomethyloxy-N-Boc-isoleucyl, iodomethyloxy-N-Fmoc-isoleucyl, and coπesponding derivatives bearing other N-protecting groups. Further useful intermediates include structures of the formula: PG-R 2 — O — i O O or O O ho- Alk r- O * • Alk X PG-R N 2' — O * PG-R2 — O- PG-R2'— O * where Alk is C,-C 4 alkylene or C 2 -C 4 alkenylene and X is OH or an activating group. Prefeπed intermediates of the above structure thus include: 24 malonic acid 2,3-b/s-(L-valyloxy)-propyl ester, malonic acid 2,3-bw-(N-CBZ-L-valyloxy)-propyl ester, malonic acid 2,3-bw-(N-Fmoc-L-valyloxy)-propyl ester, malonic acid 2,3-b/5-(N-Boc-L-valyloxy)-propyl ester, malonic acid 2,3-bw-(L-isoleucyloxy)-propyl ester, malonic acid 2,3-bw-(N-CBZ-L-isoleucyloxy)-propyl ester, malonic acid 2,3-b/s-(N-Fmoc-L-isoleucyloxy)-propyl ester, malonic acid 2,3-bώ-(N-Boc-L-isoleucyloxy)-propyl ester, succinic acid 2,3-bw-(L-valyloxy)-propyl ester, succinic acid 2,3-b/s-(N-CBZ-L-valyloxy)-propyl ester, succinic acid 2,3-bw-(N-Fmoc-L-valyloxy)-propyl ester, succinic acid 2,3-b/s-(N-Boc-L-valyloxy)-propyl ester, succinic acid 2,3-bw-(L-isoleucyloxy)-propyl ester, succinic acid 2,3-bt5-(N-CBZ-L-isoleucyloxy)-propyl ester, succinic acid 2,3-bt5-(N-Fmoc-L-isoleucyloxy)-propyl ester, succinic acid 2,3-b/s-(N-Boc-L-isoleucyloxy)-propyl ester, glutaric acid 2,3-bw-(L-valyloxy)-propyl ester, glutaric acid 2,3-bts-(N-CBZ-L-valyloxy)-propyl ester, glutaric acid 2,3-b/.s*-(N-Fmoc-L-valyloxy)-propyl ester, glutaric acid 2,3-bt.s-(N-Boc-L-valyloxy)-propyl ester, glutaric acid 2,3-b/s-(L-isoleucyloxy)-propyl ester, glutaric acid 2,3-b/s-(N-CBZ-L-isoleucyloxy)-propyl ester, glutaric acid 2,3-bw-(N-Fmoc-L-isoleucyloxy)-propyl ester, glutaric acid 2,3-bw-(N-Boc-L-isoleucyloxy)-propyl ester, and the coπesponding acid halides, in particular the chloride, acid anhydrides and triesters of each of the above, for instance succinic acid 2,3-b/s-(N-CBZ-L-valyloxy)-propyl ester,4-methoxybenzyl ester succinic acid 2,3-bw-(N-CBZ-L-valyloxy)-propyl ester, 1,1-dimethylethyl ester, etc. A particularly prefeπed group of intermediates within the above structure include: malonic acid l,3-b/s-(L-valyloxy)-propyl ester, 25 malonic acid l,3-bw-(N-CBZ-L-valyloxy)-propyl ester, malonic acid l,3-b/s-(N-Fmoc-L-valyloxy)-propyl ester, malonic acid 1 ,3-bt5-(N-Boc-L-valyloxy)-propyl ester, malonic acid l,3-bw-(L-isoleucyloxy)-propyl ester, malonic acid l,3-bύ-(N-CBZ-L-isoleucyloxy)-propyl ester, malonic acid l,3-b«-(N-Fmoc-L-isoleucyloxy)-propyl ester, malonic acid l,3-bz ' 5-(N-Boc-L-isoleucyloxy)-propyl ester, succinic acid l,3-bw-(L-valyloxy)-propyl ester, succinic acid l,3-bw-(N-CBZ-L-valyloxy)-propyl ester, succinic acid l,3-b«-(N-Fmoc-L-valyloxy)-propyl ester, succinic acid l,3-b/s-(N-Boc-L-valyloxy)-propyl ester, succinic acid l,3-bts-(L-isoleucyloxy)-propyl ester, succinic acid 1 ,3-bw-(N-CBZ-L-isoleucyloxy)-propyl ester, succinic acid l,3-bώ-(N-Fmoc-L-isoleucyloxy)-propyl ester, succinic acid l,3-bw-(N-Boc-L-isoleucyloxy)-propyl ester, glutaric acid l,3-bw-(L-valyloxy)-propyl ester, glutaric acid l,3-bw-(N-CBZ-L-valyloxy)-propyl ester, glutaric acid l,3-bw-(N-Fmoc-L-valyloxy)-propyl ester, glutaric acid l,3-bw-(N-Boc-L-valyloxy)-propyl ester, glutaric acid l,3-bts-(L-isoleucyloxy)-propyl ester, glutaric acid l,3-bts-(N-CBZ-L-isoleucyloxy)-propyl ester, glutaric acid l,3-bts-(N-Fmoc-L-isoleucyloxy)-propyl ester, glutaric acid l,3-bts-(N-Boc-L-isoleucyloxy)-propyl ester, and the coπesponding acid halides, in particular the chloride, acid anhydrides and diesters of each of the above, for instance succinic acid l ,3-bw-(N-CBZ-L-valyloxy)-propyl ester,4-methoxybenzyl ester succinic acid 13-bts-(N-CBZ-L-valyloxy)-propyl ester, 1,1-dimethylethyl ester, etc. Drugs Representative drugs having carboxyl functional groups include; angiotensin-converting enzyme inhibitors such as alecapril, captopril, l-[4-carboxy- 2-methyl-2R,4R-pentanoyl]-2,3-duhydro-2S-indole-2-carboxylic acid, enalaprilic 26 acid, lisinopril, N-cyclopentyl-N-[3-[(2,2-dimethyl-l-oxopropyl)thio]-2-methyl-l- oxopropyljglycine, pivopril, (2R, 4R)-2-hydroxyphenyl)-3-(3-mercaptopropionyl)-4- thiazolidinecarboxylic acid, (S) benzamido-4-oxo-6-phenylhexenoyl-2- carboxypyπolidine, [2S-1[R*(R*))] ] 2α, 3αβ, 7αβ]-l[2-[[l-carboxy-3- phenylpropyl]-amino]-l-oxopropyl]octahydro-lH-indole-2-carboxylic acid, [3S- 1 [R*(R*))] ], 3R*]-2-[2-[[l-carboxy-3-phenylproρyl]-amino]-l-oxopropyl]-l,2,3,4- tetrahydro-3-isoquinolone carboxylic acid and tiopronin; cephalosporin antibiotics such as cefaclor, cefadroxil, cefamandole, cefatrizine, cefazedone, cefazuflur, cefazolin, cefbuperazone, cefrnenoxime, cefrnetazole, cefodizime, cefonicid, cefoperazone, ceforanide, cefotaxime, cefotefan, cefotiam, cefoxitin, cefpimizole, ce irome, cefroxadine, cefsulodin, cefpiramide, ceftazidime, ceftezole, ceftizoxime, ceftriaxone, cefuroxime, cephacetrile, cephalexin, cephaloglycin, cephaloridine, cephalosporin, cephanone, cephradine and latamoxef; penicillins such as amoxycillin, ampicillin, apalcillin, azidocillin, azlocillin, benzylpencillin, carbenicillin, carfecillin, carindacillin, cloxacillin, cyclacillin, dicloxacillin, epicillin, flucloxacillin, hetacillin, methicillin, mezlocillin, nafcillin, oxacillin, phenethicillin, piperazillin, sulbenicllin, temocillin and ticarcillin; non-steroidal antiinflammatory agents such as acametacin, alclofenac, alminoprofen, aspirin (acetylsalicylic acid), 4-biphenylacetic acid, bucloxic acid, carprofen, cinchofen, cinmetacin, clometacin, clonixin, diclenofac, diflunisal, etodolac, fenbufen, fenclofenac, fenclosic acid, fenoprofen, ferobufen, flufenamic acid, flufenisal, flurbiprofm, fluprofen, flutiazin, ibufenac, ibuprofen, indomethacin, indoprofen, ketoprofen, ketorolac, lonazolac, loxoprofen, meclofenamic acid, mefenamic acid, 2-(8-methyl- 10,11-dihydro-l l-oxodibenz[b,f]oxepin-2-yl)proρionic acid, naproxen, nifluminic acid, O-(carbamoylphenoxy)acetic acid, oxoprozin, pi rofen, prodolic acid, salicylic acid, salicylsalicylic acid, sulindac, suprofen, tiaprofenic acid, tolfenamic acid, tolmetin and zopemirac; prostaglandins such as ciprostene, 16-deoxy-16-hydroxy-16-vinyl prostaglandin E 2 , 16, 16-dimethylprostaglandin E 2 , epoprostostenol, meteneprost, nileprost, prostacyclin, prostaglandins E„ E 2 , or F 2α and thromboxane A 2 ; 27 quinolone antibiotics such as acrosoxacin, cinoxacin, ciprofloxacin, enoxacin, flumequine, naladixic acid, norfloxacin, ofloxacin, oxolinic acid, pefloxacin, pipemidic acid and piromidic acid. Representative drugs containing amine groups include: acebutalol, albuterol, alprenolol, atenolol, bunolol, butopamine, butoxamine, carbuterol, cartelolol, colterol, deterenol, dexpropanolol, diacetolol, dobutamine, exaprolol, exprenolol, fenoterol, fenyripol, labotolol, levobunolol, metolol, metaproterenol, metoprolol, nadolol, pamatolol, penbutalol, pindolol, pirbuterol, practolol, prenalterol, primidolol, prizidilol, procaterol, propanolol, quinterenol, rimiterol, ritodrine, solotol, soterenol, sulfmiolol, sulfmterol, sulictidil, tazaolol, terbutaline, timolol, tiprenolol, tipridil, tolamolol, thiabendazole, albendazole, albutoin, alinidine, alizapride, amiloride, aminorex, aprinocid, cambendazole, cimetidine, clonidine, cyclobenzadole, etintidine, fenbendazole, fenmetazole, flubendazole, fludorex, lobendazole, mebendazole, metazoline, nocodazole, oxfendazole, oxibendazole, oxmetidine, parbendazole, ranitidine, tetrahydrazoline, tiamenidine, tinazoline, tiotidine, tolazoline, tramazoline, xylometazoline, dimethoxyphenethylamine, N-[3(R)-[ 2-piperidin-4-yl)ethyl]-2-piperidone-l- yl]acetyl-3(R)-methyl-β-alanine adrenolone, aletamine, amidephrine, amphetamine, aspartame, bamethan, betahistine, clorprenaline, chlortermine, dopamine, ephrinephrine etryptamine, fenfluramine, methyldopamine, norepinephrine, tocainide enviroxime, nifedipine, nimodipine, triamterene, norfloxacin and similar compounds such as pipedemic acid, l-ethyl-6-fluoro-l,4- dihydro-4-oxo-7-(l -piperazinyl)- 1 ,8-napthyridine-3-carboxylic acid, 1 -cyclopropyl- 6-fluoro-l,4-dihydro-4-oxo-7-(piperazinyl)-3-quinolinecarboxylic acid. A favoured amine drug, [[3(R)-2-piperidin-4-ylethyl)-2-oxopiperidinyl]acetyl]-3(R)- methyl-β-alanine (also known as L-734,217) has the formula: 28 A further prefeπed amino drug are the bicyclam anti HIV agents, such as AMD 3100: Representative drugs containing hydroxy groups include: steroidal hormones such as allylestrenol, cingestol, dehydroepiandrosteron, dienostrol, diethylstilbestrol, dimethisteron, ethyneron, ethynodiol, estradiol, estron, ethinyl estradiol, ethisteron, lynestrenol, mestranol, methyl testosterone, norethindron, norgestrel, norvinsteron, oxogeston, quinestrol, testosteron and tigestol; tranquilizers such as dofexazepam, hydroxyzin, lorazepam and oxazepam; neuroleptics such as acetophenazine, carphenazine, fluphenazine, perphenyzine and piperaetazine; cytostatics such as aclarubicin, daunorubicin, dihydro-5-azacytidine, doxorubicin, epirubicin, estramustin, etoposide, 7-hydroxychlorpromazin, neplanocin A, pentostatin, podophyllotoxin, vinblastin, vincristin, vindesin; hormones and hormone antagonists such as buserilin, gonadoliberin, icatibrant and leuprorelin acetate; antihistamines such as terphenadine; analgesics such as diflunisal, naproxol, paracetamol, salicylamide and salicyclic acid; 29 antibiotics such as azidamphenicol, cefamandol, chloramphenicol, clavulanic acid, clindamycin, comptothecin, demeclocyclin, doxycyclin, imipenem, latamoxef, novobiocin, oleandomycin, oxytetracyclin, tetracyclin and thiamenicol; prostaglandins such as arbaprostil, carboprost and prostacydin; antidepressives such as 8-hydroxychlorimipramine and 2-hydroxyimipramine; antihypertonics such as sotarol and fenoldopam; anticholinerogenics such as biperidine, carbidopa, procyclidin and trihexyphenidal; antiallergenics such as cromolyn; glucocorticoids such as betamethasone, budenosid, chlorprednison, clobetasol, clobetasone, corticosteron, cortisone, cortodexon, dexamethason, flucortolon, fludrocortisone, flumethasone, flunisolid, fluprednisolon, flurandrenolide, flurandrenolon acetonide, hydrocortisone, meprednisone, methylpresnisolon, paramethasone, prednisolon, prednisol, triamcinolon and triamcinolon acetonide; narcotic agonists and antagonists such as apomorphine, buprenorphine, butorphanol, codein, cyclazocin, hydromorphon, ketobemidon, levallorphan, levorphanol, metazocin, moφhine, nalbuphin, nalmefen, naloxon, naloφhine, naltrexon, oxycodon, oxymoφhon and pentazocin; stimulants such asmazindol and pseudoephidrine; anaesthetics such as hydroxydion and propofol; β-receptor blockers such as acebutolol, albuterol, alprenolol, atenolol, betazolol, bucindolol, cartelolol, celiprolol, cetamolol, labetalol, levobunelol, metoprolol, metipranolol, nadolol, oxyprenolol, pindolol, propanolol and timolol; α-sympathomimetics such as adrenalin, metaraminol, midodrin, norfenefrin, octapamine, oxedrin, oxilofrin, oximetazolin and phenylefrin; β-sympathomimetics such as bamethan, clenbuterol, fenoterol, hexoprenalin, isoprenalin, isoxsuprin, orciprenalin, reproterol, salbutamol and terbutalin; bronchodilators such as carbuterol, dyphillin, etophyllin, fenoterol, pirbuterol, rimiterol and terbutalin; cardiotonics such as digitoxin, dobutamin, etilefrin and prenalterol; antimycotics such as amphotericin B, chloφhenesin, nystatin and perimycin; anticoagulants such as acenocoumarol, dicoumarol, phenprocoumon and warfarin; vasodilators such as bamethan, dipyrimadol, diprophyllin, isoxsuprin, vincamin and xantinol nicotinate; 30 antihypocholesteremics such as compactin, eptastatin, mevinolin and simvastatin; miscellaneous drugs such as bromperidol (antipsychotic), dithranol (psoriasis) ergotamine (migraine) ivermectin (antihelminthic), metronidazole and secnizadole (antiprotozoals), nandrolon (anabolic), propafenon and quinadine (antiarythmics), srotonin (neurotransmitter) and silybin (hepatic disturbance). The invention is applicable to L and D- nucleosides bearing di, tri and tetrahydric (that is bearing 2, 3 or 4 hydroxy groups on the (pseudo)saccharide, such as those of the formula N-3: R N3° N-3 R N4 0(CH 2 ) n CHR N5 N2 where B is a natural or unnatural nucleotide base, R N1 is O or -CH 2 -, S R N2 and R N3 are each H or R N2 is methyl ene or -CH(OH)- and R N5 is a bond thereto, or R N2 and R N5 together are a bond; n is 0 or 1 ; one of R N3 and R N4 comprises a linker-R 2 structure such as those of formulae Ilaa, H'aa, lie', He', IIP, id' and the other is hydrogen or a further linker-R, structure. An alternative group drugs to which the invention is applicable includes those of formula N-3 a: B A N-3a O O I I RN3 N4 31 where B, NR3 and NR4 are as defined above. Preferably the linker(R 2 ') k -R 2 structure is esterified to R 3 in the above two structures, that is the nominal 5' hydroxy group of the nucleoside analogue. An alternative group of drugs within the scope of the invention has the formula N-3b: NR3 — O N-3b NR4 where B, RN3and RN4 are as defined above and RN6 is fluoro and RN7 is hydrogen or RN6 and RN7 are both fluoro or RN6 and RN7 together define an exo-methenyl group. The prefeπed base is guanine in this alternative. A further group of nucleosides within the scope of the invention has the formula N- 3c RN9 N-3c where B, RN3 and RN4 are as defined above, RN8 and RN9 are fluoro (or one of them is fluoro and the other is hydrogen) or RN8 and RN9 together define exomethenyl or exomethenyl mono or di-subsituted with fluoro. These nucleosides have anticancer activity. The invention is also applicable to other nucleosides having at least two hydroxy groups, but outside the scope of formula N-3a-c, for instance, 9-[3,3- dihydroxymethyl-4-hydroxy-but-l-yl] guanine as described in WO 95/22330 and 9- 32 [4-hydroxy-(2-hydroxymethyl)butyl]guanine as described in EP 343 133. The invention is applicable to both L and D stereo forms of the various nucleoside analogues The compounds of the invention, especially cytosine or guanine derivatives where NRl is oxygen, n is 1 and NR2 and NR5 define a ring are also active against certain retroviral infections, notably SIV, HIV-1 and HIV-2, and Hepatitis B virus. The compounds of the invention, especially cytosine, guanosine or 6-methoxyguanosine derivatives wherein NRl is oxygen, n is 0 and NR2 and NR5 define an arabinose ring are potent anticancer compounds. The compounds of the invention, especially derivatives comprising a 1,2,4-triazole- 3-carboxamide base, where NRl is O, NR2 is -CH(OH)-, NR3 is a bond thereto and n is 0 (ribavirin) are expected to be active against hepatitis C virus (HCV). Compounds comprising a substituted benzimidazole base, where NRl is O, NR2 is - CH(OH)-, NR5 is a bond thereto and n is 0 (for instance Glaxo Wellcome' s 1263W94 where the base is 2-isopropylamin-5,6-dichloro-benzimidazol-3-yl) are expected to be active against CMV. Compounds comprising an adenine base, where NRl is O, NR2 is -CH(OH)-, NR5 is a bond thereto and n is 0 (vidarabine) are expected to be active against HSV encephalitis. Compounds comprising a 2- chloroadenine base with a 2'-deoxyribose sugar are expected to have anticancer activity. The nucleoside derivatives of the invention are particularly useful for guanine nucleoside and analogues which tend to have poorer uptake than pyrimidine nucleosides. Accordingly B is preferably guanine or a guanine derivative. A group of hydroxy bearing drugs which are particularly amenable to the prodrugs of the invention are the ring hydroxy compounds. By ring hydroxy is meant that the hydroxy function to which the prodrug of the invention is bound is bonded directly onto an aromatic or non-aromatic, heterocyclic or carbocyclic ring structure. 33 Examples of ring hydroxy compounds include the cyclic urea HIV protease inhibitors, such as those described in WO 9843969, WO9820008, and WO 9419329. Representative protease inhibitors include: O O j H H " ^X O where Rl is NH 2 (DMP 450) or ' NH NH ^ (SD 146). Some examples of phenolic ring hydroxy compounds include the PETT NNRTI discussed below or the compound described in J Med Chem 35 3467 (1992): Pancratistatin described in Anticancer Drug Design 10: 243 & 299 (1995) and Bioorg Med Chem Lett 6 157 1996: OH O 34 has both phenolic and carbocyclic ring hydroxy functions. A further useful drug with a combination of phenolic and carbocyclic hydroxy functions is etoposide: as described in Bioorg Med Chem Lett 4 2567 (1994) and Clinical Cancer Res 1 105 1995. A further convenient Drug for appying the prodrugs of the invention is the anti- Parkinsonian agent levodopa: O OH NH HO OH This drug has four accessible functions for applying the prodrugs of the invention, namely the 3 and 4 hydroxy groups on the phenyl and the amino and carboxy functions on the side chain. A structure of the formula Ila or IF'b can be esterified to one or both of the aromatic hydroxyl functions or amide-bonded to the levodopa amino function. A trifunctional linker of Formula III or Formula lid, can be carbonyl bonded to the levodopa carboxyl function. Such "blocked" carboxyl levodopa compounds are conceivably less susceptible to in vivo peripheral decarboxylation than levodopa and may thus allow the diminution or omission of the customarily coadministered decarboxylase inhibitors such as carbidopa. 35 A further convenient Drug for applying the prodrugs of the invention is chromoglycate, also known as cromolyn, useful in the treatment of asthma, allergic rhinitis, mastocytosis, ulcerative colitis and inflammatory bowel disease: It will be apparent that cromolyn has three accessible functions suitable for applying the prodrugs of the invention. In particular, a linker of the formula lid can be carbonyl linked to either of the carboxy groups. As cromolyn is a symmetric compound it may be advantageous to bond a respective linker to each of the carboxyl groups. Alternatively or additionally, a linker of the formula Ila, lid, such as those wherein T is a bond or -O- and V is a bond can be esterified to the hydroxy group depending from the propylene bridge, optionally in conjunction with conventional pharmaceutical esters on the carboxy groups. A further group of Drugs which are amenable to the prodrugs of the invention are the pain-killer opiates such as moφhine: H 3 C- N Moφhine and many of its analogues have a pair of hydroxy functions accessible to the prodrug approach of the invention. For instance a structure of formula Ila wherein T is a bond or -O- and V is a bond would be convenient for esterification with the 3 and/or 6 hydroxy groups. 36 A further convenient group of compounds include the macrolide antibiotics such as erythromycin and roxitromycin and antibacterial glycopeptides such as vancomycin. A further convenient group of Drugs for applying the prodrugs of the invention are the rifamycin antibiotics: wherein the asterisks define the requisite number of aromatic bonds, including rifampicin (R a is OH, R,, is -CH=N-(4-N-methylpiperazine), R c is hydroxy), rifamide (R a is OCH 2 CONH(C 2 H 5 ) 2 , R b is hydrogen, R c is hydroxy), rifamycin B (R^ is -OCH 2 COOH, R b is hydrogen, R c is hydroxy), rifamycin O (R,, is -l,3-dioxolan-4-on)-2-yl, R b is hydrogen, R c is hydroxy), rifamycin S (R a is =0, R b is hydrogen, R c is =O), rifamycin SV (R a is -OH, R b is hydrogen R c is -OH), rifaximin (R a and R b together define a structure: • N ' . , R c is hydroxy), and rifabutinum (R a and R b together define a structure: , R, is =O). It will be apparent that the rifamycins have a number of free hydroxyls and secondary amines available for esterification or amide bonding with respective linker-R 2 groups 37 in accordance with the invention such as those of Formula Ila above, which linker group is bonded to one of said hydroxy or amino groups. A further group of Drugs which are amenable to the prodrugs of the invention is the cephalosporin antibiotics: R^ R A ■ AN . O Rμ =O OH Representative cephalosporins include: cefpodoxime (R a is [(2-amino-4-thiazolyl)(methoximino)acetyl]amino-, R b is H, R c is ethyl), cefaclor (R a is aminophenylacetylamino, R b is H, R c is chloro), cefadroxil (R_, is [amino-(4-hydroxyphenyl)acetyl]amino, R b is H, R c is methyl); cefamandole (R a is [amino-(4-hydroxyphenyl)acetyl]amino, R b is H, R c is [1-methyl- 1 H-tetrazol-5-yl)thio]methyl); cefatrizine, (R a is is [amino-(4-hydroxyphenyl)acetyl]amino, R b is H, R c is [IH- 1,2,3- triazol-4-ylthio]methyl) ; cefazedone (Ra is [(3,5-dichloro-4-oxo-l(4H)-pyridinyl)acetyl]amino, R b is H, R,. is [(5-methyl-l,3,4-thiadiazol-2-yl)thio]methyl), cefazolin (Ra is (lH-tetrazol-l-ylacetyl)-amino Rb is H, Rc is [(5-methyl-l,3,4- thiadiazol-2-yl)thio]methyl, cefbuparazone (Ra is [2-[[(4-ethyl-2,3-dioxo-l-piperazinyl)carbonyl]amino]-3- hydroxy-l-oxobutyl]amino, Rb is OCH 3 , Rc is [(1 -methyl- lH-tetrazoly- 5yl)thio]methyl, cefixime (Ra is [(2-amino-4-thiozolyl)[carboxymethoxy)imino]acetyl]amino, Rb is H, Rc is -CH=CH 2 ), cefmonoxime, (Ra is [(2-amino-4-thiazolyl)(methoxyimino)acetyl]amino, Rb is h, rc is [( 1 -methyl- 1 H-tetrazol-5-yl)thio]methyl), 38 cefmetazole ([[(cyanomethyl)thio]acetyl]amino, Rb is H, Rc is [ 1 -methyl- 1H- tetrazol-5-yl)thio]methyl), cefrninox (Ra is [[(2-amino-2-carboxyethyl)thio]acetyl]amino, Rb is OCH 3 , Rc is is [ 1 -methyl- 1 H-tetrazol-5-yl)thio]methyl), cefodoxime (Ra is [(2-amino-4-thiazolyl)(methoxyimino)acetyl]amino, Rb is H, Rc is [[5-(carboxymethyl)-4-methyl-2-thiazolyl]thio]methyl), cefonicid (Ra is (hydroxyphenylacetyl)amino, Rb is H, Rc is [[l-8sulfomethyl)-lH- tetrazol-5-y]thio]methyl), cefoperazone (Ra is [[[(4-ethyl-2,3-dioxo-l-piperazinyl)carbonyl]amino](4- hydroxyphenyl)acetyl]amino, Rb is H, Rc is [(1 -methyl- lH-tetrazol-5- yl)thio]methyl), ceforanide (Ra is [[2-(aminomethyl)phenyl]acetyl]amino, Rb is H, Rc is [[1- (carboxymethyl)- 1 H-tetrazol-5-yl]thio]methyl), cefotaxime (Ra is [(2-amino-4-thiazolyl)(methoxyimino)acetyl]amino, Rb is H, Rc is (acetyloxy)methyl), cefotetan (Ra is [[4-(2-amino-l-carboxy-2-oxoethylidine)-l,3-dithietan-2- yl]carbonyl]amino, Rb is OCH 3 , Rc is [(1 -methyl- lH-tetrazol-5-yl)thio]methyl, Rc is [(1 -methyl- lH-tetrazol-5-yl)thio]methyl), cefotiam (Ra is [(2-amino-4-thiazolyl)acetyl]amino, Rb is H, Rc is [[l-[2- (dimethylamino)ethyl]-lH-tetrazol-5-yl]thio]methyl), cefoxitin (Ra is (2-thienylacetyl)amino, Rb is OCH 3 , Rc is [aminocarbonyl)oxy]methyl), ceφimizole (Ra is [[[(5-carboxy-lH-imidazol-4- yl)carbonyl]amino]phenylacetyl]amino, Rb is H, Rc is (4'-(2-sulfoethyl)pyridinium) methyl hydroxide inner salt, cefpiramide (Ra is [[[(4-hydroxy-6-methyl-3-pyridinyl)carbonyl]amino](4- hydroxyphenyl)acetyl]amino, Rb is H, Rc is [(1 -methyl- lH-tetrazol-5- yl)thio]methyl), cefroxadine (Ra is (amino- 1 ,4-cyclohexadi en- 1 -yl-acetyl)amino, Rb is H, Rc is OCH 3 ), 39 cefsulodin (Ra is (phenylsulfoacetyl)amino, Rb is H, Rc is (4'-carbamoyl pyridinium)methyl hydroxide inner salt), ceftazidime (Ra is [(2-amino-4-thiazolyl)[(l-carboxy-l- methylethoxy)imino]acetyl]amino, Rb is H, Rc is pyridiniummethyl hydrochloride inner salt), cefteram (Ra is [(2-amino-4-thiazolyl)methoxyimino)acetyl]amino, Rb is H, Rc is (5- methyl-2H-tetrazol-2-yl)methyl), ceftezole (Ra is (lH-tetrazol-l-ylacetyl)amino, Rb is (l,3,4-thiadiazol-2- ylthio)methyl), ceftibuten (Ra is [2-(2-amino-4-thiazolyl)-4-carboxy-l-oxo-2-butenyl]amino, Rb is H, Rc is H) ceftiofur (Ra is [(2-amino-4-thiazoyl)(methoxyimino)acetyl]amino, Rb is H, Rc is [(2-furanylcarbonyl)thio]methyl), ceftizoxime (Ra is [(2-amino-4-thiazolyl)(methoxyimino)acetyl]amino, Rb is H, Rc is H), ceftriaxone (Ra is [(2-amino-4-thiazolyl)methoxyimino)acetyl]amino, Rb is H, Rc is [l,2,5,6-tetrahydro-2-methyl-5,6-dioxo-l,2,4-triazin-3-yl)thio]methyl), cefuroxime (Ra is [2-furanyl(methoxyimino)acetyl]amino, Rb is H, Rc is [(aminocarbonyl)oxy]methyl), cefuzonam (Ra is [(2-amino-4-thiazolyl)(methoxyimino)acetyl]amino, Rb is H, Rc is (l,2,3-thiadiazol-5-ylthio)methyl), cephacetrile (Ra is (cyanocetyl)amino, Rb is H, Rc is (acetyloxy)methyl), cephalexin (Ra is (aminophenylacetyl)amino, Rb is H, Rc is methyl), cephaloglycin (Ra is (aminophenylacetyl)amino, Rb is H, Rc is (acetyloxy)methyl), cephaloridine (Ra is (2-thienylacetyl)amino, Rb is H, Rc is pyridinium methyl hydroxide inner salt), cephalosporin C (Ra is (5-amino-5-carboxy-l-oxopentyl)amino, Rb is H, Rc is (acetyloxy)methyl), cephalothin (Ra is (2-thienylacetyl)amino, Rb is H, Rc is (acetyloxy)methyl), cephamycin A (Ra is (5-amino-5-carboxy-l-oxopentyl)amino, Rb is OCH 3 Rc is -CH 2 OCOC(OCH 3 )=CH-(4-oxysulphyl)phenyl), 40 cephamycin B (Ra is (5-amino-5-carboxy-l-oxopentyl)amino, Rb is OCH 3 Rc is -CH 2 OCOCC(OCH 3 )=CH-(4-hydroxy)phenyl), cephamycin C (Ra is (5-amino-5-carboxy-l-oxopentyl)amino, Rb is OCH 3 Rc is -CH 2 OCONH 2 ) cephapirin (Ra is [(4-pyridinylthio)acetyl]amino, Rb is H, Rc is (acetyloxy)methyl), cephradine (Ra is (amino- l,4-cyclohexadien-l-yl-acetyl)amino, Rb is H, Rc is CH 3 ). Common for the above cephalosporins is the presence of a carboxy group at the 2- position which is amenable to derivation with a linker group, in particular those of the Formula lid defined above. The above listed Ra, Rb and Rc groups may also be combined in various permutations and the invention includes prodrugs of all such cephalosporins. A further group of Drugs which are amenable to the prodrugs of the invention are the anticholinesterases such as tacrine: where R is H or OH. It will be apparent that the tacrine itself (R=H) has a free amine group suitable for derivatisation with a linker-R 2 group such as those of Formula Ila, for instance when T is a bond or -O- and V is a bond. The tacrine metabolite (R = OH), which is also active in vivo has an additional hydroxy function which can alternatively or additionally be derivatised with a linker such as those of Formula Ila, for instance when T is a bond or -O- and V is a bond. A further group of Drugs which are amenable to the prodrugs of the invention are the sulphonamide diuretics such as furosemide: It will be apparent that furosemide has a free carboxylic function, a primary amine and a secondary amine amenable to the prodrugs of the invention. In particular an R 2 bearing linker, such as those of Formula III, or Formula lid can be carbonyl linked to the free carboxy function. Alternatively or additionally, an R 2 bearing linker, such as those of Formula Ila, for instance where T is a bond or -O- and V is a bond can be amide bonded to the primary and/or secondary amine groups. A further group of Drugs amenable to the prodrugs of the invention include the α-1 and β-blocker carvedilol compounds: Carvedilol has a free hydroxy function, a secondary heterocyclic amine and a further secondary amine on the side chain, which are amenable to the prodrugs of the invention, such as those of Formula IF a, for instance where T is a bond or -O- and V is a bond which is in turn linked to the hydroxy and/or the ring amine and/or the side chain amine functions on carvedilol. A further group of Drugs which are amenable to the prodrugs of the invention are the hypolipaemic statins, such as flustatin or compounds of the formula: 42 Rc Rd such as pravastatin (Ra = H, Rb = OH, Rc = H , Rd = OH) and simvastatin (Ra = CH 3 , Rb = CH 3 , Rc and Rd together define a bond). Taking simvastatin as an example, it will be apparent that there is a free side chain hydroxyl which is available for linkage with an R 2 bearing linker, such as those of Formula Ila, for instance where T is a bond or -O- and V is a bond. The statin pravastatin also bears a coπesponding hydroxy function and can be derivatised with a linker in the same fashion. Pravastatin also bears a ring hydroxyl and a further side chain hydroxyl function which can be derivatised with a linker in a coπesponding fashion. Pravastatin also bears a carboxyl function which can additionally or alternatively be derivatised with an R 2 bearing linker such as those of Formula III, or Formula lid. A further group of Drugs which are amenable to the prodrugs of the invention are peptides and pseudopeptides such protease inhibitors including antifibrinolytics like aprotinin or peptidomimetic aspartyl protease inhibitors such as renin inhibitors. Other peptide Drugs include hormones such as vasopressins. Taking vasopressins as an example, peptide Drugs may be cyclic oligopeptides consisting solely of amino acids such as desmopressin or oxytocin, wherein the N and C terminals represent accessible functions for derivatisation in accordance with the invention. Additionally many peptide drugs include amino acids with side chains bearing accessible functions such as arginine, serine or aspartate. Alternatively a peptide Drug, particularly peptidomimetics can be derivatised with non-amino acid structures bearing accessible functions such as somatostatin octreotide. 43 Useful oligopeptides for derivisation acording to the invention include MK 383, an Arg-Gly-Asp analogue useful as an antithrombotic, DADLE (Tyr-D-Ala-Gly-Phe-D- Leu), an encephalin analogue and NISIN. An exemplary group of protease inhibitors amenable to the invention comprises the HIV protease inhibitors bearing one or more chain hydroxy functions and/or one or more ring hydroxy functions such as the indanolamine terminal group in Mercks indinavir: Favoured prodrugs of indinavir in accordance with the invention include [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(3-valyloxypropionyloxy)-lH- inden-l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(3-isoleucyloxypropionyloxy)- lH-inden-l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(4-valyloxybutyryloxy)-lH-inden- l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(4-isoleucyloxybutyryloxy)-lH- inden- 1 -yl)-5-[2-[[( 1 , 1 -dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)- 1 - piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(4-valyloxybut-2-en-oyl)-lH- inden-l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, 44 [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(4-isoleucyloxybut-2-enoyloxy)- lH-inden-l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(5-valyloxypent-2-en-oyl)-lH- inden-l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(5-isoleucyloxypent-2-enoyloxy)- 1 H-inden- 1 -yl)-5-[2-[[( 1 , 1 -dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)- 1 - piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(5-valyloxypent-3-en-oyl)-lH- inden- 1 -yl)-5-[2-[[( 1 , 1 -dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)- 1 - piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(5-isoleucyloxypent-3-enoyloxy)- 1 H-inden- 1 -yl)-5-[2-[[( 1 , 1 -dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)- 1 - piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(2-valyloxypropionyloxy)-lH- inden-l-yl)-5-[2-[[(l,l-dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)-l- piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, [1-(1S,2R), 5(S)]-2,3,5-trideoxy-N-(2,3-dihydro-2-(2-isoleucyloxypropionyloxy)- 1 H-inden- 1 -yl)-5-[2-[[( 1 , 1 -dimethylethyl)amino]carbonyl]-4-(3-pyridinylmethyl)- 1 - piperazinyl]-2-(phenylmethyl-D-erythro-pentonamide, and the like. A further indanol based HIV protease inhibitors is Novartis/BMS SDZ PRI 053: O O. .NH T 0 Favoured compounds include the analogues listed as for indinavir, 45 A further group of HIV protease inhibitors include the hexose derived compounds described in WO 98/45330, such as: A further useful group of compounds for applying the compounds of the invention are the phenolic hydroxy compounds of the PETT series of NNRTI disclosed in WO 93/03022, WO95/06034 and PCT/SE99/00053, the contents of which are incoφorated by reference. Favoured ring hydroxy compounds of this class have the formula P 1 : Rp4 Rp5 R p6 RP1 Rp7 N 77 Rp3 H ' N XX Rp2 where one of Rpl-3 is hydroxy and the others are hydrogen, halo, C,. 6 alkanoyl, C,. 6 alkyl, C,_ 6 alkoxy etc as defined in WO95/06034, Rp4 and Rp5 are hydrogen or join to form a cis-cyclopropyl or cyclobutyl group, Rp6 is O or S and Rp7 is halo, cyano, amino etc as defined in WO95/06034. Particularly prefeπed compounds of this class have the formula P2: Rp10 wherein Rp8 is halo; Rp9 is C,-C 3 alkyl; 46 RplO is halo, especially bromo or cyano The phenolic hydroxy function is bonded to any of the generic structures above, such as those depicted in formula Ila, lib, lie, lid, He, Ilf, Id, etc. These compounds are prepared by acylation of the relevant mother compound of formula P-l or P-2 with the activated structure Ila, lib etc, wherein the or each R 2 group is conventionally N- protected, followed by deprotection. As the compounds of formula P2 include an electron withdrawing group on the phenol ring to which the prodrug moiety is attached it is generally prefeπed to avoid direct esters such as 4-valyloxybutyric acid derivatives which are otherwise effective on phenols and carbocyclic ring hydroxy functions. Using these NNRTIs as an example of a phenolic hydroxy, a convenient group of prodrugs have the formula: wherein Rp8, Rp9, RplO, R 2 , R 4 and R 4 ' are as defined above. Typically both of R 4 and R 4 are H. An alternative prefeπed group of phenolic prodrugs of the invention have the Formula P4: 47 Rp10 where Rp8, Rp9, RplO, R and R 4 , are as defined above. L and R 2 define a linker group and residue of an aliphatic amino acid, such as those of Formulae Ila, lib, lie, lid, He, Ilf or those depicted in Formulae la and Id. Typically both of R 4 and R 4 , are H. Favoured compounds within the class described in the immediately preceding paragraph include those of the formula P5: Rp10 R 2 Rp9 Ry O P5 where Rp8 Rp9, RplO, R 4 , R 4 . and R 2 are as defined above and Alk b is C,-C 6 optionally branched, optionally monounsaturated alkyl. One variant of a branched Alk b in Formula P5 can be substituted with hydroxy which in turn is esterified with a further R 2 , thus defining a linker of the formula Ila, as depicted in Formula P6: 48 P6 where Rp8, Rp9, RplO, Alk, R 4 , R 4 ', m, n and R 2 are as defined above. Preferably each occuπence of Rx and Rx' is H. Particularly favoured values for Alk, m and n include: methylene: 1 :1 and absent: 1 :0 respectively. A further favoured group of compounds has the Formula P7: Rp10 On "0 - R 2 Rp9 R, O () m -O- R 2 P7 where Rp8, Rp9, RplO, Alk, R 4 , R 4 ', m, n and R 2 are as defined above or wherein the -() m -O-R, arm is absent. Preferably each occuπence of Rx and Rx' is H. Particularly favoured values for Alk, m and n include:absent: 1 :1, thus defining a glycerol derivative, wherein or -() m -O-R 2 ar is absent and Alk and n are absent: 1 with R 4 , R 4 and R 4 ' as H. A further favoured group of phenolic hydroxy compounds omit the methyloxy group immediately adjacent the phenolic hydroxy function: 49 Rp10 O H H R. Rp9 ° P8 where Rp8, Rp9, RplO, R 2 , and Alk b are as defined above. Cuπently favoured values for Alk include methylene, ethylene, 1,1-dimethylethylene, propylene, butylene and, in the case of said -OR 2 substitution, glycerol. As with Formula P5/P6 and P7/P7', Alk b in formula P8 can comprise an additional -O-R, substitution to define a compound of the formula P8' Rpδ Q R PlO U N N ^Alk ^°^ R2 \ ()m-0— R2 P8 * where each of the variables is as defined above. It will be appreciated that the NNRTI mother compound in formulae P-3-8' has been shown as an example of a phenolic hydroxy and that the respective prodrug moiety will be applicable to otther ring hydroxy functions of a drug, particularly those subject to electron withdrawing effects. Compounds of this phenolic hydroxy aspect of the invention are typically prepared by alkylation of the coπesponding mother compounds. In particular, the preparation of compounds of formula P-3 or P-4 generally proceeds by alkylation using conventional coupling conditions of the mother compound with the coπesponding intermediate: 50 R4 R4 halo - halo •> - % * or L R iA' R4' where Rx and L are as defined above and R 2 * is R 2 as defined, but N-protected with a conventional N-protecting group. Preferably the halogen activating group is iodo, which is in turn prepared by iodination of the coπesponding chloro analogue. Typical coupling conditions include treatment with a base in an organic solvent such as THF prior to addition of the halogenated intermediate followed by conventional deprotection of the R 2 N-protecting group. Compounds of formula P-8 are generally prepared by esterification of a compound of the formula P-2 with an intermediate of the formula: O k ha .lo / ^ O^Alk b* where Alk b * is a functionalised Alk b as described above, for example chloromethyl chloro formate, in an organic solvent, followed by iodination of the terminal chloro with Nal (or other activation of the functionalising group) and reaction with an N- protected R 2 . It will be apparent that many linker (R 2 ')-R 2 ) groups, particularly trifunctional linkers or those wherein R 4 and R 4 ' differ will define chiral structures and the phamraceutical compounds or intermediates of the invention include all enantiomers thereof, as racemates or as preparations of > 80%, preferably > 95% enantiomerically pure compound. The compounds of the invention can form salts which form an additional aspect of the invention. Appropriate pharmaceutically acceptable salts of the compounds of Formula I include salts of organic acids, especially carboxylic acids, including but not limited to acetate, trifluoroacetate, lactate, gluconate, citrate, tartrate, maleate, malate, pantothenate, isethionate, adipate, alginate, aspartate, benzoate, butyrate, 51 digluconate, cyclopentanate, glucoheptanate, glycerophosphate, oxalate, heptanoate, hexanoate, fumarate, nicotinate, palmoate, pectinate, 3-phenylpropionate, picrate, pivalate, proprionate, tartrate, lactobionate, pivolate, camphorate, undecanoate and succinate, organic sulphonic acids such as methanesulphonate, ethanesulphonate, 2-hydroxyethane sulphonate, camphorsulphonate, 2-napthalenesulphonate, benzenesulphonate, p-chlorobenzenesulphonate and p-toluenesulphonate; and inorganic acids such as hydrochloride, hydrobromide, hydroiodide, sulphate, bisulphate, hemisulphate, thiocyanate, persulphate, phosphoric and sulphonic acids. The compounds of Formula I may in some cases be isolated as the hydrate. The pharmaceutical compounds of the invention are generally prepared by alkylation or acylation of the respective mother compounds. Alkylation or acylation generally proceeds via an activated derivative. The activated derivative used in an acylation may comprise e.g, the acid halide, acid anhydride, activated acid ester or the acid in the presence of coupling reagent, for example dicyclohexylcarbodiimide, where "acid" to a precursor group such as those of the formula PGNHC(R d )COO-Lα- COOH, where R d is defined above, PG is a conventional N-protecting group and L α is the residue of the linker. The activated derivative used in the acylation may comprise e.g, the acid halide, acid anhydride, activated acid ester or the acid in the presence of coupling reagent, for example dicyclohexylcarbodiimide. Representative activated acid derivatives include the acid chloride, anhydrides derived from alkoxycarbonyl halides such as isobutyloxycarbonylchloride and the like, N-hydroxysuccinamide derived esters, N-hydroxyphthalimide derived esters, N-hydroxy-5-norbornene- 2,3-dicarboxamide derived esters, 2,4,5-trichlorophenol derived esters and the like. Further activated acids include those where X in the formula RX represents an OR'moiety where R is linker(R 2 ) k -R 2 or R 2 as defined herein, and R' is, for example COCH 3 , COCH 2 CH 3 or COCF 3 or where X is benzotriazole. Activated L-R y groups wherein L is derived from an hydroxyalkanoic acid are conveniently prepared by esterification of conventionally carboxy protected hydroxyalkanoic acid, such as glycollic acid or lactic acid or more preferably 52 an ω-hydroxyalkanoic acid such as 3-hydroxypropionic acid, 4-hydroxybutyric acid, 5-hydroxypentanoic acid etc with the appropriate N-protected R y derivative, such as N-Cbz-isoleucine, either as the free acid in conjunction with a coupling agent such as DCC, or activated, for instance to the coπesponding acid halide. The carboxy protecting group is removed as is known in the art and the resulting intermediate activated and esterified with the mother compound with the methodology described above. The N-protecting group on R y is then removed by conventional deprotection conditions. Activated L-R y groups wherein L is derived from a cis-alkenoic acid, such as 4- hydroxy-cis-but-2-en are conveniently prepared from the coπesponding haloalkanoic acids, such as 4-bromo-cis-but-2-enoic acid which is carboxy protected, for instance with t-butyl prior to conventional esterification under with the appropriately N-protected R y moiety, sicha N-Cbz-valine. The carboxy protecting group is removed and the free carboxy activated and esterified with the mother compound as described above, followed by deprotection of the N- protecting group. Activated L-R y groups wherein L is derived from a 2-hydroxymethylbenzoic acid can be prepared from 2-methylbenzoic acid which is carboxy protected and brominated by conventional techniques. This activated intermediate is esterified with an appropriately N-protected R y moiety, such as Cbz-valine. This intermediate is carboxy deprotected and esterified with the mother compound as described above, followed by deprotection of the R y N-protecting group. The reactive derivatives of the X-linker(N-PG-R 2 ')-N-PG-R 2 intermediates implied above may be pre-formed or generated in situ by the use of reagents such as dicyclohexylcarbodiimide (DCC) or O-(lH-benzotriazol-l-yl) N,N,N',N'-tetramethyluronium tetrafluoroborate (TBTU). When an acid halide, such as the acid chloride is used, a tertiary amine catalyst, such as triethylamine, N,N'-dimethylaniline, pyridine or dimethylaminopyridine may be added to the reaction mixture to bind the liberated hydrohalic acid. 53 The reactions are preferably carried out in an unreactive solvent such as N,N- dimethylformamide, tetrahydrofuran, dioxane, acetonitrile or a halogenatated hydrocarbon, such as dichloromethane. If desired, any of the above mentioned tertiary amine catalysts may be used as solvent, taking care that a suitable excess is present. The reaction temperature can typically be varied between 0° C and 60° C, but will preferably be kept between 5° and 50° C. After a period of 1 to 60 hours the reaction will usually be essentially complete. The progress of the reaction can be followed using thin layer chromatography (TLC) and appropriate solvent systems. In general, when the reaction is completed as determined by TLC, the product is extracted with an organic solvent and purified by chromatography and/or recrystallisation from an appropriate solvent system. By-products where acylation has taken place on inappropriate places on the Drug can be separated by chromatography, but such misacylation can be minimized by controlled reaction conditions. These controlled conditions can be achieved, for example, by manipulating the reagent concentrations or rate of addition, especially of the acylating agent, by lowering the temperature or by the choice of solvent. The reaction can be followed by TLC to monitor the controlled conditions.. Linkers of Formula Ila may alternatively be amide bonded to free primary or secondary amine functions on the Drug using conventional chemistry in the peptide art. Linkers of Formula Ilia or IVd or the coπesponding derivatives of Formula III' and Il'd will generally be acylated to free carboxyl functions on the Drug in an analogous, but reversed fashion to the above described acylation of Drugs with hydroxy functions. US 4 486 425 which is incoφorated by reference illustrates a convenient process. 54 Linkers of Formula IVa wherein V comprises a structure of the formula lice can be prepared by a by a two stage process. In particular a compound of the formula ClC(=O)OC(R 4 )(R 4 ')Cl can be reacted with a suitable accessible hydroxy function on the Drug (optionally protected on other functions with conventional protecting groups) as is known in the cephalosporin art. The resulting Drug-O- C(=O)OC(R 4 )(R 4 ')chloride is then reacted with an R 2 bearing linker wherein a free function comprises a carboxyl function, such as the potassium salt. Intermediates of the formula lid are conveniently prepared by acylation of a carboxy- protected hydroxy alkanoic acid, typically a 2-hydroxy-l -alkanoic acid, with the appropriate activated and N-protected R 2 derivative, such as N-CBZ valyl or isoleucyl in conjunction with a conventional coupling reagent such as DMAP/DCC or with the amino acid halide. The carboxy protecting group is then removed, for instance by acid hydrolysis and the resulting intermediate is activated as described above or the free acid is unsed in conjunction with a coupling reagent to esterify the the nucleoside under conventional esterification conditions. Compounds within the scope of the invention are also conveniently prepared by the methodology in the immediately preceding paragraph, namely esterification of a carboxy protected α- hydroxy, ω-carboxy acid, such as glycollic acid, lactic acid, hydroxybutyric acid etc with the appropriate N-protected R, derivative, either as the free acid in conjunction with a coupling agent or activated, for instance to the coπesponding acid halide. The carboxy protecting group is removed and the resulting intermediate esterified with the nucleoside with the methodology described above. Compounds comprising a structure of the formula He or Ilf are prepared by carboxy protecting the terminal carboxy groups of the respective dicarboxylic acid, such as L- tartaric acid or L-malic acid, with conventional carboxy protecting groups such as benzyl. The free hydroxy group (s) are then esterified with conventional esterification techniques, such as DMAP & DCC in DMF with the appropriate N-protected R, amino acid, such as N-Boc-L-valyl or N-Boc-L-isoleucyl. The benzyl carboxy protecting groups are removed and the resulting product is esterified to the 5'- 55 hydroxy function of a monohydric nucleoside, using conventional conditions, such as those in the accompanying Examples. Finally, the free carboxy function is esterified with an R, group or, more preferbably a conventional pharmaceutically acceptable ester, such as the ethyl ester. Trifunctional of formula Ila wherein and n and m are 1 and Alk is absent can be prepared from glycerol by regioselective esterification as described in PCT/SE98/01467. In short R 2 and R 2 ' are regioselectively esterified to positions 1 and 3 of the glycerol and position 2 is then converted to the appropriate -T-C(=O)- group, which is then esterified to an accessible function on the Drug, or alternatively to a cooperating function on an intermediate linker, such as succinic acid which is in turn linked to the accessible funciton on the Drug. Glycerol based linkers where T comprises an -NH- group can be prepared by analogous regioselective esterification followed by conversion of the free hydroxyl to amine, reduction to azide and reaction with phosgene to form the coπesponding chlorocarbamate. Linkers where m and n are 1, Alk is alkylene or alkenylene and T is a bond can be prepared analagously to the methodology in PCT/SE98/01467. Other permutations of m, n, Alk and the various functions in the trifunctional linker group L, of formula Ila can be prepared analagously to the above with the coπesponding starter materials, such as 1,2,4-trihydroxybutane (CA registry number 3968-00-6), 3,4-dihydroxybutanoic acid (1518-61-2 & 22329-74-4), (S)-3,4-dihydroxybutanoic acid (51267-44-8), (R)-3,4-dihydroxybutanoic acid (158800-76-1), 1,2,5-pentanetriol (51064-73-4 & 14697-46-2), (S)- 1,2,5-pentanetriol (13942-73-9), (R)-l,2,5- pentanetriol (171335-70-9), 4,5-dihydroxypentanoic acid (66679-29-6 & 129725- 14-0), 1,3,5-pentanetriol (4328-94-3) and 3-(2-hydroxyethyl)-l,5-pentanediol (53378-75-9). The preparation of each of these starting materials is described in the references to the respective registry number. Ohsawa et al in Chem Pharm Bull 41 (11) 1906-1909 (1993) and Terao et al Chem. Pharm. Bull. 39(3) 823-825 (1991) describe the control of the sterochemistry of trifunctional linker groups with lipase P. Pharmaceutical compounds in accordance with the invention may also be prepared in a step wise manner, for instance a compound of the formula ClC(=O)OC(R 4 )(R 4 ')Cl 56 or can be reacted with an hydroxy group of the Drug (optionally protected on the other vulnerable functional groups with conventional protecting groups). The resulting drug-O-C(=O)OC(R 4 )(R 4 ')chloride is then reacted with an N-protected-R 2 or a di or tri trifunctional linker bearing an N-protected R 2 in which the third function comprises a carboxyl function. The amino acid derivative of R 2 and, if present, R, can alternatively be esterified to the linker group with the 2-oxa-4-aza-cycloalkane-l,3-dione methodology described in international patent application no. WO 94/29311, the contents of which are hereby incoφorated by reference. Linking of the carboxy function of R 2 to an amine group on the linker derivative proceeds by conventional peptide chemistry, generally in conjunction with protection of the α-amine with conventional N-protecting groups. Formation of an amide bond between a carboxyl function on the linker and the α-amine group of R 2 also proceeds by conventional peptide chemistry, generally in conjunction with protection of the α- carboxy function. The preparation of further linker groups and their application to Drugs is shown in the following Examples. As the Drugs envisaged in the use of the present invention are proven pharmaceuticals, the starting materials for preparing the prodrugs of the invention are either available in commerce or are extensively described in the medical literature, including the FDA and other registration files for the respective drugs. As used herein "Optional substituents" can include hydroxy, C,-C 6 alkyl, C,-C 6 alkoxy, C,-C 6 alkoxy C r C 6 alkyl, C,-C 6 alkanoyl, haloC,-C 6 alkyl, amino, halo, cyano, azido, oxo, mercapto and nitro, and the like."Ring" as used herein includes atoms including monocyclic rings such as furyl, thienyl, pyranyl, pyπolyl, pyπolinyl, pyπolidinyl, pyrazolyl, pyrazolinyl, pyrazolidinyl, imidazolyl, 57 imidazolinyl, imidazolidinyl, pyridyl, piperidinyl, pyrazinyl, piperazinyl, pyrimidinyl, pyridazinyl, oxazolyl, oxazolidinyl, isoxazolyl, isoxazolidinyl, moφholinyl, thiazolyl, thiazolidinyl, isothiazolyl, isothiazolidinyl, and the like or bicyclic rings especially of the above fused to a phenyl ring such as indolyl, quinolinyl, isoquinolinyl, benzimidazolyl, benzothiazolyl, benzoxazolyl, benzothienyl etc. The carbo or heterocyclic ring may be bonded via a carbon to the remainder of the linker via a hetero atom, typically a nitrogen atom, such as N- piperidyl, N-moφholinyl etc. The symbol () is used in its conventional sense, that is a methylene group. The term "N-protecting group" or "N-protected" as used herein refers to those groups intended to protect the N-terminus of an amino acid or peptide or to protect an amino group against undesirable reactions during synthetic procedures. Commonly used N- protecting groups are disclosed in Greene, "Protective Groups in Organic Synthesis" (John Wiley & Sons, New York, 1981), which is hereby incoφorated by reference. N-protecting groups include acyl groups such as formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoracetyl, trichloroacetyl, phthalyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, and the like; sulfonyl groups such as benzenesulfonyl, p- toluenesulfonyl, and the like, carbamate forming groups such as benzyloxycarbonyl, p-chlorobenzyloxycarbonyl, p-methoxybenzyloxycarbonyl, p-nitrobenzyloxycarbonyl, 2-nitrobenzyloxycarbonyl, p-bromobenzyloxycarbonyl, 3,4-dimethoxybenzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 2-nitro-4,5-dimethoxybenzyloxycarbonyl, 3,4,5-trimethoxybenzyloxycarbonyl, l-(p-biphenylyl)-l-methylethoxycarbonyl, α,α-dimethyl-3,5- dimethoxybenzyloxycarbonyl, benzhydryloxycarbonyl, t-butoxycarbonyl, diisopropylmethoxycarbonyl, isopropyloxycarbonyl, ethoxycarbonyl, methoxycarbonyl, allyloxycarbonyl, 2,2,2-trichloroethoxycarbonyl, phenoxycarbonyl, 4-nitrophenoxycarbonyl, fluorenyl-9-methoxycarbonyl, cyclopentyloxycarbonyl, adamantyloxycarbonyl, cyclohexyloxycarbonyl, phenylthiocarbonyl, and the like; alkyl groups such as benzyl, triphenylmethyl, 58 benzyloxymethyl and the like; and silyl groups such as trimethylsilyl and the like. Favoured N-protecting groups include formyl, acetyl, allyl, F-moc, benzoyl, pivaloyl, t-butylacetyl, phenylsulfonyl, benzyl, t-butoxycarbonyl (BOC) and benzyloxycarbonyl (Cbz). Hydroxy and/or carboxy protecting groups are also extensively reviewed in Greene ibid and include ethers such as methyl, substituted methyl ethers such as methoxymethyl, methylthiomethyl, benzyloxymethyl, t-butoxymethyl, 2- methoxyethoxymethyl and the like, silyl ethers such as trimethylsilyl (TMS), t- butyldimethylsilyl (TBDMS) tribenzylsilyl, triphenylsilyl, t-butyldiphenylsilyl triisopropyl silyl and the like, substituted ethyl ethers such as 1 -ethoxymethyl, 1- methyl-1-methoxyethyl, t-butyl, allyl, benzyl, p-methoxybenzyl, dipehenylmethyl, triphenylmethyl and the like, aralkyl groups such as trityl, and pixyl (9-hydroxy-9- phenylxanthene derivatives, especially the chloride). Ester hydroxy protecting groups include esters such as formate, benzylformate, chloroacetate, methoxyacetate, phenoxyacetate, pivaloate, adamantoate, mesitoate, benzoate and the like. Carbonate hydroxy protecting groups include methyl vinyl, allyl, cinnamyl, benzyl and the like. While it is possible for the active agent to be administered alone, it is preferable to present it as part of a pharmaceutical formulation. Such a formulation will comprise the above defined active agent together with one or more acceptable carriers/excipients and optionally other therapeutic ingredients. The carrier(s) must be acceptable in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient. The formulations include those suitable for rectal, nasal, topical (including buccal and sublingual), vaginal or parenteral (including subcutaneous, intramuscular, intravenous and intradermal) administration, but preferably the formulation is an orally administered formulation. The formulations may conveniently be presented in 59 unit dosage form, e.g. tablets and sustained release capsules, and may be prepared by any methods well known in the art of pharmacy. Such methods include the step of bringing into association the above defined active agent with the carrier. In general, the formulations are prepared by uniformly and intimately bringing into association the active agent with liquid carriers or finely divided solid carriers or both, and then if necessary shaping the product. The invention extends to methods for preparing a pharmaceutical composition comprising bringing a pharmaceutical compound of the invention or its pharmaceutically acceptable salt in conjunction or association with a pharmaceutically acceptable caπier or vehicle. If the manufacture of pharmaceutical formulations involves intimate mixing of pharmaceutical excipients and the active ingredient in salt form, then it is often prefeπed to use excipients which are non-basic in nature, i.e. either acidic or neutral. Formulations for oral administration in the present invention may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active agent; as a powder or granules; as a solution or a suspension of the active agent in an aqueous liquid or a non-aqueous liquid; or as an oil-in-water liquid emulsion or a water in oil liquid emulsion and as a bolus etc. With regard to compositions for oral administration (e.g. tablets and capsules), the term suitable carrier includes vehicles such as common excipients e.g. binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, polyvinylpyπolidone (Povidone), methylcellulose, ethylcellulose, sodium carboxymethylcellulose, hydroxypropylmethylcellulose, sucrose and starch; fillers and carriers, for example corn starch, gelatin, lactose, sucrose, microcrystalline cellulose, kaolin, mannitol, dicalcium phosphate, sodium chloride and alginic acid; and lubricants such as 60 magnesium stearate, sodium stearate and other metallic stearates, glycerol stearate stearic acid, silicone fluid, talc waxes, oils and colloidal silica. Flavouring agents such as peppermint, oil of wintergreen, cherry flavouring or the like can also be used. It may be desirable to add a colouring agent to make the dosage form readily identifiable. Tablets may also be coated by methods well known in the art. A tablet may be made by compression or moulding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active agent in a free flowing form such as a powder or granules, optionally mixed with a binder, lubricant, inert diluent, preservative, surface-active or dispersing agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may be optionally be coated or scored and may be formulated so as to provide slow or controlled release of the active agent. Other formulations suitable for oral administration include lozenges comprising the active agent in a flavoured base, usually sucrose and acacia or tragacanth; pastilles comprising the active agent in an inert base such as gelatin and glycerin, or sucrose and acacia; and mouthwashes comprising the active agent in a suitable liquid carrier. Detailed description Various aspects of the invention will now be described by way of example only with reference to the following Examples 61 Preparation of intermediates. Example AA-I-1 2.3-Bis-(N-CBz-L-valyloxy)-propionic acid. O N-CBz-Valyl— O ' N-CBz-Valyl— O a) t-Butyl 2,3-bis (N-CBz-L-valyloxy)propionate. To a solution of t-butyl 2,3-dihydroxypropionate (2.43g, 15 mmole), N-CBz-L- valine (7.54g, 30 mmole) and DMAP (0.37g, 3 mmole) in 150 ml dichloromethane was added DCC (7.2g 35 mmole) and the mixture was stiπed for two days at room temperature. The mixture was cooled to about 5°C and the urethane was filtered. The filtrate was evaporated, ethyl acetate was added and the organic phase washed twice with 5% acetic acid, 5% sodium hydrogen carbonate and water. The organic phase was dried with sodium sulfate filtered and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 8.2g = 86% b) 2,3-Bis-(N-CBz-L-valyloxy)-propionic acid. To a solution of t-butyl -2,3-bis-(N-CBz-L-valyloxy)-propionate (7.2g, 11.4 mmole) in dichloromethane (25 ml) was added trifluoroacetic acid (25 ml) and the solution was stiπed for five hours at room temperature. The solution was evaporated under reduced pressure and coevaporated two times with toluene. The product was isolated by silica gel column chromatography. Yield : 5.9g = 90% 'H-NMR (DMSO-d6) 0.92 (m, 12H) 2.08 (m, 2H) 3.92-4.17 (m, 2H) 4.30-4.67 (m, 2H) 5.04 (s, 4H) 5.28 (m, IH) 7.32 (m, 10H) 7.70 (m, 2H) Example AA-I-2 ( SV ( +y2- ( N-CBz-L-valyloxy ) propionic acid a) 4-Methoxybenzyl (S) (+)-2-hydroxypropionate. To a stiπed solution of (S)(+)2 hydroxypropionic acid (9.0g, 100 mmole) in 100 ml dry DMF was added potassium tert-butoxide (12.34g, 110 mmole) and the mixture was stiπed for one hour at 25°C. 4-Methoxybenzyl chloride (18.8g 120 mmole) was added and the mixture was stiπed for six hours at 60°C. The mixture was evaporated under reduced pressure and 250 ml ethyl acatate was added. The organic phase was washed four times with water.The organic phase was dried with sodium sulfate and concentrated in vacuo. Yield: 15.6g = 74% b) 4-Methoxybenzyl (S)-(+)-2-(N-CBz-L-valyloxy)propionate. To a solution of 4-methoxybenzyl (S)-(+)-2-hydroxypropionate (7.6g, 36 mmole), N- CBZ-L-valine (10.05g, 40 mmole) and DMAP (0.98g, 8 mmole) in 150 ml dichloromethane was added a solution of DCC (8.3g, 40 mmole) and the mixture was stiπed overnight at room temperature. The mixture was cooled to about 5°C and the urethane was filtered. The filtrate was evaporated and the product was isolated by silica gel column chromatography. Yield: 14.4g = 90% c) (S)-(+)-2-(N-CBz-L-valyloxy)propionic acid. To a solution of 4-methoxybenzyl (S)-(+)-2-(N-CBz-L-valyloxy)propionate (14.0g, 31.5 mmole) in dichloromethane (50 ml) was added trifluoroacetic acid (25 ml) and the solution was stiπed for five hours at room temperature. The solution was evaporated under reduced pressure and coevaporated two times with toluene. The product was isolated by silica gel column chromatography. Yield: 9.4g = 92% 0 • H-NMR (DMSO-d6) 0.94 (m, 6H) 1.46 (d, 3H) 2.12 (m, IH) 4.05 (m, IH) 4.92 (m, IH) 5.06 (s, 2H) 7.34 (m, 5H) 7.68 (d, IH) Example AA-I-3 3.3-Bis (N-CBz-L-valyloxymethvD-propionic acid 63 N-CBz-Valyl— O ~ /\ >H N-CBz-Valyl-O-^ {j a) 4,4-bis (N-CBZ-L-valyloxymethyl)-but-l-ene. To a solution of 2-allyl-l,3-propanediol (2.32g, 20 mmole), N-CBZ-L-valine (10.06g, 40 mmole) and DMAP (0.488g, 4 mmole) in 120ml dichloromethane was added DCC (9.08g, 44 mmole) in portions and the mixture was stiπed overnight at room temperature. The mixture was cooled to 5°C and the urethane was filtered. The filtrate was evaporated and the product was isolated by silica gel column chromatography. Yield : 9.0g b) 3,3-Bis (N-CBZ-L-valyloxymethyl)-propionic acid. To a cooled solution of 4,4-bis (N-CBZ-L-valyloxymethyl)-but-l-ene (14.6g, 25 mmole) and tetrabutylammonium bromide (1.3g, 4 mmole) in 120ml benzene was added 100ml water. Under strong stirring potassium permanganate (15.8g, 100 mmole) was addded in portions and the mixture was stiπed for 2 hours between 15°C and 20°C . A sodium bisulfite aqueous solution was added to the slurry until the mixture was discolored. The mixture was acidified with 2N hydrochloric acid and extracted four times with ethyl acetate. The organic phase was washed two times with water, dried with sodium sulfate and evaporated under reduced pressure . The product was isolated by silica gel column chromatography. Yield: 7.5g 'H-NMR (CDC1 3 ) 0.89 (m, 12H) 2.05 (m, 2H) 2.46 (m, 2H) 2.62 (m, IH) 4.20 (m, 6H) 5.11 (s, 4H) 5.30 (m, 2H) 7.35 (m, 10H) Example AA-I-4 2-(N-CBZ-L-valyloxy)-propionic acid a) 4-methoxybenzyl 2-hydroxypropionate. To a stiπed solution of DL -2 hydroxypropionic acid (9.0g , 100 mmole) in 100 ml dry DMF was added potassium tert-butoxide (12.34g, 110 mmole) and the mixture was stiπed for one hour at 60°C. 4-methoxybenzyl chloride (18.8g 120 mmole) was added and the mixture was stiπed for eight hours at 60°C. The mixture was 64 evaporated under reduced pressure and 250 ml ethyl acatate was added .The organic phase was washed four times with water. The organic phase was dried with sodium sulfate and concentrated in vacuo. Yield: 16.8g b) 4-methoxybenzyl 2-(N-CBZ-L-valyloxy)propionate. To a solution of 4-methoxybenzyl 2-hydroxyproρionate (4.2g, 20 mmole), N-CBZ-L- valine (5.02g, 20 mmole) and DMAP (0.24g, 2 mmole) in 100 ml dichloromethane was added a solution of DCC (4.54g, 22 mmole) and the mixture was stiπed overnight at room temperature. The mixture was cooled to 5°C and the urethane was filtered. The filtrate was evoporated and the product was isolated by silica gel column chromatography. Yield: 7.9g c) 2-(N-CBZ-L-valyloxy)-ρropionic acid. To a solution of 4-methoxybenzyl 2-(N-CBZ-L-valyloxy)-propionate (7.8g, 17.5 mmole) in dichloromethane (100 ml) was added trifluoroacetic acid (10 ml) and the solution was stiπed for one hour at room temperature. The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography. Yield: 5.0g 'H-NMR (CDC1 3 ) 0.94 (m, 6H) 1.56 (d, 3H) 2.30 (m, IH) 4.42 (m, IH) 5.12-5.30 (m, 4H) 7.28 (m, 5H) Example AA-I-5 Succinic acid 2.3-b^-(N-CBZ-L-valyloxy propyl ester N-CBz-Valyl— O- N-CBz-Valyl— O— O * — O OH O a) 4-Methoxybenzyl succinate monoester. To a mixture of succinic anhyride (75g, 750 mmole) and 4-methoxybenzyl alcohol (69. Ig, 500 mmole) in 1,4-dioxane (300ml) was added pyridine (79. Ig, 1000 mmole) and the mixture was stiπed for five hours at 80°C . The mixture was evaporated 65 under reduced pressure and 600 ml of ethyl acetate and 60 ml of acetic acid were added. The organic phase was washed three times with water, dried with sodium sulfate and evaporated under reduced pressure. The product was recrystallized from toluene. Yield: 104 g. b) Succinic acid 2,3-dihydroxy-propyl ester, 4-methoxybenzyl ester . To a solution of glycerol (23. Og, 250 mmole), 4-methoxybenzyl succinate monoester (5.96 g, 25 mmole) and DMAP (0.36g, 3 mmole) in DMF (200ml) was added DCC (6.2g 30 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and 150ml dichloromethane was added. The mixture was filtered and the solution washed twice with water. The water phase was extracted two times with dichloromethane and the combined organic phases were dried with sodium sulfate. The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography. Yield: 3.0g c) Succinic acid 2,3-bw-(N-CBZ-L-valyloxy)-propyl ester, 4- methoxybenzyl ester. To a stiπed solution of succinic acid 2,3-dihydroxy-propyl ester, 4-methoxybenzyl ester (2.9g, 9.28 mmole), N-CBZ-L-valine (5.03g, 20 mmole) and DMAP (0.244g, 2 mmole) in dichloromethane (60ml) was added DCC (4.5g, 22 mmole) and the mixture was stiπed overnight at room temperature. The mixture was filtered and the solution was evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 2.5g d) Succinic acid 2,3-bw-(N-CBZ-L-valyloxy)propyl ester. To a solution of the above intermediate (2.3g, 2.95 mmole) in dichloromethane (25ml) was added trifluoroacetic acid (2.5ml) and the solution was stiπed for two hours at roomtemperature. The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography. Yield: l,8g Η-NMR (CDC1 3 ) 0.92 (m, 12H) 2.12 (m, 2H) 2.64 (m, 4H) 4.32 (m, 4H) 5.10 (s, 4H) 5.22-5.50 (m, 3H) 7.34 (m, 10H) 66 Example AA-I-6 Succinic acid l,3-b/s-(N-CBZ-L-valyloxyV2-propyl ester N-CBz-Valyl— O— I O OH N-CBz-Valyl— O— O a) Succinic acid l,3-dibromo-2-propyl ester, 4-methoxybenzyl ester. To a solution of l,3-dibromopropan-2-ol (21.8g, 100 mmole), succinic acid 4- methoxybenzyl ester (28.6g,120 mmole) and DMAP (1.22g, 10 mmole) in dichloromethane (400ml) was added DCC (24.8g, 120 mmole) in portions at about 10°C. The mixture was stiπed overnight at room temperature and cooled to about 5°C. The mixture was filtered and the solution was evaporated under reduced pressure. 600ml of ethyl acetate was added and the organic phase was washed twice with 5% acetic acid, 5% sodium hydrogen carbonate and water. The solution was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 34.8g. b) Succinic acid l,3-bw-(N-CBZ-L-valyloxy)-2-propyl ester, 4- methoxybenzyl ester. To a solution of N-CBZ-L-valine ( 58.5 g, 232.8 mmole) in dried DMF (300ml) was added potassium-tert.-butoxide (24,68 g, 220 mmole) and the mixture was stiπed for one hour at room temperature. A solution of succinic acid l,3-dibromo-2-propyl ester, 4-methoxybenzyl ester (34 g, 77.6 mmole) in dried DMF (50ml) was added and the mixture was stiπed for eighteen hours at 60°C. The potassium bromide was filtered and the solution was evaporated under reduced pressure. 600ml of ethyl acetate was added and the organic phase washed twice with 5% sodium hydrogen carbonate and with water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 45g c) Succinic acid l,3-bzs-(N-CBZ-L-valyloxy)-2-propyl ester. 67 To a cooled solution of the intermediate immediately above (44.5 g, 57.1 mmole) in dichloromethane (500ml) was added trifluoroacetic acid (50ml) between 5°C and 10°C and the solution was stiπed for two hours at 10°C. The solution was evaporated under reduced pressure and two times coevaporated with toluene. 400ml of ethanol was added and the mixture was stiπed for 30 minutes at 40°C. The mixture was cooled and the biproduct filtered. The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography. Yield: 33g 'H-NMR (DMSO-d6) 0.88 (m, 12H) 2.04 (m, 2H) 2.46 (m, 4H) 3.94-4.40 (m, 6H) 5.02 (s, 4H) 5.18 (m, IH) 7.32 (m, 10H) 7,74 (d , 2H) Example AA-I-7 Alternative route to succinic acid 3-bz ' s-(N-CBZ-L-valyloxyV2-propyl ester a) Succinic acid l,3-dibromo-2-propyl ester, 1,1-dimethylethyl ester. To a solution of l,3-dibromopropan-2-ol (10.9 g 50 mmole), succinic acid 1,1- dimethylethyl ester (J. Org.Chem 59 (1994) 4864) (10.45g, 60 mmole) and DMAP (0.61 g, 5 mmole) in dichloromethane (180ml) was added DCC (12.4 g, 60 mmole) in portions at about 10°C. The mixture was stiπed overnight at room temperature and cooled to about 5°C. The mixture was filtered and the solution was evaporated under reduced pressure. 250ml ethyl acetate was added and the organic phase was washed twice with 5% citric acid, 5% sodium hydrogen carbonate and water. The solution was dried with sodium sulfate and evaporated under reduced pressure. The product was distilled in vacuo. (bp 0,5 135-140°C ) Yield: 16.8 g b) Succinic acid l,3-b/s-(N-CBZ-L-valyloxy)-2-propyl ester, 1,1- dimethylethyl ester. To a solution of N-CBZ-L-valine (18.85 g, 75 mmole) in dried DMF (100ml) was added potassium tert.-butoxide (7.85 g, 70 mmole) and the mixture was stiπed for one hour at room temperature. A solution of succinic acid l,3-dibromo-2-propyl ester, 1,1-dimethylethyl ester (9.35g, 25 mmole) in dried DMF (20ml) was added and the mixture was stiπed for eighteen hours at 60°C. The potassium bromide was filtered and the solution evaporated under reduced pressure. 300ml of ethyl acetate 68 were added and the organic phase washed twice with 5% sodium hydrogen carbonate and with water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 14g c) l,3-bis-( N-CBZ-L-valyloxy )-2-propyl succinate monoester . To a cooled solution of succinic acid l,3-bis-(N-CBZ-L-valyloxy)-2-propyl ester, 1,1-dimethylethyl ester (13 g, 18.18 mmole) in dichloromethane (100ml) was added trifluoroacetic acid (20ml) and the solution was stiπed for six hours at room temperature. The solution was evaporated under reduced pressure. 200ml ethyl acetate was added and the organic phase was washed with 5% sodium hydrogen carbonate and water. The solution was evaporated under reduced pressure. Yield: 11.7g Example AA- 1-8 3-benzyloxycarbonylpropionic acid chloromethyl ester a) Succinic acid monobenzyl ester Succinic anhydride (30 g, 300 mmole) was dissolved in methylene chloride (300 ml). To the solution were added benzyl alcohol (10.2 ml, 100 mmole), 4- dimethylaminopyridine (1.22 g, 10 mmole) and pyridine (48 ml). After 3 hours the reaction mixture was poured in to citric acid aqueous solution. The organic phase was concentrated to small volume and sodium hydrogen carbonate and water were added. Then mixture was stiπed for 30 min. The aqueous phase was collected, and to it was added citric acid aqueous solution. The product precipitated out, was collected and dried. 15.3 g. b) 3-benzyloxycarbonylpropionic acid chloromethyl ester Succinic acid monobenzyl ester (4.16 g, 20 mmole) was dissolved in dioxane (20 ml). To the solution was added tetrabutylammonium hydroxide aqueous solution (40 %, 11.6 ml, 18 mmole). The solution was dried in vacuo and coevaporated with toluene several times. The residue was dissolved in methylene chloride (60 ml) and then chloroiodomethane (14.5 ml, 200 mmole) was added to the solution. The 69 reaction solution was stiπed for 18 hr and then evaporated and the product was isolated with silica gel column chromatography. 3.64 g c) 3-Benzyloxycarbonylpropionic acid iodomethyl ester. 3-Benzyloxycarbonylpropionic acid chloromethyl ester (2 g, 1.38 mmole) was dissolved in acetonitrile (30 ml). Sodium iodide (1.6 g, 10.9 mmole) was added to the solution. After reaction at 70° C for 3 hr, the reaction mixture was filtered and the residue was dissolved in methylene chloride (20 ml) and refiltered. The solution was dried and gave intermediate 3-benzyloxycarbonylpropionic acid iodomethyl ester in quantitative yield. This intermediate is bonded to an accessible function of a drug, such as a ring hydroxy or carboxy function using conventional alkylation/acylation conditions as described generally herein. Following deprotection of the terminal carboxy, a di/trifunctional linker bearing R 2 , such as 1,3-bis- O-(L-valyl)glycerol or iodomethyloxy-L-valyl is acylated/alkylated thereon or R 2 amide bonded thereon by conventional techniques as described herein, such as with DCC coupling agent. Example AA-I-9 1 ,3-bis(N-tert-butoxycarbonyl-L-valyloxyV2-propyl 1 -iodoethyl carbonate (a) l,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propyl 1 -chloroethyl carbonate. To a solution of 1 ,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propanol (0.545 g, 1.11 mmol) in 5 mL dry CH 2 C1 2 were added pyridine (540 μL, 6.68 mmol), with cooling and stirring in an ice bath, followed by 1 -chloroethyl chloro formate (242 μL, 2.22 mmol). After 1 h, the reaction mixture was diluted with 5 mL CH,C1 2 and washed with water (5 mL) and brine (5 mL). The organic phase was dried over anhydrous Νa;,SO 4 and concentrated on a rotavapor, coevapoating several times with 70 toluene. Column chromatogaphy (silica, 4/1 petroleum ether - ethyl acetate) gave the chloride (596 mg, 90%) as a white solid. (b) 1 ,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propyl 1 -iodoethyl carbonate. A mixture of the chloride (596 mg, 1.0 mmol) from step (a) and Νal (684 mg, 4.57 mmol) in 10 ml dry MeCΝ was refluxed at 80 °C for 4 h. The reaction mixture was concentrated under vacuum and then partitioned between 30 mL diethyl ether and 10 mL water. The organic phase was washed with 5% aqueous sodium thiosulfate (2 x 5 mL), and the last aqueous layer was reextracted with ether (5 mL). The organic phases were combined, washed with brine, dried over Νa^SO^ and concentrated. Flash column chromatography (silica, 4/1 petroleum ether - ethyl acetate) gave a fraction (275 mg) containing 80% iodide, as determined from 'H ΝMR, and small amounts of the starting chloride and alkene from the elimination side reaction. Η ΝMR (250 MHz, CDC1 3 ) δ 0.81-0.85 (m, 6H), 0.88-0.92 (m, 6H), 1.37 (s, 18H), 2.05 (m, 2H), 2.17 (d, 3H, J= 6.1 Hz), 4.12-4.46 (m, 6H), 5.00 (d, 2H, J= 8.8 Hz), 5.11 (m, IH), 6.68 and 6.69 (2 sets of q, IH, J= 6.1 Hz). Example A-I- 10 3-(N-benzyloxycarbonyl-L-valyloxy -2,2-dimethylpropyl iodomethyl carbonate O O Ό A 0. O x^ HΝ Y O (a) 3-(N-benzyloxycarbonyl-L-valyloxy)-2,2-dimethyl-l -propanol. A mixture of N-benzyloxycarbonyl-L-valine (2.50 g, 10.0 mmol), 2,2-dimethyl-l,3- propanediol (5.30 g, 50.9 mmol), dicyclohexylcarbodiimide (2.60 g, 12.6 mmol), and 4-dimethylaminopyridine (125 mg, 1.0 mmol) in 100 mL dry CH 2 C1, was stiπed for 23 h. The reaction mixture was filtered and washed successively with 50 mL each of water, saturated aqueous ΝH 4 C1, saturated aqueous NaHCO 3 , and water. The organic phase was dried over anhydrous Na 2 SO 4 and concentrated. The title compound (2.99 71 g, 87%) was isolated by flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate) as a white waxy solid. (b) 3-(N-benzyloxycarbonyl-L-valyloxy)-2,2-dimethylpropyl chloromethyl carbonate Chloromethyl chloroformate (1.50 mL, 16.6 mmol) was added to a solution of the alcohol (2.74 g, 8.12 mmol) from step (a) and pyridine (4.9 mL, 61 mmol) in 40 mL dry CH 2 C1 2 , in an ice bath. After stirring for 1 h, the mixture was diluted with CH 2 C1 2 and washed successively with water, saturated ΝaHCO 3 , and brine. The organic phase was dried over anhydrous Na 2 SO 4 and concentrated, coevaporating several times with toluene on a rotavapor. Flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate) gave 3.31 g (95%>) of the title compound. (c) 3-(N-benzyloxycarbonyl-L-valyloxy)-2,2-dimethylpropyl iodomethyl carbonate A mixture of the chloride (3.14 g, 7.30 mmol) from step (b) and Νal (4.37 g, 29.2 mmol) in 73 mL dry MeCΝ was refluxed at 80 °C for 3 h. After removal of solvent under vacuum, the mixture was partitioned between 80 mL ethyl acetate and 40 mL water. The organic phase was washed with 5% Νa^O^ and then brine, dried over anhydrous Νa,SO 4 , and concentrated. Flash column chromatography (silica, petroleum ether - ethyl acetate) gave 3.68 g (97%) of the title compound. Η ΝMR (250 MHz, CDC1 3 ) δ 0.88 and 0.96 (2d, 3H each), 0.98 (s, 6H), 2.18 (m, IH), 3.94 and 4.02 (2s, 2H each), 4.32 (dd, IH, J= 9.0, 4.7 Hz), 5.11 (s, 2H), 5.26 (d, IH), 5.92 and 5.93 (ABq, 2H, J AB = 5.1Hz), 7.35 (s, 5H). Example AA-I- 11 4-( Ν-Boc-L-valyloxy)butyric acid OH * 0 ' O- HN O O- 72 a) Preparation of 4-bromobutyric acid benzyl ester 4-bromobutyric acid (10.6g, 60 mmole) was dissolved in thionyl chloride (20 mml), and the reaction was kept for 4 hr. The solution was evaporated and coevaporated with toluene several times. The residue was redissolved in dichloromethane (120 ml), and then benzyl alcohol (4.14 ml, 40 mmole) was added. The solution was cooled down to -50° C and triethylamine (10 ml, 72 mmole) was added. The reaction mixture was slowly warmed to room temperature. After 3 hr, the reaction mixture was poured into sodium bicarbonate aqueous solution and the organic phase was washed with water and dried, giving the titled product, 6.8 g. b) Preparation of 4-(N-Boc-L-valyloxy)butyric acid benzyl ester N-Boc-L-valine (1.3 g, 6 mmole) was dissolved in dioxane (5 ml). To the solution was added tetrabutylammonium hydroxide aqueous solution (40 %, 3.8 ml, 6 mmole), and the solution was evaporated and coevaporated with toluene several times. The residue was dissolved in DMF (15 ml) and 4-bromobutyric acid benzyl ester (1.28g, 5mmole) was added to it. The reaction was kept for 18 hr, and then poured into sodium bicarbonate aqueous solution and extracted with dichloromethane. The organic phase was dried and the product was isolated with silica gel column chromatography, 1.2 g. c) 4-( N-Boc-L-valyloxy)butyric acid. To a solution of 4-(N-Boc-L-valyloxy)butyric acid benzyl ester (1.2 g , 3 mmole) in ethyl acetate/methanol (5ml/5ml) was added palladium black (20 mg). The reaction mixture was kept under hydrogen at atmospheric pressure for 2 hr. The suspension was filtered through Celite and dried, giving the title product, 840 mg. 'H-NMR (CDC1 3 ): 5.05 (d, IH) 4.20 (m, 3H) 2.48 (t, 2H) 2.00 (m, 2H) 1.46 (s, 9H) 0.96 (m, 6H). Example AA-I- 12 N-BOC-L-isoleucine iodomethyl ester 73 O ,0 " ° H o a) N-BOC-L-isoleucine chloromethyl ester. To a solution of N-BOC-L-isoleucine (23.1 g, 0.1 mol) in dioxane (500 mL), was added dropwise a 40% aqueous solution of tetrabutylammonium hydroxide (65.6 mL, 0.1 mol). After stirring for 15 min, the solution was evaporated to dryness through co-evaporation with dioxane and toluene. The residue was dissolved in dichloromethane (500 mL) and then chloroiodomethane (72.8 mL, 1 mol) was added and the solution was stiπed for 6h at room temperature. The solution was concentrated under reduced pressure and the residue was shaken with hexane / ethyl acetate (1 :1 v/v, 400 mL). The yellow crystalline solid was filtered off and the filtrate was washed with aqueous solution of sodium thiosulfate (0.1 M) and then filtered through anhydrous sodium sulfate and evaporated to dryness. The residue was column chromatographed (silica gel, 1-2% MeOH in CH 2 C1 2 ), to give 20.8 g of N- BOC-L-isoleucine chloromethyl ester. b) N-BOC-L-isoleucine iodomethyl ester. To a solution of N-BOC-L-isoleucine chloromethyl ester (19.6 g, 70 mmol) in acetonitrile (300 mL), was added sodium iodide (31.5 g, 210 mmol). The solution was stiπed for 4 h at 60 °C. The resulting suspension was filtered and the filtrate was evaporated. The residue was dissolved in CH 2 C1 2 and washed with aqueous sodium thiosulfate (0.1 M). The organic phase was dried (Na^SO and concentrated under reduced pressure. The crude product was column chromatographed (silica gel, 2% MeOH in CH 2 C1 2 ), to give 22.6 g of N-BOC-L-isoleucine iodomethyl ester. 'H-NMR (CDCl j ): 6.04 (d, IH), 5.82 (d, IH), 4.97 (d, IH), 4.25 (dd, IH), 1.98-1.80 (m, IH), 1.43 (s, 9H), 1.50-1.05 (m, 2H), 0.97-0.88 (m, 6H). Example AA-I- 13 2.2-dimethyl-3-(N-Boc-L-valyloxy propionic acid iodomethyl ester 74 a) 2,2-dimethyl-3-( N-Boc-L-valyloxy)propionic acid: N-Boc-L-valine (10.8g, 50 mmole), 4-dimethylaminopyridine (610 mg, 5 mmole) and DCC (6.18 g, 30 mmole) were dissolved in methylene chloride (100 ml). After stirring for 2 hour the mixture was filtered. To the filtrate were added 2,2-dimethyl-3- hydroxy-propionic acid (3.54g, 30 mmole) and pyridine (10 ml). After 18 hr, the reaction mixture was filtered, and the filtrate was poured into sodium hydrogen carbonate aqueous solution, the organic phase was then washed with citric acid aqueous solution and water succesively. After evaporation the product was isolated with silica gel column chromatography to yield 4.4g. This compound can be activated and esterified directly to a drug or further modified as described below. b) 2,2-dimethyl-3-(N-Boc-L-valyloxy)propionic acid chloromethyl ester . 2,2-dimethyl-3-(N-Boc-L-valyloxy)propionic acid (3.9 g, 12.3 mmole) was dissolved in dioxane (60 ml). To the solution was added tetrabutylammonium hydroxide aqueous solution (40 %, 7.78 ml, 12 mmole). The solution was dried in vacuo, and it was coevaporated with toluene for several times. The residue was dissolved in methylene chloride and then chloroiodomethane (18.9 ml, 260 mmole) was added to the solution. After 18 hr, the reaction solution was evaporated and the product was isolated with silica gel column chromatography to yield 3.7 g. c) 2,2-dimethyl-3-(N-Boc-L-valyloxy)propionic acid iodomethyl ester . 2,2-Dimethyl-3-( N-Boc-L-valyloxy)propionic acid chloromethyl ester ( 3.6 g, 10 mmole ) was dissolved in acetonitrile (50 ml). Sodium iodide (2.1 g, 14 mmole) was added to the solution. After reaction at 70° C for 2 hr, the reaction mixture was filtered and the residue was dissolved in methylene chloride (20 ml) and refiltered. The solution was dried and gave 4.34g of the titled product.. 'H-NMR (CDC1 3 ): 5.92 (dd, 2H) 5.10 (d, IH) 4.24 (m, IH) 4.15 (dd, 2H) 2.01 (m, IH) 1.44 (s, 9H) 1.25 (d, 6H) 0.91 (m, 6H ) 75 Example AA-I- 14 3.3- bis (N-CBz-L-valyloxymethyl)-propionic acid iodomethyl ester a) Preparation of 3,3-bis (N-CBz-L-valyloxymethyl)-propionic acid chloromethyl ester. 3,3- bis (N-CBz-L-valyloxymethyl)-propionic acid (3 g, 5 mmole) was dissolved in dioxane (20 ml). To the solution was added tetrabutylammonium hydroxide aqueous solution (40 %, 3.11 ml, 4.8 mmole). The solution was dried in vacuo, and it was coevaporated with toluene several times. The residue was dissolved in methylene chloride (15 ml) and then chloroiodomethane (7.3 ml, 100 mmole) was added to the solution. The reaction solution was refluxed for 18 hr and then evaporated and the product was isolated with silica gel column chromatography. 900 mg. b) 3,3-bis-(N-CBz-L-valyloxymethyl)propionic acid iodomethyl ester. 3,3-bis (N-CBz-L-valyloxymethyl)-propionic acid chloromethyl ester (900 mg, 1.38 mmole) was dissolved in acetonitrile (5 ml). Sodium iodide (289 mg, 1.93 mmole) was added to the solution. After reaction at 70° C for 3 hr, the reaction mixture was filtered and the residue was dissolved in methylene chloride (5 ml) and refiltered. The solution was dried and gave the titled product. 800 mg. 'H-NMR (CDC1 3 ): 7.35 (m, 10 H) 5.88 (dd, 2H) 5.25 (d, 2H) 4.29 (m, 2H) 4.18 (m, 4H) 2.56 (m, IH) 2.42 (d, 2H) 2.16 (m, 2H) 0.93 (m 12 H) Example AA-I- 15 2-fN-CBz-L-valyloxy)ethoxycarbonyloxymethyl iodide 2-(N-CBz-L-valyloxy)ethoxycarbonyloxymethyl chloride (1.16 g, 3 mmole) was dissolved in acetonitrile (10 ml). Sodium iodide (630 g, 4.2 mmole) was added to the solution. After reaction at 65° C for 2.5 hr, the reaction mixture was cooled down to room temperature and filtered and the residue was dissolved in methylene chloride (5 ml) and refiltered. The solution was dried and gave the titled product. 1.2 g. 'H-NMR (CDC1 3 ): 7.35 (m, 5H) 5.93 (dd, 2H) 5.26 (d, IH) 5.11 (s, 2H) 4.39 (m, 5H) 2.18 (m, lH) 0.94 (m, 6 H). Example AA-I- 16 1.3-bisrN-tert-butoxycarbonyl-L-valyloxy -2-propyl iodomethyl carbonate O N-Boc-Valyl — O "I N-Boc-Valyl — a) 1 -O-(N-tert-butoxycarbonyl-L-valyl)glycerol N-tert-Butoxycarbonyl-L-valine (32.53 g, 0.150 mol), NN'-dicyclohexyl- carbodiimide (37.85 g, 0.183 mol, and 4-dimethylaminopyridine (1.83 g, 0.015 mol) were added to glycerol (138.12 g., 1.5 mol) in 500 mL dry DMF and the mixture was stiπed at rt under Ν 2 for 3 days. The reaction mixture was filtered, concentrated under vacuum, and then partitioned between 300 mL EtOAc and 150 mL H 2 O. The aqueous phase was reextracted with 150 mL EtOAc. The organic phases were combined and washed successively with 100 mL each of saturated aqueous NaHCO 3 , saturated NH 4 C1, and brine. Drying over anhydrous Na 2 SO4, and concentration under vacuum gave a viscous light yellow oil as crude product. Flash column chromatography on silica gel with 4/1 EtOAc - petroleum ether (BP 40-60 °C) gave 18.27 g (42%) of product (alternative nomenclature: 3-(N-tert- butoxycarbonyl-L-valyloxy)-l,2-propanediol). Reactions done overnight gave similar yields. 77 b) 1 ,3-di-O-(N-tert-butoxycarbonyl-L-valyl)glycerol l-O-(N-tert-butoxycarbonyl-L-valyl)glycerol (17.95 g. 61.6 mmol), Boc-L-valine (6.69 g, 30.8 mmol), DMAP (0.38 g, 3.1 mmol), and DCC (7.10 g, 34.4 mmol) in 240 mL CH 2 C1 2 and 60 mL DMF were stiπed at rt under Ν 2 for 18 h. The reaction mixture was filtered, concentrated under vacuum, and redissolved in 200 mL EtOAc. The organic solution was washed with 50 mL saturated NH 4 C1. The aqueous phase was reextracted with 50 mL EtOAc. The organic phases were combined, washed successively with 50 mL saturated NaHCO 3 and 50 mL brine, dried over Na ^ SO^ and concentrated under vacuum. Flash column chromatography of the crude material on silica gel (eluent 2/1 petroleum ether - EtOAc, and then EtOAc) gave 7.41 g (49%) of the title compound (alternative nomenclature: l,3-bis(N-tert-butoxycarbonyl-L- valyloxy)-2-propanol). c) 2-O-chloromethoxycarbonyl-l,3-di-O-(N-tert-butoxycarbonyl-L-valyl)glycerol. Chloromethyl chloroformate (2.70 mL, 30 mmol) was added to a solution of 1,3-di- O-(N-tert-butoxycarbonyl-L-valyl)glycerol (7.27 g, 14.8 mmol) and pyridine (7.2 mL, 89 mmol) in 60 mL dry CH 2 C1 2 , in an ice bath, under Ν 2 . After stirring for 1 h 45 min, the reaction mixture was diluted with 100 mL CH 2 C1 2 and washed with 40 mL water. The aqueous phase was reextracted with 20 mL H 2 O. The organic phases were combined, washed with 40 mL saturated NaHCO 3 , followed by 2 x 50 mL brine, dried over Na ^ SO,,, and concentrated under vacuum. Flash column chromatography on silica gel with 2/1 hexane- EtOAc gave 8.03 g (93%) of the title compound (alternative nomenclature: l,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2- propyl chloromethyl carbonate). d) 2-O-iodomethoxycarbonyl-l,3-di-O-(N-tert-butoxycarbonyl-L- valyl)glycerol. A solution of 2-O-chloromethoxycarbonyl- 1 ,3-di-O-(N-tert-butoxycarbonyl-L- valyl)propane-l,2,3-triol (7.86 g, 13.5 mmol) and Νal (8.09 g, 54.0 mmol) in 135 mL dry acetonitirile was refluxed at 80 °C for 4 h under Ν 2 . The reaction mixture was concentrated under vacuum, and then partitioned between 150 mL diethyl ether and 50 mL H 2 O. The aqueous layer was reextracted with 2 x 25 mL ether. The combined organic phases were washed successively with 25 mL aqueous Na 2 S 2 O 3 and 50 mL 78 brine, dried over Na 2 SO 4 , and concentrated. Flash column chromatography (silica gel, 2/1 hexane-ethyl acetate gave 8.38 g (92%) title product (alternative name: 2- iodomethoxycarbonyloxy-l,3-bis-(N-tert-butoxycarbonyl-L-valyloxy)propane or 1,3- bis(Ν-tert-butoxycarbonyl-L-valyloxy)-2-propyl iodomethyl carbonate) as a white solid.'H NMR (250 MHz, CDC1 3 ) δ 0.81 (d, 6H), 0.88 (m, 6H), 1.36 (s, 18H), 2.06 (m, 2H), 4.11-4.46 (m, 6H), 5.0 (br d, 2H), 5.12 (m, IH), 5.88 (s, 2H). Example A-I-l Iodomethyl 2-methyl-2- N-benzyloxycarbonyl-L-valyloxymethyl) propionate a) 4-Methoxybenzyl 2-(hydroxymethyl)-2-methyl propionate. 2-(Hydroxymethyl)-2-methyl propionic acid was esterified by alkylation with 4- methoxybenzyl chloride by conventional means, namely treatment with aqueous NaOH, followed by evaporation and dissolution in an organic solvent such as DMF to which the 4-methoxybenzyl chloride is added and the reaction warmed and agitated, such as stirring at 60 C for one hour. The reaction mixture is cooled, concentrated by rotavapor and the resulting concentrated suspension partitioned between water and dichloromethane. The organic phase is evaporated and the reside subjected to silica gel column chromatography, for example with 0, 2, 4% EtOH in dichloromethane to yield the title compound (7.10 g). R f (2%MeOH/CHCl 3 ) 0.40. b) 4-Methoxybenzyl 2-(N- benzyloxycarbonyl-L-valyloxymethyl)-2- methyl propionate. 4-Methoxybenzyl 2-(hydroxymethyl)-2-methyl propionate (2.50 g, 10.5 mmol), N- benzyloxy carbonyl-L-valine (2.51 g, 10 mmole), 4-dimethylaminopyridine (183 mg) and 1 -hydroxybenzotriazole (1.35g, 10 mmole) were mixed and dissolved in N,N- dimethylformamide (90 ml). Then dicyclohexyl-carbodiimide (2.47 g 12 mmol) was added. After stirring for 3 days at room temperature the suspension was filtered and the filtrate evaporated in vacuo. The residue was partitioned between 0.1M citric acid and dichloromethane. The organic phase was then extracted with aqueous saturated NaHCO 3 and evaporated in vacuo. The residue was silica gel column chromatographed (0, 1, 2, 3% ethanol in dichloromethane). The appropriate fractions were pooled and evaporated in vacuo to give the title compound (2.72 g). 79 d) 2-(N- benzyloxycarbonyl-L-valyloxymethyl)-2-methyl propionic acid. To a solution of 4-methoxybenzyl 2-(N- benzyloxycarbonyl -L-valyloxymethyl)-2- methyl propionate (2.72 g, 5.76 mmole), was added trifluoroacetic acid (11.5 ml) and the emerging dark red solution was stiπed for 30 min at room temperature. The solution was evaporated to dryness with dioxane and toluene. The residue was silica gel column chromatographed (2, 3, 4% ethanol in dichloromethane). The appropriate fractions were pooled and evaporated in vacuo to give the title compound (1.86 g). The compound can be activated and esterified direct to a drug or further modified as described below. R f (2%MeOH/CHCl 3 ) 0.30. 'H-NMR (CDC1 3 ): 7.32 (s, 5H), 5.32 (d, IH), 5.10 (s, 2H), 4.32 (d,d, IH), 4.21 (d,d, 2H), 2.13 (m, IH), 1.26 (s, 3H), 1.25 (s, 3H), 0.95 (d, 3H), 0.86 (d, 3H). c) Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2-methyl propionate. 2-(N- benzyloxycarbonyl -L-valyloxymethyl)-2-methyl propionic acid was esterified by conventional techniques, namely dissolution in an organic solvent such as dioxane and dropwise addition of aqueous tetrabutylammonium hydroxide, followed by evaporation. The residue is dissolved in dichloromethane and then chloroiodomethane and the mixture stiπred for 6 hours at room temperature, followed by partition, shaking the filtrate with aqueous sodium thiosulphate. 0.1M, filtration and evaporation. The title compound (1.40 g) was obtained after silica gel column chromatography (0, 1, 2, 3% ethanol in dichloromethane). c) Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2-methyl propionate. Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2 -methyl propionate was converted to iodide by conventional techniques, namely addition to Nal in acetonitrile, stirring and heating, for instance to 75 C for four hours. The resulting suspension is filtered and the filtrate evaporated, dissolved in organic solvent such as toluene and shaken with aqueous sodium thiosulphate (0.1M) and evaporation to give the title compound (1.25 g) practically pure. R f (2%MeOH CHCl 3 ) 0.80. 80 'H-NMR (CDCI 3 ): 7.35 (s. 5H), 5.90 (d,d, 2H), 5.24 (d, IH), 5.10 (s, 2H), 4.31 (d,d, IH), 4.14 (d,d, 2H), 2.16 (m, IH), 1.22 (s, 6H), 0.96 (d, 3H), 0.87 (d, 3H). Example A-I-2 Iodomethyl 2-fN-benzyloxycarbonyl-L-valyloxyVDL-propionate. O O O. CBzNH ° a) Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-DL-propionate. 2-(N-benzyloxycarbonyl-L-valyloxy) propionic acid (1 g) was esterified by the method described in Example A-I-I, step d. The title compound (0.76 g) was obtained after silica gel column chromatography (0, 1% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.75. b) Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-DL-propionate Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2-methyl propionate was converted to iodide by the method described in Example A-I-1, step e to give the title compound (0.95 g) practically pure. R f (2%MeOH/CHCl 3 ) 0.75. 'H-NMR (CDC1 3 ): 7.33 (s, 5H), 5.98 (d, IH), 5.86 (d, IH), 5.26 (d, IH), 5.10 (s, 2H), 5.07 (q, IH), 4.38 (d,d, IH), 2.30 (m, IH), 1.49 (d, 3H), 1.03 (d, 3H), 0.95 (d, 3H). Example A-I-3 Iodomethyl (1.3-di-( -benzyloxycarbonyr)-L-valyloxy)-2-propyl carbonate. O N-CBz-Valyl— O \ Λ /\. O O I N-CBz-Valyl— O a) Chloromethyl (1 ,3-di-(N-benzyloxycarbonyl)-L-valyloxy)-2-propyl carbonate. To a solution of l,3-di-((N-benzyloxycarbonyl)-L-valyloxy)propan-2-ol (1.34 g, 2.4 mmole) in dichloromethane (10 ml) was added dry pyridine (1.15 ml, 14.4 mmol) 81 and chloromethyl chloroformate (0.43 ml, 4.8 mmole) at 0°C. The reaction was then stiπed for 30 min and then poured into aqueous 50% saturated sodium chloride / 0.1M citric acid solution and extracted with dichloromethane. The organic phase was evaporated and the residue silica gel column chromatographed (0, 1, 1.5% ethanol in dichloromethane). The appropriate fractions were pooled and evaporated in vacuo to give the title compound (1.26g). R f (2%MeOH/ CHC1 3 ) 0.85. b) Preparation of iodomethyl (l,3-di-(N-benzyloxycarbonyl)-L-valyloxy)- 2-propyl carbonate. Chloromethyl (l,3-di-(N-benzyloxycarbonyl)valyloxy)-2-propyl carbonate was converted to iodide by the method described in Example A-I-1, step e) to give the title compound (1.37 g) practically pure. R f (2%MeOH/CHCl 3 ) 0.85. 'H-NMR (CDC1 3 ): 7.34 (s, 10H), 5.93 (d, IH), 5.89 (d, IH), 5.21 (m, 3H), 5.11 (s, 4H), 4.50-4.17 (m, 6H), 2.12 (m, 2H), 0.97 (d, 6H), 0.88 (d, 6H). Example A-I-4 Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy isobutyrate. O O, CBzNH- O ' O a) 4-Methoxybenzyl 2-hydroxyisobutyrate. 2-hydroxy isobutyric acid (1.56 g) was esterified by alkylation with 4- methoxybenzyl chloride by the method described in Example A-I-1, step a). The title compound (2.65 g) was obtained after silica gel column chromatography (0, 1, 2% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.45. b) 4-Methoxybenzyl 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyrate. 4-methoxybenzyl 2-hydroxyisobutyrate was acylated with N-benzyloxycarbonyl-L- valine by the method described in Example A-I-1, step b). The title compound (3.21 g) was obtained after silica gel column chromatography (0, 1, 1.5% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.70. 82 c) 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyric acid. 4-methoxybenzyl 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyrate was de-esterified by the method described in Example A-I-1 step c. The title compound (2.01 g) was obtained after silica gel column chromatography (2, 10, 20% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.30. This compound may be activated and esterified directly to a drug, or further modified as described below. 'H-NMR (CDCl j ): 7.32 (s, 5H), 5.33 (d, IH), 5.10 (s, 2H), 4.31 (d,d, IH), 2.22 (m, IH), 1.57 (s, 6H), 0.98 (d, 3H), 0.89 (d, 3H). d) Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyrate. 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyric acid was esterified by the method described in Example A-I-1, step d. The title compound (1.90 g) was obtained after silica gel column chromatography (0, 1, 1.5% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.80. e) Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyrate. Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy) isobutyrate was converted to iodide by the method described in Example A-I-1, step e to give the title compound (2.32 g) practically pure. R f (2%MeOH/CHCl 3 ) 0.80. 'H-NMR (CDC1 3 ): 7.33 (s, 5H), 5.89 (s, 2H), 5.22 (d, IH), 5.11 (s, 2H), 4.29 (d,d, IH), 2.21 (m, IH), 1.55 (s, 3H), 1.53 (s, 3H), 1.00 (d, 3H), 0.93 (d, 3H). EXAMPLE A-I-5 Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy -3-methyl-(S)-(+)-butyrate. ^^ O CBZNH /' Y 0 ' Ό'^ O a) 4-Methoxybenzyl 2-hydroxy-3-methyl-(S)-(+)-butyrate. 2-hydroxy-3-methyl-(S)-(+)-butyric acid (1.77 g) was esterified by alkylation with 4- methoxybenzyl chloride by the method described in Example A-I-1, step a. The title 83 compound (3.10 g) was obtained after silica gel column chromatography (0, 1, 2% ethanol in dichloromethane). R f (2%MeOH CHCl 3 ) 0.50. b) 4-Methoxybenzyl 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)- (+)-butyrate. 4-Methoxybenzyl 2-hydroxy-3-methyl-(S)-(+)-butyrate was acylated with N- benzyloxycarbonyl-L-valine by the method described in Example A-I-1, step b. The title compound (5.74 g) was obtained after silica gel column chromatography (0, 1, 1.5% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.70. c) 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)-(+)-butyric acid. 4-methoxybenzyl 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)-(+)-butyrate was de-esterified by the method described in Example A-I-1, step c. The title compound (3.41 g) was obtained after silica gel column chromatography (2, 10, 20% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.45. The compound may be activated and esterified directly to a drug or further modified as described below: 'H-NMR (CDC1 3 ): 7.36 (s, 5H), 5.38 (d, IH), 5.11 (s, 4H), 4.90 (d, IH), 4.41 (d,d, IH), 2.28 (m, 2H), 1.04-0.89 (m, 12H). d) Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)-(+)- butyrate. 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)-(+)-butyric acid was esterified by the method described in Example A-I-1, step d. The title compound (2.96 g) was obtained after silica gel column chromatography (0, 1 , 2% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.85. e) Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-3-methyl-(S)-(+)- butyrate. Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-3 -methyl-(S)-(+)-butyrate was converted to iodide by the method described in Example A-I-1, step e to give the title compound (3.64 g) practically pure. R f (2%MeOH/CHCl 3 ) 0.85. 'H-NMR (CDCI 3 ): 7.36 (s, 5H), 6.00 (d, IH), 5.83 (d, IH), 5.28 (d, IH), 5.11 (s, 4H), 4.83 (d, IH), 4.41 (d,d, IH), 2.29 (m, 2H), 1.05-0.90 (m, 12H). 84 EXAMPLE A-I-6 Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetate. O O, CBzNH O O a) 4-Methoxybenzyl 2-hydroxy-2-phenyl-DL-acetate. DL-mandelic acid (2.28 g) was esterified by alkylation with 4-methoxybenzyl chloride by the method described in Example A-I-1, step a. The title compound (3.69 g) was obtained after silica gel column chromatography (0, 1, 1.5% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.55. b) 4-Methoxybenzyl 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL- acetate. 4-Methoxybenzyl 2-hydroxy-2-phenyl-DL-acetate was acylated with N- benzyloxycarbonyl-L-valine by the method described in Example A-I-1, step b. The title compound (6.50 g) was obtained after silica gel column chromatography (0, 1, 1.5% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.75. c) 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetic acid. 4-Methoxybenzyl 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetate was de-esterified by the method described in Example A-I-1, step c. The title compound (4.75 g) was obtained after silica gel column chromatography (2, 10, 20% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.40. The compound may be activated and esterified directly to a drug or further modified as described below. 'H-NMR (CDC1 3 ): 7.36 (m, 10H), 5.91 (d, IH), 5.27 (m, IH), 5.04 (s, 2H), 4.57-4.40 (2xd,d, IH), 2.30 (m, IH), 1.01-0.82 (m, 6H). d) Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL- acetate. 85 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetic acid was esterified by the method described in Example A-I-1, step d. The title compound (1.69 g) was obtained after silica gel column chromatography (0, 1 , 2% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.80. e) Iodomethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetate. Chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxy)-2-phenyl-DL-acetate was converted to iodide by the method described in Example A-I-1, step e to give the title compound (1.89 g) practically pure. R f (2%MeOH/CHCl 3 ) 0.80. 'H-NMR (CDC1 3 ): 7.36 (m, 10H), 5.94-5.82 (m, 3H), 5.28 (m, IH), 5.10 (s, 2H), 4.46 (m, IH), 2.21 (m, IH), 1.08-0.85 (m, 6H). Example A-I-7 Iodomethyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate. O a) 4-Methoxybenzyl 4-hydroxybenzoate. 4-Hydroxybenzoic acid (1.38 g) was esterified by alkylation with 4-methoxybenzyl chloride by the method described in Example A-I-1, step a. The title compound (2.06 g) was obtained after silica gel column chromatography (0, 1, 2, 3% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.40. b) 4-Methoxybenzyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate. 4-Methoxybenzyl 4-hydroxybenzoate was acylated with N-benzyloxycarbonyl-L- valine by the method described in Example A-I-1, step b. The title compound (2.71 g) was obtained after silica gel column chromatography (0, 1% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.70. c) 4-(N-benzyloxycarbonyl-L-valyloxy) benzoic acid. 86 4-Methoxybenzyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate was de-esterified by the method described in Example A-I-1, step c. The title compound (1.86 g) was obtained after silica gel column chromatography (2, 10, 20% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.20. The compound can be activated and esterifed directly to a drug or further modifed as described below. 'H-NMR (CDCl j ): 8.15 (d, 2H), 7.34 (m, 5H), 7.22 (d, 2H), 5.38 (d, IH), 5.17 (s, 2H), 4.58 (d,d, IH), 2.34 (m, IH), 1.12 (s, 3H), 0.96 (d, 3H). d) Chloromethyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate. 4-(N-benzyloxycarbonyl-L-valyloxy) benzoic acid was esterified by the method described in Example A-I-1, step d. The title compound (0.95 g) was obtained after silica gel column chromatography (0, 1% ethanol in dichloromethane). R f (2%MeOH/CHCl 3 ) 0.80. e) Iodomethyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate. Chloromethyl 4-(N-benzyloxycarbonyl-L-valyloxy) benzoate was converted to iodide by the method described in Example A-I-1, step e to give the title compound (1.16 g) practically pure. R f (2%MeOH CHCl 3 ) 0.80. 'H-NMR (CDC1 3 ): 8.11 (d, 2H), 7.35 (m, 5H), 7.21 (d, 2H), 6.15 (s, 2H), 5.32 (d, IH), 5.14 (s, 2H), 4.55 (d,d, IH), 2.34 (m, IH), 1.10 (s, 3H), 1.03 (d, 3H). Example A- 1-8 Iodomethyl 5-(N-CBz-L-valyloxy)-2.2-dimethylvalerate O a) 4-Methoxybenzyl 2,2-dimethyl-4-pentenoate To a solution of 2,2-dimethyl-4-pentenoic acid (11.5 g, 90 mmol) in DMF (250 mL) at room temperature, was added potassium tert-butoxide (11.1 g, 99 mmol). The reaction mixture was stiπed at 60 °C for lh. 4-Methoxybenzyl chloride (16.9 g, 108 mmol) was added and the reaction mixture was stiπed at 60 °C for 4h. The DMF was evaporated under vacuum, the residue was dissolved in ether (500 mL) and washed 87 with water (3 x 200 mL). The organic phase was dried with Na 2 SO 4 and evaporated to give 21.4 g of 4-methoxybenzyl 2,2-dimethyl-4-pentenoate. b) 4-Methoxybenzyl 5-hydroxy-2,2-dimethylvalerate A mixture of 4-methoxybenzyl 2,2-dimethyl-4-pentenoate (9.50 g, 38 mmol) and 9- BBN (115 mL, 57 mmol, 0.5 M in THF) was stiπed at 60 °C for 60 min, whereupon the reaction mixture was cooled to -5 °C. H 2 O (35 mL) was added, the reaction mixture was stiπed for 5 min at -5 °C, an aqueous solution of NaOH (35 mL, 3M) was added and the reaction mixture was stiπed for a further 10 min at -5 °C. An aqueous solution of H 2 O 2 (35 mL, 30%) was added dropwise and the temperature of the reaction mixture was allowed to assume room temperature, whereupon the reaction mixture was stiπed for 30 min at room temperature. After evaporation, water (200 mL) was added and the resulting mixture was extracted with CH 2 C1 2 (5 x 200 mL). The combined organic layers were dried (Na,SO 4 ) and concentrated under reduced pressure. The crude product was column chromatographed (silica gel, 1→8% MeOH in CH 2 C1 2 ), to give 6.32 g of 4-methoxybenzyl 5-hydroxy-2,2- dimethylvalerate. c) 4-Methoxybenzyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate To a mixture of DCC (9.41 g, 46 mmol), DMAP (0.586 g, 4.8 mmol) and N-CBz-L- valine (12.1 g, 48 mmol) in CH 2 C1 2 (200 mL) at 0 °C, was added dropwise a solution of 4-methoxybenzyl 5-hydroxy-2,2-dimethyl-valerate (6.40 g, 24 mmol) in CH 2 C1 2 (50 mL). After lh at 0 °C, the temperature of the reaction mixture was allowed to assume room temperature and then the mixture was stiπed for 5h at room temperature. The mixture was filtered through a glass filter and the solvent was removed under reduced pressure. The crude product was column chromatographed (silica gel, 1→4% MeOH in CH 2 C1 2 ), to give 8.61 g 4-methoxybenzyl 5-(N-CBz-L- valyloxy)-2,2-dimethylvalerate. d) 5-(N-CBz-L-valyloxy)-2,2-dimethylvaleric acid To a solution of 4-methoxybenzyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate (8.24 g, 16.5 mmol) in CH 2 C1, (100 mL) at room temperature, was added trifluoroacetic acid (5 mL). After lh at room temperature, the reaction mixture was concentrated 88 under reduced pressure. The crude product was column chromatographed (silica gel, 3- 5% MeOH in CH 2 C1 2 ), to give 6.00 g of 5-(N-CBz-L-valyloxy)-2,2- dimethylvaleric acid. The compound can be activated and directly esterified to a drug or further modified as described below. 'H-NMR (CDCl j ): 10.94 (br s, IH), 7.35 (s, 5H), 5.45 (d, IH), 5.1 1 (s, 2H), 4.30 (dd, IH), 4.21-4.00 (m, 2H), 2.28-2.07 (m, IH), 1.68-1.51 (m, 4H), 1.21 (s, 6H), 0.97 (d, 3H), 0.89 (d, 3H). e) Chloromethyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate To a solution of 5-(N-CBz-L-valyloxy)-2,2-dimethylvaleric acid (5.88 g, 15.5 mmol) in dioxane (100 mL), was added dropwise a 40% aqueous solution of tetrabutylammonium hydroxide (10.1 g). After stirring for 5 min, the solution was evaporated to dryness through co-evaporation with dioxane and toluene. The residue was dissolved in dichloromethane (100 mL) and then chloroiodomethane (11.3 mL, 155 mmol) was added and the solution was stiπed for 6h at room temperature. The solution was concentrated under reduced pressure and the residue was shaken with hexane / ethyl acetate (1 :1 v/v, 200 mL). The yellow crystalline solid was filtered off and the filtrate was washed with aqueous solution of sodium thiosulfate (0.1 M) and the filtered through anhydrous sodium sulfate and evaporated to dryness. The residue was column chromatographed (silica gel, 1-4% MeOH in CH 2 C1 2 ), to give 3.95 g of chloromethyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate. f) Iodomethyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate. To a solution of chloromethyl 5-(N-CBz-L-valyloxy)-2,2-dimethylvalerate (3.85 g, 9 mmol) in acetonitrile (50 mL), was added sodium iodide (5.40 g, 36 mmol). The solution was stiπed for 4 h at 60 °C. The resulting suspension was filtered and the filtrate was evaporated. The residue was dissolved in CH 2 C1 2 and washed with aqueous sodium thiosulfate (0.1 M). The organic phase was dried (N&,SO 4 ) and concentrated under reduced pressure. The crude product was column chromatographed (silica gel, 1% MeOH in CH 2 C1 2 ), to give 4.26 g of iodomethyl 5- (N-CBz-L-valyloxy)-2,2-dimethylvalerate 89 'H-NMR (CDCI 3 ): 7.34 (s, 5H), 5.90 (s, 2H), 5.32 (d, IH), 5.10 (s, 2H), 4.29 (dd, IH), 4.18-4.02 (m, 2H), 2.26-2.08 (m, IH), 1.65-1.50 (m, 4H), 1.17 (s, 6H), 0.97 (d, 3H), 0.89 (d, 3H). Example A- 1-9 2-(N-CBz-L-valyloxy -ethyl iodomethyl carbonate O . ^ r A O-(N-Cbz)-Val O O a) 2-(N-CBz-L-valyloxy)-ethanol. To a mixture of DCC (11.4 g, 55 mmol), DMAP (0.611 g, 5 mmol) and ethyleneglycol (55.8 mL, 1 mol) in CH 2 C1 2 (300 mL) at 0 °C, was added dropwise a solution of N-CBz-L-valine (12.6 g, 50 mmol) in CH 2 C1 2 (100 mL). After lh at 0 °C, the temperature of the reaction mixture was allowed to assume room temperature and then the mixture was stiπed for 5h at room temperature. The mixture was filtered through a glass filter and the solvent was removed under reduced pressure. The crude product was column chromatographed (silica gel, 5— >10% MeOH in CH 2 C1 2 ), to give 12.0 g 2-(N-CBz-L-valyloxy)-ethanol. b) 2-(N-CBz-L-valyloxy)-ethyl chloromethyl carbonate To a mixture of 2-(N-CBz-L-valyloxy)-ethanol (12.0 g, 40.6 mmol) and pyridine (19.7 mL, 0.24 mmol) in CH 2 C1 2 (300 mL) at 0 °C, was added dropwise chloromethyl chloroformate (10.5 g, 81.2 mmol). After 30 min at 0 °C, the reaction mixture was washed with H 2 O (200 mL). The H 2 O phase was washed with CH 2 C1 2 (100 mL) and the solvent of the combined organic phases was removed under reduced pressure. The crude product was column chromatographed (silica gel, 0.5→1% MeOH in CH 2 C1 2 ), to give 8.26 g 2-(N-CBz-L-valyloxy)-ethyl chloromethyl carbonate. c) 2-fN-CBz-L-valyloxyVethyl iodomethyl carbonate To a solution of 2-(N-CBz-L-valyloxy)-ethyl chloromethyl carbonate (3.88 g, 10 mmol) in acetonitrile (50 mL), was added sodium iodide (7.50 g, 50 mmol). The solution was stiπed for 4 h at 60 °C. The resulting suspension was filtered and the 90 filtrate was evaporated. The residue was dissolved in CH 2 C1 2 and washed with aqueous sodium thiosulfate (0.1 M). The organic phase was dried (Na^O and concentrated under reduced pressure, to give 4.51 g 2-(N-CBz-L-valyloxy)-ethyl iodomethyl carbonate. 'H-NMR (CDCl j ): 7.34 (s, 5H), 5.93 (s, 2H), 5.26 (d, IH), 5.11 (s, 2H), 4.48-4.26 (m, 5H) 2.28-2.10 (m, IH), 0.97 (d, 3H), 0.90 (d, 3H). Example A-I-10 2.2-dimethyl-3-( N-CBz-D-valyloxyVpropionic acid iodomethyl ester O X HN O ' I o o a) 2,2-dimethyl-3-(N-CBz-D-valyloxy)-propionic acid To a solution of 2,2-dimethyl propionic acid 4-methoxybenzyl ester (4.7 g, 20 mmole) and N-CBz-D-valine (5.5 g, 22 mmole) in dichloromethane (100 ml) were added 4-dimethyaminopyridine (305 mg, 2.5 mmole) and DCC (5.15 g, 25 mmole). After 18 hr, the solution was washed successively with sodium bicarbonate aqueous solution, citric acid solution and water. The organic phase was dried and the residue was dissolved in dichloromethane (100 ml). To the solution was added trifluoroacetic acid (10 ml). After 3 hr, it was evaporated and the product was isolated with silica gel column chromatography. 4.5 g. The compound may be activated and esterified to a drug or further modified as described below. 'H-NMR (CDC1 3 ): 7.36 (m, 5 H) 5.11 (s, 2H) 4.30 (m, IH) 4.18 (dd, 2H) 2.17 (m, IH), 1.23 (d, 6 H) 0.93 (m, 6H). b) 2,2-dimethyl-3- ( N-CBz-D-Valyloxy )-propionic acid chloromethyl ester (2,2-dimethyl-3-(N-CBz-D-valyloxy)-propionic acid (4.5 g, 12.8 mmole) was dissolved in dioxane (20 ml). To the solution was added tetrabutylammonium hydroxide aqueous solution (40 %, 8.3 ml, 12.8 mmole). The solution was dried in vacuo, and it was coevaporated with toluene several times. The residue was dissolved in methylene chloride and then chloroiodomethane (18 ml, 260 mmole) was added to 91 the solution. After 18 hr, the reaction solution was evaporated and the product was isolated with silica gel column chromatography. 3.5 g. c) 2,2-dimethyl-3-(N-CBz-D-valyloxy)-propionic acid iodomethyl ester 2,2-Dimethyl-3-(N-CBz-D-valyloxy)-propionic acid chloromethyl ester (2.4 g, 6 mmole) was dissolved in acetonitrile (30 ml). Sodium iodide (1.26 g, 8.4 mmole) was added to the solution. After reaction at 70° C for 2 hr, the reaction mixture was filtered and the residue was dissolved in methylene chloride (20 ml) and refiltered. The solution was dried and gave the titled product. 2.68g. 'H-NMR (CDC1 3 ): 7.36 (m, 5 H) 5.90 (dd, 2H) 5.26 (d, IH) 5.11 (s, 2H) 4.31 (m, IH) 4.15 (dd, 2H) 2.18 (m, IH) 1.22 (d, 6H) 0.92 (m, 6H). Example A- 1-11 4-(N-CBz-L-valyloxy ' ) butyric acid iodomethyl ester a) 4-(N-CBz-L-valyloxy) butyric acid t-butyl ester N-CBz-L-valine (16.25 g, 65 mmole) was dissolved in DMF (40 ml). To the solution was added potassium t-butoxide (7.24 g, 65 mmole). After 10 min, 4-bromobutyric acid t-butyl ester (12 g, 53 mmole) was added. The reaction mixture was kept at 65° C for 2.5 hr and then poured into sodium bicarbonate aqueous solution and extracted with dichloromethane. The organic phase was dried and the product was isolated with silica gel column chromatography. 20.1 g. b) 4-(N-CBz-L-valyloxy)butyric acid chloromethyl ester 4-( N-CBz-L-valyloxy) butyric acid t-butyl ester (20 g, 50.8 mmole) was treated with trifluoroacetic acid (30 ml) at 0° C for 3 h and then evaporated. The residue was coevaporated with toluene several time. The intermediate acid (2.56 g, 7.6 mmole) was dissolved in dioxane (10 ml) and to the solution was added tetrabutylammonium hydroxide (40 %, 4.66 ml, 7.2 mmole). The solution was dried and dissolved in dichloromethane (20 ml) and then chloroiodomethane (10 ml, 144 mmole) was added 92 to the solution. After 18 hr, the reaction solution was evaporated and the product was isolated with silica gel column chromatography. Yield 2.1 g. c) 4-(N-CBz-L-valyloxy)butyric acid iodomethyl ester 4-(N-CBz-L-valyloxy) butyric acid chloromethyl ester (1.54 g, 4 mmole) was dissolved in acetonitrile (15 ml). Sodium iodide (840 mg, 5.6 mmole) was added to the solution. After reaction at 55° C for 3 hr, the reaction mixture was filtered and the residue was dissolved in methylene chloride (20 ml) and refiltered. The solution was dried and gave the titled product. Yield 1.9 g. 'H-NMR (CDC1 3 ): 7.36 (m, 5H) 5.90 (dd, 2 H) 5.25 (d, IH) 5.11 (s, 2H) 4.29 (dd, IH 4.18 (t, 2H) 2.43 (t, 2H) 2.20 (m, IH) 2.00 (m, 2H) 0.93 (dd, 6 H). Example A-I-12 Iodomethyl 3-fN-benzyloχycarbonyl-L-valyloxy -benzoate O O, ( X CBzNH O a) 4-Methoxybenzyl 3-hydroxybenzoate To a solution of 3-hydroxybenzoic acid (6.9g, 50 mmole) in DMF (100 ml) was added potassium-tert.-butoxide (6.17 g, 55 mmole) and the mixture was stiπed at room temperature for one hour. 4-Methoxybenzyl chloride (9.4g, 60 mmole) was added and the mixture was stiπed for 16 hours at 60°C. The mixture was evaporated under reduced pressure and ethyl acetate (250 ml) were added. The organic phase was washed five times with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with toluene/acetone. Yield: 10.5g = 81% b) 4-Methoxybenzyl 3-(N-benzyloxycarbonyl-L-valyloxy) benzoate . To a cooled solution of 4-methoxybenzyl 3-hydroxybenzoate (7.7g, 29.8 mmole), 4- dimethylaminopyridine (0.73g, 6 mmole) and N-benzyloxycarbonyl-L-valine (8.3g, 33 mmole) in 100 ml dichloromethane was added dicyclohexyl-carbodiimide (7.22g, 35 mmole) and the mixture was stiπed for 2 days at room temperature. The mixture 93 was cooled and the urethane was filtered. The solution was evaporated and ethyl acetate (250 ml) was added. The organic phase was washed twice with 5% acetic acid; 5% sodium hydrogencarbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 13.9g = 94% c) 3-(N-benzyloxycarbonyl-L-valyloxy) benzoic acid To a solution of 4-methoxybenzyl-3-(N-benzyloxycarbonyl-L-valyloxy)-benzoate (13.7g, 27.8 mmole) in dichloromethane (150 ml) was added trifluoroacetic acid (20 ml) and the mixture was stiπed for 2 hours at room temperature. The solution was evaporated under reduced pressure and the product crystallized from toluene. Yield: lO.lg = 87%). The compound can be activated and esterified to a drug or further modified as described below 'H-NMR (DMSO d-6) 1.01 (m, 6H) 2.21 (m, IH) 4.17 (d, d, IH) 5.08 (s, 2H) 7.28-7.96 (m, 10H) d) Chloromethyl 3-(N-benzyloxycarbonyl-L-valyloxy)-benzoate. To a solution of 3-(N-benzyloxycarbonyl-valyloxy)benzoic acid (7.42g, 20 mmole) in 1,4-dioxane (100 ml) was added a 40% solution of tetrabutylammonium hydroxide (12.97g, 20 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and co-evaporated two times with 1 ,4-dioxane and two times with toluene. The dried product was dissolved in dichloromethane (50 ml) and chloroiodomethane (35.3g, 200 mmole) was added. The solution was stiπed for two days at room temperature and evaporated under reduced pressure. Ethyl acetate (100 ml) was added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure: The product was isolated by silica gel column chromatography. Yield: 3.8g = 45%. e) Iodomethyl 3-(N-benzyloxycarbonyl-L-valyloxy)-benzoate. To a solution of chloromethyl 3-(N-benzyloxycarbonyl-L-valyloxy)-benzoate (2.0g, 4.76 mmole) in dry acetone (30 ml) was added sodium iodide (3.15g, 21 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated 94 under reduced pressure and extracted with ethyl actate/water. The organic phase was washed with a 5% sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield: 2.3g = 94%. 'H-NMR (CDCl j ) 1.02 (m, 6H) 2.38 (m, IH) 4.56 (d, d , IH) 5.14 (s , 2H) 5.30 (d, IH) 6.14 (s, 2H) 7.26-7.50 (m, 7H) 7.80(s, IH) 7.96 (d, IH ) Example A-I-13 Iodomethyl 3-fN-benzyloxycarbonyl-L-valyloxy)-propionate O o i^o^ o- NHCBz a) 3-buten-l-yl-3-(N-benzyloxycarbonyl)-propionate. To a solution of 3-buten-l-ol (2.16g, 30 mmole), N-benzyloxycarbonyl-1-valine (8.29g, 33 mmole) and 4-dimethylaminopyridine (0.37g, 3 mmole) in dichloromethane (80 ml) was added dicyclohexyl-carbodiimide (7.22g, 35 mmole) and the mixture was stiπed overnight at room temperature. The mixture was cooled and the urethane was filtered. The solution was evaporated under reduced pressure and ethyl acetate (200 ml) was added. The organic phase was washed twice with 5% acetic acid, 5% sodium hydrogencarbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 8.3g = 90%. b) 3-(N-benzyloxycarbonyl-L-valyloxy)-propanoic acid To a solution of 3-buten-l-yl -3-( N-benzyloxycarbonyl-L-valyloxy)-propionate (9.2g, 30 mmole) in 150 ml benzene was added tetrabutylammonium bromide (1.62g, 5 mmole) and 100 ml water. The mixture was cooled to about 5°C and potassium permanganate (14.82g, 90 mmole) was added in portions. The mixture was stiπed 2 hours at room temperature, diluted with water and decolorized by the addition of sodium bisulfite. The mixture was acidified with 2M hydrogen chloride and extracted 3 times with ethyl acetate. The combined organic phases were washed with water and dried with sodium sulfate. The solution was evaporated under 95 reduced pressure and the product isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 5.4g = 55%. The compound can be activated and esterified to a drug or further modified as described below. 'H-NMR (DMSO d-6) 0.90 (m, 6H) 2.5 (m, 2H) 3.88 (d, d, IH) 4.32 (m, 2H) 5.03 (s, 2H) 7.36 (m, 5H) 7.68 (d, IH) c) Chloromethyl 3-(N-benzyloxycarbonyl-L-valyloxy)-propionate. To a solution of 3-(N-benzyloxycarbonyl-L-valyloxy)propanoic acid (5.2g, 16.08 mmole) in 1,4-dioxane (50 ml) was added a 40% solution of tetrabutylammonium hydroxide (10.43g, 16.08 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and co-evaporated two times with 1 ,4-dioxane and two times with toluene. The dried product was dissolved in 40 ml dichloromethane and chloroiodomethane (28.4g. 160 mmole) was added. The solution was stiπed for two days at room temperature and evaporated under reduced pressure. Ethyl acetate (100 ml) was added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 2.2g = 35% d) Iodomethyl3-( N-benzyloxycarbonyl-L-valyloxy)-propionate. To a solution of chloromethyl 3-(N-benzyloxycarbonyl-L-valyloxy)-propionate (2.05g, 5.51 mmole) in dry acetone (50 ml) was added sodium iodide (4.12g, 27.5 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and extracted with ethyl acetate water. The organic phase was washed with a 5%> sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield: 2.35g = 92%. 'H-NMR (CDC1 3 ) 0.94 (m, 6H) 2.17 (m, IH) 2.68 (t, 2H) 4.40 (m, 3H) 5.12 (s, 2H) 5.91 (s, 2H) 7.26 (m, 5H). Example A-I-15 1 -(N-benzyloxycarbonyl-L-valyloxyV2-methyl-2-propyl iodomethyl carbonate 96 (a) 1 -(N-benzyloxycarbonyl-L-valyloxy)-2-methyl-2-propanol /V-Benzyloxycarbonyl-L-valine (2.02 g, 8.0 mmol), 4-dimethylaminopyridine (100 mg, 0.8 mmol), and ), and dicyclohexylcarbodiimide (2.04 g, 9.9 mmol, in 20 mL CH 2 C1 2 ) were added to 2-methyl-l,2-propanediol (12.2 mmol) in 30 mL dry CH 2 C1 2 , with cooling in an ice bath. DMF (5 mL) was added. After stirring for 5 h at 10 °C , the reaction mixture was filtered, concentrated, and then redissolved in ethyl acetate. The organic solution was washed with saturated ΝaCl, dried over anhydrous Νa^O^ and concentrated. Flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate) gave 2.3 g of the title compound. (b) 1 -(N-benzyloxycarbonyl-L-valyloxy)-2-methyl-2-propyl chloromethyl carbonate All of the alcohol from above was dissolved in 35 mL dry CH 2 C1 2 and cooled in an ice bath. Pyridine (3.50 mL, 43.4 mmol) was added, followed by chloromethyl chloro formate (1.30 mL, 14.4 mmol). After 1 h, the ice bath was removed and stirring was continued for 2 h at ambient temperature. The mixture was diluted with CH 2 C1 2 (50 mL) and washed with water (50 mL), and then brine (2 x 25 mL).Drying over anhydrous Νa 2 SO 4 of the combined organic phases and concentration under vacuum, coevaporating several times with toluene, gave a yellow-brown oil that was subjected to flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate) to yield 2.86 g (86% from N-benzyloxycarbonyl-L-valine) of the title compound. (c) l-(N-benzyloxycarbonyl-L-valyloxy)-2-methyl-2-propyl iodomethyl carbonate A mixture of the chloride (2.84 g, 6.84 mmol) from step (b) and Νal (4.15 g, 27.2 mmol) in 68 mL dry acetonitrile was refluxed at 75 °C for 4 h. After evaporation of solvent under vacuum, the residue was partitioned between ethyl acetate (80 mL) and water (40 mL), and the organic layer was washed with 5% Νa^Oj ( 15 mL) and 97 brine (25 mL). Drying the organic phase over anhydrous Na;,SO 4 and concentration gave a yellow oil that was subjected to flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate) to furnish 3.29 g (95%) of the title compound. Η NMR (250 MHz, CDC1 3 ) δ 0.90 and 0.94 (2d, 3H each, J= 6.8 Hz), 1.52 (s, 6H), 2.17 (m, IH), 4.35 (m, IH), 4.22 and 4.39 (ABq, 2H, J ΛB = 1 1.7 Hz), 5.10 (s, 2H), 5.30 (d, IH), 5.86 (s, 2H), 7.34 (s, 5H) Example A-I-16 Iodomethyl 3 ,4-di-(N-CBZ-L-valyloxy hvdrocinnamate CBz-NH CBz-NH a) 4-Methoxybenzyl-3 ,4-dihydroxyhydrocinnamate 3,4-Dihydroxycinnamic acid (6.5 g, 35.7 mmol) was dissolved in DMF (50 ml) and cooled to 0°C on an ice-bath. 4-Potassium tert-butoxide (35.7 mmol), was then added and the mixture was left for approximately 30 min at 0°C, followed by dropwise adition of 4-methoxy-benzylchloride (39 mmol) in DMF (25 ml). The mixture was allowed to reach room temperature and left over-night. The solvent was then evaporated and the crude product was purified by chromatography (ethyl acetate- hexane, 1 :1) to give 6 g of the title compound (55%). b) 4-Methoxybenzyl-3,4-di-(N-CBZ-L-valyloxy)hydrocinnamate 4-Methoxybenzyl-3,4-dihydroxyhydrocinnamate (5 g, 16.5 mmol), N,N- dimethylaminopyridine (2g, 16.5 mmol), NN'- dicychlohexyl carbodiimide (8.5 g, 41.3 mmol) and Cbz-L-valine (10.4 g, 41.3 mmol) were dissolved in dichloromethane (50 ml). After 4 h, the the mixture was filtered and evaporated onto silica gel and purified by chromatography (hexane-EtOAc, 5:2 -> 3:2) to give pure title product (10.1 g, 79 %). c) 3,4-Di-(Ν-CBZ-L-valyloxy)hydrocinnamic acid 98 4-Methoxybenzyl-3,4-di-(N-CBZ-L-valyloxy)hydrocinnamate (10 g, 13 mmol) was dissolved in dichloromethane and 1,1,1 trifluoroacetic acid (30 ml) and left at ambient temperature for 3.5 h. Evaporation under reduced pressure and purification by chromatography (chloroform-methanol, 10:1) yielded 6.7 g (80%) pure title product. The compound can be activated and esterified to a drug or further modified as described below. 'H NMR (CDCl j 45 °C): 7. 24-7.0 (m, 13H), 5.65 (br s, IH), 5.55 (br s, IH), 5.1 (m, 4H), 4.46 (m, 2H), 2.95 (t, 2H), 2.66 (t, 2H), 2.35 (m, 2H). d) Chloromethyl 3,4-di-(N-CBZ-L-valyloxy)hydrocinnamate 3,4-Di-(N-CBZ-L-valyloxy)hydrocinnamic acid (4.2 g, 6.47 mmol) was dissolved in dioxane (70 ml). Tetrabutylammonium hydroxide was added dropwise until pH=8. The solvent was then removed under reduced pressure The solid was redissolved in dioxane (30 ml) and toluene (30 ml) and evaporated. The procedure was repeated twice (for removal of water). Dichloromethane (60 ml) and chloro-iodomethane was added in one portion and the mixture was left at ambient temperature for 6 h. Evaporation of the solvent and purification by chromatography yielded 1.7 g title product (38%). e) Iodomethyl 3,4-di-(N-CBZ-L-valyloxy)hydrocinnamate Chloromethyl 3,4-di-(N-CBZ-L-valyloxy)hydrocinnamate (1.9 g, 2.7 mmol) and sodium iodide (2 g, 13.3 mmol) were dissolved in acetonitrile (50 ml) and heated to 65° C for 60 min. The solvent was removed under reduced pressure and the residue was taken up in dichloromethane and filtrated. Removal of the solvent and purification by chromatography (ethyl acetate-hexane, 2:5) gave pure title product (1.9 g, 90 %) Η NMR (CDCI 3 45 °C): 7.34-7.02 (m, 13H), 5.89 (s, 2H), 5.64 (br s, 2H), 5.14-5.02 (m, 4H), 4.47 (m, 2H), 2.96 (t, 2H), 2.64 (t, 2H), 2.33 (m, 2H), 1.08-0.99 (m, 12H) Example A-I-17 3-(N-CBZ-L-valyloxy)phenyl iodomethyl carbonate 99 a) 3-(N-CBz-L-valyloxy)phenol. CBz-L-valine (10 g, 40 mmol), 1,3-dihydroxybenzene (8.7g, 79 mmol) NN'dicychlohexylcarbodiimide (10.2g, 44 mmol) and 4-dimethylaminopyridine (2.4 g, 20 mmol) were dissolved in DMF (50 ml) and left at ambient temperature overnight. The reaction mixture was filtered, the solvent removed under reduced pressure and the crude product was taken up in dichloromethane and filtered. Removal of the solvent followed by purification by chromatography (chloro form- methanol, 10:1) yielded pure title product (10.9 g, 79%). b) (Ν-CBZ-L-valyloxy)phenyl chloromethyl carbonate. 3-(N-CBz-L-valyloxy)phenol (5.4 g, 15 7 mmol) was dissolved in dichloromethane (70 ml) and cooled in an ice-bath. Pyridine (1.2 g, 23.5 mmol was added followed by dropwise addition of 1-chloro-methylchloro formate (2.3 g, 18.8 mmol) in dichloromethane (10 ml). The mixture was left at room temperature for 4 h. Water (25 ml) was then added and the phases were separated. The organic layer was washed with 0.01 M aqueous hydrochloric acid (25 ml). Purification by chromatography (ethyl acetate-hexane, 1 :1) gave the title compound (4.5 g, 65 %) c) 3-(N-CBZ-L-valyloxy)phenyl iodomethyl carbonate (N-CBZ-L-valyloxy)phenyl chloromethyl carbonate (1.5g, 3.44 mmol) and sodium iodide (2 g, 13.3 mmol) were stiπed at 60°C in acetonitrile (50 ml) for 4.5 h.The mixture was filered, the solvent removed and the crude product was taken up in 100 ml hexane-ethyl acetate, 1 :1, and filtered through a sintered glass funnel, packed with 2 cm silica gel. Removal of the solvent yielded pure title product (1.68 g, 92%) 'H NMR (CDC1 3 45 °C): 7.38-7.02 (m, 9H), 6.03 (s, 2H), 5.2 (br s, IH), 5.14 (s, 2H), 4.48 (m, IH), 2.30 (m, IH), 1.09-1.01 (m, 6H) Example A-I-18 100 Iodomethyl 2-(N-CBZ-L-valyloxy)phenylacetate O O^l a) 4-Methoxybenzyl 2-hydroxyphenylacetate. 2-hydroxyphenylacetic acid (10 g, 66 mmol) was dissolved in NN-dimethyl- formamide (100 ml) and cooled on ice-bath. Potassium tert-butoxide (8.85 g, 78 mmol) was added. The mixture was left for 30 min and allowed to reach room temperature. 4-Methoxy-benzylchloride (11.7 g, 72 mmol) in NN-dimethyl- formamide (30 ml) was then added dropwise, under nitrogen atmosphere and left over-night. The solvent was evaporated under reduced pressure and the crude mixture was dissolved in ether (100 ml) and washed with water (25 ml), brine and dried over sodium sulphate. Chromatography (hexane-ethyl acetate, 2: 1) followed by recrystallization (hexane-ethyl acetate) gave the title compound (7.6 g, 42%). b) 4-Methoxybenzyl 2-(Ν-CBz-L-valyloxy)phenylacetate 4-Methoxybenzyl 2-hydroxyphenylacetate 3g, 11 mmol), NN-dichyclohexyl- carbodiimide (2.7 g, 13.2 mmol), dimethylaminopyridine (0.134 g, 1.1 mmol) and CBz-L-valine (3.3 g, 13.2 mmol) were dissolved in dichloromethane (50 ml). After the weekend the solid was filtered off, the solvent removed under reduced pressure and the crude product purified by chromatography (ethyl acetate, hexane, 1 :2) to give the title compound (5.2 g, 93%). c) 2-(Ν-CBz-L-valyloxy)phenylacetic acid 4-Methoxybenzyl 2-(N-CBz-L-valyloxy)phenylacetate (4.25 g, 8.4 mmol), was dissolved in dichloromethane (40 ml). Triflouroacetic acid (8 ml) was added with cooling on ice. The mixture was allowed to reach room temperature and stiπed for 40 min. The solvent was removed under reduced pressure and the crude product was recrystallized twice (hexan-ethyl acetate + a small amount of dichloromethane) to give the title compound (2.6 g, 80 %). The compound can be activated and esterified to a drug or further modified as described below. 101 'H NMR (CDC1 3 45 °C): 7.35-7.08 (m, 9H), 5.35 (br s, IH), 5.13 (s, 2H), 4.48 (m, IH), 3.57 (s, 2H), 2.33 (m, IH), 1.08 (d, 3H), 1.02 (d, 3H). d) Chloromethyl 2-(N-CBZ-L-valyloxy)phenylacetate This compound was prepared in poor yield from 2-(N-CBz-L-valyloxy)phenylacetic acid (5.5 g, 14.3 mmol) by an unoptimized procedure essentially as described in Example A-I-16 d). Yield: 0.265 g 'H NMR (CDC1 3 45 °C): 7.28-7.01 (m, 9H), 5.55 (s, 2H), 5.2 (br s, IH), 5.07 (s, 2H), 4.43 (m, IH), 3.53 (s, 2H), 2.26 (m, IH), 1.02 (d, 3H), 0.95 (d, 3H). e) Iodomethyl 2-(N-CBZ-L-valyloxy)phenylacetate Chloromethyl 2-(N-CBZ-L-valyloxy)phenylacetate is treated with Nal and purified as described in the Examples above to yield the title compound. Example A-I-19 Iodomethyl 4-(N-CBZ-L-valyloxyxy phenylacetate a) 4-Methoxybenzyl 4-hydroxyphenylacetate Prepared from 4-hydroxyphenylacetic acid (10 g, 65.7 mmol) in 70 % yield by the same procedure as for Example A-I-18 a) above, but wherein the solvent for the recrystallization was changed to hexane-ether. b) 4-Methoxybenzyl 4-(N-CBz-L-valyloxy)phenylacetate Prepared from 4-methoxybenzyl 4-hydroxyphenylacetate (3 g, 11 mmol) by the same procedure as for Example A-I-18 b) in 87 % yield. Solvent for chromatography: ethyl acetate-hexane, 1:2. 102 c) 4-(N-CBZ-L-valyloxy)phenylacetic acid Prepared in 82 % yield from 4-methoxybenzyl 4-(N-CBz-L-valyloxy)phenylacetate (1.6 g, 288 mmol) by the procedure described for Example A-I-18 c). Solvent for recrystallization: hexane-ether and a small amount of dichloromethane. The compound can be activated and esterified to a drug or further modified as described below. •H NMR (CDC1 3 45 °C): 7.36-7.27 (m, 7H), 7.02 (d, 2H), 5.25 (d, IH), 5.14 (s, 2H), 4.52 (m, IH), 3.64 (s, 2H), 2.3 (m, IH), 1.08 (d, 3H), 1.02 (d, 3H). d) Chloromethyl 4-(N-CBZ-L-valyloxy)phenylacetate Prepared from 4-(N-CBZ-L-valyloxy)phenylacetic acid (3 g, 7.8 mmol) in 26 % yield by the same procedure as described for Example A-I-18 d). Solvent for chromatography: hexane-ether, 3:2. e) Iodomethyl 4-(N-CBZ-L-valyloxy)phenylacetate Chloromethyl 4-(N-CBZ-L-valyloxy)phenylacetate (0.83 g, 1.9 mmol) and sodium iodide (1.15 g, 7.6 mmol) were heated in acetonitril (45 ml) for 5 h. The mixture was filtrated, the solvent removed, taken up in dichloromethane and filtrated again. Evaporation and purification by chromatography (ether-hexane, 2:3) yielded the title product (0.8 g, 80 %). Η NMR (CDCI 3 45 °C): 7.38-7.09 (m, 4H), 5.84 (s, IH), 5.30 (br s, IH), 5.15 (s, 2H), 4.5 (m, IH), 3.56 (s, 2H), 2.36 (m, IH), 1.10 (d, 3H), 1.00 (d, 3H). Example A-I-20 Iodomethyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl benzoate a) 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl)-toluene To a cooled solution of 4-methylphenylethanol-2 (5.0g, 36.7 mmole), 4- dimethylaminopyridine (0.98g, 8 mmole) and N-benzyloxycarbonyl-L-valine (10.05g, 40 mmole) in dichloromethane (120 ml) was added dicyclohexylcarbodiimide (9.1g, 44 mmole) and the mixture was stiπed overnight at room 103 temperature. The mixture was cooled and the urethane was filtered. The solution was evaporated under reduced pressure and ethyl acetate (250 ml) was added. The organic phase was washed twice with 5% acetic acid, 5% sodium hydrogencarbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography b) 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl)- benzoic acid . To a cooled mixture of chromic anhydride (7.55g, 75 mmole) in acetic acid (100 ml) was added dropwise a solution of 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl)- toluene (9.3g, 25.1 mmole) in acetone (50 ml). The mixture was stiπed at room temperature for 3 days and reduced to about 100 ml. 600ml 10%> sodium chloride solution was added and the mixture was extracted four times with ethyl acetate. The organic phase was washed with brine and dried with sodium sulfate. The solution was evaporated under reduced pressure and the product was islolated by silica gel column chromatography with dichloromethane/methanol. Yield : 2,lg = 21%. The product can be activated and esterified directly onto a drug or further modified as described below.'H-NMR (CDC1 3 ) 0.79 (d, 3H) 0.90 (d, 3H) 2.08 (m,lH) 3.04 (t, 2H) 4.28 (d, d,lH)4.39 (m, 2H) 5.11 (s, 2H) 5.26 (d, IH) 7.34 (m, 7H) 8.04 (d, 2H) c) Chloromethyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl)benzoate To a solution of 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl)benzoic acid (2.0g, 5.0 mmole) in 1,4-dioxane (20 ml)was added a 40% solution of tetrabutylammonium hydroxide (3.1g, 4.75 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and coevaporated two times with 1 ,4-dioxane and two times with toluene. The dried product was dissolved in dichloromethane (10 ml) and iodochloromethane (13.2g, 75 mmole) was added The solution was stiπed overnight at room temperature and evaporated under reduced pressure. About 50 ml ethyl acetate were added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography.Yield: 0.5g =23% d) Iodomethyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl) benzoate 104 To a solution of chloromethyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethyl) benzoate (0.5g, 1.11 mmole). In dry acetone (10 ml) was added sodium iodide (0.75g, 5.0 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and extracted with ethyl actate/water. The organic phase was washed with a 5% sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield: 0.53g = 88%. 'H-NMR (CDCl j ) 0.88 (d, 3H) 0.90 (d, 3H) 2.08 (m, IH) 3.02 (t, 2H) 4.28 (d, d, IH) 4.38 (m, 2H) 5.10 (s, 2H) 5.22 (d, IH) 6.15 (s, 2H) 7.35(m, 7H) 7.98 (d, 2H ) Example A-I-21 Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl 2-methyl propionate. a) 4-methoxybenzyl 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl)- 2-methyl propionate To a cooled solution of 4-methoxybenzyl 2-(hydroxymethyl)-2-methyl propionate (6.0g, 25 mmole), 4-dimethylaminopyridine (0.61g, 5 mmole) and N- benzyloxycarbonyl-L-isoleucine (6.90g, 26 mmole) in dichloromethane (100 ml) was added dicyclohexyl-carbodiimide (6.2g, 30 mmole) and the mixture was stiπed overnight at room temperature.The mixture was cooled and the urethane was filtered. The solution was evaporated and 200 ml ethyl acetate was added, The organic phase was washed twice with 5% acetic acid, 5% sodium hydrogencarbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with toluene/acetone. Yield: 11.7g = 96%. 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl)-2-methyl) propionic acid. To a solution of 4-methoxybenzyl 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl)- 2-methyl propionate (1 l.Og, 22.6 mmole) in 100 ml dichloromethane was added trifluoroacetic acid (15 ml) and the mixture was stiπed overnight at room temperature. The solution was evaporated under reduced pressure and coevaporated two times with toluene. The residue was stiπed 1 hour with 100 ml ethanol and the white solid was filtered (byproduct). The solution was evaporated under reduced 105 pressure and the product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 7.4g = 89%. The product can be activated and esterified directly to a drug, or further modified as described below. 'H-NMR (CDC1 3 ) 0.90 (m, 6H) 1.26 (m, 8H) 1.88 (m, IH) 4.12 (d, d, 2H) 4.38 (d, d, IH) 5.10 (s, 2H) 5.32 (d, IH) 7.28 (m, 5H) c) Chloromethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxy)-2-methyl propionate. To a solution of 2-(N-benzyloxycarbony-L-isoleucyloxymethyl)-2-methyl propionic acid (7.0g, 19 mmole) in 80 ml 1,4-dioxane was added a 40% solution of tetrabutylammonium hydroxide (12.4g, 19 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and co-evaporated two times with 1 ,4-dioxane and two times with toluene. The dried product was dissolved in 25 ml dichloromethane and iodochloromethane (33.7g, 190 mmole) was added . The solution was stiπed overnight at room temperature and evaporated under reduced pressure. About 100 ml ethyl actate was added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with toluene/acetone.Yield: 4.2 = 54% d) Iodomethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl)-2 -methyl propionate. To a solution of chloromethyl 2-(N-benzyloxycarbonyl-L-isoleucyloxymethyl)-2- methyl propionate (3.0g, 7.2 mmole) in 50 ml dry acetone was added sodium iodide (4.8g, 32 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and extracted with ethyl actate water. The organic phase was washed with a 5% sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield: 3.3g = 90%. 'H-NMR (CDCI 3 ) 0.93 (m, 6H) 1.23 (m, 8H) 4.12 (m, 2H) 4.38 (d, d, IH) 5.10 (s, 2H) 5.26 (d, IH) 5.92 (m, 2H) 5.35 (m, 5H) Example A-I-22 Iodomethyl 4-(N-benzyloxycarbonyl-L-valyloxy ' )cvclohexanoate. 106 a) 4-Methoxybenzyl 4-hydroxycyclohexanoate. To a solution of ethyl 4-hydroxycyclohexanoate (8.61g, 50 mmole) in 50 ml ethanol was added a solution of potassium hydroxide 85% (3.63g, 55 mmole) and the mixture was stiπed for 6 hours at 70°C. The mixture was evaporated under reduced pressure, coevaporated two times with N,N-dimethylformamide and reduced to about 100 ml. 4-Methoxybenzyl chloride (9.4g, 60 mmole) was added and the mixture was stiπed for 18 hours at 60°C. The mixture was evaporated under reduced pressure and 250 ml ethyl acetate was added. The organic phase was washed five times with water, dried with sodiun sulfate and evaporated under reduced pressure. Yield: 13.2g =100% (crude) b) 4-methoxybenzyl 4-(N-benzyloxycarbonyl-L-valyloxy)- cyclohexanoate. To a cooled solution of 4-methoxybenzyl 4-hydroxycyclohexanoate (7.5g, 28 mmole), 4-dimethylaminopyridine (0.73g, 6 mmole) and N-benzyloxycarbonyl-L- valine (7.54g, 30 mmole) in dichloromethane (90 ml) was added dicylohexyl- carbodiimide (6.8g, 33 mmole) and the mixture was stiπed for 2 days at room temperature. The mixture was cooled and the urethane was filtered. The solution was evaporated and 250 ml ethyl acetate was added.The organic phase was washed twice with 5% acetic acid, 5%> sodium hydrogencarbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with toluene/acetone. Yield : 13g = 93% c) 4-(N-benzyloxycarbonyl-L-valyloxy) cyclohexanoic acid. To a solution of 4-methoxybenzyl 4-(N-benzyloxycarbonyl-L-valyloxy)- cyclohexanoate (12g, 24.1 mmole) in dichloromethane (100 ml) was added trifluoroacetic acid (20 ml) and the mixture was stiπed for 3 hours at room temperature. The solution was evaporated under reduced pressure and coevaporated two times with toluene. The residue was stiπed 1 hour with about 100 ml ethanol and the white solid was filtered (byproduct). The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography with 107 toluene/acetone. Yield: 6.8g = 74%. The product can be activated and esterified directly to a drug or further modified as described below. 'H-NMR (CDC1 3 ) 0.91 (m, 6H) 1.52-2.54 (m, 10H) 4.28 (m, IH) 4.82-5.08 (m, IH) 5.11 (s, 2H) 5.28 (d, IH) 7.36 (m, 5H) d) Chloromethyl 4-(N-benzyloxycarbonyl-L-valyloxy)-cyclohexanoate. To a solution of 4-(N-benzyloxycarbonyl-L-valyloxy) cyclohexanoic acid (6.6g, 20 mmole) in 1 ,4-dioxane (70 ml) was added a 40% solution of tetrabutylammonium hydroxide (11.34g, 17.5 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and co-evaporated two times with 1,4-dioxane and two times with toluene. The dried product was dissolved in 60 ml dichloromethane and iodochloromethane (30.9g, 175 mmole) was added. The solution was stiπed for two days at room temperature and evaporated under reduced pressure. About 100 ml ethyl actate was added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with toluene/acetone. Yield: 4.1g = 55%. e) Iodomethyl 4-(N-benzyloxycarbonyl-L-valyloxy)-cyclohexanoate. To a solution of chloromethyl 4-(N-benzyloxycarbonyl-L-valyloxy)-cyclohexanoate (4.0g, 9.4 mmole) in dry acetone (50 ml) was added sodium iodide (6.3g, 42 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and extracted with ethyl actate water. The organic phase was washed with a 5%> sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield 4.5g = 93%. 'H-NMR (CDCI 3 ) 0.90 (m, 6H) 1.52-2.02 (m, 8H) 2.18 (m, IH) 2.43 (m, IH) 4.30 (m, IH) 4.76-5.08 (m, IH) 5.11 (s, 2H) 5.26 (d, IH) 5.91 (d, 2H) 7.34 (m, 5H) Example A-I-23 108 Iodomethyl 2-( -benzyloxycarbonyl-L-valyloxymethylV2-ethyl butyrate N-CBz-Valyf-O a) 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2-ethylbutan- 1 -ol. To a cooled solution of 2-ethyl-2-hydroxymethyl-butan-l-ol (33. Ig, 250 mmole), 4- dimethylaminopyridine (1.22g, 10 mmole) and N-benzyloxycarbonyl-L-valine (12.6g, 50 mmole) in 350 ml dichloromethane was added dropwise a solution of dicyclohexyl-carbodiimide (12.4g, 60 mmole) in 50 ml dichloromethane. The mixture was stiπed 2 days at room temperature and cooled. The urethane was filtered and the solution evaporated under reduced pressure. 350 ml ethyl acetate was added and the organic phase was washed twice with 5% acetic acid, 5%> sodium-hydrogencarbonate and water. The organic phase was dried with sodium sulfat and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with dichloromethane/methanol. Yield: 16.4g = 90%>. c) 2-(N-benzyloxycarbonyl-L-valyloxymethyl )-2-ethyl-butyric acid. To a cooled mixture of chromic anhydride (8.5g, 85,2 mmole) in 100 ml acetic acid was added dropwise a solution of 2-(N-benzyloxycarbonyl-L-valyoxymethyl)-2- ethyl-butan-1-ol (10.4g, 28.4 mmole) in 50 ml acetone and the mixture was stiπed 24 hours at room temperature. The mixture was added to 1000 ml 10% sodium chloride solution and extracted four times with ethyl acetate. The organic phase was washed twice with brine, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 7g = 65%>. The product can be activated and esterified directly to a drug or futher modified as described below. 'H-NMR (CDC1 3 ) 0.88 (m, 12H) 1.67 (m, 4H) 2.14 (m, IH) 4.26 (m, 3H) 5.10 (s, 2H) 5.30 (d, 2H) 7.34 (m, 5H) d) Chloromethyl 2-(N-benzyoxycarbonyl-L-valyloxymethyl -2-ethyl butyrate. 109 To a solution of 2-(N-benzyloxycarbony-L-valyloxymethyl)-2-ethyl-butyric acid (7.2g,18,9 mmole) in 1,4-dioxane (80 ml) was added a 40% solution of tetrabutylammonium hydroxide (12.26g, 18.9 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and co-evaporated once with 1 ,4-dioxane and two times with toluene. The dried product was dissolved in 30 ml dichloromethane and iodochloromethane (49.4g, 280 mmole) was added. The solution was stiπed for two days at room temperature and evaporated under reduced pressure. About 100 ml ethyl actate were added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 5.2g = 63% e) Iodomethyl 2-( N-benzyloxycarbonyl-L-valyloxymethyl)-2-ethyl butyrate. To a solution of chloromethyl 2-(N-benzyloxycarbonyl-L-valyloxymethyl)-2-ethyl butyrate (5.0g, 11.7 mmole) in dry acetone (60 ml) was added sodium iodide (7.5g, 50 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and extracted with ethyl actate water. The organic phase was washed with a 5% sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield: 5.4g = 90%. 'H-NMR (CDC1 3 ) 0.92 (m, 12H) 1.65 (m, 4H) 2.18 (m, IH) 4.28 (m, 3H) 5.10 (s, 2H) 5.22 (d, IH) 5.92 (s, 2H) 7.36 (m, 5H) Example A-I-24 2-flSf-(iodomethoxycarbonylV amino) -2-methyl- 1 -(N-benzyloxycarbonyl-L- valyloxyVpropane O O- • N-^-O- CBzNH H a) 2-(N-tert.-butyloxycarbonylamino)-2-methyl- 1 -(N-benzyloxycarbonyl- L-valyloxy)-propane. To a cooled solution of 2-(N-(tert.-butyloxycarbonyl)-amino)-2-methylpropan-l-ol (J. Am. Chem. Soc 113 (1991) p 8883) (4.73g, 25 mmole), 4-dimethylamino- 110 pyridine (0.6 lg, 5 mmole) and N-benzyloxycarbonyl-L-valine (6.28g, 25 mmole) in dichloromethane (70 ml) was added dicyclohexyl-carbodiimide (6.19g, 30 mmole) and the mixture was stiπed 2 days at roommtemperature. The mixture was cooled, the urethane was filtered and the solution evaporated under reduced pressure. Ethyl acetate (200 ml) was added and the organic phase was washed twice with 5% acetic acid, 5% sodium hydrogencarbonate and water. The organic phase was dried with,sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 10.2g = 96%. b) 2-amino-2-methyl- 1 -(N-benzyloxycarbonyl-L-valyloxy)-propane. To a solution of 2-(N-(tert.-butyloxycarbonyl)-amino)-2 -methyl- 1-(N- benzyloxycarbonyl-L-valyloxy)-propane (lOg, 23 mmole) in dichloromethane (150 ml) was added trifluoroacetic acid (30 ml) and the mixture was stiπed for 1 hour at room temperature. The solution was evaporated under reduced pressure and 10% sodium carbonate solution was added. The product was extracted four times with dichloromethane, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with dichloromethane/methanol. Yield: 3.0g = 40% (crude) c) 2-(N-(chloromethoxycarbonyl)-amino)-2-methyl-l- (N- benzyloxycarbonyl-L-valyloxy)-propane. To a solution of 2-amino-2-methyl-l-(N-benzyloxycarbonyl-L-valyloxy)-propane (2.9g, 9 mmole) and pyridine (2 ml) in dichloromethane (50 ml) was added chloromethyl chloroformate(1.55g, 12 mmole) and the mixture was stiπed for 3 hours at room temperature. The mixture was evaporated under reduced pressure and ethyl acetate was added. The organic phase was washed with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: l.lg = 29%>. d) 2-(N-(iodomethoxycarbonyl)-amino)-2-methyl-l-(N- benzyloxycarbonyl-L-valyloxy)-propane. To a solution of 2-(N-(chloromethoxycarbonyl)-amino)-2-methyl-l-(N- benzyloxycarbonyl-L-valyloxy)propane (1.05g, 2.53 mmole) in dry acetone (20 ml) 111 was added sodium iodide (1.8g, 12 mmole) and the mixture was stiπed for 36 hours at room temperature. The mixture was evaporated under reduced pressure and ethyl acetate and water were added. The organic phase was washed with 10% sodium thiosulfate solution and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure.Yield: 1.04g = 81 %>. 'H-NMR (CDC1 3 ) 0.92 (m, 6H) 1.35 (s, 6H) 2.10 (m,lH) 3.88 (m, IH) 4.35 (m, 2H) 5.11 (s, 2H) 5.32 (d, IH) 5.82 (s, IH) 5.91 (s, 2H) 7.35 (m, 5H) Example A-I-25 1 -(2-N-CBz-L-valyloxyethyl)-6-oxo-l .6-dihvdro-pyridine-3-carboxylic acid iodomethyl ester O O ^1 O^N^ O-Cbz-Val a) 6-oxo- l,6-dihydro-pyridine-3 -carboxylic acid 4-methoxybenzyl ester. To a solution of 6-hydroxynicotinic acid (4.87 g, 35 mmol) in DMF (100 mL) at room temperature, was added potassium tert-butoxide (3.93 g, 35 mmol). The reaction mixture was stiπed at 60 °C for lh. 4-Methoxybenzylchloride (8.30 g, 53 mmol) was added and the reaction mixture was stiπed at 60 °C for 4h. The DMF was evaporated under vacuum, the residue was dissolved in ether (200 mL) and washed with water (3 x 100 mL). The organic phase was dried with Na^O,, and evaporated to give 4.41 g of 6-oxo- l,6-dihydro-pyridine-3-carboxylic acid 4-methoxybenzyl ester. b) l-(2-Hydroxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid 4- methoxybenzyl ester To a solution of 6-oxo- 1 ,6-dihydro-pyridine-3-carboxylic acid 4-methoxybenzyl ester (4.41 g, 17 mmol) and K 2 CO 3 (2.58 g, 18.7 mmol) in DMF (100 mL) at room temperature, was added 2-bromoethanol (2.02 g, 16.2 mmol). The reaction mixture was stiπed at 80 °C for 30h, whereupon the DMF was evaporated under vacuum. 112 The crude product was column chromatographed (silica gel, 2- 5% MeOH in CH 2 C1 2 ), to give 3.91 g of l-(2-hydroxyethyl)-6-oxo-l,6-dihydro-pyridine-3- carboxylic acid 4-methoxybenzyl ester. c) 1 -(2-N-CBz-L-valyloxyethyl)-6-oxo- 1 ,6-dihydro-pyridine-3-carboxylic acid 4-methoxybenzyl ester To a mixture of DCC (5.06 g, 24.5 mmol), DMAP (318 mg, 2.6 mmol) and N-CBz- L-valine (6.48 g, 25.8 mmol) in CH 2 C1 2 (200 mL) at 0 °C, was added dropwise a solution of l-(2-hydroxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid 4- methoxybenzyl ester (6.40 g, 24 mmol) in CH 2 C1 2 (200 mL). After lh at 0 °C, the temperature of the reaction mixture was allowed to assume room temperature and then the mixture was stiπed for 5h at room temperature. The mixture was filtered through a glass filter and the solvent was removed under reduced pressure. The crude product was column chromatographed (silica gel, 2->5% MeOH in CH 2 C1 2 ), to give 6.81 g l-(2-N-CBz-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid 4-methoxybenzyl ester. d) l-(2-N-CBz-L-valyloxyethyl)-2-pyridone-5-carboxylic acid To a solution of l-(2-N-CBz-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3- carboxylic acid 4-methoxybenzyl ester (6.46 g, 12 mmol) in CH 2 C1 2 (85 mL) at room temperature, was added trifluoroacetic acid (15 mL). After lh at room temperature, the reaction mixture was concentrated under reduced pressure. The crude product was column chromatographed (silica gel, 3-»6% MeOH in CH 2 C1 2 ), to give 4.91 g 1- (2-N-CBz-L-valyloxyethyl)-2-pyridone-5 -carboxylic acid. The product can be activated and esterified direct to a drug or further modified as described below. 'H-NMR (CDC1 3 ): 12.15 (br s, IH), 8.29 (d, J= 2.2 Hz, IH), 7.93 (dd, J= 9.5, 2.2 Hz, IH), 7.31 (m, 5H), 6.69 (d, J= 9.5 Hz, IH), 5.53 (d, IH), 5.07 (s, 2H), 4.52- 4.05 (m, 5H), 2.20-2.00 (m, IH), 0.90 (d, 3H), 0.81 (d, 3H). e) l-(2-N-CBz-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid chloromethyl ester 113 To a solution of l-(2-N-CBz-L-valyloxyethyl)-2-pyridone-5-carboxylic acid (4.91 g, 11.8 mmol) in dioxane (200 mL), was added dropwise a 40%) aqueous solution of tetrabutylammonium hydroxide (7.65 g). After stirring for 5 min, the solution was evaporated to dryness through co-evaporation with dioxane and toluene. The residue was dissolved in dichloromethane (200 mL) and then chloroiodomethane (8.74 mL, 120 mmol) was added and the solution was stiπed for 12h at room temperature. The solution was concentrated under reduced pressure and the residue was shaken with hexane / ethyl acetate (1 :1 v/v, 200 mL). The yellow crystalline solid was filtered off and the filtrate was washed with aqueous solution of sodium thiosulfate (0.1 M) and the filtered through anhydrous sodium sulfate and evaporated to dryness. The residue was column chromatographed (silica gel, 2-4% MeOH in CH 2 C1 2 ), to give 1.80 g of 1 -(2-N-CBz-L-valyloxyethyl)-6-oxo- 1 ,6-dihydro-pyridine-3-carboxylic acid chloromethyl ester. f) 1 -(2-N-CBz-L-valyloxyethyl)-6-oxo- 1 ,6-dihydro-pyridine-3-carboxylic acid iodomethyl ester To a solution of l-(2-N-CBz-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3- carboxylic acid chloromethyl ester (1.80 g, 3.87 mmol) in acetonitrile (30 mL), was added sodium iodide (2.32 g, 15.5 mmol). The solution was stiπed for 4 h at 60 °C. The resulting suspension was filtered and the filtrate was evaporated. The residue was dissolved in CH 2 C1 2 and washed with aqueous sodium thiosulfate (0.1 M). The organic phase was dried (Na ^ SO and concentrated under reduced pressure. The crude product was column chromatographed (silica gel, 1%> MeOH in CH 2 C1 2 ), to give 2.04 g l-(2-N-CBz-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid iodomethyl ester. 'H-NMR (CDC1 3 ): 8.19 (d, J= 2.5 Hz, IH), 7.79 (dd, J= 9.6, 2.5 Hz, IH), 7.32 (m, 5H), 6.52 (d, J= 9.6 Hz, IH), 6.04 (s, 2H), 5.38 (d, IH), 5.07 (s, 2H), 4.54-4.06 (m, 5H), 2.20-2.00 (m, IH), 0.91 (d, 3H), 0.81 (d, 3H). Example A-I-26 Iodomethyl 5-[(N-benzyloxycarbonyl-L-valyloxy methyl]-2-fiιroate 114 o-X AX O 77i 0 (a) 5-[(N-Benzyloxycarbonyl-L-valyloxy)methyl]-2-furaldehyde A solution of 5-(hydroxymethyl)-2-furaldehyde (1.00 g, 7.69 mmol) in 5 mL dry CH 2 C1 2 was added to a mixture of N-benzyloxycarbonyl-L-valine (2.40 g, 9.57 mmol), N,N -dicyclohexylcarbodiimide (2.00 g, 9.69 mmol), and 4-dimethyl- aminopyridine (117 mg, 0.96 mmol) in 45 mL CH 2 C1 2 . After stirring overnight, the reaction slurry was filtered, concentrated under vacuum, and subjected to flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate to give the valine ester (quantitative yield). (b) 5-[(N-Benzyloxycarbonyl-L-valyloxy)methyl]-2-furoic acid A solution of ΝaClO 2 (2.8 mmol) in 3 mL water was added dropwise to a stiπed solution of 5-[(N-benzyloxycarbonyl-L-valyloxy)methyl]-2-furaldehyde (798 mg, 2.22 mmol) from step (a) in 3 mL MeCΝ, with cooling in an ice bath. After 2.5 h, the ice bath was removed, 2 mL more MeCΝ was added, and the two-phase liquid reaction mixture was stiπed at room temperature for 25 h. The reaction mixture was diluted with water, made basic with saturated ΝaHCO 3 , and extracted with ethyl acetate (3 x 50 mL). The separated aqueous solution was acidified to pH 2 with 5% aqueous HC1 and extracted with ethyl acetate (3 x 50 mL). This second ethyl acetate solution was washed with brine, dried over anhydrous Na^O^ and evaporated to dryness under vacuum to give the carboxylic acid (287 mg, 34%) which was used in the next step without further purification. The compound can be activated and esterified direct to a drug or further modified as described below. 'H NMR (250 MHz, CDC1 3 ) δ 0.84 and 0.93 (2d, 3H each, J= 6.8 Hz), 2.15 (m, IH), 4.35 (dd, IH, J= 9.0, 4.7 Hz), 5.10-5.24 (m, 4H), 5.44 (d, IH, J= 9.0 Hz), 6.54 (d, IH, J= 3.3 Hz), 7.23 (d, IH, J= 3.3 Hz), 7.33 (s, 5H), 11.05 (br s, IH). (c) Chloromethyl 5-[(N-benzyloxycarbonyl-L-valyloxy)methyl]-2-furoate 115 Tetrabutylammonium hydroxide (40 wt. % solution in water, 0.55 mL, 0.84 mmol) was added to the carboxylic acid (286 mg, 0.76 mmol) from step (b) in 5 mL dioxane. The yellow solution was concentrated under vacuum, coevaporating several times with dioxane, toluene, and, lastly, CH 2 C1 2 . The residue was charged with 10 mL dry CH 2 C1 2 and chloroiodomethane (0.55 mL, 7.55 mmol) was added. After stiπing for 20.5 h, the reaction mixture was concentrated and subjected to flash column chromatography (silica, 2/1 petroleum ether - ethyl acetate) to give the chloromethyl ester (137 mg, 42%). (d) Iodomethyl 5-[(N-benzyloxycarbonyl-L-valyloxy)methyl]-2-furoate All of the chloromethyl ester (137 mg, 0.32 mmol) from step (c) was refluxed with Νal (195 mg, 1.3 mmol) in 3.2 mL dry MeCΝ at 70 °C for 4 h. The solvent was removed under vacuum and the residue was subjected to flash column chromatography (silica, 3/1 petroleum ether - ethyl acetate) to give the iodomethyl ester (152 mg, 92%). Η ΝMR (250 MHz, CDC1 3 ) δ 0.84 and 0.93 (2d, 3H each, J= 6.8 Hz), 2.16 (m, IH), 4.33 (dd, IH, J= 9.1, 4.7 Hz), 5.09-5.21 (m, 4H), 5.36 (d, IH, J= 9.1 Hz), 6.08 (s, 2H), 6.52 (d, IH, J= 3.4 Hz), 7.19 (d, IH, J= 3.5 Hz), 7.33 (s, 5H). Example A-I-27 4-(2-Ν-benzyloxycarbonyl-L-valyloxyethyl benzoic acid . a) 4-Methoxybenzyl 4-(2-hydroxyethoxy)benzoate To a solution of 4-methoxybenzyl 4-hydroxybenzoate (7.0g, 27 mmole) in dry N,N- dimethylformamide (50 ml) was added potassium carbonate (4.15g, 30 mmole) and 2-bromoethanol.The mixture was stiπed 48 hours at 80°C, evaporated under reduced pressure and ethyl acetate and water were added. The organic phase was washed five times with water and dried with sodium sulfate. The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography with hexane/ethyl acetate. Yield: 6.8g = 83%. b) 4-methoxybenzyl 4-(2-N-benzyloxycarbonyl-L- valyloxyethoxy)benzoate. 116 To a solution of 4-methoxybenzyl 4-(2 -hydroxy ethoxy) benzoate (6.6g, 21.8 mmole), 4-dimethylaminopyridine (0.6 lg, 5 mmole) and N-benzyloxycarbonyl-L- valine (6.3g, 25 mmole) in dichloromethane (80 ml) was added dicyclohexylcarbodiimide (5.2g, 25 mmole) and the mixture was stiπed overnight at room temperature. The mixture was cooled and the urethane was filtered.The solution was evaporated and ethyl acetate (200 ml) was added. The organic phase was washed twice with 5% acetic acid, 5% sodium hydrogencarbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography with dichloromethane/methanol. Yield: 10.6g = 90 %. c) 4-(2-N-benzyloxycarbonyl-L-valyloxyethoxy)-benzoic acid. To a solution of 4-methoxybenzyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethoxy) benzoate (10.2g, 19.04 mmole) in dichloromethane (100 ml) was added trifluoroacetic acid (20 ml) and the mixture was stiπed 3 hours at room temperature. The solution was evaporated under reduced pressure and co-evaporated two times with toluene. The product was isolated by silica gel column chromatography. Yield: 6.9g = 87%). The product may be activated and esterified direct to a drug or converted to iodomethyl 4-(2-N-benzyloxycarbonyl-L-valyloxyethoxy)-benzoic acid as described above, that is by treatment with a base, chloroiodomethane, separation and then treatment with Nal. 'H-NMR (CDC1 3 ) 0.94 (m, 6H) 2.18 (m, IH) 4.22- 4.68 (m, 5H) 5.10 (s, 2H) 6.94 (d, 2H) 7.35 (m, 5H) 8.05 (d, 2H) Example 1 3.3-Bis fN-CBZ-L-valyloxymethylVpropionic acid a) 4,4-bis (N-CBZ-L-valyloxymethyl)-but-l-ene. To a solution of 2-allyl-l,3-propandiol (2.32g, 20 mmole), N-CBZ-L-valine (10.06g, 40 mmole) and DMAP (0.488g, 4 mmole) in 120ml dichloromethane was added DCC (9.08g, 44 mmole) in portions and the mixture was stiπed overnight at room temperature. The mixture was cooled to 5°C and the urethane was filtered. The 117 filtrate was evaporated and the product was isolated by silica gel column chromatography. Yield : 9.0g b) 3,3-Bis (N-CBZ-L-valyloxymethyl)-propionic acid. To a cooled solution of 4,4-bis (N-CBZ-L-valyloxymethyl)-but-l-ene (14.6g, 25 mmole) and tetrabutylammonium bromide (1.3g, 4 mmole) in 120ml benzene was added 100ml water. Under strong stirring potassium permanganate (15.8g, 100 mmole) was addded in portions and the mixture was stiπed for 2 hours between 15°C and 20°C . A sodium bisulfite aqueous solution was added to the slurry until the mixture was discolored. The mixture was acidified with 2N hydrochloric acid and extracted four times with ethyl acetate. The organic phase was washed two times with water, dried with sodium sulfate and evaporated under reduced pressure . The product was isolated by silica gel column chromatography. Yield: 7.5g 'H-NMR (CDCl j ) 0.89 (m, 12H) 2.05 (m, 2H) 2.46 (m, 2H) 2.62 (m, IH) 4.20 (m, 6H) 5.11 (s, 4H) 5.30 (m, 2H) 7.35 (m, 10H) Example 2 2 3'-Dideoxy-3'-fluoro-5'-O- [3.3-bis (L-valyloxymethylVpropionyll guanosine a) 2',3'-dideoxy-3'-fluoro-5'-O-[3,3-bis (N-CBZ-L-valyloxymethyl)- propionyljguanosine. A solution of 2',3'-dideoxy-3'-fluoroguanosine (1.35g, 5 mmole), 3,3-bis (N-CBZ- L-valyloxymethyl)-propionic acid (3.6g, 6 mmole), DMAP (0.06 lg, 0.5 mmole) and HOBT (0.8 lg, 6 mmole) was coevaporated two times with DMF and reduced to about 120ml. DCC (1.24g, 6 mmole) was added and the mixture was stiπed overnight at room temperature. The mixture was filtered and the solution was evaporated under reduced pressure. Ethyl acetate (200 ml) was added and the organic phase washed twice with 5%> acetic acid, 5% sodium hydrogen carbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 2.7g d) 2', 3'-Dideoxy-3'-fluoro-5'-O- [3,3-bis (L-valyloxymethyl)-propionicacid] guanosine. 118 A solution of 2', 3'-dideoxy-3'-fluoro-5'-O-[3,3-bis (N-CBZ-L-valyloxymethyl)- propionyl] guanosine (2.6g, 3.1 mmole) in 80ml ethyl acetate, 20ml methanol and 20ml acetic acid was hydrogenated with palladium black (0.3g) for two hours under normal pressure. The catalyst was filtered and washed with ethyl acetate and methanol. The solution was evaporated under reduced pressure and the product was isolated as the bisacetate salt by silica gel column chromatography. Yield: 1.2g 'H-NMR (DMSO d-6) 0.90 (m, 12H) 1.78 (m, 2H) 2.50-3.00 (m, 2H) 3.09 (m, 2H) 4.02-4.45 (m, 8H) 5.34-5.59 (m, IH) 6.17 (m, IH) 6.62 (s, 2H) 7.88 (s, IH) Example 3 2 3'-Dideoxy-3'-fluoro-5'-O-3- 1.3-bis-(L-valyloxy -2-propyloxycarbonyl propanoyl] guanosine a) l,3-dibenzyloxy-2-propyl succinate monoester. A solution of l,3-dibenzyloxypropan-2-ol (6.8g, 25 mmole) and succinic anhydride (7.5g, 75 mmole) and DMAP (12.2g, 100 mmole) was stiπed for one hour at 60°C. The mixture was evaporated under reduced pressure, acidified with 2N HC1 and extracted two times with ethyl actate. The combined organic phase was washed three times with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 7.8g b) Synthesis of 2', 3'-dideoxy-3'-fluoro-5'-O-[3-(l,3-dibenzyloxy-2- propyloxycarbonyl)-propanoyl] guanosine. A mixture of 2', 3'-dideoxy-3'-fluoroguanosine (l.όlg, 6 mmole), HOBT (0.972g, 7.2 mmole), DMAP (73.3mg, 0.6 mmole) and l,3-dibenzyloxy-2-propyl succinate monoester (2.68g, 7,2 mmole) was coevaporated two times with DMF and reduced to about 150ml. DCC (1.55g, 7.5 mmole) was added and the mixture was stiπed 72 hours at room temperature. The mixture was filtered and the solution was evaporated under reduced pressure. Ethyl acetate (200 ml) was added and the organic phase washed twice with 5% acetic acid, 5% sodium hydrogen carbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 3.3g 1 19 c) Synthesis of 2', 3'-dideoxy-3'-fluoro-5'-O [3-(l,3-dihydoxy-2- propyloxy carbonyl)propanoyl]guanosine. A solution of 2', 3'-dideoxy-3'-fluoro-5'-O-[3-(l,3-dibenzyloxy-2-propyloxy carbonyl)propanoyl]guanosine (3.2g, 5.13 mmole) in 50ml ethyl acetate, 50ml methanol and 10ml acetic acid was hydrogenated with palladium black (0.6g) under 40 psi overnight. The catalyst was filtered and washed with methanol, The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromathography. Yield: 1.64g d) Synthesis of 2',3'-dideoxy-3'-fluoro-5'-O- {3-[l,3-Bis ( N-CBZ-L- valyloxy)-2-propyloxycarbonyl]propanoyl } guanosine. A mixture of 2',3'-dideoxy-3'-fluoro-5'-O-[3-(l,3-dihydroxy-2-propyloxy carbonyl)- propanoyl]guanosine (1.93g, 2.93 mmole), N-CBZ-L-valine (1.76g, 7 mmole), HOBT (0.95g, 7 mmole) and DMAP (85.5mg, 0.7 mmole) was coevaporated two times with DMF and reduced to about 60ml. DCC (1.55g, 7.5 mmole) was added and the mixture was stiπed overnight at room temperature. The mixture was warmed for four hours at 60°C and then cooled to about 10°C. The mixture was filtered and the solution was reduced under reduced pressure. Ethyl acetate (150 ml) was added and the organic phase was washed twice with 5%> acetic acid, 5% sodium hydrogen carbonate and water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 1.6g. e) Synthesis of 2', 3'-dideoxy-3'-fluoro-5'-O-{3-[l,3-bis-(L-valyloxy)-2- propyloxycarbonylj-propanoyl } guanosine. A solution of 2',3'-dideoxy-3'-fluoro-5'-O-{3-[l,3-bis-(N-CBZ-L-valyloxy)-2- propyloxycarbonyl)propanoyl}guanosine(1.6g, 1.75 mmole) in 80ml ethyl acetate, 20ml methanol and 20 ml acetic acid was hydrogenated with palladium black (0.3g) for two hours at room temperature and normal pressure. The catalyst was filtered and washed with methanol. The solution was evaporated under reduced pressure and the 120 product was isolated as the diacetate salt by silica gel column chromatography.Yield: 1.02g 'H-NMR (DMSO d-6) 0.84 (m, 12H) 1.85(m, 2H) 2.58 (m, 4H) 2.60-3.10 (m, 2H) 3.11 (m, 2H) 3.61-4.39 (m, 7H) 5.19 (m, IH) 5.35-5.56 (m, lH) 6.16 (m, IH) 6.62 (s, 2H) 7.89 (s,lH) Example 4 2'. 3'-Dideoxy-3'-fluoro-5-O-F2-(-L-valyloxy)-propionyl]guanosine a) Synthesis of 2',3'-dideoxy-3'-fluoro-5-O-[2-(N-CBZ-L-valyloxy)- propionyljguanosine. A mixture of 2',3'-dideoxy-3'-fluoroguanosine (404mg, 1.5mmole), 2-(N-CBZ-L- valyloxy)-propionic acid (0.582g, 1.8 mmole), DMAP (22mg, 0.18 mmole) and HOBT (243mg, 1.8 mmole was coevaporated two times with DMF and reduced to about 30ml. DCC (412mg, 2.0 mmole) was added and the mixture was stiπed overnight at room temperature. The mixture was filtered and the solution was evaporated under reduced pressure. 100ml ethyl acetate was added and the organic phase was washed twice with 5% acetic acid, with 5% sodium hydrogen carbonate and with water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography.Yield: 0.72g b) Synthesis of 2 ' ,3 ' -dideoxy-3 ' -fluoro-5 -O-[2-(L-valyloxy)-propanoyl] guanosine A solution of 2',3'-dideoxy-3'-fluoro-5-O-[2-(N-CBZ-L-valyloxy)-ρropanoyl] guanosine (0.6g, 1.04 mmole) in 20ml ethyl acetate, 10ml methanol and 10ml acetic acid was hydrogenated with palladium black (O.lg) for two hours at room temperature and normal pressure. The catalyst was filtered and washed with methanol. The solution was evaporated under reduced pressure to yield the title compound as the acetate salt. Yield: 0.5g 'H-NMR (DMSO d-6) 0.88 (m, 6H) 1.40 (d, 3H) 1.92 (m, 4H) 2.52-3.04 (m, 2H) 3.18 (m, IH) 4.18-4.42 ( , 3H) 5.06 (m, IH) 5.32-5.58 (m, 2H) 6.18 (m, IH) 6.52 (s, 2H) 7.90 (s, IH) 121 Example 5 2'. 3'-Dideoxy-3'-fluoro-5 , -O-[2.3-bis-(L-valyloxy)propanoyl1guanosine a) 2', 3'-Dideoxy-3'-fluoro-5'-O- [2,3-bis-(N-CBZ-L- valyloxy)propanoyl]guanosine A mixture of 2', 3'-dideoxy-3'-fluoroguanosine (2.15g, 8 mmole), 2,3-bis-(N-CBZ- L-valyloxy)-propanoic acid (6.2g, 10.8 mmole), DMAP (244mg, 2 mmole) and HOBT (1.46g, 10.8 mmole) was coevaporated two times with DMF and reduced to about 120ml. DCC (2.48g, 12 mmole) was added and the mixture was stiπed for two days at room temperature. The mixture was filtered and the solution was evaporated under reduced pressure. 150ml ethyl acetate was added and the organic phase was washed twice with 5% acetic acid, with 5% sodium hydrogen carbonate and with water. The organic phase was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 2,25g = 35% 'H-NMR (DMSO d-6) 0.88 (m,12H) 2,12 (m, 2H) 2.50-3.00 (m, 2H) 3.88-4.14 (m, 2H) 4.22-4.62 (m, 6H) 5.04 (s, 4H) 5.30-5.61 (m, 2H) 6.16 (m, IH) 6.50 (s, 2H) 7.32 (m, 10H) 7.70 (m, 2H) 7.92 (s, IH) Example 6 Nl.N6-bt5 ((lS.2R -l-r2-(4-(L-valyloxy -butanoyloxy 1-indanvn-(2R.3R.4R.5R - 2.5-di(benzyloxyV3.4-dihvdroxyhexanediamide 122 a) Nl,N6-b«{(lS,2R)-l-[2-(4-(N-Boc-L-valyloxy)-butanoyloxy)]- indanyl}-(2R,3R,4R,5R)-2,5-di(benzyloxy)-3,4-dihydroxyhexanediamide. To Nl,N6-bis [(l S,2R)-l-(2-hydroxy)-indany]-(2R,3R,4R,5R)-2,5-di-(benzyloxy)- 3,4-dihydroxyhexanediamide from WO 98/45330 (326 mg, 0.5 mmole) and 4-(N- Boc-L-valyloxy)butyric acid (295 mg, 1 mmole) in dichloromethane (3 ml) were added 4-dimethylaminopyridine (12 mg, 0.1 mmole). The solution was cooled to -10° C and DCC (206 mg, 1 mmole) in dichloromethane (2 ml) was added dropwise over 2 hr. The reaction mixture was slowly warmed to room temperature, and kept for 18 hr. It was then filtered through Celite and poured into sodium bicarbonate aqueous solution. The organic phase was dried and the product was isolated with silica gel column chromatography. 103 mg. b) Nl ,N6-bis{ ( 1 S,2R)- 1 -[2-(4-(L-valyloxy)-butanoyloxy)]-indanyl} - (2R,3R,4R,5R)-2,5-di(benzyloxy)-3,4-dihydroxyhexanediamide. The intermediate of step a) (90 mg) was treated with trifluoroacetic acid (6 ml) at 0°C for 2 hr. The solution was dried and coevaporated with toluene and methanol successively, giving the titled product in quantitative yield. 'H-NMR (DMSO-d6 + D 2 O): 7.22 (m, 18H) 5.61 (m, 4H) 4.60-3.65 (m, 12H), 3.12 (dd, 4 H) 2.15 (m, 4H) 1.80 (m, 4H) 0.90 (m, 12 H). Example 7 Nl-((lS.2R -2-r4-(L-valyloxy butanoyloxyl-2.3-dihvdro-lH-l-indenyll-N6-r(lS -2- methyl-l-(methylcarbamovnpropyn-(2R.3R.4R.5R -2.5-dir4-(2-thiazolyl benzyl- oxy] -3-hvdroxy-4- 4-(L-valyloxy butanoyloxy]hexanediamide bts-trifluoroacetate. a) Nl-[(lS,2R)-2-Ηydroxy-2,3-dihydro-lH-l-indenyl]-N6-[(lS)-2- methyl-l-(methylcarbamoyl)propyl]-(2R,3R,4R,5R)-2,5-di[4-(2- thiazolyl)benzyloxy]-3,4-dihydroxyhexanediamide. A mixture of Nl-[(lS,2R)-2-hydroxy-2,3-dihydro-lH-l-indenyl]-N6-[(lS)-2-methyl- l-(methylcarbamoyl)propyl]-(2R,3R,4R,5R)-2,5-di(4-bromobenzyloxy)-3,4- dihydroxyhexanediamide, prepared analagously to Example 11 of WO98/45330 using 4-bromobenzyl (130 mg, 0.164 mmol), tributyl-2-thiazolyltin (554 mg, 1.47 123 mmol), PdCl 2 (PPh 3 ), (120 mg, 0.5 M suspension in DMF), and dry DMF (3 ml) was twice degassed and flushed with argon and then stiπed at 90°C/16h, evaporated to near dryness, washed with a little ether and purified by silica gel column chromatography (chloro form-methanol 20:1) to yield 95.5 mg (73 %) of off- white solid. b) Nl-{(lS,2R)-2-[4-(N-Boc-L-valyloxy)butanoyloxy]-2,3-dihydro-lH-l- indenyl}-Ν6-[(lS)-2-methyl-l-(methylcarbamoyl)propyl]-(2R,3R,4R,5R)-2,5-di[4- (2-thiazolyl)benzyloxy]-3-hydroxy-4-[4-(N-Boc-L-valyloxy)butanoyloxy] hexanediamide. To obtain the di-acylated derivative, a solution of the intermediate of step a) (49.5 mg, 0.062 mmol), 4-(L-valyloxy)butyric acid (100 mg, 0.33 mmol), dicyclohexylcarbodiimide (50 mg, 0.24 mmol), and 4-(N,N-dimethylamino)pyridine (10 mg, 0.082 mmol) in dichloromethane (1 ml) was kept at room temperature overnight. The precipitated dicyclohexylurea was filtered off and the solution evaporated to small volume and then purified by silica gel column chromatography (chloro form-hexane-methanol 20:10:1) to yield the title compound as a glass (71 mg, 84 %). c) Νl-{(lS,2R)-2-[4-(L-valyloxy)butanoyloxy]-2,3-dihydro-lH-l- indenyl}-N6-[(lS)-2-methyl-l-(methylcarbamoyl)propyl]-(2R,3R,4R,5R)-2,5-di[4- (2-thiazolyl)benzyloxy]-3-hydroxy-4-[4-(L-valyloxy)butanoyloxy]hexanediamide b/s-trifluoroacetate. The intermediate of step b) (71 mg, 0.0518 mmol) was dissolved in 1 ml of neat trifluoroacetic acid with cooling and kept at room temperature for lh. The solution was evaporated to small volume, lyophilized with dioxane, then with water containing 10 % of dioxane, to give 66.6 mg (92 %) of the title compound as off- white, light powder. 1 C NMR (CDC1 3 ; 62.9 MHz) δ 17.5, 18.0, 23.6, 30.0, 31.1, 58.5, 65.0, 71.2, 71.6, 119.1, 123.2, 124.0, 126.8, 128.2, 128.5, 128.8, 133.4, 137.9, 139.3, 143.5, 161.7, 168.8, 169.1, 171.3. 124 Example 8 Application of a trifunctional linker to an hydroxyl bearing Drug a) 6/18/20-O-mono-(6-(N-tritylvalyloxy)-5-(l-stearoyloxy methyl) hexanoyl) rifabutin Dried rifabutin (343 mg, 0.42 mmol) and 6-(N-tritylvalyloxy)-5-(l-stearoyloxy methyl) hexanoic acid (323 mg, 0.42 mmol) were dissolved together in dry dichloromethane (3.5 ml). Then dimethylaminopyridine (6 mg, 0.05 mmol) and dicyclohexylcarbodiimide (93 mg, 0.45 mmol) were added and the reaction mixture was stiπed for 24 h at 20° C. The mixture was filtered and extracted with 5% aqueous sodium bicarbonate and dichloromethane three times. The residue obtained by evaporation of the organic phase was chromatographed on silica gel and the product was eluted with 0%— »2%>EtOH / dichloromethane. (Yield 316 mg). R f (5%MeOH / CHC1 3 ): 0.75. b) 6/18/20-O-mono-(6-(valyloxy)-5-(l-stearoyloxy methyl) hexanoyl) rifabutin. The product from step a) (316 mg, 0.2 mmol) was dissolved in dioxane (2 ml) and then 80% acetic acid (20 ml) was added and the solution was stiπed for 5 min at 20° C. The solution was evaporated and coevaporated with dioxane two times and toluene one time. The residue was chromatographed on silica gel and the product was eluted with 0%→5%EtOH / dichloromethane. (Yield 230 mg). R f (5%MeOH / CHC1 3 ): 0.50. 'H-NMR (CHCI 3 ): 8.35 (br, IH); 7.77 (s, IH); 6.42 (d,d, IH); 6.12 (m, 2H); 5.91 (d,d, IH); 5.12 (d, IH); 5.07 (d,d, IH); 4.94 (d, IH); 4.18-3.96(m, 4H); 3.46 (d, IH); 3.31 (d,d, IH); 3.05 (s, 3H); 2.98 (m, 2H); 2.86 (d,d, IH); 2.65 (m, 2H); 2.48 (q, IH); 2.38-2.32 (m, 5H); 2.30 (s, 3H); ); 2.13 (t, 2H); 2.05 (s, 3H); 2.01 (s, 3H); 2.00 (m, 2H); 1.85-1.73 (m, 11H); 1.78 (s, 3H); 1.68-1.50 (m, 5H); 1.25 (m, 28H); 1.15 (m, 2H); 1.05-0.85 (m, 21H); 0.47 (d, 3H); -0.18 (d, 3H). Example 9 Application of a trifunctional linker to an alternative hvdroxy Drug 125 a) Preparation of dibenzyl ester of l,3-bis-(2-carboxychromon-5-yloxy)propan-2-ol. l,3-bis(2-carboxychromon-5-yloxy)-propan-2-ol disodium salt (2.5g, 5.2 mmol), was suspended in DMF. To the suspension was added benzyl bromide (0.734 ml, 6.2 mmol) and the reaction was kept overnight under stirring. An additional portion of benzyl bromide (0.734 ml, 6.2 mmol) was added. After 24 hr, the reaction mixture was poured into sodium hydrogen carbonate aqueous solution and extracted dichloromethane. The organic phase was washed with water two times and evaporated to give the dibenzyl ester of l,3-bis-(2-carboxychromon-5-yloxy)propan- 2-ol (1.72 g). b) Preparation of the dibenzyl ester of 2-[5-( N-trityl-L-valyloxymethyl)-6- stearoyloxyhexanoyloxy]-l,3-bis-(2-carboxychromon-5-yloxy)propane. To a solution of the dibenzyl ester of l,3-bis-(2-carboxychromon-5-yloxy)propan-2- ol (270 mg, 0.42 mmole), 5-(N-Trityl-L-valyloxymethyl)-6-stearoyloxyhexanoic acid (323 mg, 0.42 mmol) and dimethylaminopyridine (6 mg, 0.05 mmol) in dichloromethane was added DCC (92 mg, 0.45 mmol). After 3 days, the reaction mixture was filtered through Celite and the filtrate was washed with sodium hydrogen carbonate aqueous solution and dried. The product dibenzyl ester of 2-[5- (N-trityl-L-valyloxymethyl)-6-stearoyloxyhexanoyloxy]- 1 ,3-bis-(2-carboxychromon- 5-yloxy)propane was isolated from silica gel column chromatography. 250 mg. c) Preparation of 2-[5-(L-valyloxymethyl)-6-stearoyloxyhexanoyloxy]-l,3-bis-(2- carboxychromon-5-yloxy)propane. Dibenzyl ester of 2-[5-( N-trityl-L-valyloxymethyl)-6-stearoyloxyhexanoyloxy]-l,3- bis-(2-carboxychromon-5-yloxy)propane (238 mg, (0.17 mmol) was dissolved in ethyl acetate (1.5 ml). To the solution was added 80 % acetic acid (10 ml). After two hr, the solution was evaporated and purified by column chromatography to yield 197 mg of 2-[5-(L-valyloxymethyl)-6-stearoyloxyhexanoyloxy]-l,3-bis-(2- carboxychromon-5-yloxy)propane. d) Preparation of 2-[5-(L-valyloxymethyl)-6-stearoyloxy-hexanoyloxy]-l,3-bis-(2- carboxychromon-5-yloxy)propane. 126 2-[5-(L-valyloxymethyl)-6-stearoyloxyhexanoyloxy]-l,3-bis-(2-carboxychromon-5- yloxy)propane (190 mg, 0.16 mmole) was dissolved in a mixed solvent of methanol (6 ml), ethyl acetate (2 ml) and acetic acid (0.5 ml) and hydrogenated on palladium black (30 mg) for 1 hr. After filtration, the solution was dried and coevaporated with toluene giving 160 mg titled product. 'H-NMR ( DMSO δ-6): 7.77 (t, 2 H), 7.27 (d, 2 H), 7.12 (d, 2 H), 6.68 (s, 2H), 5.60 (m, IH), 4.60 (m, 4H), 4.05 (m, 5H), 2.50-2.10 (m, 6H), 1.90-1.50 (m, 6H), 1.26 (m, 28H), 0.93 (m, 9H). 10 Example 10 1 -[(1 ,3-bis(L-valyloxy)-2-propoxy)carbonyloxy]ethyl (7R)-3-acetoxymethyl-7-|YZ)- 2-(2-aminothiazol-4-yl -2-(methoxyimino)acetamido1-3-cephem-4-carboxylate 15 (a) a) 1 -[( 1 ,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propoxy)carbonyloxy]ethyl (7R)-3-acetoxymethyl-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(methoxyimino)acetamido]- 3-cephem-4-carboxylate (b) 20 A solution of l,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propyl 1-iodoethyl carbonate (0.156 mmol) and cefotaxime sodium (67.8 mg, 0.142 mmol) in 3.2 mL dry NN'-dimethylformamide was stiπed under argon for 22 h. The reaction mixture was concentrated and subjected to column chromatography (silica, 2/1 petroleum 127 ether - ethyl acetate, and then 20/1 CH 2 C1 2 - methanol) to yield an oil enriched in the desired product. The oil was dissolved in 10 mL ethyl acetate, washed with water, dried, and concentrated. A second chromatography (silica, 40/1 CH 2 C1 2 - methanol) gave the title compound (59.7 mg) as cream-colored solids. 5 (c) b) l-[(l,3-bis(L-valyloxy)-2-propoxy)carbonyloxy]ethyl (7R)-3-acetoxymethyl- 7-[(Z)-2-(2-aminothiazol-4-yl)-2-(methoxyimino)acetamido]-3-cephem-4- carboxylate. (d) A solution of the Boc-protected cefotaxime ester (247 mg) prepared as in step (a) was 10 dissolved in 1.5 mL CH 2 C1 2 and 1.5 mL CF 3 COOH. After 7 min, the solvent was removed under vacuum to give fine, light yellow solids of the title compound as the trifluoroacetate salt. 'H NMR (250 MHz, DMSO-d 6 ) δ 0.94-1.04 (m, 12H), 1.53 (d, 3H, J= 5.4 Hz), 2.07 and 2.08 (2s, 3H total), 2.19 (m, 2H), 3.57-3.77 (m, 2H), 3.92 (s, 3H), 4.03 (br s, 15 2H), 4.37-4.68 (m, 4H), 4.72-4.97 (ABq, 2H), 5.18-5.27 (br, IH), 5.23 (d, 1H, J= 4.9 Hz), 5.88 (m, IH), 6.80-6.95 (m, 2H), 8.50 (br s), 9.74 and 9.79 (2d, IH total, J= 8.1 Hz). Example 11 20 1 -[(1.3-bis(L-valyloxy)-2-propoxy)carbonyloxy]ethyl (Z)-7-| " 2-f2-aminothiazol-4-ylV 2-methoxyiminoacetamido]-3-cephem-4-carboxylate H ? H 9 N- H ' i \ N O r O\ / ° ( O O H 2 N a) 1 -[( 1 ,3-bis(N-tert-butoxycarbonyl-L-valyloxy)-2-propoxy)carbonyloxy]ethyl (Z)-7-[2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido]-3-cephem-4-carboxylate 128 A mixture of ceftizoxime sodium (550 mg, 1.36 mmol) and l,3-bis(N-tert- butoxycarbonyl-L-valyloxy)-2-propyl 1-iodoethyl carbonate (1.5 mmol) in 27 mL dry DMF was stiπed under nitrogen for 3 h. DMF was removed under vacuum and the residue was partitioned between ethyl acetate and water. The organic phase was washed successively with 5% Νa^^ and brine, stiπed with anhydrous Νa 2 SO 4 and activated carbon for 15 min, filtered through celite, and concentrated. Silica gel column chromatography (2/1 petroleum ether - ethyl acetate, 20/1 CH 2 C1 2 - methanol) yielded fractions enriched in the desired product. A second column chromatography (silica, 40/1 CH 2 C1 2 - methanol) gave the title compound (410 mg). b) l-[(l,3-bis(L-valyloxy)-2-propoxy)carbonyloxy]ethyl (Z)-7-[2-(2- aminothiazol-4-yl)-2-methoxyiminoacetamido]-3-cephem-4-carboxylate. The Boc-protected ceftizoxime ester (347 mg) from step (a) was dissolved in 2.5 mL CH 2 C1 2 and 2.5 mL CF 3 COOH. After 15 min, the solvent was removed under vacuum to give fine light yellow solids of the title compound as the trifluoroacetate salt. 'H NMR (250 MHz, DMSO-d 6 ) δ 0.95-1.04 (m, 12H), 1.54 (d, 3H, J= 5.4 Hz), 2.20 (m, 2H), 3.64-3.66 (m, 2H), 3.88 (s, 3H), 3.97 (br s, 2H), 4.37-4.66 (m, 4H), 5.15- 5.20 (m, 2H), 5.87 (dd, IH, J= 8.1, 5.0 Hz), 6.67 (m, IH), 6.78 (s, IH), 6.82 (q, IH), 8.46 (br s), 9.54 and 9.55 (2d, IH total, J= 8 Hz) Example 12 (IS. 2SVN-lc/ -2-[6-fluoro-2-(L-isoleucyloxymethyloxy -3-propionylphenyl1 cvclopropyl}-N'-[2-(5-cyanopyridvD]urea a) (IS, 2S)-N-{c/5-2-[6-fluoro-2-(N-BOC-L-isoleucyloxymethyloxy)-3- propionylphenyl] cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea. To a solution of (IS, 2S)-N-{cw-2-[6-fluoro-2-hydroxy-3-propionylphenyl] cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea prepared as shown in PCT/SE99/00053 (2.03 g, 5.5 mmol) in THF (50 mL) at 20 °C, was added NaH (60%, 220 mg, 5.5 mmol). After the mixture was stiπed 1.5h at 20 °C, N-BOC-L-isoleucine iodomethyl ester (16.5 g, 16.5 mmol) was added. The solution was stiπed for 6h at room temperature and then concentrated under reduced pressure. The crude product was 129 column chromatographed (aluminium oxide 90, 1% MeOH in CH 2 C1 2 ), to give 1.76 g of the title product. b) (IS, 2S)-N-{cώ-2-[6-fluoro-2-(L-isoleucyloxymethyloxy)-3- propionylphenyl] cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea . To TFA (30 mL) at 0 °C, was added (IS, 2S)-N-{cw-2-[6-fluoro-2-(N-BOC-L- isoleucyloxymethyloxy)-3-propionylphenyl] cyclopropyl}-N'-[2-(5- cyanopyridyl)]urea(1.81 g, 2.96 mmol). The reaction mixture was stiπed at 0 °C for 30 min and then concentrated under reduced pressure at 0 °C. The crude product was column chromatographed (silica gel, 10% MeOH in CH 2 C1 2 ), to give 1.48 g of the title compound as the TFA-salt. 'H-NMR (CDC1 3 ): 9.50 (br s, IH), 9.42 (br s, IH), 8.34 (s, IH), 7.73 (dd, IH), 7.27 (m, IH), 7.10 (d, IH), 6.81 (dd, IH), 6.16 (d, IH), 5.73 (d, IH), 3.87 (d, IH), 3.39 (m, IH), 3.05-2.68 (m, 2H), 2.29 (dd, IH), 2.10-1.88 (m, 2H), 1.57-1.21 (m, 3H), 1.09 (t, 3H), 1.02 (d, 3H), 0.91 (t, 3H). Example 13 (IS. 2S)-N-{CM-2 [6 -fluoro-2-( L-valyloxymethyloxy -3-propionylphenyr)1 cvclopropyl|-N'-[2-(5-cvanopyridyr)]urea a) (IS, 2S)-N-{cw-2-[6-fluoro-2-(N-CBz-L-valyloxymethyloxy)-3- propionylphenyl)]cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea To a solution of (IS, 2S)-N-{ct5-2-[6 -fluoro-2-hydroxy-3- propionylphenyl]cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea (368 mg, 1 mmole ) in THF (5 ml) was added sodium hydride in paraffin (60 %>, 38 mg, 0.95 mmole). After 1.5 hour, N-CBz-L-valyloxymethyl iodide (1.09g, 2.8 mmole) prepared analogously to the N-BOC-L-isoleucyloxymethyl iodide described above was added to the solution and reaction was kept 18 hours. The mixture was filtered through Celite and poured into sodium hydrogen carbonate aqueous solution, and extracted with methylene chloride. The organic phase was dried and the product was isolated with silica gel column chromatography to yield 210 mg. 130 b) (IS, 2S)-N-{c«-2-[-fluoro-2-(L-valyloxymethyloxy)-3- propionylphenyl)]cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea (I S, 2S)-N-{ -2-[6-fluoro-2-(N-CBz-L-valyloxymethyloxy)-3- propionylphenyl)]cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea (200 mg, 0.32 mmole) was dissolved in a mixed solvent of methanol (5 ml), ethylacetate (2 ml) and acetic acid (1 ml). To the solution was added palladium black (35 mg). It was kept under hydrogen at atmospheric pressure for two hours. After filtration, the solution was evaporated and the product was purified by silica gel column chromatography yielding 66 mg. 'H-NMR (CDCl j ) 8.20 (d, IH), 7.73 (dd, IH), 7.44 (dd, IH), 6.94 (m, 2H), 5.80 (dd, 2H), 3.37 (IH), 2.88 (m, 2H), 2.10 (m, 2H), 1.60 (m, IH), 1.46 (m, IH), 1.08 (t, 3H), 0.94 (m, 6H). Example 14 (IS. 2S -N-{ctj*-2 [6 -fluoro-2-(2.2-dimethyl-3-(L-valyloxy)-propionyloxy- methyloxy)-3-propionylphenyl]-cyclopropyll-N'-[2-( , 5-cyanopyridvD] urea a) (IS, 2S)-N-{c/5-2-[6-fluoro-2-(2,2-dimethyl-3-(N-Boc-L- valyloxy)propionyloxymethyloxy)-3-propionylphenyl]cyclopropyl}-N'-[2-(5- cyanopyridyl)]urea To a solution of (IS, 2S)-N-[cis-2-(6 -fluoro-2-hydroxy-3-propionylphenyl) cyclopropyl]-N'-[2-(5-cyanopyridyl)] urea (368 mg, 1 mmole) in THF (5 ml) was added sodium hydride in paraffin (60 %, 38 mg, 0.95 mmole). After one hour, 2,2- dimethyl-3-(N-Boc-L-valyloxy)propionic acid iodomethyl ester (1.35g, 3 mmole) was added to the solution. After 5 hr at room temperature, it was then raised to 50 °C and reaction was kept 18 hours. The reaction mixture was poured into sodium hydrogen carbonate aqueous solution and extracted with methylene chloride. The organic phase was dried and the product was isolated with alumina column chromatography. 140 mg. b) (IS, 2S)-N-{c/s-2-[6-fluoro-2-(2,2-dimethyl-3-(L-valyloxy)propionyl- oxymethyloxy)-3-propionylphenyl]-cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea 131 (lS, 2S)-N-{cw-2-[6-fluoro-2-(2,2-dimethyl-3-(N-Boc-L-valyloxy)- propionyloxymethyloxy)-3-propionylphenyl)] cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea (120 mg) was treated with trifluoroacetic acid at 0° C for 20 min. The solution was evaporated and coevaporated with toluene and methanol succesively, giving the titled product in quantitative yield. 'H-NMR (CDC1 3 ): 8.33 (d, IH) 7.89 (d, IH) 7.48 (t, IH) 7.16 (m, IH) 6.96 (t, IH) 5.70 (dd, 2H) 4.18 (dd, 2H) 4.01 (m, IH) 3.38 (m, IH) 2.88 (m, 2H) 2.16 (m, IH) 1.58 (m, 2H) 1.25 (d, 6H) 1.04 (m, 9H). Example 15 (IS. 2SVN- 1 cis-2-\6 -fluoro-2-(3 ,3-bis-(L-valyloxymethyl propionyloxymethyloxy) -3-propionylphenyllcvclopropyll-N'-[2-(5-cvanopyridyl ]urea a) (IS, 2S)-N-{cts-2-[6-fluoro-2-(3,3-bis ( N-CBz-L-valyloxymethyl) propionyloxymethyloxy)-3-propionylphenyl)]cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea To a solution of (IS, 2S)-N-{cώ-2-[6-fluoro-2-hydroxy-3-propionylphenyl] cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea (331 mg, 1 mmole) in THF (5 ml) was added sodium hydride in paraffin (60 %, 32 mg, 0.81 mmole). After one hour, 3,3- bis-(N-CBz-L-valyloxymethyl) propionic acid iodomethyl ester (1.3g, 1.8 mmole) was added to the solution. After 5 hr at room temperature, it was then raised to 50 °C and reaction was kept 18 hours. The mixture was poured into sodium hydrogen carbonate aqueous solution, and extracted with methylene chloride. The organic phase was dried and the product was isolated with alumina column chromatography. 185 mg. b) (IS, 2S)-N-{cw-2-[6 -fluoro-2-( 3,3-bis (L-valyloxymethyl) propionyloxy- methyloxy)-3-propionylphenyl]cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea (I S, 2S)-N-{ -2-[6-fluoro-2-(3,3-bis ( N-CBz-L-valyloxymethyl) propionyloxymethyloxy )-3-propionylphenyl]cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea (170 mg, 0.17 mmole) was dissolved in a mixed solvent of methanol (5 ml), ethyl acetate (2 ml) and acetic acid (1 ml). To the solution was added palladium 132 black (30 mg). It was kept under hydrogen at atmospheric pressure for four hours. After filtration, the solution was evaporated and the product was purified by silica gel column chromatography. 80 mg. 'H-NMR (DMSO-d6): 8.38 (d, IH) 8.02 (d, IH) 7.42 (m, 2H) 7.12 (t, IH ) 5.70 (dd, 2H) 4.00 (s, 4H) 3.16 (m, IH) 3.08 (d, 2H) 2.80 (m, IH) 2.40 (m, 2H), 2.11 (m, IH) 1.52 (m, IH) 0.95 (t, 3H) 0.98 (dd, 12 H). Example 16 (IS. 2S -N-lc/ -2-[6-fluoro-2-(2-(L-valyloxy -ethoxycarbonyloxymethyloxy -3- propionylphenyl ]cyclopropyl } -N '- [2-(5 -cvanopyridvD] urea a) (IS, 2S)-N-{c/s-2-[6-fluoro-2-(2-(N-CBz-L-valyloxy)- ethoxycarbonyloxymethyloxy)-3-propionylphenyl)]cyclopropyl}-N'-[2-(5- cyanopyridyl)] urea To a solution of (IS, 2S)-N-{cts-2 [6-fluoro-2-hydroxy-3-propionylphenyl] cyclopropyl}-N'-[2-(5-cyanopyridyl)]urea (368 mg, 1 mmole) in THF (5 ml) was added sodium hydride in paraffin (60 %, 38 mg, 0.95 mmole). After 1.5 hr, 2- (N- CBz-L-valyloxy)ethoxycarbonyloxymethyl iodide (864 mg, 1.7 mmole) was added to the solution. The reaction was kept for 48 hours. The mixture was poured into sodium hydrogen carbonate aqueous solution, and extracted with methylene chloride. The organic phase was dried and the product was isolated with silica gel column chromatography. 210 mg. 'H-NMR (CDC1 3 ): 8.21 (d, IH) 7.72 (d, IH) 7.28 (m, 6H) 6.90 (m, 2H) 5.75 (dd, 2H) 5.09 (s, 2H) 4.35 (m, 4H) 2.85 (m, 2H) 2.50 (m, 2H) 2.16 (m, IH), 1.65 (m, IH) l.l l (t, 3H) 0.93 (dd, 6 H). b) IS, 2S)-N-{c/s-2-[6-fluoro-2-(2-(L-valyloxy)-ethoxycarbonyloxymethyloxy)- 3-propionylphenyl)]cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea. (IS, 2S)-N-{ -2-[6-fluoro-2-(2-(N-CBz-L-valyloxy)-ethoxycarbonyloxymethyl oxy)-3-propionylphenyl)]cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea is deprotected by conventional techniques such as palladium black in a mixed solvent of methanol, ethyl acetate and acetic acid under hydrogen at atmospheric pressure followed by 133 conventional work up such as filtration, evaporation and silica gel column chromatorgraphy. Example 17 (lS.2S)-N-[c^-2-(6-fluoro-2-(1.3-bis-L-valyloxy-2-(propoxycarbonyloxymethyloxy - 3-propionylphenyl)cvclopropyl]-N'-[2-(5-cvanopyridyl)]urea a) (lS,2S)-N-[c/s-2-(6-fluoro-2-(l,3-bis-(N-BOC-L-valyloxy-2- (propoxycarbonyloxymethyloxy)-3-propionylphenyl)cyclopropyl]-N'-[2-(5- cyanopyridyl)]urea. NaH (121 mg, 60% w/w in mineral oil, 3.0 mmol) was added to a mixture of (1S,2S)- N- [c/s-2-(6-fluoro-2-hydroxy-3 -propionylphenyl)cyclopropyl] -N ' - [2-(5 - cyanopyridyl)]urea (1.05 g, 2.85 mmol) in 15 mL dry THF under N 2 . After 1 h, the solution was concentrated to dryness and redissolved in 10 mL DMF. 2-O- iodomethoxycarbonyl-l,3-di-O-(N-tert-butoxycarbonyl-L-valyl)glycerol (2.96 g, 4.39 mmol) in 15 mL DMF was added and the reaction mixture was stiπed for 20 h. Removal of solvent under vacuum followed by flash column chromatography (silica gel, 2/1 ethyl acetate - petroleum ether) gave 1.46 g (56%) of the title product as a white solid. b) (lS,2S)-Ν-[cώ-2-(6-fluoro-2-(l,3-bis-L-valyloxy-2- (propoxycarbonyloxymethyloxy)-3-propionylphenyl)cyclopropyl]-N'-[2-(5- cyanopyridyl)]urea. Ice-cold trifluoroacetic acid (30 mL) was added to the intermediate of step a (1.69 g, 1.85 mmol) in an ice bath, under N 2 . After 7 min, the reaction mixture was concentrated under vacuum, coevaporating several times with, initially, toluene and, finally, CH 2 C1 2 . The oily residue was chromatographed immediately on a silica gel column with 10-20 % methanol in CH 2 C1 2 to give 1.37 g of the product as a trifluoroacetate salt. 'H NMR (250 MHz, CD 3 OD) δ 1.07-1.12 (m, 15H), 1.26 (m, IH), 1.63 (m, IH), 2.19 (m, IH), 2.35 (m, 2H), 2.89 (m, 2H), 4.08 (m, 2H), 4.44-4.71 (m, 4H), 5.26 (m, IH), 5.79 and 5.91 (AB q, 2H), 7.10-7.18 (m, 2H), 7.59 (dd, IH), 7.93 (dd, IH), 8.30 (d, 1H).* 9 F NMR (235 MHz, CD 3 OD) δ -103.5, -73.5. 134 Example 18 (lS.2S)-N- c/^-2-(6-fluoro-2-(L-valyloxy)methoxycarbonyloxy-3- propionylphenvDcvclopropyl]-N'-[2-(5-cvanopyridyl) ~ ]urea a) (lS,2S)-N-[cώ-2-(6-fluoro-2-chloromethoxycarbonyloxy-3- ρropionylphenyl)cyclopropyl]-N'-[2-(5-cyanopyridyl)]urea Chloromethyl chloroformate (2.3 mL, 25 mmol) was added by syringe to a mixture of ( 1 S,2S)-N- [c/s-2-(6-fluoro-2-hydroxy-3 -propionylphenyl)cyclopropyl] -N ' - [2-(5 - cyanopyridyl)]urea (4.695 g, 12.7 mmol) and pyridine (6.1 mL, 76 mmol) in 65 mL dry CH 2 C1 2 with cooling in an ice bath, under N 2 . After 10 min, the ice bath was removed and the mixture was stiπed at room temperature for lh 40 min. The mixture was diluted with 100 mL CH 2 C1 2 and washed with 50 mL H 2 O. The aqueous phase was reextracted with 25 mL CH,C1 2 . The combined organic phases were washed with 50 mL saturated NaHCO 3 , followed by 2 x 50 mL brine. Drying over Na 2 SO 4 and concentration under vacuum gave a crude material that was subjected to flash column chromatography (silica gel, 1/1 ethyl acetate - petroleum ether) to give 4.05 g (69%>) title product. 'H NMR (250 MHz, CDC1 3 ) δ 1.15 (t, 3H), 1.30 (m, IH), 1.59 (m, IH), 2.02 (m, IH), 2.87 (q, 2H), 3.29 (m, IH), 5.87 (s, 2H), 6.97 (d, IH), 7.09 (m, IH), 7.72 (dd, IH), 7.76 (dd, IH), 8.10 (dd, IH), 9.26 (br s, IH), 10.09 (brs, IH). b) (1 S,2S)-N-[cw-2-(6-fluoro-2-iodomethoxycarbonyloxy-3- propionylphenyl)cyclopropyl]-N'-[2-(5-cyanopyridyl)]urea (lS,2S)-N-[ct5-2-(6-fluoro-2-chloromethoxycarbonyloxy-3-propionylphenyl) cyclopropyl]-N'-[2-(5-cyanopyridyl)]urea (3.97 g, 8.6 mmol) and Nal (5.17 g, 34.5 mmol) in 85 mL dry acetonitrile were refluxed at 70 °C for 4 h under N 2 . The solvent was removed in vacuo, the residue was partitioned between 100 mL CH 2 C1 2 and 25 mL H 2 O, the aqueous phase was reextracted with 10 mL CH 2 C1 2 , and the organic phases were combined, washed successively with 2 x 25 mL 5%> Na^O-, and 2 x 25 mL brine, and dried over Na^O^ Flash column chromatography (silica gel, 2/1 ethyl acetate - petroleum ether) of the crude product obtained after concentration in vacuo gave 4.15 g material containing 92% of the title compound and traces of the starting material. 135 'H NMR (250 MHz, CDC1 3 ) δ 1.18 (t, 3H), 1.34 (m, IH), 1.62 (m, lH), 2.03 (m, IH), 2.86 (q, 2H), 3.32 (m, IH), 6.08 (s, 2H), 6.97 (d, IH), 7.08 (m, IH), 7.70-7.76 (m, 2H), 8.13 (d, IH), 8.90 (br s, IH), 9.30 (br s, IH). c) (lS,2S)-N-[ -2-(6-fluoro-2-(N-BOC-L- valyloxy)methoxycarbonyloxy-3-ρropionylphenyl)cyclopropyl]-N'-[2-(5- cyanopyridyl)]urea Tetrabutylammonium hydroxide (40 wt %> solution in water, 6.4 mL, 9.8 mmol) was added to Boc-L-valine (2.54 g, 11.7 mmol) in 30 mL dioxane. The solution was concentrated in vacuo, coevaporating several times with dioxane, toluene, and CH 2 C1 2 , and dried under vacuum overnight. The resulting Q salt was dissolved in 30 mL dry CH 2 C1 2 and (lS,2S)-N-[c/s-2-(6-fluoro-2-(iodomefhoxycarbonyloxy)-3- propionylphenyl)cyclopropyl]-N'-[2-(5-cyanopyridyl)]urea (7.1 mmol) in 65 mL dry CH 2 C1 2 was added. After stirring under N 2 for 18 h, the reaction mixture was washed with 3 x 50 mL H 2 O, 1 x 50 mL 5% Na^A, and 2 x 50 mL H 2 O. The organic phase was dried over Na^O^ concentrated, and submitted to flash column chromatography (silica gel, 3/1 ethyl acetate - petroleum ether) to give 2.21 g (49%) product. 'H NMR (250 MHz, CD 3 OD) δ 0.98 (d, 3H), 1.02 (d, 3H), 1.17 (t, 3H), 1.24 (m, IH), 1.47 (s, 9H), 1.59 (m, IH), 2.06 (m, IH), 2.24 (m, IH), 2.96 (q, 2H), 3.24 (m. IH), 4.15 (d, IH), 5.94 and 6.02 (AB q, 2H), 7.12 (d, IH), 7.26 (m, IH), 7.91 (dd, IH), 7.94 (dd, IH), 8.23 (dd, IH). d) (lS,2S)-N-[cw-2-(6-fluoro-2-(L-valyloxy)methoxycarbonyloxy-3- propionylpheny l)cyclopropyl]-N ' - [2-(5 -cyanopyridyl)]urea Cold trifluoroacetic acid (40 mL) was added to (lS,2S)-N-[c«-2-(6-fluoro-2-(N- BOC-L-valyloxymethoxycarbonyloxy)-3-propionylphenyl)cyclopropyl]-N'-[2-(5- cyanopyridyl)]urea (1.94 g, 3.02 mmol) with cooling in an ice bath, under N 2 . After 5 min, the solution was concentrated in vacuo, coevaporating several times with toluene, and then CH 2 C1 2 , and dried under vacuum for several hours to give the compound as a trifluoroacetate salt in quantitative yield. 136 Η NMR (250 MHz, CD 3 OD) δ 1.12-1.18 (m, 9H), 1.25 (m, IH), 1.59 (m, IH), 2.07 (m, IH), 2.47 (m, IH), 2.97 (q, 2H), 3.26 (m, IH), 4.16 (d, IH), 6.01 and 6.37 (AB q, 2H), 7.1 1 (d, IH), 7.29 (m,lH), 7.92 (dd, IH), 7.99 (dd, IH), 8.22 (d, IH). 19 F NMR (235 MHz, CD 3 OD) δ -102.7, -74.0. Example 20 (IS. 2S )-N-{c/s-2 [6 -fluoro-2-(3-carboxylpropionyloxymethyloxy V3- propionylphenyl]cyclopropyll-N'-[2-(5-cyanopyridyl urea a) (IS, 2S)-N-{cis-2-[6 -fluoro-2-(3 -benzyloxycarbonylpropionyl- oxymethyloxy)-3-propionylphenyl]cyclopropyl}-N ' -[2-(5-cyanopyridyl)]urea. 3-Benzyloxycarbonylpropionic acid iodomethyl ester (522 mg, 1.5 mmole) was added to a solution of (IS, 2S)-N-{cώ-2-[6 -fluoro-2-hydroxy-3-propionylphenyl] cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea (185 mg, 0.5 mmole) in THF (5 ml) which had been treated with sodium hydride in paraffin (60 %, 20 mg, 0.5 mmole) for 30 min. After 18 hr at room temperature, the reaction mixture was poured into sodium hydrogen carbonate aqueous solution, and extracted with methylene chloride. The organic phase was dried and the product was isolated with alumina column chromatography. 115 mg. b) (IS, 2S)-N-{c/5-2-[6-fluoro-2-(3-carboxylpropionyloxymethyloxy)-3- propionylphenyl]cyclopropyl}-N'-[2-(5-cyanopyridyl)] urea (IS, 2S)-N-{cw-2-[6-fluoro-2-(3-carboxylpropionyloxymethyloxy)-3- propionylphenyl)]cyclopropyl}-N'-[2-(5cyanopyridyl)] urea (100 mg, 0.17 mmole) was dissolved in a mixed solvent of ethylacetate (3 ml) and acetic acid (1 ml). To the solution was added palladium black (30 mg). It was kept under hydrogen at atmospheric pressure for three hours. After filtration, the solution was evaporated and the product was purified by silica gel column chromatography. 81 mg. 'H-NMR (CDC1 3 ): 8.21 (s, IH) 7.75 (d, IH) 7.49 (dd, IH) 7.08 (d, 5H) 6.97 (t, IH) 5.73 (dd, 2H) 5.17 (s, 2H) 3,26 (m, IH) 2.87 (m, 2H) 2.60 (m, 4H) 2.09 (m, IH) 1.58 (m, IH) 1.11 (t, 3H) 137 Example 21 (I S. 2S)-N-[c/s-2-(6-fluoro-2-O-f4-L-valyloxybenzoylV3propionylphenyl)- cvclopropyl " |-N'-(5-cyanopyrid-2-yl) urea a) 4-benzyloxybenzoic acid. To a solution of 4-hydroxybenzoic acid (6.9g, 50 mmole) in 150 ml DMF was added potassium tert. -butoxide (12.34g, 110 mmole) and the mixture was stiπed at room temperature for one hour. Benzyl bromide (20.5g, 120 mmole) was added and the mixture was stiπed for two days at room temperature. The mixture was evaporated under reduced pressure and 100ml 1,4-dioxane and a solution of sodium hydroxide (6.0g, 150 mmole)in 50 ml water was added. The mixture was refluxed for two hours, cooled and evaporated under reduced pressure. Water was added and the mixture was acidified with acetic acid. The product was filtered, washed with cold water and dried. Yield: 10.2g = 89%. b) 4-benzyloxybenzoyl chloride. To a mixture of 4-benzyloxybenzoic acid (2.28g, 10 mmole) in 20 ml dried dichloromethane were added five drops of DMF and 2.5 ml thionyl chloride. The mixture was refluxed for three hours and evaporated under reduced pressure. Yield: 2.45g = 100% c) (IS, 2H)-N-[cw-2-(6-fluoro-2-O-(4-benzyloxybenzoyl)-3- propionylphenyl)cyclopropyl]-N'-[2-(5-cyanopyrid-2-yl) urea . To a solution of (IS, 2S)-N-[cts-2-(6-fluoro-2-hydroxy-3-propionylphenyl) cyclopropyl]-N'-(5-cyanopyrid-2-yl) urea (184mg, 0.5 mmole) in 3 ml DMF was added potassium tert. butoxide (78.5mg, 0.7 mmole) and the mixture was stiπed for one hour at room temperature. A solution of 4-benzyloxybenzoylchloride (185mg, 0.75 mmole) in 1ml DMF was added and the mixture was stiπed overnight at room temperature. 40 ml ethyl acetate were added and the organic phase was washed four times with water. The solution was dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 180mg = 62%. 138 d) (I S, 2S)-N-[cw-2-(6-fluoro-2-O (4-hydroxybenzoyl)-3- propionylphenyl) cyclopropyl]-N'-(5-cyanopyrid-2-yl)] urea-O-4-hydroxybenzoate A solution of the intermediate of step c) (170 mg, 0.29 mmole) in 15 ml ethyl acetate and 15 ml methanol was hydrogenated with 10% palladium on charcoal (30mg) three times at room temperature and normal pressure. The catalyst was filtered and washed with ethyl acetate and methanol and the solution was evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 100 mg = 70%. 'H-NMR (DMSO δ-6) 0.93 (m, 4H) 1.32 (m, IH) 1.88 (m,lH) 2.85 (m, 2H) 3.05 (m, IH) 6.92 (m, 2H) 7.38 (m, 2H) 8.00 (m, 4H) 8.38 (m, IH) e) (IS, 2S)-N-[ciϊ-2-(6-fluoro-2-O (4-L-valyloxybenzoyl)-3- propionylphenyl)-cyclopropyl]-N'-(5-cyanopyrid-2-yl) urea. An R 2 group, such as N-protected L-valyl is acylated to the exposed ring hydroxy group using conventional acylation conditions as described herein and deprotected to yield a compound of the invention. Example 22 (IS. 2SyN-[ -2-(6-fluoro-2-O ((4-isoleucyloxybenzoyloxymethylV3- propionylphenyl -cvclopropyll-N'-f2-(5-cvanopyridvD1urea-O-methylene-4- hvdroxybenzoate-O-L-isoleucyl ester a) Methyl-4-(4-methoxybenzyloxy) benzoate. To a solution of methyl 4-hydoxybenzoate (6.85g, 45 mmole) in 80 ml DMF was added potassium tert. butoxide (5.6 g, 51 mmole) and the mixture was stiπed at room temperature for one hour. 4-Methoxybenzyl chloride (8.3 g, 52 mmole) was added and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and 200 ml ethyl acetate was added. The organic phase was washed four times with water, dried with sodium sulfate and evaporated under reduced pressure. Yield: 12.3g = 100% b) 4- (4-methoxybenzyloxy) benzoic acid 139 To a solution of methyl 4-(4-methoxybenzyloxy) benzoate (12.2 g. 44.8 mmole) in 50 ml 1,4-dioxane was added a solution of lithium hydroxide ( 2.15 g, 89,6 mmole) and the mixture was stiπed overnight at 60°C. The mixture was evaporated under reduced pressure and 5%> acetic acid was added. The product was filtered, washed with water and dried. Yield: 10.1 g = 87% c) Chloromethyl 4-(4-methoxybenzyloxy)benzoate To a solution of 4-(4-methoxybenzyloxy) benzoic acid (5.16 g, 20 mmole) in 100 ml 1,4-dioxane was added a 40%> solution of tetrabutylammonium hydroxide (14.27 g, 22 mmole) and the mixture was stiπed 2 hours at room temperature. The mixture was evaporated under reduced pressure and co-evaporated two times with 1 ,4-dioxane and two times with toluene. The dried product was dissolved in 60 ml dichloromethane and iodochloromethane (35.3 g 200 mmole) was added. The solution was stiπed for two days at room temperature and evaporated under reduced pressure. About 100 ml ethyl actate was added and the organic phase washed twice with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography.Yield: 4.48 g = 73% d) Iodomethyl 4-(4-methoxybenzyloxy) benzoate To a solution of chloromethyl 4-(4-methoxybenzyloxy) benzoate (0.77g, 2.5 mmole) in 15 ml dry acetone was added sodium iodide (1.87g, 12.5 mmole) and the mixture was stiπed overnight at room temperature. The mixture was evaporated under reduced pressure and extracted with ethyl actate/water. The organic phase was washed with a 5%o sodium thiosulfate solution, dried with sodium sulfate and evaporated under reduced pressure. Yield 0.86g = 86% e) (IS, 2S)-N-[cώ-2-(6-fluoro-2-O-(4(4-methoxybenzyloxy)- benzoyloxymethyl)-3 -propionylphenyl (cyclopropyl] -N'-[2-(5-cyanopyridyl)urea To a solution of (1 S, 2S)-N-[ ' s-2-(6-fiuoro-2-hydroxy-3-propionylphenyl) cyclopropyl]-N'-[2-(5-cyanopyridyl)]urea (368mg, 1 mmole) in 5 ml DMF was added a suspension of 60% sodium hydride in mineral oil (44mg, 1.1 mmole) and the mixture was stiπed for one hour at room temperature. A solution of iodomethyl-4-(4- 140 methoxybenzyloxy) benzoate (0.84 g, 2.1 mmole) in 2 ml THF was added and the mixture was stiπed overnight at room temperature. 50 ml ethyl acetate were added and the organic phase was washed four times with water, dried with sodium sulfate and evaporated under reduced pressure. The product was isolated by silica gel column chromatography. Yield: 525 mg = 82% f) (IS, 2S)-N-[c/s-2-(6-fluoro-2-O (4-hydroxybenzoyloxymethyl)-3- propionylphenyl)cyclopropyl]-N'- [2-(5-cyanopyridyl)]urea-O-methylene-4- hydroxybenzoate To a solution of the intermediate of step e) (100 mg, 0.156 mmole) in 4 ml dichloromethane was added TFA (0.5 ml) and the solution was stiπed for one hour at room temperature. The solution was evaporated under reduced pressure and the product was isolated by silica gel column chromatography. Yield: 45mg = 55%. 'H-NMR (DMSO δ-6) 0.84 (m, 3H) 1.10 (m, IH) 1.48 (m, IH) 2.12 (m, IH) 2.80 (m, 2H) 3.19 (m, IH) 5.85-6.02 (m, 2H) 6.84 (m, 2H) 7.18 (m, IH) 7.46 (m, 2H) 7.74 (m, 2H) 8.04 (m, 2H) 8.38 (m, IH) g) (IS, 2S)-N-[cz ' s-2-(6-fluoro-2-O (4-isoleucyloxybenzoyloxymethyl)-3- propionylphenyl)-cyclopropyl]-N'-[2-(5-cyanopyridyl)]urea-O-methylene-4- hydroxybenzoate-O-L-isoleucyl ester An R 2 group, such as N-protected L-isoleucine is acylated to the exposed hydroxy group using conventional acylation condtions as described herein and deprotected to yield a compound of the invention. Biological Example 1 Pharmacokinetics Confirmation that orally administered prodrugs as envisaged by the invention release the respective mother compound in vivo is obtained in a rat model which is recognized as a useful model for assessing pharmacokinetic parameters of nucleoside analogues. The oral compositions are administered in a pharmaceutical vehicle comprising propylene glycol, or in the case of the more soluble compounds such as that of Example 26 or Example 34, in water, to duplicate fasted animals in a dosage 141 coπesponding to 0.1 mmol/kg. For comparison, a set of rats is iv dosed with 0.01 mmol/kg of the metabolite 2',3'-dideoxy-3'-fluoroguanosine. Serum levels of the metabolite are then monitored in serum collected at intervals from individual animals from 0.5 to up to 12 hours following administration (5 min to 6 hours for FLG). The metabolite is analysed with HPLC with UV detection at 254 nm, in a manner analogous to Stahle et al 1995, J Pharm. Biomed. Anal. 13, 369-376. An HPLC system can be based on a 0.05 M ammonium-dihydrogen-phosphate buffer, with 1.2 % 2-propanol solvent, buffered to pH 4.5 or 30 mM sodium dihydrogen phosphate buffer with 2% acetonitrile solvent buffered to pH 7.0. The column may be a 100 x 2.1 mm BAS C18 5 μm particle size with a 7 μm C18 guard column or Zorbax SB-CN C18 150x4.6mm, 5μm column. Protein binding of the compounds of the invention is neglible as is that of the metabolite and ultrafiltration through Amicon or Microcon 30 filters is useful for serum samples. Advantageously the main peak is subject to further column chromatography to better aid in resolution of FLG over low weight serum components. The iv levels are multiplied by a factor often in order to obtain AUC values for comparison with the oral values. Absolute oral bioavailability is determined as the ratio between ° ∞ AUC iv and ° "∞ AUC oral . Table 1 6h absolute 12h absolute bioavail. % bioavail. % FLG 9%** 5'-O- [3,3-bis (L-valyloxymethyl)-propionyl] 67% FLG 5'-O-[2-(-L-valyloxy)-propionyl]FLG 68% 5'-O- [3,3-bis (L-valyloxymethyl)-propionyl] 67.5% FLG 5'-O-3-[l,3-bis-(L-valyloxy)-2- 51% propyloxycarbonyl propanoyljTLG * estimated. **literature value 142 The compounds of the invention thus provide significantly enhanced oral bioavailability relative to the active metabolite 2',3'-dideoxy-3'-fluoroguanosine. Notably, the compounds are released into the blood in a relatively sustained manner, rather than in an immediate peak. This means that effective amounts of the active metabolite are available in the blood for many hours assisting once daily dosage. Additionally, a sustained release avoids the problems of acute toxicity seen in compounds with a more rapid release rate. Although the rat is well recognized as a good model for predicting human bioavailability of nuceoside analogues, species independent bioavailability of a 5'-O- 3-[l,3-bis-(L-valyloxy)-2-propyloxycarbonyl propanoyl]FLG was confirmed in ≡l 1.5 kg male and female beagle dogs administered orally with 0.05 mmol/kg (38 mg/kg) compound in water or iv 0.005 mmol/kg (1.35 mg/kg) metabolite in water. Plasma collection and analysis as above. Male dog 12 hour absolute bioavailability 51 % Female dog 12 hour absolute bioavailability 74% Biological Example 2 Bioavailability The release of the phenolic mother compound from a prodrug of the invention were monitored in rats. The compounds of Examples PI -4, 6&7 were made up in a propylene glycol vehicle and orally administered to paired fasted male Sprague Dawley rats at a dose coπesponding to 0.027 mmol/kg. At 30, 60, 120, 240 & 360 minutes, 0.2 ml blood were collected, centrifuged and frozen for later analysis. The released phenolic drug, (IS, 2S)-N-[c/.s-2-(6 -fluoro-2-hydroxy-3-propionylphenyl) cyclopropyl]-N'-[2-(5-cyanopyridyl)] urea was assayed by HPLC. Aliquots comprising 40-100 μl of each plasma sample are mixed with an equal volume of 143 acetonitrile (10 seconds, Vibrofex). The sample is centrifuged (2 min, 14000 RPM) and 30 μl of the supernatant is injected into an HPLC system, as follows. Pre column: RP-18, 7 μm, 15 x 3.2 mm Column: YMC basic, 3μm, 150 x 3 mm Mobile phase: 60 % acetonitrile in 3 mM ammonium acetate, pH 6.4 Flow rate: 0.4 ml/min Detection: UV, 250 nm TABLE P-l Example Bioavailability 0 . 6 hours P-l 34 % P-2 18 % P-3 27 % P-4 18 % P-6 50 % P-7 70 % The above bioavailabilities coπespond to sustained plasma levels of the active metabolite well above the ED 50 for HIV-1. Biological Example 3 Bioavailability of the ring indanolic ring hydroxy compound of Example B-1 was assessed in rats by the procedure of Biological Example 2 also using a propylene glycol vehicle, 58mg/kg (0.047 mmol/kg), but wherein the mother compound Nl, N6-di [(lS,2R)-2-hydroxy-2,3-dihydro-l-H-l-indenyl]-(2R, 3R, 5R)-2,5- di(benzyloxy)-3,4-dihydroxyhexanediamide was assayed by LC-MS using SiM (single ion monitoring) with M/Z ion detector 653. Plasma results are presented as μM in the table below: 144 Time Rat 1 Rat 2 Rat 3 0 <0.02 <0.02 <0.02 0.5 0.17 0.46 0.23 1 0.73 1.4 1.22 2 0.86 1.7 1.09 4 0.52 0.67 0.43 6 0.23 0.24 0.08 The average bioavailability is thus 57%. This should be contrasted with the bioavailability of the mother compound (below level of detection). Interestingly, the bioavailability of the analogue bearing R 2 groups (depicted immediately below) but lacking the linker component of the invention was also below the level of detection in the same assay:

Claims: 145 CLAIMS 1. A pharmaceutical compound or an intermediate therefor, having the formula: D*-Linker* (R 2 ') k -R 2 where R 2 and R 2 ' (if present) is the amide or ester residue of an aliphatic amino acid, k is 0 or 1, D* is a Drug residue bearing an accessible function selected from amine, hydroxy and carboxy, or a group amenable to attachment to said accesible function, Linker* is an at least bifunctional linker comprising a first function bound to said accessible function spaced from a second function forming an amide or acyl bond with the aliphatic amino acid; wherein the compound is free from long chain fatty acid esters; and with the provisos that Linker* does not consist solely of alkoxy when the Drug comprises a lactamcarboxy or enolic hydroxy function and that the Drug is not a monohydric nucleoside. 2. A compound according to claim 1, with the formula: R 4L o PG-R 2 — O — ()ql- Qqr-T 11 x Rm wherein PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected, R 4L is H, C,. 3 alkyl or phenyl, Rm is H, C,. 3 alkyl, phenyl or -() m -O-R 2 ql is 0-3, qr is 0-3, m is 0-2 T is a bond, -NR 4 - or -O- R 4 is H or C,. 3 alkyl; 146 X is OH, an activating group, an ester linkage to a Drug bearing an accessible hydroxy function, an amide linkage to a Drug bearing an accessible amine function or a structure of the formula: • ,4R — O - X' R 4R' where R 4R and R 4R ' are independently H, C,_ 3 alkyl or phenyl; and X' is halo or an ether linkage to a drug bearing an accessible hydroxy function or an ester linkage to a Drug bearing an accessible carboxy function; and pharmaceutically acceptable salts thereof. 3. A compound according to claim 2, with the structure: R 4L O R 4. R R 2 -0- ()ql- - ()qr -T O- X' Rm R • 4. A compound according to claim 3, wherein R 4R and R 4R ' are hydrogen. 5. A compound according to claim 3 wherein R 4R and R 4R ' are methyl. 6. A compound according to claim 3 wherein R 4R is H and R 4R ' is methyl. 7. A compound according to claim 3, wherein R 4L and Rm are respectively: methyl, methyl; methyl, hydrogen; or ethyl, ethyl. 8. A compound according to claim 3 wherein R 4L and Rm are H 147 9. A compound according to claim 3 wherein R 4L is H and Rm is -()m-O- R2. 10 A compound according to claim 3, wherein ql and qr are respectively 1,0; 2,0 3,0 4,0 1 1 A compound according to claim 3, wherein ql and qr are respectively ι,i; 2,1 3,1 4,1 ; or 2,2. 12 A compound according to claim 3, wherein T is a bond. 13 A compound according to claim 3, wherein T is -NH-. 14 A compound according to claim 3, wherein T is -O-. 15 A compound according to claim 3, wherein PG-R 2 is derived from L- valyl or L-isoleucyl. 16 A compound according to claim 3 wherein X' is halo and PG-R, is N- Fmoc-L-valyl, N-Boc-L-valyl, N-CBz-L-valyl, N-Fmoc-L-isoleucyl, N-Boc-L- isoleucyl or N-CBz-L-isoleucyl. 17 A compound according to claim 15, selected from: 2,2-dimethyl-3-(N-PG-L-valyloxy)propionic acid iodomethyl ester 2-(N-PG-L-valyloxy)ethoxycarbonyloxymethyl iodide 148 3,3- bis (N-PG-L-valyloxymethyl)-propionic acid iodomethyl ester, Iodomethyl l ,3-bis(N-PG-L-valyloxy)-2-propyl carbonate, l,3-bis(N-PG-L-valyloxy)-2-propyl 1-iodoethyl carbonate Iodomethyl 2-methyl-2-(Ν-PG-L-valyloxymethyl) propionate, Iodomethyl 2-(N-PG-L-valyloxy)-DL-propionate. Iodomethyl 2-(N-PG-L-valyloxy)isobutyrate. Iodomethyl 2-(N-PG-L-valyloxy)-3-methyl-(S)-(+)-butyrate. Iodomethyl 2-O-(N-PG-L-valyloxy)-2-phenyl-DL-acetate Iodomethyl 5-(N-PG-L-valyloxy)-2,2-dimethylvalerate 2-(N-PG-L-valyloxy)-ethyl iodomethyl carbonate 4-(N-PG-L-valyloxy) butyric acid iodomethyl ester Iodomethyl-3-(N-PG-L-valyloxy)-propionate 3-(N-PG-L-valyloxy)-2,2-dimethylpropyl iodomethyl carbonate Iodomethyl 2-(Ν-PG-L-valyloxymethyl)-2-ethyl butyrate 2-(N-(iodomethoxycarbonyl)-amino)-2-methyl- 1 -(N-PG-L-valyloxy)-propane 2,2-dimethyl-3-(N-PG-L-isoleucyloxy)propionic acid iodomethyl ester 2-(N-PG-L-isoleucyloxy)ethoxycarbonyloxymethyl iodide 3,3- bis (N-PG-L-isoleucyloxymethyl)-propionic acid iodomethyl ester Iodomethyl l,3-bis(N-PG-L-isoleucyloxy)-2-propyl carbonate l,3-bis(N-PG-L-isoleucyloxy)-2-propyl 1-iodoethyl carbonate Iodomethyl 2-methyl-2-(Ν-PG-L-isoleucyloxymethyl) propionate, Iodomethyl 2-(N-PG-L-isoleucyloxy)-DL-propionate. Iodomethyl 2-(N-PG-L-isoleucyloxy)isobutyrate. Iodomethyl 2-(N-PG-L-isoleucyloxy)-3-methyl-(S)-(+)-butyrate. Iodomethyl 2-(N-PG-L-isoleucyloxy)-2-phenyl-DL-acetate Iodomethyl 5-(N-PG-L-isoleucyloxy)-2,2-dimethylvalerate 2-(N-PG-L-isoleucyloxy)-ethyl iodomethyl carbonate 4-(N-PG-L-isoleucyloxy) butyric acid iodomethyl ester Iodomethyl-3-(N-PG-L-isoleucyloxy)-propionate l,3-bis(N-PG-L-isoleucyloxy)-2-propyl 1 -iodoethyl carbonate 3-(N-PG-L-isoleucyloxy)-2,2-dimethylpropyl iodomethyl carbonate 149 Iodomethyl 2-(N-PG-L-isoleucyloxymethyl)-2-ethyl butyrate, 2-(N-(iodomethoxycarbonyl)-amino)-2-methyl-l-(N-PG-L-isoleucyloxy)-propane, where PG is an N-protecting group. 18 A compound according to claim 17, wherein PG is Boc, Fmoc or especially CBz. 19 A compound according to claim 3, wherein X' is an ether linkage to a Drug bearing an accessible hydroxy function. 20. A compound according to claim 2, with the formula: R M,L o PG-R2 — O — ()ql ()qr-T — L x Rm wherein R 4L is H, C,. 3 alkyl or phenyl, Rm is H, C,. 3 alkyl, phenyl or -() m -O-R 2 ql is 0-3, qr is 0-3, m is 0-2 T is a bond, -NR 4 - or -O- R 4 is H or C,. 3 alkyl; PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected. X is OH, an activating group, an ester linkage to a Drug bearing an accessible hydroxy function, an amide linkage to a Drug bearing an accessible amine function 21. A compound according to claim 20, wherein R 4L and Rm are respectively: methyl, methyl; methyl, hydrogen; or ethyl, ethyl. 22. A compound according to claim 20 wherein R 4L and Rm are H 23 A compound according to claim 20 wherein R 4L is H and Rm is 150 -()m-O-R2. 24 A compound according to claim 20, wherein ql and qr are respectively 1,0; 2,0 3,0 4,0. 25 A compound according to claim 20, wherein ql and qr are respectively 1,1: 2,1 3,1 4,1 ; or 2,2. 26 A compound according to claim 20, wherein T is a bond. 27 A compound according to claim 20, wherein T is -NH- 28 A compound according to claim 20, wherein T is -O- 29 A compound according to claim 20, wherein PG-R 2 is derived from L- valyl or L-isoleucyl. 30 A compound according to claim 20 wherein X' is halo and PG-R 2 is N- Fmoc-L-valyl, N-Boc-L-valyl, N-CBz-L-valyl, N-Fmoc-L-isoleucyl, N-Boc-L- isoleucyl or N-CBz-L-isoleucyl. 31. A compound according to claim 20 selected from 3-N-PG-valyloxypropanoic acid 4-N-PG-valyloxybutyric acid 4-N-PG-valyloxy cis-but-2-enoic acid 5-N- PG -valyloxypentanoic acid 151 5-N- PG -valyloxy-cis-pent-2-enoic acid 6-N- PG -valyloxyhexanoic acid 3-N- PG -isoleucyloxypropanoic acid 4-N- PG -isoleucyloxybutyric acid 4-N- PG -isoleucyloxy-cis-but-2-enoic acid 5-N- PG -isoleucyloxypentanoic acid 5-N- PG -isoleucyloxy-cis-pent-2-enoic acid 6-N- PG -isoleucyloxyhexanoic acid, 2,2-dimethyl-3-(N-PG-L-valyloxy)propionic acid 3,3- bis (N-PG-L-valyloxymethyl)-propionic acid, 2-methyl-2-(N-PG-L-valyloxymethyl) propionate, 2-(N-PG-L-valyloxy)-DL-propionate. 2-(N-PG-L-valyloxy)isobutyrate. 2-(N-PG-L-valyloxy)-3-methyl-(S)-(+)-butyrate. 2-O-(N-PG-L-valyloxy)-2-phenyl-DL-acetate 5-(N-PG-L-valyloxy)-2,2-dimethylvalerate 4-(N-PG-L-valyloxy) butyric acid 3 -(N-PG-L-valyloxy)-propionate 2-(N-PG-L-valyloxymethyl)-2-ethyl butyrate 2,2-dimethyl-3-(N-PG-L-isoleucyloxy)propionic acid 3,3- bis (N-PG-L-isoleucyloxymethyl)-propionic acid 2-methyl-2-(N-PG-L-isoleucyloxymethyl) propionate, 2-(N-PG-L-isoleucyloxy)-DL-propionate. 2-(N-PG-L-isoleucyloxy)isobutyrate. 2-(N-PG-L-isoleucyloxy)-3-methyl-(S)-(+)-butyrate. 2-(N-PG-L-isoleucyloxy)-2-phenyl-DL-acetate 5-(N-PG-L-isoleucyloxy)-2,2-dimethylvalerate 4-(N-PG-L-isoleucyloxy) butyric acid 3-(N-PG-L-isoleucyloxy)-propionate and the coπesponding activated acid halides where PG is an N-protecting group. 152 32 A compound according to claim 31 , wherein the protecting group is Fmoc, Boc or CBz. 33. A compound according to claim 20, wherein the drug is esterified to 3-valyloxypropanoic acid 4-valyloxybutyric acid 4-valyloxy cis-but-2-enoic acid 5-valyloxypentanoic acid 5-valyloxy-cis-pent-2-enoic acid 6-valyloxyhexanoic acid 3-isoleucyloxypropanoic acid 4-isoleucyloxybutyric acid 4-isoleucyloxy-cis-but-2-enoic acid 5-isoleucyloxypentanoic acid 5-isoleucyloxy-cis-pent-2-enoic acid or 6-isoleucyloxyhexanoic acid 34 A compound according to claim 20 with the structure: O PG-R 2 — O X PG-R 2 — O 35. A compound according to claim 34 selected from (R) 2,3-bis-(N-FmocL-valyloxy)-propanoic acid (R) 2,3-bis-(N-FmocL-isoleucyloxy)-propanoic acid (R) 2,3-bis-(N-Boc-L-valyloxy)-propanoic acid (R) 2,3-bis-(N-Boc-L-isoleucyloxy)-propanoic acid (R) 2,3-bis-(N-CBz-L-valyloxy)-propanoic acid (R) 2,3-bis-(N-CBzL-isoleucyloxy)-propanoic acid and the coπesponding acid halides. 36 A compound according to claim 20 with the formula: 153 PG-R 2 PG-R 2 O O O O c- Op— L -o q - JL -χ R Γ 0 TΓ- ( )p— ^Oq ~A~ x O or where PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected R j is H or a carboxy protecting group, p is 0-5, q is 0-5 and X is hydroxy, an activating group or an ester linkage to an hydroxy bearing Drug. 37 A compound according to claim 36 selected from the group consisting of: 2-N-Y-L-valyloxy-L-malic acid 2-N-Y-L-isoleucyloxy-L-malic acid 2-N-Y-L-valyloxy-L-lactic acid 2-N-Y-L-valyloxy-L-lactic acid, and the coπesponding activated acid halides, where Y is Fmoc, Boc or CBz,. 38 A compound according to claim 1, wherein the Linker* (R 2 ' ) k -R 2 comprises a structure of the formula: PG-R 9 - O-π O O O O l-O-U— Alk — Li— x O ^AI ^ x PG-R 2 ' — O- 1 PPGG--RR22 —— OO— PG-R2 * — O— ' where Alk is C,-C 4 alkylene or C 2 -C 4 alkenylene and X is OH, an activating group or an ester linkage to the hydroxy bearing Drug. 154 39 A compound according to claim 38, wherein Alk is methylene or ethylene. 40. A compound according to claim 38, wherein X is OH or an activating group and PG-R 2 and PG-R-," are N-protected Lvalyl or N-protected L-isoleucyl. 41 A compound according to claim 1, wherein Linker* (R 2 ' ) k -R 2 comprises a structure of the formula O PG-R 2 — O — ()ql — Ring — ()qr-T — U — X wherein PG-R 2 is the acyl residue of an aliphatic amino acid, optionally N-protected, ql is 0-3, qr is 0-3, T is a bond, -NR 4 - or -O- R 4 is H or C,. 3 alkyl; ring is an optionally substituted hetero- or carbocyclic ring structure, X is OH, an activating group, an ester linkage to a Drug bearing an accessible hydroxy function, an amide linkage to a Drug bearing an accessible amine function or a structure of the formula: Ft '4,R — O- X' R 4R* where R 4R and R 4R ' are independently H, C,. 3 alkyl or phenyl; and X' is halo or an ether linkage to a drug bearing an accessible hydroxy function or an ester linkage to a Drug bearing an accessible carboxy function; and pharmaceutically acceptable salts thereof. 42. A compound according to claim 41, wherein R 4R and R 4R ' are hydrogen. 43 A compound according to claim 41 , wherein R 4R and R 4R ' are methyl. 155 44 A compound according to claim 41, wherein R 4R is H and R 4R ' is methyl.. 45 A compound according to claim 41, wherein, the optional substituent to ring is PG-R 2 -O-( ) m - where m is 0-2. 46 A compound according to claim 41 wherein ring is phenyl, cyclobutyl, cyclopentyl, cyclohexyl, furyl or pyridyl. 47 A compound according to claim 41, wherein ql and qr are respectively: 1,0; 2,0 3,0 4,0 48 A compound according to claim 41, wherein ql and qr are respectively: ι,i; 2,1; 3,1 ; 4,1; or 2,2. 49 A compound according to claim 41, wherein T is a bond. 50 A compound according to claim 41, wherein T is -NH- 51 A compound according to claim 41, wherein T is -O-. 52 A compound according to claim 41, wherein PG-R 2 is derived from L- valyl or L-isoleucyl. 156 53 A compound according to claim 52 wherein X' is halo and PG-R 2 is N- Fmoc-L-valyl, N-Boc-L-valyl, N-CBz-L-valyl, N-Fmoc-L-isoleucyl, N-Boc-L- isoleucyl or N-CBz-L-isoleucyl. 54 A compound according to claim 52 selected from Iodomethyl 4-(N-PG-L-valyloxy) benzoate. Iodomethyl-3-(N-PG-L-valyloxy)-benzoate Iodomethyl 3 ,4-di-(N-PG-L-valyloxy)hydrocinnamate 3-(N-PG-L-valyloxy)phenyl iodomethyl carbonate Iodomethyl 2-(N-PG-L-valyloxy)phenylacetate Iodomethyl 4-(N-PG-L-valyloxyxy)phenylacetate Iodomethyl 4-(2-N-PG-L-valyloxyethyl) benzoate Iodomethyl 4-(N-PG-L-valyloxy)cyclohexanoate l-(2-N-PG-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid iodomethyl ester Iodomethyl 5-[(N-PG-L-valyloxy)methyl]-2-furoate Iodomethyl 4-(2-Ν-PG-L-valyloxyethoxy)-benzoic acid Iodomethyl 4-(N-PG-L-isoleucyloxy) benzoate. Iodomethyl 3,4-di-(N-PG-isoleucyloxy)hydrocinnamate 3-(N-PG-L-isoleucyloxy)phenyl iodomethyl carbonate Iodomethyl 2-(N-PG-L-isoleucyloxy)phenylacetate Iodomethyl 4-(N-PG-L-isoleucyloxy)phenylacetate Iodomethyl 4-(2-N-PG-L-isoleucyloxyethyl) benzoate Iodomethyl 4-(N-PG-L-isoleucyloxy)cyclohexanoate, 1 -(2-N-PG-isoleucyl)-6-oxo- 1 ,6-dihydro-pyridine-3-carboxylic acid iodomethyl ester iodomethyl 5-[(N-PG-L-isoleucyloxy)methyl]-2-furoate iodomethyl 4-(2-Ν-PG-L-isoleucyloxyethoxy)-benzoic acid wherein PG is an N-protecting group 55 A compound according to claim 54 wherein PG is Fmoc, Boc and especially CBz. 56 A compound according to claim 41 , selected from the group: 157 4-(N-PG-L-valyloxy) benzoate. 3-(N-PG-L-valyloxy)-benzoate 3,4-di-(N-PG-L-valyloxy)hydrocinnamate 2-(N-PG-L-valyloxy)phenylacetate 4-(N-PG-L-valyloxyxy)phenylacetate 4-(2-N-PG-L-valyloxyethyl) benzoate 4-(N-PG-L-valyloxy)cyclohexanoate l-(2-N-PG-L-valyloxyethyl)-6-oxo-l,6-dihydro-pyridine-3-carboxylic acid 5-[(N-PG-L-valyloxy)methyl]-2-furoate 4-(2-Ν-PG-L-valyloxyethoxy)-benzoic acid 4-(N-PG-L-isoleucyloxy) benzoate. 3,4-di-(N-PG-isoleucyloxy)hydrocinnamate 2-(N-PG-L-isoleucyloxy)phenylacetate 4-(N-PG-L-isoleucyloxy)phenylacetate 4-(2-N-PG-L-isoleucyloxyethyl) benzoate 4-(N-PG-L-isoleucyloxy)cyclohexanoate, l-(2-N-PG-isoleucyl)-6-oxo-l,6-dihydro-pyridine-3 -carboxylic acid 5-[(N-PG-L-isoleucyloxy)methyl]-2-furoate 4-(2-Ν-PG-L-isoleucyloxyethoxy)-benzoic acid wherein PG is an N-protecting group 57 A compound according to claim 56 wherein PG is Fmoc, Boc and especially CBz. 58. A compound according to claim 1 with the structure: R4 O Ro — O ' ' O- -O — Drug Ft, where R 4 and R 4 ' are independently H or C,. 3 alkyl and the Drug bears an accessible hydroxy function 158 59 A compound according to claim 58, wherein linker*(R 2 ' ) k -R 2 is a derivative of L-valyloxymethylcarbonate or L-isoleucyloxymethylcarbonate. 60 A compound according to claim 1 with the structure R4 Ro — O ' O —Drug R„ where R 4 and R 4 ' are H or C,. 3 alkyl and the Drug has an accessible carboxy or hydroxy function. 61 A compound of the formula 60, wherein linker*(R 2 ' ) k -R 2 is an L- valyloxym ethyl ether, L-valyloxymethyl ester or L-isoleucyloxymethyl ether or L-isoleucyloxymethyl ester. 62. A compound according to claim 1, wherein the Drug is a di- or trihydric nucleoside analogue, an NNRTI, an HIV protease inhibitor, a peptidomimetic or oligopeptide, levodopa, cromolyn, an opiate, an antibacterial glycopeptide, a rifamycin, a cephalosporin, a tacrine, carvedilol, a statin, etoposide or a taxol. 63. A compound according to claim 62 wherein the nucleoside analogue has the formula: R N 3 0 RN3 RN4 where B is a natural or unnatural nucleotide base, R N1 is O or -CH 2 - or S 159 R N2 and R N3 are each H or R N2 is methylene or -CH(OH)- and R N3 is a bond thereto, or R N2 and R N3 together are a bond; n is 0 or 1 ; one of R N3 and R N4 comprises a linker* -(R 2 ) k -R 2 structure 64 A compound according to claim 63, wherein the linker*-(R 2 ) k -R 2 structure ia attached to the (nominal) 5' hydroxy. 65 A compound according to claim 62, where the nucleoside analogue has the formula: RN3— O RN3- 0 - or RN4 RN9 RN4 — O where B, RN3 and RN4 are as defined in claim 52 and RN6 is fluoro and RN7 is hydrogen or RN6 and RN7 are both fluoro or RN6 and RN7 together define an exo-methenyl group RN8 and RN9 are fluoro (or one of them is fluoro and the other is hydrogen) or RN8 and RN9 together define exomethenyl or exomethenyl mono or di-subsituted with fluoro. 66 A compound according to claim 62 wherein the nucleoside analogue is selected from ribavirin, Ara A, Ara G, Ara C, 1592U89, lobucovir, BMS 200 475 (9- [2-methylen-3-hydroxymethyl-4-hydroxycyclopentyl]guanine, H2G, pencicovir, ganciclovir and 9-[2,3-(trans)dihydroxymethylcyclobutyl]guanine. 67 Use of a structure of the formula linker*(R 2 ') k -R 2 as defined in claim 1 as a prodrug moiety for a pharmaceutical compound bearing an accesible hydroxy, amine or carboxy function, wherein either 160 a structure of the formula linker*(N-PG-R 2 ') k -N-PG-R 2 where N-PG is an N- protecting group is attached to said accessible function; or wherein the the linker* moiety is first attached to the accessible function and the R 2 group(s) are then attacehd thereto.

Inventors: JOHANSSON NILS GUNNAR, LINDSTROEM STEFAN, SALVADOR LOURDES, SUND CHRISTIAN, WAEHLING HORST, WALLBERG HANS, ZHOU XIAO-XIONG, JOHANSSON, NILS, GUNNAR, LINDSTROEM, STEFAN, SALVADOR, LOURDES, SUND, CHRISTIAN, WAEHLING, HORST, WALLBERG, HANS, ZHOU, XIAO-XIONG
Applicants: MEDIVIR AB
Application year: 1999
Main classification: C07K5
IPC codes: C07B61, C07D213, C07D307, C07D311, C07D473, C07D498, C07D501, C07D513, C07H17, C07H19, C07K5