The asymmetric reduction of ethyl 4-chloro-3-oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE) was investigated. Escherichia coli cells expressing both the carbonyl reductase (S1) gene from Candida magnoliae and the glucose dehydrogenase (GDH) gene from Bacillus megaterium were used as the catalyst. In an organic-solvent-water two-phase system, (S)-CHBE formed in the organic phase amounted to 2.58 M (430 g/l), the molar yield being 85%. E. coli transformant cells coproducing S1 and GDH accumulated 1.25 M (208 g/l) (S)-CHBE in an aqueous monophase system by continuously feeding on COBE, which is unstable in an aqueous solution. In this case, the calculated turnover of NADP+ (the oxidized form of nicotinamide adenine dinucleotide phosphate) to CHBE was 21,600 mol/mol. The optical purity of the (S)-CHBE formed was 100% enantiomeric excess in both systems. The aqueous system used for the reduction reaction involving E. coli HB101 cells carrying a plasmid containing the S1 and GDH genes as a catalyst is simple. Furthermore, the system does not require the addition of commercially available GDH or an organic solvent. Therefore this system is highly advantageous for the practical synthesis of optically pure (S)-CHBE.

Chiral alcohols are useful intermediates for many pharmaceuticals and chemicals. Enzymatic asymmetric reduction of prochiral carbonyl compounds is a promising method for producing chiral alcohols. There have been many attempts to construct bioreduction systems for the industrial production of chiral alcohols. This review focuses on the establishment of a novel bioreduction system using an Escherichia coli transformant co-expressing genes for carbonyl reductase and cofactor-regeneration enzyme. This bioreduction system could be useful as an all-purpose catalyst for asymmetric reduction reactions.

Arthrobacter sp. KNK168 shows (R)-enantioselective transaminase [(R)-transaminase] activity, which converts prochiral ketones into the corresponding chiral (R)-amines in the presence of an amino donor. The cultural conditions and reaction conditions for asymmetric synthesis of chiral amines with this microorganism were examined. The transaminase was inducible, and its production was enhanced by the addition of sec-butylamine and 3-amino-2,2-dimethylbutane to the culture medium. (R)-1-Phenylethylamine was a good amino donor for amination of 3,4-dimethoxyphenylacetone with Arthrobacter sp. KNK168. Under the optimum conditions, 126 mM (R)-3,4-dimethoxyamphetamine (DMA) [>99% enantiomeric excess (ee)] was synthesized from 154 mM 3,4-dimethoxyphenylacetone and 154 mM (R)-1-phenylethylamine through the whole cell reaction with an 82% conversion yield. (R)-Enantiomers of other amines, such as (R)-4-methoxyamphetamine, (R)-1-(3-hydroxyphenyl)ethylamine and (R)-1-(3-hydroxyphenyl)ethylamine, were also synthesized from the corresponding carbonyl compounds through asymmetric amination with Arthrobacter sp. KNK168.

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