Alpha-acyloxy-beta-aminothiolcarboxylic esters and method and intermediates for their production

Abstract: Alpha-Hydroxy-beta-aminothiolcarboxylic esters of formula (II), in which R 1 , R 2 , R 3 , R 4 and R 5 are as defined in Claim 9, are intermediates in producing various HIV protease inhibitors, renin inhibitors and carcinostatics. These compounds are prepared starting from N-protected alpha-amino acid ester, which converted to a beta-ketosulphoxide, which is then reacted with an acid to give and alpha-keto-hemimercaptal. This is acylated and then processed with a base to obtain an N-protected alpha-acyloxy-beta-aminothiolester, which is then saponified to obtain the intended compound.

Description: The present invention relates to α-hydroxy-β-aminocarboxylic acid derivatives, examples of which are important as inhibitors for enzymes, such as HIV protease and renin, or as carcinostatics. Particularly mentioned are HIV protease inhibitor KNI-272 (see Chem. Pharm. Bull., 40, 2251 (1992)), renin inhibitor KRI-1314 (see J. Med. Chem., 33, 2707 (1990)), carcinostatic Bestatin (see Biochem. Pharmacol., 32, 1051 (1983)), and carcinostatic Taxol (see Bull. Cancer, 80, 326 (1993)), which comprise, as the constitutive ingredients, (2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid, (2R,3S)-3-amino-2-hydroxy-4-cyclohexylbutyric acid, (2S,3R)-3-amino-2-hydroxy-4-phenylbutyric acid, and (2R,3S)-phenylisoserine. Background There are known conventional methods for producing the above-mentioned compounds, which start from the corresponding α-amino acids, and comprise preparing N-protected α-aminoaldehydes from the starting acids, reacting them with prussic acid derivatives to give cyanohydrin intermediates, and hydrolyzing them at the cyano group to obtain the intended compounds (see Japanese Patent Application Laid-Open No. 62-33141; Iizuka et al., J. Med. Chem., 33, 2707 (1990); M.T. Reets et al., Tetrahedron Lett., 29, 3295 (1988)). However, since these methods are disadvantageous in that they require an oxidation-reduction step, that they use toxic cyano derivatives, and that they produce, as intermediates, N-protected α-aminoaldehydes which are unstable in quantity production, they are not suitable to the production of large quantities of the compounds. On the other hand, another method is known, which comprises reacting an N-protected α-aminoaldehyde with nitromethane through aldol reaction in the presence of an asymmetric catalyst, followed by hydrolyzing the resulting compound with an acid to obtain an intended product (see EP-657415). However, this method is also unsuitable to the quantity production of the product, since the intermediate α-aminoaldehyde is unstable and the asymmetric catalyst to be used is expensive. Another method, which does not involve preparing such an α-aminoaldehyde intermediate, comprises reacting an N-protected α-aminocarboxylic acid chloride, derived from the corresponding α-amino acid, with trimethylsilyl cyanide to give an α-oxonitrile, then converting it into an α-ketocarboxylate, and thereafter reducing it to obtain an intended product (see Japanese Patent Application Laid-Open No. 6-184069). However, this method is also unsuitable to the quantity production of the product, since it uses such an expensive and toxic cyano compound. It is therefore desirable to provide an industrial method for producing α-hydroxy-β-aminocarboxylic acids and their esters. J. Org Chem 41 , pp 1118-1124 discloses acid catalysed cyclisation of β-ketosulfoxides, for instance including an iridole or thiophene group. Summary of the invention The present invention provides a method for stereoselectively producing α-hydroxy-β-aminocarboxylic acids and their esters, which comprises rearranging a β-ketosulfoxide, obtainable from an N-protected α-aminocarboxylate, using an aqueous acid to give an α-keto-hemimercaptal, then acylating it to give an α-keto-hemimercaptal-carboxylate, and thereafter rearranging it in the presence of a base. Specifically, the present invention provides a method for producing α-acyloxy-thioesters of a general formula (II) : wherein R 1 represents an optionally-substituted, linear, branched or cyclic alkanoyl group having from 2 to 18 carbon atoms, an optionally-substituted, linear, branched or cyclic alkoxycarbonyl group having from 2 to 18 carbon atoms, an aralkyloxycarbonyl group having from 7 to 18 carbon atoms, or an optionally-substituted benzyl group, or represents, together with R 2 , a residue of a dibasic acid having from 8 to 18 carbon atoms; R 2 represents a hydrogen atom or an optionally-substituted benzyl group, or represents, together with R 1 , a residue of a dibasic acid having from 8 to 18 carbon atoms; R 3 represents an optionally-substituted, linear, branched or cyclic alkyl group having from 1 to 18 carbon atoms, an aralkyl group having from 7 to 18 carbon atoms, or an aryl group having from 6 to 18 carbon atoms; R 4 represents an optionally-substituted, linear, branched or cyclic alkanoyl group having from 2 to 18 carbon atoms, or an arylcarbonyl group having from 7 to 18 carbon atoms; and R 5 represents an alkyl group having 1 or 2 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms, which method comprises rearranging, in the presence of a base, an α-keto-hemimercaptal-carboxylate of a general formula (I): wherein R 1 , R 2 , R 3 , R 4 and R 5 have the same meanings as above. Compounds of formula (I) can be obtained by reacting an N-protected α-aminocarboxylate of a general formula (III) : wherein R 1 , R 2 and R 3 have the same meanings as above; and R 6 represents a linear or branched alkyl group having from 1 to 5 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms, with a carbanion of a general formula (IV): wherein R 5 has the same meaning as above, to thereby convert the ester into a β-ketosulfoxide of a general formula (V): wherein R 1 , R 2 , R 3 and R 5 have the same meanings as above, then rearranging the sulfoxide in the presence of an aqueous solution of an acid to give an α-keto-hemimercaptal of a general formula (VI) : wherein R 1 , R 2 , R 3 and R 5 have the same meanings as above, and thereafter acylating the hemimercaptal. Detailed description of the invention N-protected α-aminocarboxylates (III) which are used in the present invention can be derived from α-aminocarboxylic acids according to the means employable in ordinary peptide synthesis. The α-aminocarboxylic acids may be naturally-existing amino acids and synthetic amino acids. Their esters are represented by the following structural formula: wherein R 3 represents an optionally-substituted, linear, branched or cyclic alkyl group having from 1 to 18 carbon atoms, an aralkyl group having from 7 to 18 carbon atoms, or an aryl group having from 6 to 18 carbon atoms, including for example benzyl, cyclohexyl-methyl, phenyl, isopropyl, isobutyl and sec-butyl groups; and the amino acid moiety includes, for example, phenylalanine, cyclohexylalanine, phenylglycine, valine, leucine and isoleucine. R 1 and R 2 in N-protected α-aminocarboxylates (III) indicate amino-protecting groups or indicate the protected condition of the esters. The protecting groups are not specifically defined but may be any that are used in ordinary peptide synthesis. For example, R 1 may be an optionally-substituted, linear, branched or cyclic alkanoyl group having from 2 to 18 carbon atoms, an optionally-substituted, linear, branched or cyclic alkoxycarbonyl group having from 2 to 18 carbon atoms, an aralkyloxycarbonyl group having from 7 to 18 carbon atoms, or an optionally-substituted benzyl group, or may be, together with R 2 , a residue of a dibasic acid having from 8 to 18 carbon atoms; and R 2 may be a hydrogen atom or an optionally-substituted benzyl group, or may be, together with R 1 , a residue of a dibasic acid having from 8 to 18 carbon atoms. Thus, R 1 and R 2 each are independently a hydrogen atom or an amino-protecting group, or they form, as combined, a bifunctional, amino-protecting group. The amino-protecting group includes, for example, so-called, urethane-type protecting groups such as a benzyloxycarbonyl group and a t-butyloxycarbonyl group; acyl-type protecting groups such as an acetyl group and a benzoyl group; and a benzyl-type protecting groups such as a benzyl group and a dibenzyl group. One example of the bifunctional amino-protecting group is a phthaloyl group. R 6 in N-protected α-aminocarboxylates (III) indicates an ester residue of an amino acid. R 6 may be a linear or branched alkyl group having from 1 to 5 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms. It includes, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl and benzyl groups. The reaction of an N-protected α-aminocarboxylate (III) with a carbanion (IV) to give a β-ketosulfoxide (V) may be conducted by dissolving the N-protected α-aminocarboxylate in an inert solvent such as tetrahydrofuran, diethyl ether or methyl t-butyl ether, followed by dropwise adding the resulting solution to a solution of a carbanion of methylsulfoxide as prepared in the manner as mentioned below. The temperature at which the former solution is dropwise added to the latter solution may fall between -70°C and 20°C, preferably between -20°C and 10°C. The reaction temperature may fall between -70°C and 20°C, preferably between -20°C and 10°C. The carbanion can be prepared by reacting a methylsulfoxide of the following general formula (III') with a base. R 5 in the methylsulfoxide of formula (III') represents an alkyl group having 1 or 2 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms. Specific examples of the methylsulfoxide include dimethylsulfoxide, methylethylsulfoxide, methylphenylsulfoxide, and methyl-p-tolylsulfoxide. Of these, preferred is dimethylsulfoxide in view of the economical aspect and its easy availability. To prepare the anion, any base capable of forming it can be employed. However, preferred are sodium amide, sodium hydride, potassium t-butoxide and lithium diisopropylamide. To prepare the anion, one may use an inert solvent such as dimethylsulfoxide, tetrahydrofuran, diethyl ether or methyl t-butyl ether, or mixtures thereof. The temperature at which the anion is prepared lies between -70°C and 80°C, preferably between -20°C and 70°C. The time to be taken for the preparation may be approximately from 30 minutes to 2 hours. The concentration of the anion thus prepared may be approximately from 0.5 mol/litre to 5 mol/litre. To post-treat the reaction mixture, it is poured into an aqueous, acidic solution or, alternatively, the latter is poured into the former. The aqueous, acidic solution may be, for example, an aqueous solution of citric acid, acetic acid or hydrochloric acid. The reaction gives a second asymmetric centre on the sulfur atom in the product, which, therefore, generally consists of two diastereomers or two pairs of diastereomers depending on the starting compound, either a racemic amino acid derivative or an optically-active amino acid derivative. These diastereomers can be used in the next reaction without being specifically isolated. When used to produce the α-keto-hemimercaptal (VI) in the next reaction, the β-keto-sulfoxide is not always required to be purified but a crude product or a non-processed reaction mixture comprising it can be directly used in the next reaction. β-ketosulfoxides (V) as produced after the reaction are novel compounds. To obtain α-keto-hemimercaptals (VI) by reacting the β-ketosulfoxide (V) as obtained in the above with an acid, for example, the β-ketosulfoxide is dissolved in a water-soluble solvent, such as dimethylsulfoxide, dimethylformamide, tetrahydrofuran, dioxane, or alcohol (e.g., methanol, ethanol), and then an aqueous solution of an acid, such as hydrochloric acid, sulfuric acid, hydrobromic acid or p-toluenesulfonic acid is added thereto and reacted at from -20°C to 50°C. The reaction solvent is preferably dimethylsulfoxide, and the acid is preferably hydrochloric acid, since few side reactions occur. The reaction temperature is preferably from 0°C to 30°C. α-keto-hemimercaptals can also be obtained by reacting the β-ketosulfoxide with an acid anhydride followed by hydrolyzing the product. The solvent usable in the reaction includes, for example, dichloromethane, chloroform, tetrahydrofuran, dioxane, diethyl ether, dimethylformamide, dimethylacetamide, pyridine, toluene and ethyl acetate. The acid anhydride includes, for example, acetic anhydride, trifluoroacetic anhydride and trichloroacetic anhydride. In order to smoothly carry out the reaction, a base, such as pyridine, 2-picoline, 2,6-lutidine, 2,4,6-collidine or triethylamine, can be added to the reaction system. In the next reaction of acylating the hydroxyl group of the α-keto-hemimercaptal (VI) to give an α-keto-hemimercaptal-carboxylate (I), the α-keto-hemimercaptal is dissolved in a solvent which is generally used in ordinary acylation, such as dichloromethane, chloroform, tetrahydrofuran, dioxane, diethyl ether, dimethylformamide, dimethylacetamide, pyridine, toluene or ethyl acetate, and then treated with an acylating agent. The acylating agent may be selected from acid chlorides, acid bromides and acid anhydrides. It includes, for example, acetyl chloride, acetic anhydride, benzoyl chloride and benzoyl bromide. In order to smoothly carry out the reaction, a base, such as pyridine, 2-picoline, 2,6-lutidine, 2,4,6-collidine or triethylamine, can be added to the reaction system. The reaction temperature may be from -50°C to 50°C but is preferably in the range -20°C to 30°C. α-keto-hemimercaptal-carboxylates (I) can also be obtained by reacting a β-ketosulfoxide (V) with an acid anhydride. The solvent usable in the reaction includes, for example, dichloromethane, chloroform, tetrahydrofuran, dioxane, diethyl ether, dimethylformamide, dimethylacetamide, pyridine, toluene and ethyl acetate. The acid anhydride includes, for example, acetic anhydride and trichloroacetic anhydride. In order to smoothly carry out the reaction, a base, such as pyridine, 2-picoline, 2,6-lutidine, 2,4,6-collidine or triethylamine, can be added to the reaction system. The α-keto-hemimercaptal-carboxylate prepared as above is rearranged in the presence of a base into a β-amino-α-acy loxythioester (II). The base includes, for example, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, 4-dimethylaminopyridine, pyridine, 2-picoline, 2,6-lutidine, 2,4,6-collidine, triethylamine and diisopropylethylamine. Of these, preferred are 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene. The solvent usable in the reaction includes, for example, dichloromethane, chloroform, tetrahydrofuran, dioxane, diethyl ether, dimethylformamide, dimethylacetamide, dimethylsulfoxide, pyridine, toluene, ethyl acetate, methanol, ethanol, isopropanol and t-butanol. The reaction temperature may be from -80°C to 50°C, but, in general, the diastereoselectivity in the reaction is higher at lower reaction temperatures. The reaction also gives a second asymmetric center in the product, which generally consists of two diastereomers or two pairs of diastereomers depending on the starting compound, either a racemic amino acid derivative or an optically-active amino acid derivative. The ratio of the diastereomers formed, ie the diastereoselectivity, varies depending on the solvent used and the reaction temperature. The diastereomers formed after the reaction can be isolated, for example, through column chromatography or crystallization. The compound as produced according to the method of the present invention has two asymmetric centres (if R 1 and R 2 do not have any additional asymmetric center) and therefore includes four stereoisomers. Only one of the two asymmetric centers is formed through the reaction in the method of the present invention, while the stereo-configuration with respect to the other asymmetric center is kept as such throughout the method. Therefore, when an optically-active α-amino acid derivative is used as the starting compound in the method of the present invention, it always gives a mixture of two diastereomers. Having different physical properties, these two diastereomers can be separated from each other. Accordingly, the present invention is especially advantageous in producing α-hydroxy-β-amino acids having the same stereo-configuration. α-carboxy-thioesters (II) obtained after the above reaction can be hydrolyzed or alcoholyzed into N-protected β-amino-α-hydroxycarboxylic acids or their esters of the following general formula (VII) : wherein R 1 , R 2 and R 3 have the same meanings as above; and R 7 represents a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms. Solvents which may be used in the hydrolysis include, for example, alcoholic solvents such as methanol, ethanol and 2-propanol, and mixed solvents comprising tetrahydrofuran or dioxane, and water. The reagent to be used in the reaction is suitably a metal hydroxide, preferably sodium hydroxide or potassium hydroxide. The reaction temperature may fall between -20°C and 80°C, but preferably between 0°C and 40°C. The solvent used in the alcoholysis may be an alcohol corresponding to the intended ester, preferably methanol or ethanol. Bases which can be used in the reaction include, for example, metal alkoxides, preferably sodium methoxide and sodium ethoxide; metal hydroxides, preferably sodium hydroxide and potassium hydroxide; and metal carbonates, preferably sodium carbonate and potassium carbonate. The present invention is illustrated by the following examples, which, however, are not intended to restrict the scope of the present invention. Example 1 Production of N,N-dibenzyl-(L)-phenvlalanine benzyl ester: 25.0 g (151.3 mmol) of (L)-phenylalanine and 66.67 g (482.4 mmol) of potassium carbonate were dissolved in 100 ml of water, and then 57.51 g (454.3 mmol) of benzyl chloride was added thereto and stirred under heat at 95°C for 19 hours. After having been cooled to room temperature, this was subjected to phase separation with 67 ml of n-heptane and 50 ml of water as added thereto. The organic layer thus separated was washed two times with 50 ml of a solution of methanol/water (1:2) and then dried with anhydrous sodium sulfate. This was filtered and concentrated to obtain 61.64 g (90.5 wt%, 121.8 mmol) of the above compound. The yield was 84.7%. 1H-NMR (300 MHz, CDCl3) δ: 3.00 (dd, 1H), 3.14 (dd, 1H), 3.53 (d, 2H), 3,71 (t, 1H), 3.92 (d, 2H), 5.12 (d, 1H), 5.23 (d, 1H), 6.99-7.40 (m, 20H). Mass spectrum (FAB) 436 (MH + ) Example 2 Production of (3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane: 3.76 g (96.39 mmol) of sodium amide was suspended in 40 ml of dimethylsulfoxide and heated at from 74 to 75°C for 30 minutes. 40 ml of tetrahydrofuran was added to the resulting solution and cooled to 0°C. To this was dropwise added a solution of 15.47g (90.5 wt%, 32.14 mmol) of N,N-dibenzyl-(L)-phenylalanine benzyl ester as dissolved in 20 ml of tetrahydrofuran, while keeping it at 0°C. After these were reacted at 0°C for 30 minutes, 120 ml of an aqueous solution of 10% citric acid and 100 ml of ethyl acetate were added to the reaction mixture, which was thus subjected to phase separation. The aqueous layer thus separated was extracted once with 50 ml of ethyl acetate, and the resulting extract was combined with the previously-separated organic layer and then washed with 60 ml of a saturated saline solution. This was dried with anhydrous sodium sulfate, filtered and concentrated, and the resulting residue was purified through silica gel column chromatography (hexane/ethyl acetate from 2:1 to 1:3) and then crystallized in toluene/hexane to obtain 11.16g of the above compound. The yield was 85.6%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it is about 1:1. 1H-NMR (300 MHz, CDCl3) δ: 2.27 (s, 3/2H), 2.35 (s, 3/2H), 2.97 (dd, 1H), 3.14 (dd, 1/2H), 3.19 (dd, 1/2H), 3.55-3.65 (m, 7/2H), 3.75 (d, 1/2H), 3.85 (d, 2H), 4.01 (d, 1/2H), 4.07 (d, 1/2H), 7.10-7.40 (m, 15H). Mass spectrum (FAB) 406 (MH + ) Example 3 Production of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane: 309.6 mg (0.763 mmol) of (3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane was dissolved in 6 ml of dimethylsulfoxide, and 1.5 ml of 2 N hydrochloric acid was added thereto and stirred at room temperature for 16 hours. While being cooled in an ice bath, this was neutralized with 5 ml of a saturated aqueous solution of sodium hydrogencarbonate added thereto, and then subjected to phase separation with 20 ml of ethyl acetate and 10 ml of water added thereto. The resulting aqueous layer was extracted twice with 10 ml of ethyl acetate. The organic layers were combined, then washed with 20 ml of water and 20 ml of a saturated saline solution in that order, and thereafter dried with anhydrous sodium sulfate. This was filtered and concentrated to obtain 371.5 mg of a crude product of the above compound. 1H-NMR (300 MHz, CDCl3) δ: 1.13 (s, 3H), 3.05 (dd, 1H), 3.18 (dd, 1H), 3.52 (d, 2H), 3.82 (d, 2H), 4.24 (dd, 1H), 5.44 (d, 1H), 7.12-7.38 (m, 15H). Example 4 Production of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane: 173.0 mg of the crude product of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane as obtained in Example 3 was dissolved in 4 ml of dichloromethane and 0.1 ml of pyridine, and 0.05 ml (0.703 mmol) of acetyl chloride was added thereto, while cooling in an ice bath, and stirred at room temperature for 30 minutes. The reaction mixture was extracted with 5 ml of 0.2 N hydrochloric acid and 10 ml of dichloromethane as added thereto. The resulting organic layer was washed with 5 ml of a saturated aqueous solution of sodium hydrogencarbonate and 8 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 144.8 mg (0.324 mmol) of the above compound. The yield was 91.1% (two steps). The integral ratio in 1H-NMR of the compound verified that the compound is a mixture of diastereomers of about 20:1. The data of the major diastereomer are shown below. 1H-NMR (300 MHz, CDCl3) δ: 1.18 (s, 3H), 2.14 (s, 3H), 3.03 (dd, 1H), 3.17 (1H, dd), 3.54 (d, 2H), 3.87 (d, 2H), 4.22 (dd, 1H), 6.41 (s, 1H), 7.10-7.40 (m, 15H). Mass spectrum (FAB) 448 (MH + ) Example 5 Production of methylthio (3S)-(2R,S)-2-acetoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate: 89.5 mg (0.200 mmol) of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 2 ml of toluene and cooled to -30°C, and 0.03 ml (0.201 mmol) of 1,8-diazabicyclo[5.4.0]undec-7-ene was added thereto. After having been stirred at -30°C for 23 hours, this was extracted with 7 ml of toluene and 6 ml of 0.2 N hydrochloric acid as added thereto. The resulting organic layer was washed with 5 ml of a saturated aqueous solution of sodium hydrogencarbonate and 5 ml of a saturated saline solution, then dried with anhydrous sodium sulfate, filtered and concentrated. The resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 95.6 mg (0.214 mmol) of the above compound. The yield was 106.8%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it, of (2S,3S) : (2R,3S), is about 58:42. (2S,3S) diastereomer: 1H-NMR (300 MHz, CDCl3) δ: 2.23 (s, 3H), 2.24 (s, 3H), 2.80 (dd, 1H), 3.08 (dd, 1H), 3.39 (d, 2H), 3.65 (ddd, 1H), 3.88 (d, 2H), 5.83 (d, 1H), 6.96-7.30 (m, 15H). Mass spectrum (FAB) 448 (MH + ) (2R,3S) diastereomer: 1H-NMR (300 MHz, CDCl3) δ: 2.23 (s, 3H), 2.24 (s, 3H), 2.81 (dd, 1H), 3.10 (dd, 1H), 3.56 (d, 2H), 3.59 (m, 1H), 4.04 (d, 2H), 5.07 (d, 1H), 6.96-7.30 (m, 15H). Mass spectrum (FAB) 448 (MH + ) Example 6 Production of methylthio (3S)-(2R,S)-2-acetoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate: 50.6 mg (0.113 mmol) of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 1.1 ml of dimethylformamide and cooled to -30°C, and 0.02 ml (0.134 mmol) of 1,8-diazabicyclo[5.4.0]undec-7-ene was added thereto. After having been stirred at -30°C for 1 hour and 15 minutes, this was extracted with 10 ml of ethyl acetate and 6 ml of 0.2N hydrochloric acid as added thereto. The resulting organic layer was washed with 6 ml of water and 8 ml of a saturated saline solution, then dried with anhydrous sodium sulfate, filtered and concentrated. The resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 44.6 mg (0.100 mmol) of the above compound. The yield was 88.2%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it, of (2S,3S):(2R,3S), is about 92:8. Example 7 Production of (3S)-1-benzoxy-3-(N,N-dibenzyl)amino-1-methyl-thio-2-oxo-4-phenylbutane: 671.2 mg (1.655 mmol) of (3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane was dissolved in 10 ml of dimethylsulfoxide and 7 ml of tetrahydrofuran, and 5 ml of 2N hydrochloric acid was added thereto and stirred at room temperature for 15 hours. While being cooled in an ice bath, this was neutralized with 15 ml of a saturated aqueous solution of sodium hydrogencarbonate as added thereto, and then subjected to phase separation with 50 ml of ethyl acetate and 50 ml of water as added thereto. The resulting aqueous layer was extracted twice with 25 ml of ethyl acetate. The organic layers were combined, washed with 50 ml of water and 50 ml of a saturated saline solution in that order, and then dried with anhydrous sodium sulfate. This was filtered and concentrated to obtain 371.5 mg of a crude product. The crude product was dissolved in 17 ml of dichloromethane and 0.67 ml of pyridine, and 0.23 ml (1.95 mmol) of benzoyl bromide was added thereto, while cooling it in an ice bath, and then stirred at room temperature for 35 minutes. The reaction mixture was extracted with 20 ml of 5N hydrochloric acid and 20 ml of dichloromethane as added thereto. The resulting organic layer was washed with 15 ml of a saturated aqueous solution of sodium hydrogencarbonate and 20 ml of a saturated saline solution, and the dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was purified through silica gel column chromatography (hexane/ethyl acetate from 15:1 to 10:1) to obtain 774.3 mg (1.519 mmol) of the above compound. The yield was 91.8% (two steps). The integral ratio in 1H-NMR of the compound verified that the compound is a mixture of diastereomers of about 13:1. The data of the major diastereomer are shown below. 1H-NMR (300 MHz, CDCl3) δ: 1.31 (s, 3H), 3.05 (dd, 1H), 3.20 (dd, 1H), 3.57 (d, 2H), 3.91 (d, 2H), 4.27 (dd, 1H), 6.66 (s, 1H), 7.12-7.60 (m, 18H), 8.06-8.10 (m, 2H). Mass spectrum (FAB) 510 (MH + ) Example 8 Production of methylthio (3S)-(2R,S)-2-benzoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate: 54.2 mg (0.106 mmol) of (3S)-1-benzoxy-3-N,N-dibenzylamino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 1.1 ml of toluene and cooled to 0°C, and 0.03 ml (0.201 mmol) of 1,8-diazabicyclo[5.4.0]undec-7-ene was added thereto. After having been stirred at 0°C for 2 hours and 20 minutes, this was extracted with 10 ml of toluene and 6 ml of 0.2N hydrochloric acid as added thereto. The resulting organic layer was washed with 5 ml of water, 5 ml of a saturated aqueous solution of sodium hydrogencarbonate and 5 ml of a saturated saline solution, then dried with anhydrous sodium sulfate, filtered and concentrated. The resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 45.0 mg (0.088 mmols) of the above compound. The yield was 83.3%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it, of (2S,3S) : (2R,3S), is about 50:50. (2S,3S) diastereomer: 1H-NMR (300 MHz, CDCl3) δ: 2.23 (s, 3H), 2.97 (dd, 1H), 3.22 (dd, 1H), 3.43 (d, 2H), 3.78 (m, 1H), 3.93 (d, 2H), 6.11 (d, 1H), 7.01-7.26 (m, 15H), 7.50-7.56 (m, 2H), 7.63-7.68 (m, 1H), 8.17-8.19 (m, 2H). Mass spectrum (FAB) 510 (MH + ) (2R,3S) diastereomer: 1H-NMR (300 MHz, CDCl3) δ: 2.24 (s, 3H), 2.90 (dd, 1H), 3.15 (dd, 1H), 3.65 (d, 2H), 3.74 (m, 1H), 4.15 (d, 2H), 5.37 (d, 1H), 7.02-7.05 (m, 2H), 7.19-7.37 (m, 13H), 7.43-7.48 (m, 2H), 7.58-8.63 (m, 1H), 8.09-8.12 (m, 2H). Mass spectrum (FAB) 510 (MH + ) The mixture of diastereomers as obtained in Example 8 was crystallized in ethyl acetate/hexane to give only crystals of the (2R,3S) diastereomer. Example 9 Production of methylthio (3S)-(2R,S)-2-benzoxy-3-(N,N-dibenzyl) amino-4-phenylbutyrate: 54.2 mg (0.106 mmol) of (3S)-1-benzoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 1.1 ml of dimethylformamide and cooled to -30°C, and 0.02 ml (0.134 mmol) of 1,8-diazabicyclo[5.4.0]undec-7-ene was added thereto. After having been stirred at -30°C for 30 minutes, this was extracted with 15 ml of ethyl acetate and 10 ml of 0.2N hydrochloric acid as added thereto. The resulting organic layer was washed with 10 ml of water and 8 ml of a saturated saline solution, then dried with anhydrous sodium sulfate, filtered and concentrated. The resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 50.1 mg (0.098 mmols) of the above compound. The yield was 83.3%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it, of (2S,3S) : (2R,3S), is about 87:13. Example 10 Production of (3S)-(2R,S)-3-(N,N-dibenzyl)amino-2-hydroxy-4-phenylbutyric acid: 87.1 mg (0.171 mmol) of methylthio (3S)-(2R,S)-2-benzoxy-3-N,N-dibenzylamino-4-phenylbutyrate was dissolved in 1.7 ml of tetrahydrofuran, and 0.68 ml of an aqueous solution of 1N sodium hydroxide was added thereto and stirred at room temperature for 2 days. After having been concentrated, this was subjected to phase separation with 2 ml of water, 7 ml of dichloromethane and 0.68 ml of 1 N hydrochloric acid as added thereto. The resulting aqueous layer was extracted twice with 4 ml of dichloromethane. The organic layers as combined were dried with anhydrous sodium sulfate, then filtered and concentrated, and the resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 44.9 mg of the above compound. The yield was 69.9%. Mass spectrum (FAB) 376 (MH + ) Example 11 Production of methyl (3S)-(2R,S)-3-N,N-dibenzylamino-2-hydroxy-4-phenylbutyrate: 53.6 mg (0.105 mmol) of methylthio (3S)-(2R,S)-2-benzoxy-3-N,N-dibenzylamino-4-phenylbutyrate was dissolved in 2 ml of methanol and 0.5 ml of tetrahydrofuran, and 0.04 ml of sodium methoxide (28% methanolic solution) was added thereto and stirred at room temperature for 3 hours and 20 minutes. After having been concentrated, this was subjected to phase separation with 20 ml of ethyl acetate, 5 ml of water and 0.5 ml of 1N hydrochloric acid as added thereto. The resulting organic layer was washed with a saturated saline solution. This was dried with anhydrous sodium sulfate, then filtered and concentrated, and the resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 9.8 mg (0.0252 mmol; yield 24.0%) of (2S,3S) diastereomer of the above compound and 4.5 mg (0.0116 mmol; yield 11.0%) of (2R,3S) diastereomer thereof. (2S,3S) diastereomer: 1H-NMR (300 MHz, CDCl3) δ: 2.81 (dd, 1H), 3.03 (dd, 1H), 3.10 (br. d, 1H, -OH), 3.42 (dt, 1H), 3.53 (s, 3H), 3.66 (d, 2H), 3.81 (d, 2H), 4.48 (m, 1H), 7.05-7.29 (m, 15H). Mass spectrum (FAB) 390 (MH + ) (2R,3S) diastereomer: 1H-NMR (300 MHz, CDCl3) δ: 3.05-3.24 (m, 4H), 3.41 (s, 3H), 3.46 (d, 2H), 4.00 (br. t, 1H), 4.12 (d, 2H), 7.19-7.35 (m, 15H). Mass spectrum (FAB) 390 (MH + ) Example 12 Production of N-benzyloxycarbonyl-(L)-phenylalanine methyl ester: 20.0 g (92.73 mmol) of (L)-phenylalanine methyl ester hydrochloride was suspended in 93 ml of toluene, and 15.82 g (92.73 mmol) of benzyl chloroformate was added thereto. 130 ml of an aqueous solution of 1M sodium carbonate was dropwise added thereto, while keeping it at 7°C or lower, and stirred for 3 hours. After this was subjected to phase separation, the resulting organic layer was washed with 60 ml of 0.1N hydrochloric acid and 60 ml of a saturated aqueous solution of sodium bicarbonate, and then dried with anhydrous sodium sulfate. This was filtered and concentrated to obtain 28.75 g (96.8 wt%, 88.81 mmol) of the above compound. The yield was 95.8%. 1H-NMR (300 MHz, CDCl3) δ: 3.11 (m, 2H), 3.72 (s, 3H), 4.66 (m, 1H), 5.09 (s, 2H), 5.21 (br. d, 1H, -NH), 7.08-7.39 (m, 10H). Mass spectrum (FAB) 314 (MH + ) Example 13 Production of (3S)-3-(N-benzyloxycarbonyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane: 4.98 g (127.7 mmol) of sodium amide was suspended in 40 ml of dimethylsulfoxide and heated at from 72 to 76°C for 50 minutes. 50 ml of tetrahydrofuran was added thereto and cooled to 0°C. To this was dropwise added a solution of 10.33 g (96.8 wt%, 31.91 mmol) of N-benzyloxycarbonyl-(L)-phenylalanine methyl ester as dissolved in 20 ml of tetrahydrofuran, while keeping it at 0°C. After these were reacted at 0°C for 1 hour, the reaction mixture was extracted with 120 ml of an aqueous solution of 10% citric acid and 100 ml of dichloromethane as added thereto. The resulting aqueous layer was extracted once with 60 ml of dichloromethane. The resulting organic layers were combined and washed with 80 ml of a saturated saline solution. This was dried with anhydrous sodium sulfate, then filtered and concentrated, and the resulting residue was crystallized in dichloromethane/ hexane to obtain 8.14 g (22.65 mmols) of the above compound. The yield was 71.0%. The integral ratio in 1H-NMR of the compound verified that the compound is a mixture of diastereomers of about 3:1. 1H-NMR (300 MHz, CDCl3) δ: 2.63 (s, 3/4H), 2.66 (s, 9/4H), 2.94-3.01 (m, 1H), 3.12-3.21 (m, 1H), 3.57 (d, 3/4H), 3.69 (d, 1/4H), 3.89 (d, 1/4H), 4.04 (d, 3/4H), 4.45-4.59 (m, 1H), 5.07 (m, 2H), 5.44 (br. d, 1/4H), 5.64 (br. s, 3/4H), 7.14-7.39 (m, 10H). Mass spectrum (FAB) 360 (MH + ) Example 14 Production of (3S)-3-(N-benzvloxycarbonyl)amino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane: 708.6 mg (1.971 mmol) of (3S)-3-N-benzyloxycarbonylamino-1-methylsulfinyl-2-oxo-4-phenylbutane was dissolved in 15 ml of dimethylsulfoxide and 6 ml of tetrahydrofuran, and 7.5 ml of 2N hydrochloric acid was added thereto and stirred at room temperature for 18 hours. While being cooled in an ice bath, this was neutralized with 15 ml of a saturated aqueous solution of sodium hydrogencarbonate as added thereto, and then subjected to phase separation with 50 ml of ethyl acetate and 50 ml of water as added thereto. The resulting aqueous layer was extracted twice with 25 ml of ethyl acetate. The organic layers were combined, washed with 50 ml of water and 30 ml of a saturated saline solution in that order, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was crystallized in hexane/ethyl acetate to obtain 659.7 mg (1.835 mmol) of a crude product of the above compound. The yield was 93.2%. 1H-NMR (300 MHz, CDCl3) δ: 1.78 (s, 3H), 2.97 (dd, 1H), 3,24 (dd, 1H), 3.87 (dd, 1H), 4.86 (m, 1H), 5.05 (m, 2H), 5.55 (d, 1H), 7.18-7.39 (m, 10H). Mass spectrum (FAB) 360 (MH + ) Example 15 Production of (3S)-1-acetoxy-3-(N-benzyloxycarbonyl)amino-1-methylthio-2-oxo-4-phenylbutane: 404.5 mg (1.125 mmol) of (3S)-3-N-benzyloxycarbonylamino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane was dissolved in 11 ml of dichloromethane and 0.27 ml of pyridine, and 0.12 ml (1.69 mmol) of acetyl chloride was added thereto, while cooling it in an ice bath, and then stirred at room temperature for 3 hours and 30 minutes. The reaction mixture was extracted with 20 ml of 0.5N hydrochloric acid and 15 ml of dichloromethane as added thereto. The resulting organic layer was washed with 12 ml of a saturated aqueous solution of sodium hydrogencarbonate and 15 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was purified through silica gel column chromatography (hexane/ethyl acetate = from 5:1 to 4:1) to obtain 413.3 mg (1.029 mmol) of the above compound. The yield was 91.5%. The integral ratio in 1H-NMR of the compound verified that the compound is a mixture of diastereomers of about 1:1. 1H-NMR (300 MHz, CDCl3) δ: 1.75 (s, 3/2H), 1.98 (s, 3/2H), 2.14 (s, 3/2H), 2.17 (s, 3/2H), 2.99 (m, 1H), 3.17 (m, 1H), 4.97-5.29 (m, 4H), 6.01 (s, 1/2H), 6.15 (s, 1/2H), 7.17-7.37 (m, 10H). Mass spectrum (FAB) 402 (MH + ) Example 16 Production of methylthio (3S)-(2R,S)-2-acetoxy-3-(N-benzyloxycarbonyl)amino-4-phenylbutyrate: 124.5 mg (0.310 mmol) of (3S)-1-acetoxy-3-N-benzyloxycarbonylamino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 3 ml of toluene, and 0.05 ml (0.334 mmol) of 1,8-diazabicyclo[5.4.0] undec-7-ene was added thereto. After having been stirred at room temperature for 1 hour and 55 minutes, this was extracted with 15 ml of ethyl acetate and 7 ml of 1N hydrochloric acid as added thereto. The resulting organic layer was washed with 7 ml of a saturated aqueous solution of sodium hydrogencarbonate and 7 ml of a saturated saline solution, then dried with anhydrous sodium sulfate, filtered and concentrated. The resulting residue was purified through partitioning, silica gel thin-layer chromatography to obtain 121.4 mg (0.302 mmol) of the above compound. The yield was 97.5%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it is about 6:4. 1H-NMR (300 MHz, CDCl3) δ: 2.18 (s, 3H), 2.25 (s, 6/5H), 2,31 (s, 9/5H), 2.77-2.99 (m, 2H), 4.53 (m, 1H), 4.81 (br. d, 2/5H, -NH), 5.04 (d, 2H), 5.11 (br. d, 3/5H, -NH), 5.21 (d, 3/5H), 5.43 (d, 2/5H), 7.16-7.38 (m, 10H). Mass spectrum (FAB) 402 (MH + ) Example 17 Production of (3S)-1-acetoxy-3-(N-benzyloxycarbonyl)amino-1-methylthio-2-oxo-phenylbutane (I, R 1 =benzyloxycarbonyl, R 2 =H, R 3 =benzyl, R 4 =acetyl, R 5 =methyl) 166.2 mg (0.462mmol) of 3S)-3-(N-benzyloxycarbonyl)amino-1-methyl sulfinyl-2-oxo-phenylbutane was dissolved in 4.6 ml of dichloromethane, 0.5 ml of pyridine and 0.5 ml of acetic anhydride, and 3 mg of 4-dimethylaminopyridine was added thereto, and stirred at room temperature for 17.5 hours. To the reaction mixture was added 15 ml of ethyl acetate and 10 ml of 1N hydrochloric acid. The resulting organic layer was washed with 10 ml of a saturated aqueous solution of sodium bicarbonate and 10 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated,and the resulting residue was purified through silica gel thin-layer chromatography to obtain 124.5 mg (0.310 mmol) of the above-entitled compound. The yield was 67.1%. Example 18 Production of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio -2-oxo-phenylbutane (I, R 1 =R 2 =R 3 =benzyl, R 4 =acetyl, R 5 =methyl) 102.4 mg (0.252mmol) of (3S)-3-(N,N-dibenzy)amino-1-methylsulfinyl-2-oxo-phenylbutane was dissolved in 2 ml of dichloromethane, 0.2 ml of pyridine and 0.2 ml of acetic anhydride, and 3 mg of 4-dimethylamino-pyridine was added thereto, and stirred at room temperature for 10 days. To the reaction mixture was added 10 ml of ethyl acetate and 10 ml of 1N hydrochloric acid. The resulting organic layer was washed with 6 ml of water, 7 ml of a saturated aqueous solution of sodium bicarbonate and 7 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was purified through silica gel thin-layer chromatography to obtain 86.6 mg (0.193 mmol) of the above-entitled compound. The yield was 76.8%. Example 19 Production of (3S)-3-(N,N-dibenzyl)amino-1-methyl-sulfinyl-2-oxo-4-phenylbutane (V, R 1 =R 2 =R 3 =benzyl,R 5 =methyl) 3.55g (91.0mmol) of sodium amide was suspended in 53 ml of tetrahydorofuran and 10.8 ml (152 mmol) of dimethylsulfoxide and heated at from 47 to 51°C for 3 hours. The resulting suspension was cooled to -12°C. To this was dropwise added a solution of 13.63g (96.9 wt%, 30.33 mmol) of N,N-dibenzyl-L-phenylalanine methyl ester as dissolved in 18 ml of tetrahydrofuran, while keeping it at -12 to -6°C for 35 minutes. After these were reacted at -12 to -8°C for 1 hour, 110 ml of an aqueous solution of 10% citric acid and 44 ml of ethyl acetate were added to the reaction mixture, which was thus subjected to phase separation. The organic layer was washed with 30 ml of a saturated aqueous solution of sodium bicarbonate and 30ml of a saturated saline solution. This was dried with anhydrous sodium sulfate, filtered and concentrated to obtain the crude above-entitled compound. As the result of HPLC analysis, 12.38 g (30.53mmol) of the above-entitled compound was obtained. The yield was 100%. Example 20 Production of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio -2-oxo-phenylbutane hydrogen chloride salt (VI,R 1 =R 2 =R 3 =benzyl, R 5 =methyl) The crude compound of (3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl -2-oxo-4-phenylbutane (12.38 g (30.53 mmol) was contained ) as obtained in Example 19 was dissolved in 68 ml of acetone and 22.8 ml of dimethylsulfoxide, and 22.8 ml of 2N hydrochloric acid was added thereto and stirred at 30°C for 16 hours. While being cooled in an ice bath, this was neutralized with 50 ml of a saturated aqueous solution of sodium hydrogencarbonate added thereto, and concentrated to remove acetone. Then the resulting solution was subjected to phase separation with 60 ml of ethyl acetate added thereto. The organic layer was washed with 40 ml of a saturated saline solution, and thereafter dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was dissolved in 45.5 ml of ethyl acetate and 55ml of hexane. To this was dropwise added 9.1 ml of 4N hydrogen chloride solution in ethyl acetate. The resulting solid was filtered and washed with 45 ml of ethyl acetate/hexane 1:2, and dried to obtain 11.48 g of a crude product of the above-entitled compound. Example 21 Production of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-phenylbutane (I, R 1 =R 2 =R 3 =benzyl, R 4 =acetyl, R 5 =methyl) 11.48 g of the crude product of (3S)-3-(N,N-dibenzyl) amino-1-hydroxy-1-methylthio-2-oxo-phenylbutane hydrogen chloride salt as obtained in Example 20 was dissolved in 52 ml of dichloromethane and 4.62 ml of pyridine, and 2.22 ml of acetyl chloride was added thereto, while cooling in an ice bath for 5 minutes, and stirred at 10°C for 1 hour. The reaction mixture was extracted with 30 ml of an aqueous solution of 10% citric acid added thereto. The resulting organic layer was washed with 30 ml of a saturated aqueous solution of sodium bicarbonate and 30 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated to obtain the crude above-entitled compound. As the result of HPLC analysis, this crude product contained 9.395 g (20.99mmol) of the above-entitled compound, and the yield was 69.2% (2 steps). Example 22 Production of methylthio (2S,3S)-2-acetoxy-3-(N,N-dibenzyl) amino-4-phenylbutyrate (II, R 1 =R 2 =R 3 =benzyl, R 4 =acetyl, R 5 =methyl) The crude compound of (3S)-1-acetoxy-3-(N,N-dibenzyl) amino-1-methylthio-2-oxo-phenylbutane (9.395 g, 20.99 mmol) as obtained in Example 21 was dissolved in 45 ml of N,N-dimethylformamide and cooled to -31°C, and a solution of 641 mg (4.21mmol) of 1,8-diazabicyclo[5,4,0]undec-7-ene dissolved in 3 ml of N,N-dimethylformamide was added thereto for 10 minutes. After having been stirred at -30°C for 16 hours, this was extracted with 50 ml of an aqueous solution of 10% citric acid and 77 ml of ethyl acetate as added thereto. The resulting organic layer was washed with 50 ml of water + 10 ml of a saturated saline solution, 30 ml of a saturated aqueous solution of sodium bicarbonate and 30 ml of a saturated saline solution in that order, and then dried with anhydrous sodium sulfate. This was filtered and concentrated to the crude above-entitled compound. As the result of HPLC analysis, the ratio of diastereomers constituting it, of (2S,3S) : (2R,3S), is about 89:11 and 8.101 g (18.10mmol) of (2S,3S)-diastereomer was obtained. The yield of (2S,3S)-diastereomer was 86.2%. Example 23 Production of (2S,3S)-3-(N,N-dibenzyl)amino-2-hydroxy-4-phenyl butyric acid dicyclohexylamine salt (VII, R 1 =R 2 =R 3 =benzyl, R 7 =H) The crude compound of methylthio (2S,3S)-2-acetoxy-3 -(N,N-dibenzyl) amino-4-phenylbutyrate (8.101 g, 18.10 mmol) as obtained in Example 22 was dissolved in 90 ml of methanol, and 36 ml of 2N aqueous solution of sodium hydroxide was added thereto and stirred at room temperature for 3.5hours. After these were concentrated to remove methanol, 50 ml of dichloromethane and 12 ml of 6N hydrochloric acid to adjust to pH 1.9 were added to the reaction mixture. After separation, the resulting organic layer was washed with 30 ml of saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was dissolved in 50 ml of acetone. After filtration to remove the insoluble matter and washing it with 30 ml of acetone, to this filtrate was dropwise added 4.43g (24.43mmol) of dicyclohexylamine and the resulting crystal was filtered and washed with 30 ml of acetone, and dried under vacuum to obtain 9.02 g (95.0 wt%, 15.39mmol) of the above-entitled compound. The yield was 85.0%. 1H-NMR (300 MHz,CDCl3) δ: 0.95-1.42 (m, 5H),1.50-1.97 (m, 5H), 2.48 (dd, 1H), 2.77 (m, 2H), 3.03 (dd, 1H), 3.50 (ddd, 1H), 3.60 (d, 2H), 4.02 (d, 2H), 4.44 (d, 1H), 6.95-7.35 (m, 15H). 13C-NMR (75 MHz,CDCl3) δ: 24.61, 25.07, 28.96, 32.69, 52.29, 54.09, 62.06, 69.93, 125.50, 126.21, 127.68, 127.77, 128.55, 129.73, 140.63, 140.83, 178.18. Mass spectrum (FAB) 557 (MH ) Example 24 Production of (3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-5-methyl-2-oxo-hexane (V, R 1 =R 2 =benzyl, R 3 =isobutyl, R 5 =methyl) 1.00g (25.63mmol) of sodium amide was suspended in 10ml of dimethylsulfoxide and heated at from 50 to 60°C for 30 minutes. 10 ml of tetrahydrofuran was added to the resulting solution and cooled to -5°C. To this was dropwise added a solution of 3.38g (10.39mmol) of N,N-dibenzyl-(L)-leucine methyl ester dissolved in 6.5ml of tetrahydrofuran, while keeping it at -5°C for 40 minutes. After these were reacted at -5°C for 1 hour and 20 minutes, 40 ml of an aqueous solution of 10% citric acid and 50ml of ethyl acetate were added to the reaction mixture which was thus subjected to phase separation. The organic layer was washed with 30 ml of a saturated aqueous solution of sodium bicarbonate and 20ml of a saturated saline solution. This was dried with anhydrous sodium salfate, filtered and concentrated, and the resulting residue was purified through silica gel column chromatography (hexane/ethyl acetate 1:1 to 1:3 ) to obtain 3.86 g of the above-entitled compound. The yield was 100%. The integral ratio in 1H-NMR of the compound verified that the ratio of the diastereomers constituting it is about 1:1. 1H-NMR (300 MHz,CDCl3) : 0.80 (d, 3/2H), 0.86 (d, 3/2H), 0.89 (d, 3/2H), 0.90 (d, 3/2H), 1.36-1.50 (m, 2H), 1.83 (m, 1H), 2.57 (s, 3/2H), 2.61 (s, 3/2H), 3.34 (br.d, 1H), 3.48 (dd, 2H), 3.72 (br.d, 2H), 3.81-3.96 (m, 3/2H), 4.09 (d, 1/2H), 7.24-7.39 (m, 10H). Mass spectrum (ESI) 372 (MH ) Example 25 Production of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methyl thio-5-methyl-2-oxo-hexane (VI,R 1 =R 2 =benzyl,R 3 =isobutyl,R 5 =methyl) 2.35g (6.324mmol) of (3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl -5-methyl-2-oxo-hexane was dissolved in 19 ml of dimethyl sulfoxide, and 4.74 ml of 2 N hydrochloric acid was added thereto and stirred at 30°C for 14 hours. While being cooled in an ice bath, this was neutralized with 15 ml of a saturated aqueous solution of sodium bicarbonate added thereto, and then subjected to phase separation with 30 ml of ethyl acetate and 20 ml of water added thereto. The organic layer was washed with 20 ml of water and 20 ml of a saturated saline solution in that order, and thereafter dried with anhydrous sodium sulfate. This was filtered and concentrated to obtain 2.16 g of a crude product of the above-entitled compound. The integral ratio in 1H-NMR of the compound verified that the coupound is a mixture of diastereomers of about 10:1. The data of the major diastereomer are shown below. 1H-NMR(300MHz I CDCl3) δ: 0.85 (d, 3/2H), 0.94 (d, 3/2H), 1.35-1.50 (m, 2H), 1.74 (s, 3H), 1.93 (m, 1H), 3.41 (d, 2H), 3.68 (d, 2H), 3.82-3.90 (m, 2H), 5.50 (br.s, 1H), 7.23-7.36 (m, 10H). Example 26 Production of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio -5-methyl-2-oxo-hexane (I, R 1 =R 2 =benzyl,R 3 =isobutyl, R 4 =acetyl, R 5 =methyl) 1.66g (4.47mmol) of the crude product of (3S)-3-(N,N-dibenzyl) amino-1-hydroxy-1-methylthio-5-methyl-2-oxo-hexane as obtained in Example 25 was dissolved in 16 ml of dichloromethane and 0.54 ml of pyridine, and 0.38 ml of acetyl chloride was added thereto, while cooling in an ice bath, and stirred at room temperature for 1 hour. The reaction mixture was extracted with 15 ml of an aqueous solution of 10% citric acid and 10 ml of dichloromethane as added thereto. The resulting organic layer was washed with 15 ml of a saturated aqueous solution of sodium bicarbonate and 15 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was purified through partitioning, silica gel column chromatography to obtain 1.48g (3.58mmol) of above-entitled compound. The yield was 80.1%. The integral ratio in 1H-NMR of the compound verified that the coupound is a mixture of diastereomers of about 10:1. The data of the major diastereomer are shown below. 1H-NMR(300MHz I CDCl3) δ: 0.83 (d,3H), 0.91 (d,3H), 1.38-1.47 (m,2H), 1.84 (s,3H), 1.86 (m, 1H), 2.18 (s,3H), 3.43 (d,2H), 3.72 (d,2H), 3.84 (dd,1H), 6.48 (s,lH), 7.22-7.37(m,10H). Mass spectrum (ESI) 414 (MH ) Example 27 Production of methylthio (2S,3S)-2-acetoxy-3-(N,N-dibenzyl) amino-5- methylhexanoate (II, R 1 =R 2 =benzyl, R 3 =isobutyl, R 4 =acetyl, R 5 =methyl) 0.61g (1.48 mmol) of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-5-methyl-2-oxo-hexane was dissolved in 7.5 ml of N,N-dimethylformamide and cooled to -30°C, and 0.066 ml of 1, 8-diazabicyclo[5,4,0]undec-7-ene was added thereto. After having been stirred at -30°C for 15.5 hours, this was extracted with 20 ml of an aqueous solution of 10% citric acid and 30 ml of ethyl acetate as added thereto. The resulting organic layer was washed with 20 ml of a saturated aqueous solution of sodium bicarbonate and 20 ml of a saturated saline solution, and then dried with anhydrous sodium sulfate. This was filtered and concentrated, and the resulting residue was purified through partitioning, silica gel column chromatography to obtain 0.60 g of above-entitled compound. The yield was 98%. The integral ratio in 1H-NMR of the compound verified that the ratio of diastereomers constituting it, of (2S,3S):(2R,3S), is about 95:5. The data of the major diastereomer((2S,3S)-form) are shown below. 1H-NMR(300MHz I CDCl3) δ: 0.37 (d, 3H), 0.87 (d, 3H), 1.01 (m, 1H), 1.76-1.86 (m, 2H), 2.23 (s, 3H), 2.26 (s, 3H), 3.25 (m, 1H), 3.31 (d, 2H), 3.92 (d, 2H), 5.83 (d, 1H), 7.21-7.33 (m,10H). Mass spectrum (ESI) 414 (MH )

Claims: A method for producing α-acyloxy-thioesters of a general formula (II) : wherein R 1 represents an optionally-substituted, linear, branched or cyclic alkanoyl group having from 2 to 18 carbon atoms, an optionally-substituted, linear, branched or cyclic alkoxycarbonyl group having from 2 to 18 carbon atoms, an aralkyloxycarbonyl group having from 7 to 18 carbon atoms, or an optionally-substituted benzyl group, or represents, together with R 2 , a residue of a dibasic acid having from 8 to 18 carbon atoms; R 2 represents a hydrogen atom or an optionally-substituted benzyl group, or represents, together with R 1 , a residue of a dibasic acid having from 8 to 18 carbon atoms; R 3 represents an optionally-substituted, linear, branched or cyclic alkyl group having from 1 to 18 carbon atoms, an aralkyl group having from 7 to 18 carbon atoms, or an aryl group having from 6 to 18 carbon atoms; R 4 represents an optionally-substituted, linear, branched or cyclic alkanoyl group having from 2 to 18 carbon atoms, or an arylcarbonyl group having from 7 to 18 carbon atoms; and R 5 represents an alkyl group having 1 or 2 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms, which method comprises rearranging, in the presence of a base, an α-keto-hemimercaptal-carboxylate of a general formula (I) : wherein R 1 , R 2 , R 3 , R 4 and R 5 have the same meanings as above. The method as claimed in claim 1, in which the compound of formula (I) is obtained by reacting an N-protected α-aminocarboxylate of a general formula (III) : wherein R 1 , R 2 and R 3 are as defined in claim 1 and R 6 represents a linear or branched alkyl group having from 1 to 5 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms, with a carbanion of a general formula (IV) : wherein R 5 is as defined in claim 1 to thereby convert the ester into a β-ketosulfoxide of a general formula (V): wherein R 1 , R 2 , R 3 and R 5 have the same meanings as above, then rearranging the sulfoxide in the presence of an aqueous solution of an acid to give an α-keto-hemimercaptal of a general formula (VI) : wherein R 1 , R 2 , R 3 and R 5 have the same meanings as above, and thereafter acylating the hemimercaptal. The method as claimed in claim 1 or claim 2, in which R 3 in formula (I) is bonded to the carbon atom as existing therein in the S-configuration. The method as claimed in claim 1 or claim 2, in which R 3 in formula (I) is bonded to the carbon atom as existing therein in the R-configuration. Compounds of a general formula (V): wherein R 1 , R 2 , R 3 and R 5 are as defined in claim 1; provided that if R 1 is acetyl, R 2 is hydrogen and R 5 is methyl, then R3 is neither nor Compounds as claimed in claim 5, having a (3S)-configuration. Compounds as claimed in claim 5, having a (3R)-configuration. Compounds of a general formula (I): wherein R 1 , R 2 , R 3 , R 4 and R 5 are as defined in claim 1. Compounds of a general formula (II) : wherein R 1 , R 2 , R 3 , R 4 and R 5 are as defined in claim 1. Compounds of a general formula (VI): wherein R 1 , R 2 , R 3 and R 5 are as defined in claim 1. A method for producing an α-hydroxy-β-aminocarboxylic acid of general formula (VII) : wherein R 1 , R 2 and R 3 are as defined in claim 1, and R 7 represents a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, an aryl group having from 6 to 18 carbon atoms, or an aralkyl group having from 7 to 18 carbon atoms, which method comprises (a) carrying out the method of any of claims 1 - 4 to produce an α-acyloxy-thioester of formula (II); and (b) hydrolyzing or alcoholyzing said α-acyloxy-thioester (II) to produce a compound of formula (VII).

Inventors: HONDA YUTAKA, IZAWA KUNISUKE, SUZUKI TAKAYUKI, HONDA, YUTAKA, IZAWA, KUNISUKE, SUZUKI, TAKAYUKI, Honda, Yutaka, c/o Ajinomoto Co., Inc., Izawa, Kunisuke, c/o Ajinomoto Co., Inc., Suzuki, Takayuki, c/o Ajinomoto Co., Inc.
Applicants: AJINOMOTO KK, AJINOMOTO CO., INC.
Application year: 1996
Main classification: C07C327
IPC codes: C07C317, C07C323, C07C327