SYNTHESIS N-PROTECTED AMINO ACIDS, ESPECIALLY N-BOC-L-PROPARGYLGLYCINE BY ZINC-MEDIATED ADDITION OR ORGANIC HALIDES TO GLYCINE CATION EQUIVALENT

Abstract: A method is described for synthesis of N-protected amino acids, especially N-Boc-L-propargylglycine, a key intermediate used in the preparation of high-potency, orally-active renin inhibitors. This method involves reaction of an organic halide with a glycine cation equivalent, such as methyl N-Boc-2-acetoxyglycine, in the presence of zinc dust to give Boc-protected amino acid derivatives in high yield. Typically useful organic halides are allylic, benzylic and propargylic halides. Resolution of methyl N-Boc-propargylglycine with alpha-chymotrypsin provides N-Boc-L-propargylglycine in high yield.

Description: SYNTHESIS N-PROTECTED AMINO ACIDS, ESPECIALLY N-BOC-L-PROPARGYLGLYCINE BY ZINC-MEDIATED ADDITION OF ORGANIC HALIDES TO GLYCINE CATION EQUIVALENT FIE QF THE INVENTION Renin-inhibiting compounds are known for control of hypertension. Of particular interest herein are methods useful to synthesize key intermediates for preparation of renin inhibiting agents. EftCKSRQUNP QF THE INVENTION Renin is a proteolytic enzyme produced and secreted into the bloodstream by the juxtaglomerular cells of the kidney. In the bloodstream, renin cleaves a peptide bond in the serum protein angiotensinogen to produce a decapeptide known as angiotensin I. A second enzyme known as angiotensin converting enzyme, cleaves angiotensin II. Angiotensin II is a potent pressor agent responsible for vasoconstriction and elevation of cardiovascular pressure. Attempts have been made to control hypertension by blocking the action of renin or by blocking the formation of angiotensin II in the body with inhibitors of angiotensin I converting enzyme. Many classes of compounds have been described as inhibitors of the action of renin or angiotensinogen. Renin inhibitors of most interest are high potency, orally-active compounds having a low-cost method of synthesis. Several families of renin inhibitor compounds have been described which possess the medicinally- significant properties of high potency and therapeutically-effective oral bioavailability. These families of peptide mimetic renin inhibitors are characterized by the presence of a propargyl moiety attached to glycyl residue within the backbone of the peptide mimetic structure. Other families of peptide mimetic compounds are characterized by the presence of an allyl moiety attached to a glycyl residue within the peptide mimetic backbone. Renin inhibitors containing propargyl glycyl or allyl glycyl residues are described in published patent documents. For example, EP Appl. #186,977 published 9 July 1986 describes renin-inhibiting compounds containing an alkynyl moiety, specifically a propargyl glycine moiety, attached to the main chain between the N-terminus and the C-terminus, such as N-[4 (S)-[ (N)-[bis(1-naphthylmethyl)acetyl]-D,L- propargylglycylamino]-3 (S)-hydroxy-6-methylheptanoyl]-L- isoleucinol. U.S. Patent No. 5,212,185 issued 18 May 1993 describes piperidinyl-terminated alkylamino ethynyl alanine amino diol compounds as renin inhibitors. U.S. Patent No. 5,223,535 issued 29 June 1993 describes propargyl glycine amino propargyl diol compounds as renin inhibitors. U.S. Patent No. 5,227,401 issued 13 July 1993 describes alkylamino-alkylamino-terminated ethynyl alanine amino diol compounds as renin inhibitors. U.S. Patent No. 5,246,969 issued 21 September 1993 describes di-propargyl-containing aryl-alkylsulfonyl-terminated amino diol compounds as renin inhibitors. U.S. Patent No. 5,252,591 issued 12 October 1993 describes pyridinyl/quinolinyl-terminated alkylamino ethynyl alanine amino diol compounds as renin inhibitors. PCT Application WO 94/04508 published 3 March 1994 describes imidazolyl/benzimadazolyl-terminated alkylamino ethynyl alanine amino diol compounds as renin inhibitors. PCT Application WO 94/04518 published 3 March 1994 describes morpholino-thio orpholino-terminated alkylamino ethynyl alanine amino diol compounds as renin inhibitors. PCT Application WO 94/04536 published 3 March 1994 describes ethynyl alanine amino diol compounds having a piperazinyl-terminated group or a piperazinyl-alkylamino- terminated group as renin inhibitors. There are many conventional methods known for making protected amino acids which can be used as intermediates in synthesis of a wide variety of peptides and peptide mimetics [W.N. Speckamp et al, J. Orσ. Chem.. 58, 3259- 3268 (1993)]. For example, amidoalkylation of C-nucleophiles with glycine cation equivalents has been used to make protected α-substituted glycine derivatives [P. Munster et al, Synthesis. 223-225 (1987)]. Also, certain γ,δ unsaturated N-protected α-am © acid methyl esters have been made by coupling allylsilanes with glycine cation equivalents in the presence of a Lewis acid catalyst, but which method when used to react propynyltrimethylsilane with glycidyl cation equivalent gave an unusable Diels-Alder adduct [H.H. Mooiweer et al, Tetrahedron. 45, 4627-4636 (1989)]. Many of these methods are inappropriate for making N-protected α- substituted amino acids because such processes frequently require the presence of a Lewis acid to which certain amino acid protecting groups are sensitive. All of the earlier-mentioned propargyl-glycine or ethynyl-alanine-containing renin inhibitors are characterized by multi-step synthetic routes involving expensive or hard-to-make intermediates. In particular, these multi-step synthetic routes require the use of a stereo-specific N-protected α-substituted amino acid key intermediate, namely, Boc-protected L-propargylglycine, which is not readily available at low cost from commercial sources. Some methods are known for making this key intermediate. For example, one earlier method involves alkylation of diethylacetamidomalonate with propargyl bromide followed by multi-step manipulations to obtain chiral N-Boc-L-propargylglycine [0. Leukart et al, Helv. Chem. Acta.. 59. 2181-2183 (1976)]. In U.S. Patent No. 5,212,185 published 18 May 1993, there is described a reaction of L-propargylglycine with di-tert-butyl- dicarbonate in the presence of potassium carbonate to make Boc-protected L-propargylglycine intermediate. Because of these complicated multi-step syntheses and the high cost of this L-propargylglycine intermediate, there has been delay in the commercial development of propargylglycine-containing renin inhibitors. Thus, there remains need for new synthetic routes for making low cost N-protected α-substituted amino acids which can be used in peptide synthesis, particularly for making medicinal products such as renin inhibitors. DESCRIPTION OF THE INVENTION Natural and unnatural amino acid derivatives may be prepared by reacting an N-protected-α-substituted- glycine cation derivative of Formula I: with an organic halide of Formula II: R3X (Π) to provide an N-protected-α-substituted-glycine racemic ester of Formula III: wherein P is N-protecting group; wherein R^ is selected from hydrido, alkyl, cycloalkyl, alkoxyalkyl, acyl, aralkyl, aryl and aroyl; wherein R^ is selected from alkyl, cycloalkyl, alkoxyalkyl, aralkyl and aryl; wherein X is selected from chloro, bromo and iodo; wherein R^ is a radical selected from alkyl, cycloalkyl, alkoxyalkyl, alkoxycarbonylalkyl, allyl and benzyl, wherein further any of said cycloalkyl, allyl and benzyl radicals may be substituted with one or more moieties selected from alkyl, alkoxy, cyano and phenyl; and wherein R is further selected from propargyl and substituted-propargyl radicals of the formula: wherein each of R 4 and R is a radical independently selected from hydrido, alkyl, alkenyl and phenyl; wherein R is selected from hydrido, alkyl, benzyl and phenyl; wherein p is a number selected from zero through five, inclusive; wherein q is a number selected from zero through five, inclusive. The reaction of glycine cation derivative I with organic halide II to provide glycine derivative III proceeds, preferably, in the presence of zinc metal. More preferably the zinc metal is used in a finely- divided form, such as zinc dust. This reaction is usually carried out in a polar aprotic solvent and, preferably, in the absence of a Lewis acid. Examples of suitable polar aprotic solvents are dimethylformamide (DMF) , dimethylsulfoxide (DMSO) , hexamethylphosphoramide (HMPA) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)- pyrimidinone (DMPU) . Typically, the reaction mixture is maintained at a temperature in a range, from about 10°C to about 25°C during formation of racemic ester derivative III. Resolution and hydrolysis of racemic ester III with an α-carbon resolution enzyme provides N-protected chiral free acid IV: wherein P and R- are as defined above The term "N-protecting group" or "N-protected" as used herein refers to those groups intended to protect a nitrogen atom against undesirable reactions during synthetic procedures. Each term includes, but is not limited to, acyl groups such acetyl and t-butylacetyl, pivaloyl, alkoxycarbonyl groups such as methyloxycarbonyl and t-butyloxycarbonyl (Boc) , aryloxycarbonyl groups such as benzyloxycarbonyl (Cbz) and fluorenylmethoxycarbonyl (Fmoc) , aroyl groups such as benzoyl, and an L- or D- aminoacyl residue which may itself be N-protected similarly. The hydrolysis reaction is typically carried out at pH in a range from about 6.5 to about 8.5, preferably at a pH of about 8, in the presence of a suitable buffer. Examples of suitable buffers are phosphate and potassium chloride aqueous buffer solutions. The phrase "α-carbon resolution enzyme" embraces hydrolase enzymes capable of recognizing an α-chiral center of amino acid racemic ester III. Examples of such hydrolase enzymes are α-chymotrypsin, papain, subtilisin and trypsin. A preferred hydrolase enzyme is α-chymotrypsin. In a preferred embodiment of this method, P is an N-protecting group selected from acyl, pivaloyl, alkoxycarbonyl, aryloxycarbonyl and aroyl; R 1 is selected from hydrido, alkyl, cycloalkyl, acyl and benzoyl, wherein said alkyl or alkyl portion of said acyl is. a linear or branched moiety of one to about 20 carbon atoms; R^ is a linear or branched alkyl moiety of one to about 20 carbon atoms; X is selected from chloro, bromo and iodo; R is a radical selected from alkyl, cycloalkyl, alkσxycarbonylalkyl, allyl, alkyl-substituted-allyl, benzyl, alkoxybenzyl and cyanobenzyl, wherein said alkyl or alkyl portion of said R^ radical is a linear or branched moiety of one to about 20 carbon atoms; and R 3 is further selected from propargyl and substituted-propargyl groups of the formula "(CH 2 ) c≡C-R* 7 q wherein R is selected from hydrido and alkyl; and wherein q is a number selected from zero through three, inclusive. In a more preferred embodiment of this method, P is a protecting group selected from acetyl, t-butylacetyl, benzoyl, methyloxycarbonyl, t-butyloxycarbonyl and benzyloxycarbonyl; R^ is selected from hydrido, alkyl, acyl and benzoyl, wherein said alkyl or alkyl portion of said acyl is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl and neo-pentyl; R^ is selected from methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso- pentyl and neopentyl; X is selected from chloro, bromo and iodo; R^ is selected from alkoxycarbonylalkyl, allyl, alkyl-substituted-allyl, benzyl, alkoxybenzyl and cyanobenzyl, wherein the alkyl portion of any of said R- radicals is selected from methyl, ethyl and n-propyl; and R 3 is further selected from CH 2 c≡≡C-R e wherein R is hydrido or methyl; and wherein q is a number selected from zero through three, inclusive. In an even more preferred embodiment of this method, P is a protecting group selected from acetyl, t-butylacetyl, benzoyl, methyloxycarbonyl, t-butyloxycarbonyl and benzyloxycarbonyl; R- is selected from methyl, ethyl, n-propyl, acetyl, propionyl and benzoyl, R^ is selected from methyl, ethyl and n-propyl; X is selected from chloro, bromo and iodo; R- is selected from ethoxycarbonylmethyl, allyl, methylallyl, benzyl, p-methoxybenzyl and p-cyanobenzyl; and R is further selected from i CH 2 j c ≡C- -IR < 'q wherein R is hydrido or methyl; and wherein q is a number selected from zero through two, inclusive. The term "hydrido" denotes a single hydrogen atom (H) . This hydrido group may be attached, for example, to an oxygen atom to form a hydroxyl group; or, as another example, one hydrido group may be attached to * CH— a carbon atom to form a — group; or, as another example, two hydrido groups may be attached to a carbon atom to form a -CH - group. Where the term "alkyl" is used, either alone or within other terms, the term "alkyl" embraces linear or branched radicals having one to about twenty carbon atoms or, preferably, one to about twelve carbon atoms. More preferred alkyl radicals are "lower alkyl" radicals having one to about ten carbon atoms. Most preferred are lower alkyl radicals having one to about six carbon atoms. The term "cycloalkyl" embraces cyclic radicals having three to about ten ring carbon atoms, preferably three to about six carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. The term "alkoxy" embraces linear or branched oxy-containing radicals having alkyl portions of one to about ten carbon atoms, such as methoxy group. The "alkoxy" radical may be further substituted with one or more halo atoms, such as fluoro, chloro or bromo, to provide haloalkoxy groups. The term "acyl" whether used alone, or within a term such as acyloxy, denotes a radical provided by the residue after removal of hydroxyl from an organic acid, an example of such radical being acetyl. "Lower alkanoyl" is an example of a more preferred sub-class of acyl. The term "aryl" embraces aromatic radicals such as phenyl, naphthyl and biphenyl. Preferred aryl groups are those consisting of one, two or three benzene rings. The term "aralkyl" embraces aryl- substituted alkyl radicals such as benzyl, diphenylmethyl, triphenylmethyl, phenylethyl, phenylbutyl and dipenylethyl. The terms "benzyl" and "phenylmethyl" are interchangeable. The term "aroyl" embraces an aryl group attached to a carbonyl radical, such as benzoyl. The term "alkenyl" embraces linear or branched radicals having two to about twenty carbon atoms, preferably three to about ten carbon atoms, and containing at least one carbon-carbon double bond, which carbon-carbon double bond may have either cis or trans geometry within the alkenyl moiety. The term "alkenyl" includes "allyl" and "methylallyl" (or "methallyl") radicals. The term "alkynyl" embraces linear or branched radicals having two to about twenty carbon atoms, preferably two to about ten carbon atoms, and containing at least one carbon-carbon triple bond. The term "alkynyl" embraces "propargyl" and "propargyl-like" moieties which may be optionally substituted with one or more of alkyl, benzyl or phenyl on any substitutable carbon atom. For any of the foregoing defined radicals, preferred radicals are those containing from one to about fifteen carbon atoms. Specific examples of alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopenty1, methylbutyl, dimethylbutyl and neopentyl. Typical alkenyl and alkynyl groups may have one unsaturated bond, such as an allyl group, or may have a plurality of unsaturated bonds, with such plurality of bonds either adjacent, such as allene- type structures, or in conjugation, or separated by several saturated carbons. Generic Scheme In the following general schemes, there is illustrated a practical application of the general concept of the invention. As shown in Scheme I, methyl glyoxalate hemiacetal 1 is condensed with t-butylcarbamate to give the glycine analogue 2. Acylation (acetic anhydride, pyridine, THF) affords the key intermediate methyl 2-acetoxy-2-[ ( (1,1- dimethylethoxy)carbony1)amino]acetate, 3. Treatment of intermediate _. with zinc dust in DMF and an organic halide affords amino acid analogues 4 a-g. With regard to synthesis of amino acid analogues 4 a-g, two equivalents of organic halide were added to a 0.5 M solution of 3 (2.0 mmol) and zinc dust (4.0 mmol, 325-mesh) in DMF with cooling, at a rate to keep internal temperature between 20-25 * C. Table I, below, shows yields of amino acids 4 a-g after extractive work up and silica gel chromatography. The reaction with organic halide g did not yield the expected p-cyanophenylalanine derivative but instead gave exclusively the substituted phenylglycine derivative, 4g, in 57% yield, having the structure: Table I Zinc-Mediated Additions of Organic Halide to Intermediate 3 Organic Halide Product (Yield) Br„ - 4a ( 97%) 4b ( 68% ) Biv ^ C0 2 CH 2 CH 3 f Br.^ To oCH, 4f (37%) It is believed that the selected solvent plays an important role in the formation of amino acid ester 4. For example, using dime hylformamide (DMF) , the metallation reaction initiates quickly with intermediate 3 and the addition reaction is usually complete within 1 hour. When the reaction is carried out in tetrahydrofuran (THF) , no reaction occurs unless a Lewis acid, e.g., Me_AlCl (0.5 eq) , is present. Even under these conditions, the isolated yields are high and both the Boc group and the ester remain unaffected. It is thus another aspect of this invention that in certain solvents, generally characterized as cyclic-ether type solvents, such as tetrahydrofuran and dioxane, there is permitted the use of a Lewis acid in the synthesis of N-protected α-substituted glycine derivatives. Examples of Lewis acids which may be used in combination with an ether solvent to promote the zinc addition reaction, are dimethylaluminum chloride, methylaluminum dichloride, borontrifluoride etherate complex, (BF*Et20) , titanium (IV) chloride and titanium (IV) dichlorodiisopropoxide, Scheme II! Boc R = Propargyl Resolution of the racemic ester 4a with α-chymotrypsin at 25'C in O.lM phosphate buffer (pH 8) afforded N-Boc-L-propargylglycine 5a in 96% yield based on 50% conversion (88% e.e.). One recrystallization from Et-O/petroleum ether gave a 67% yield of 5a enriched to 99% e.e.. Specific Methods As further exemplification of the generic methods shown in the foregoing General Schemes I and II, there are now shown specific preparations with reactants, amounts, conditions and treatments, for intermediates and amino acid products made by methods of the invention as described in the following Examples 1-5: E ample I Preparation of methyl 2-. ( (1.l-dimethvlet ~ hoxv) carbonvl)amino1 -2-hvdroxvace ate A solution of methyl glyoxalate hemiacetal (5.66 g, 47.2 mmol) and ϋ-butylcarbamate (5.02 g, 42.9 mmol) in benzene (50 mL) was refluxed for 18 hours. The reaction was concentrated under reduced pressure to approximately one-fifth its volume then stirred rapidly while adding 100 mL of petroleum ether. Stirring continued until a dispersed white solid had formed. The product was filtered, washed with petroleum ether and dried affording 6.64 g (75%) of product ( .p. 96-97'C) . Anal, calc'd for C 8 H- 5 N0 5 : C,46.82;H,7.37;N,6.83. Found: C,47.04;H,7.71;N,6.90. Exam le 2 Preparation of methvl 2-acetoxv-2-T ( (1.1- dimethvlethoxv) arbonvl)amino1acetate. To a solution of the product of Example 1 (10.0 g, 48.8 mmol), pyridine (7.71 g, 97.6 mmol) and DMAP (300 mg, 2.5 mmol) in THF (50 ML) was added acetic anhydride (5.47 g, 53.6 mmol) slowly at room temperature. After stirring at ambient temperature for 3 hours, the reaction was diluted with EtOAc and washed successively with IN NaHSO. and sat'd NaHCO.,. The organic phase was dried (MgSO , filtered and concentrated under reduced pressure affording 11.8 g (98%) of product as a colorless oil. Anal. calc'd for C 10 H 17 NO-.l/4H-O: C,47.71;H,7.01;N,5.56. Found: C,47.68;H,6.75;N,5.55. Example 3 Preparation of ethvl 2-f ( (1.1-dimethvlethoxv) carbonvl)amino1 -4-pentvnoate. To an ice cooled suspension of the product of Example 2 (4.00 g, 16.2 mmol) and zinc dust (2.63 g, 40.5 mmol) in DMF (30 mL) under nitrogen was added slowly via syringe propargyl bromide (80% w/w in toluene) (6.02 g, 40.5 mmol). The bromide was added at such a rate as to maintain the internal temperature between 20-25 * C, then stirred at that temperature for an additional 1 hour. The reaction mixture was diluted with 100 mL of EtOAc, washed successively with 0.5 N HC1 (200 mL) , sat'd NaHC0 3 (200 mL) and sat'd NaCl and then dried (MgS0 4 ) . After filtration and concentration under reduced pressure, the residue was purified by filtration through a bed of silica gel (30% EtOAc/hexane)to give 3.59 g (97%) of product as a colorless oil after concentration under reduced pressure. Anal. calc'd for C 11 H 17 N0 4 « 1/3H 2 0 : C , 56 . 64 ; H, 7 . 63 ; N, 6 . 01 . Found : C , 56 . 96 ; H , 7 . 60 ; H, 6 . 03 . Example 4 Preparation of methyl 7 - ~ ( (1.1- dimethylethoxy)carbonyl)amino1-4-pentenoate. To an ice cooled suspension of the product of Example 2 (0.525 mg, 2.12 mmol) and zinc dust (278 mg, 4.25 mmol) in DMF (4 mL) under nitrogen was added slowly via syringe neat allyl bromide (514 mg, 4.25 mmol) . The bromide was added at such a rate as to maintain the internal temperature between 20 and 25'C, then stirred at that temperature for an additional 1 hour. Extractive workup and silica gel chromatography as described in Example 3 afforded 486 mg (100%) of product as a colorless oil. Example 5 Preparation of 2(f?.-. ( .1.1- dimethvlethoxv)carbonvl)amino1-4-pentvnoate. To a suspension of the product of Example 3 (3.53 g, 15.5 mmol) in 60 mL of a 0.1 M phosphate buffer (pH 8) was added α-chymotrypsin (25 mg) . The reaction mixture was stirred at 25 * C for 22 hours while the pH was kept constant within a range of 7.5-8 by the periodic addition of IN NaOH. After the unreacted ester was recovered by extracting with EtOAc, the aqueous fraction was acidified (pH 3) with 2 N HC1 and extracted with EtOAc. During the first extraction of the acidic fraction, the precipitated enzyme made partitioning of the two layers difficult. As a result, the biphasic mixture was filtered through a bed of celite. The layers were then separated and the aqueous phase was extracted again with EtOAc. The organic fractions were combined, dried (MgS04), filtered and . concentrated under reduced pressure affording 1.53 c (92% based on 50% conversion) of product as a viscous oil (88% e.e.). Crystallization of the product from EtO/petroleum ether gave 1.00 g (61%) of product (m.p. 84-85'C, 99% e.e.). Enantiomeric purity was determined by chiral HPLC analysis using a Crownpak CR(+) column (15 cm x 4.6 mm) at O'C and isocratic elution with 1% aq. HC10 4 at 0.5 mL/min. The detector was set at 205 nm. Anal, calc'd for C 10 H 15 NO 4 : C,56,32;H,7.09;N,6.57. Found: C,56.27;H,7.25;N,6.51. [α] D 25 =+23.5' (MeOH, c=9.1 mg/mL) . The methods of this invention provide economical, high yield synthetic routes for making N-protected amino acid esters using a wide variety of organic halides. In particular, the propargyl- type N-protected amino acid racemic esters may be subjected to hydrolase enzyme resolution to provide, for example, N-Boc-2-propargylglycine, which is an intermediate used in preparation of high-potency, orally-bioavailable renin inhibitor compounds. Specific examples of renin inhibitor compounds, which may be prepared from this N-Boc-L- propargylglycine intermediate, are shown in Table II, below, along with the published patent documents in which such renin inhibitor compounds appear. Table II L-Propargvl-Glvcine-Containinσ Renin Inhibi or- In U.S. Patent No. 5,212,185 issued 18 May 1993: Example 1 Nl- riR*-r r πs.lR*- ( ~ vr.lohexvlmethvl) -2S* .3R*-dihvdroxv-5- methvlhexv] 1 aminol carbonvll -3-butvnvll -NJ-methvl-2S*- ( phenvlmethvl) -NJ- ~ 2- (1 -piper idinvl) ethvllbutanediamide Example _. Nl-riR*-Γ Γ nS. lR*- ( ~ vclohexvlmethvl) -2S* ■ 3R*-dihvdroxv-5- methvlhexv] 1aminolcarbonvll -3-butvnvll -NJ- .2- (1.3- dihvdro-2H-isoindol-2-vl)ethvl1-Nl-methvl-2S*- (phenvlmethvl)butanedia ide Example 3 Nl- ' IR*-f r US.IR*- (cvclohexvlmethvl) -2S* .3R*-dihvdroxv-5- methvlhexvllaminol carbonvll -3-butvnvll -NJ-n.ethvl-2S*- (phenvlmethvl)-Ni-r2-(N-3-azabicvclor3.2.21nonanvl) ethvl1butanediamide In U.S. Patent No. 5,223,535 issued 29 June 1993: Example 1 Nl- r IR*- r r riS . IR*- ( cvclohexylmethvl ) -2S* . R*-dihvdroxv- hexvnvll aminol carbonvll -3-butvnvll -N4- ~ 2- ( dimethyl - amino) thyl l -N4-methvl-2S*- (phenvlmethvl ) butanediamide Example 2 riR*-T T riR*-f T US. IR*- (cvclohexvlmethvl ) -2S*.3R*- dihvdroxv-hexvnvllaminol arbonvll -3- butvnvll minol arbonvll -2-phenvlethvl) ~ 2- (dimethvlamino) ethvllmethvlcarbamate In U.S. Patent No. 5,227,401 issued 13 July 1993 gyample I Nl-riR*-rrr S.lR*- (cvclohexvlmethvl) -2S*.3R*-dihvdroxv-5- methvlhexv11aminolcarbonvll -3-butvnvll -N4- \2- (dimethvl- amino) thvll -N4-m hvl-2S*- (phenvlmethvl)butanediamide Example 2 riR*-rrΓIR*-rrns. R*-(cvclohexvlm vl)-2s*.3R*- dihvdroxv-5-methvlhexvllaminol carbonvll -3- butvnvllaminolcarbonvll -2-phenvlethvl) \2- (dimethvlamino. ethvllmethylcarbamate Example 3 riR*- r r ri- r r riS. IR*- (cvclohexylmethvl) -2S* .3R*-dihvdroxv- 5-methylhexyllaminolcarbonyll -3-butvnyllaminolcarbonyll -2- phenylethyll \2- (dimethylamino)ethyllmethylcarbamate In U.S. Patent No. 5,252,591 issued 12 October 1993: Example 1 Nl- riR*- r r US. IR*- (cvclohexvlmethvl) -2S* -3_R*-dihvdroxv- 5 -p ~ ethyll-e? ~ γl . aminc> . carbonyll -3 -frutvnvl 1 -N^-met vl -25*- (Phenvlmethvl) -NJ- r2- (2-pvridinvl)ethvllbutanediamide In PCT Application WO 94/04508 Published 3 March 1994: Example 1 Nl-riR*-rrriS.lR*-(cvclohexvlmethvl)-2S*.3R*-dihvdroxv-5- methvlhexv!1 minolcarbonvll -3-butvnvll -NJ-12- (1H- imidazol-1-yl)ethyll -NJ-methyl-2S*- (phenvlmethvl)butanediamide In PCT Application WO 94/04518 published 3 March 1994: Example 1 Nl-riR*-r r riS.IR*-(cvclohexvlmethvl)-2S*. R*-dihvdroxv- 5-methvlhexv11aminolcarbonvll-3-butvnvll-NJ-methvl-NJ- .2- (4-morphnlinvl )ethvll-2S*- (phenvlmethvl)butanediamide In PCT Application No. WO94/04536 published 3 March 1994: Example 1 (2S) -2-Benzyl-3-(l-methylpiperazin-4-ylsulfonyl) propionyl-L-proparαylglvcyl Amide of (2S.3R.4S) -2- amino-l-cvclohexyl-3, -dihvdroxy-6-methylheptane Although this invention has been described with respect to specific embodiments, the details of these embodiments are not to be construed as limitations.

Claims: What Is Claimed la: 1. A method for preparing a natural or unnatural amino acid derivative, said method comprising reacting an N-protected-α-substituted-glycine cation derivative of Formula I: with an organic halide of Formula II: R3χ (II) to provide an N-protected-α-substituted-glycine racemic ester of Formula III: wherein P is N-protecting group; wherein R^ is selected from hydrido, alkyl, cycloalkyl, alkoxyalkyl, acyl, aralkyl, aryl and aroyl; wherein R2 is selected from alkyl, cycloalkyl, alkoxyalkyl, aralkyl and aryl; wherein X is selected from chloro, bromo and iodo; wherein R^ is a radical selected from alkyl, cycloalkyl, alkoxyalkyl, alkoxycarbonylalkyl, allyl and benzyl, wherein further any of said cycloalkyl, allyl and benzyl radicals may be substituted with one or more moieties selected from alkyl, alkoxy, cyano and phenyl; and wherein R is further selected from propargyl and substituted-propargyl radicals of the formula: wherein each of R and R is a radical independently selected from hydrido, alkyl, alkenyl and phenyl; wherein R is selected from hydrido, alkyl, benzyl and phenyl; wherein p is a number selected from zero through five, inclusive; wherein q is a number selected from zero through five, inclusive. 2. The method of Claim 1 further characterized by reacting a glycine cation derivative of Formula I with an organic halide of Formula II in the presence of zinc metal. 3. The method of Claim 2 wherein said zinc metal is in a finely-divided form. 4. The method of Claim 1 wherein further characterized by reacting a glycine cation derivative of Formula I with an organic halide of Formula II in a polar aprotic solvent in the absence of a Lewis acid. 5. The method of Claim 1 further comprising the step of resolving and hydrolyzing a racemic ester III with an α-carbon resolution enzyme to provide N-protected chiral free acid of Formula IV: (IV) wherein P is N-protecting group; wherein R^ is selected from alkyl, cycloalkyl, alkoxyalkyl and aryl; wherein R^ is a radical selected from alkyl, cycloalkyl, alkoxyalkyl, alkoxycarbonylalkyl, allyl and benzyl, wherein further any of said cycloalkyl, allyl and benzyl radicals may be substituted with one or more moieties selected from alkyl, alkoxy, cyano and phenyl; and wherein R is further selected from propargyl and substituted-propargyl radicals of the formula: wherein each of R 4 and R is a radical independently selected from hydrido, alkyl, alkenyl and phenyl; wherein R 6 is selected from hydrido, alkyl, benzyl and phenyl; wherein p is a number selected from zero through five, inclusive; wherein q is a number selected from zero through five, inclusive. 6. The method of Claim 5 wherein said resolving and hydrolyzing step is carried out in an aqueous solution having a pH in a range from about 6.5 to about 8.5. 7. The method of Claim 5 wherein said α-carbon resolution enzyme is selected from α-chymotrypsin, papain, subtilisin and trypsin. 8. The method of Claim 5 wherein P is an N- protecting group selected from acyl, pivaloyl, alkoxycarbonyl, aryloxycarbonyl and aroyl; I " is selected from hydrido, alkyl, cycloalkyl, acyl and benzoyl, wherein said alkyl or alkyl portion of said acyl is a linear or branched moiety of one to about 20 carbon atoms; R^ is a linear or branched alkyl moiety of one to about 20 carbon atoms; X is selected from chloro, bromo and iodo; R 3 is a radical selected from alkyl, cycloalkyl, alkoxycarbonylalkyl, allyl, alkyl- substituted-allyl, benzyl, alkoxybenzyl and cyanobenzyl, wherein said alkyl or alkyl portion of said R^ radical is a linear or branched moiety of one to about 20 carbon atoms; and R 3 is further selected from propargyl and substituted-propargyl groups of the formula —(CH-)— C≡≡ C-R fc wherein R 6 is selected from hydrido and alkyl; and wherein q is a number selected from zero through three, inclusive. 9. The method of Claim 8 wherein P is an N- protecting group selected from acetyl, t-butylacetyl, benzoyl, methyloxycarbonyl, t-butyloxycarbony1 and benzyloxycarbonyl; R^ is selected from hydrido, alkyl, acyl and benzoyl; wherein said alkyl or alkyl portion of said acyl is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl and neo-pentyl; R^ is selected from methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso- pentyl and neopentyl; X is selected from chloro, bromo and iodo; R^ is selected from alkoxycarbonylalkyl, allyl, alkyl-substituted-allyl, benzyl, alkoxybenzyl and cyanobenzyl, wherein the alkyl portion of any of said R- radicals is selected from methyl, ethyl and n-propyl; and R is further selected from —(CH 2 )— C≡ C-R fc wherein R is hydrido or methyl; and wherein q is a number selected from zero through three, inclusive. 10. The method of Claim 9 wherein P is an N- protecting group selected from acetyl, t-butylacetyl, benzoyl, methyloxycarbonyl, t-butyloxycarbony1 and benzyloxycarbonyl; R! is selected from methyl, ethyl, n-propyl, acetyl, propionyl and benzoyl; R^ is selected from methyl, ethyl and n-propyl; X is selected from chloro, bromo and iodo; R^ is selected from ethoxycarbonylmethyl, allyl, methylallyl, benzyl, p-methoxybenzyl and p-cyanobenzyl; and R is further selected from —(CH 2 }— C≡ C-R 6 wherein R is hydrido or methyl; and wherein q is a number selected from zero through two, inclusive. 11. The method of Claim 10 wherein said N- protected chiral free acid is N-Boc-L-propargylglycine. 12. A method for preparing -an N-protected chiral free acid of Formula IV: said method comprising the step of treating an N- protected-α-substituted glycine racemic ester of Formula III: wherein P is N-protecting group; wherein R^ is selected from alkyl, cycloalkyl and alkoxyalkyl; wherein R^ is a radical selected from alkyl, cycloalkyl, alkoxyalkyl, haloalkyl, hydroxyalkyl, sulfonylalkyl, alkoxycarbonylalkyl and benzyl, wherein further any of said cycloalkyl and benzyl radicals may be substituted with one or more moieties selected from alkyl, alkoxy, cyano and phenyl; and wherein R 3 is further selected from propargyl and substituted-propargyl radicals of the formula: wherein each of R 4 and R 5 is a radical independently selected from hydrido, alkyl, alkenyl and phenyl; wherein R is selected from hydrido, alkyl, benzyl and phenyl; wherein p is a number selected from zero through five, inclusive; wherein q is a number selected from zero through five, inclusive. 13. The method of Claim 12 wherein said treating step is carried out at a pH in a range from about 6.5 to about 8.5. 14. The method of Claim 12 wherein said α- carbon resolution enzyme is a hydrolase enzyme capable of recognizing an α-chiral center of an amino acid racemic ester of Formula III. 15. The method of Claim 14 wherein said hydrolase enzymes is selected from α-chymotrypsin, papain, subtilisin and trypsin. 16. The method of Claim 15 wherein said hydrolase enzyme is α-chymotrypsin. 17. The method of Claim 12 wherein P is an N- protecting group selected from acyl, pivaloyl, alkoxycarbonyl, aryloxycarbonyl and aroyl; R- is a linear or branched alkyl moiety of one to about 20 carbon atoms; R is a radical selected from alkyl, cycloalkyl, alkoxycarbonylalkyl, benzyl, alkoxybenzyl and cyanobenzyl, wherein said alkyl or alkyl portion of said R3 radical is a linear or branched moiety of one to about 20 carbon atoms; and R is further selected from propargyl and substituted-propargyl groups of the formula —(CH 2 ) • C-R 6 g wherein R 6 is selected from hydrido and alkyl; and wherein q is a number selected from zero through three, inclusive. 18. The method of Claim 17 wherein P is a protecting group selected from acetyl, t-butylacetyl, benzoyl, methyloxycarbonyl, t-butyloxycarbonyl and benzyloxycarbonyl; R^ is selected from methyl, ethyl, n- propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert- butyl, n-pentyl, iso-pentyl and neopentyl; R^ is selected from alkoxycarbonylalkyl, benzyl, alkoxybenzyl and cyanobenzyl, wherein the alkyl portion of any of said R^ radicals is selected from methyl, ethyl and n-propyl; and R is further selected from —( CH 2)—- C≡ C- R- wherein R is hydrido or methyl; and wherein q is a number selected from zero through three, inclusive. 19. The method of Claim 18 wherein P is a protecting group selected from acetyl, t-butylacetyl, benzoyl, methyloxycarbonyl, t-butyloxycarbony1 and benzyloxycarbonyl; R^ is selected from methyl, ethyl and n-propyl; R^ is selected from ethoxycarbonylmethyl, benzyl, p-methoxybenzyl and p-cyanobenzyl; and R is further selected from —( H 2 )—-C≡ C- R 6 wherein R 6 is hydrido or methyl; and wherein q is a number selected from zero through two, inclusive. 20. The method of Claim 19 wherein P is t-butyloxycarbony1; wherein R^ is methyl or ethyl; and wherein R^ is selected from propargyl and alkyl- substituted propargyl. 21. The method of Claim 12 wherein said N-protected chiral free acid is N-Boc-L-propargylglycine.

Inventors: ABOOD NORMAN A, NOSAL ROGER A, ABOOD, NORMAN, A., NOSAL, ROGER, A.
Applicants: ABOOD NORMAN A, NOSAL ROGER A, SEARLE & CO, ABOOD, NORMAN, A., G.D. SEARLE & CO., NOSAL, ROGER, A.
Application year: 1995
Main classification: C07C269
IPC codes: C07C269, C07C271, C12P13, C12P41, C12S1, C12S9