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A key intermediate, S-(−)-3-benzoylthio-2-methylpropanoic acid (1) was made in high optical purity by the lipase-catalyzed stereoselective esterification of racemic 1 with methanol in an organic solvent system. Among various lipases evaluated, Amano P-30 lipase from Pseudomonas sp. efficiently catalyzed the esterification of 1 to yield R-(+) methyl ester and unreacted S-(−) 1. A reaction yield of 40 mol% and an optical purity of 97.2% were obtained for compound 1 at a substrate concentration of 0.1 m (22 mg/ml). Lipase P-30 was immobilized on Accurel polypropylene (PP) and the immobilized enzyme was reused (23 cycles) in the esterification reaction without loss of enzyme acitivity, productivity or optical purity. Among various solvents evaluated, toluene was found to be the most suitable organic solvent and methanol was the best alcohol for the esterification of racemic 1 by immobilized lipase. Substrate concentrations as high as 1.0 m were used in the esterification reaction. When the temperature was increased from 28° C to 60° C, the reaction time required for the esterification of 0.1 m substrate decreased from 16 h to 2 h. On increasing the methanol to substrate molar ratio from 1:1 to 4:1, the rate of esterification decreased. A lipase fermentation using Pseudomonas sp. ATCC 21 808 was developed. In the batch-fermentation process, 56 units/ml of extracellular lipase activity was obtained. A fed-batch process using soybean oil gave a significant increase in the lipase activity (126 units/ml). Crude lipase recovered from the filtrate by ethanol precipitation and immobilized on Accurel PP was also effective: S-(−) compound 1 was obtained in 35 mol% yield and 95% optical purity.

Several microbial cultures were screened for the ability to catalyse the reduction of N-(4-(1-oxo-2-chloroacetyl ethyl) phenyl methane sulfonamide (1). The chiral intermediate (+)N-(4-(1-hydroxy-2-chloroethyl) phenyl methane sulfonamide (2) was prepared by the stereoselective microbial reduction of the parent ketone 1. Compound 2 is a potential chiral intermediate for synthesis of 4-(2-isopropylamino-1-hydroxyethyl) phenyl methanesulfonanilide (d-sotalol), a beta-receptor antagonist. Microorganisms from the genera Rhodococcus, Nocardia, and Hansenula reduced 1 to 2. A reaction yield of >50% and optical purities of >90% were obtained. The best strain (H.polymorpha ATCC 26012) effectively reduced compound 1 to compound 2 in 95% reaction yield and 99% optical purity. Compound 2 (8.2 g) was isolated from a 3-1 preparative batch in 68% overall yield. Isolated compound 2 had a specific rotation of +20° (CH2Cl2, C-1), an optical purity of 99.5%, and a chemical purity of 97% as analyzed by gas chromatography and HPLC. The nuclear magnetic resonance and mass spectra of compound 2 prepared by bioreduction and a standard chemical sample of 2 were virtually identical. Cell extracts of H. polymorpha in the presence of glucose dehydrogenase, glucose and nicotinamide adenine dinucleotide (NAD +) catalyzed the reduction of 1 to 2 with 98% reaction yield and resulted in an optical purity of 99.4%.

A chiral compound [4R-[4α,6s(E)]]-6-[4,4-bis(4-fluorophenyl)-3-(1-methyl-1H-tetrazol-5-yl)-1,3-butadienyl]-tetrahydro-4-hydroxy-2H-pyran-2-one (R-(+)-1) was prepared by the lipase-catalysed stereoselective acetylation of racemic 1 in an organic solvent. Chiral R-(+)-1 is a hydroxymethyl glutaryl coenzyme A (HMG CoA) reductase inhibitor and a potential anticholesterol drug candidate. Among various lipases evaluated, lipase PS-30 from Pseudomonas species efficiently catalysed acetylation of the undesired enantiomer of racemic 1 to yield the S-(−)-acetylated product 2 and unreacted desired R-(+)-1. A reaction yield of 48 mol% and an optical purity of 98% were obtained for R-(+)-1 when the reaction was conducted in toluence as solvent in the presence of isopropenyl acetate as acyl donor. Lipase PS-30 was immobilized on Accurel polypropylene (PP) and the immobilized enzyme was reused (five cycles) in the acetylation reaction without loss of enzyme activity, productivity, or optical purity of the R-(+)-1. The enzymatic acetylation process was scaled-up to 501 and a 640-l volume (preparative batches) at a substrate concentration of 4 g/l. R-(+)–1 was recovered from the preparative batches in 68–71% recovery yield with 98.5% gas chromatography homogeneity index and 98.5% optical purity. The S-(−) acetate 2 produced by the acetylation reaction was enzymatically hydrolysed by lipase PS-30 in a biphasic system to prepare the corresponding S-(−)-1.

Biotransformations were developed to oxidize N epsilon-carbobenzoxy(CBZ)-L-lysine and to reduce the product keto acid to L-CBZ-oxylysine. Lysyl oxidase (L-lysine: O2 oxidoreductase, EC 1.4.3.14) from Trichoderma viride was relatively specific for L-lysine and had very low activity with N epsilon-substituted derivatives. L-Amino acid oxidase (L-amino acid: O2 oxidoreductase [deaminating], EC 1.4.3.2) from Crotalus adamanteus venom had low activity with L-lysine but high activity with N epsilon-formyl-, t-butyoxycarbonyl(BOC)-, acetyl-, trifluoroacetyl-, or CBZ-L-lysine. L-2-Hydroxyisocaproate dehydrogenase (EC 1.1.1.-) from Lactobacillus confusus catalyzed the reduction by NADH of the keto acids from N epsilon-acetyl-, trifluoroacetyl-, formyl- and CBZ-L-lysine but was inactive with the products from oxidation of L-lysine, L-lysine methyl ester, L-lysine ethyl ester or N epsilon-t-BOC-L-lysine. Providencia alcalifaciens (SC9036, ATCC 13159) was a good microbial substitute for the snake venom oxidase and also provided catalase (H2O2:H2O2 oxidoreductase EC 1.11.1.6). N epsilon-CBZ-L-Lysine was converted to CBZ-L-oxylysine in 95% yield with 98.5% optical purity by oxidation using P. alcalifaciens cells followed by reduction of the keto acid using L-2-hydroxyisocaproate dehydrogenase. NADH was regenerated using formate dehydrogenase (formate: NAD oxidoreductase, EC 1.2.1.2) from Candida boidinii. The Providencia oxidase was localized in the particulate fraction and catalase activity was predominantly in the soluble fraction of sonicated cells. The pH optima and kinetic constants were determined for the reactions.

A key chiral intermediate lactol(3)[3aS (3aα,4α,7α,7aα)]-hexahydro-4,7-epoxy-isobenzofuran-1 (3H)-one was prepared for the total synthesis of a new thromboxane antagonist. The stereoselective hydrolysis of (exo,exo)-7-oxabicyclo[2.2.1]heptane-2,3-dimethanol, diacetate ester (1) to the corresponding chiral monoacetate ester (2) was carried out with lipases, among which Amano P-30 lipase from Pseudomonas sp. was most effective since it gave the desired enantiomer of monoacetate ester. A yield of 75 mol% and optical purity of >99% was obtained when the reaction was conducted in a biphasic system with 10% toluene at 5 g/l of the substrate. Lipase P-30 was immobilized on Accurel polypropylene (PP) and the immobilized enzyme was reused (five cycles) without loss of enzyme activity, productivity or optical purity. The reaction process was scaled-up to 80 1 (400 g substrate) and monoacetate (2) was isolated in 80 mol% yield with 99.3% optical purity as determined by chiral HPLC and nuclear magnetic resonance (NMR) analysis. A gas chromatography of 99.5% and specific rotation, [α]D of -7.6° was obtained. The chiral monoacetate ester (2) was oxidized to its corresponding aldehyde and subsequently hydrolyzed to give lactol (3).

A key intermediate (S(−) 2-cyclohexyl-1,3-propanediol monoacetate) was made with high optical purity for the total synthesis of a new angiotensin converting enzyme inhibitor, Fosinopril. The stereoselective hydrolysis of 2-cyclohexyl-1,3-propanediol diacetate (I) and 2-phenyl-1,3-propanediol diacetate (II) was carried out with lipases. Among various lipases evaluated, only porcine pancreatic lipase (PPL) and Chromobacterium viscosum lipase demonstrated efficient conversion and gave the desired enantiomer of monoacetate. In aqueous solution, the desired S(−) monoacetate exhibited an optical purity of 65%–80% (30%–60% enantiomeric excess [e.e.]). However, when the same reactions were conducted in a biphasic system, the product S(−) monoacetate exhibited an optical purity of 99%–100% (98%–100% e.e.). The high purity product was achieved with 65 mol% yield at 1% substrate concentration. Among various solvents evaluated in biphasic systems, efficient hydrolysis was achieved in toluene, cyclohexane, and trichloro-trifluoroethane. The crude PPL was partially purified and two lipase fractions (A and B) were identified. Lipases A and B had a molecular mass of 38 000 and 40 000 daltons, respectively, and both were found to catalyze the hydrolysis of I and II to the appropriate monoacetate in a biphasic system.