Stereoselective reduction of ethyl 4-chloro-3-oxobutanoate by Escherichia coli transformant cells coexpressing the aldehyde reductase and glucose dehydrogenase genes

The asymmetric reduction of ethyl 4-chloro-3-oxobutanoate (COBE) to ethyl ( R)-4-chloro-3-hydroxybutanoate [(R)-CHBE] using Escherichia coli cells, whi ch coexpress both the aldehyde reductase gene from Sporobolomyces salmonico lor and the glucose dehydrogenase (GDH) gene from Bacillus megaterium as a catalyst was investigated. In an organic solvent-water two-phase system, (R )-CHBE formed in the organic phase amounted to 1610 mM (268 mg/ml), with a molar yield of 94.1% and an optical purity of 91.7% enantiomeric excess. Th e calculated turnover number of NADP(+) to CHBE formed was 13 500 mol/mol. Since the use of E. coli JM109 cells harboring pKAR and pACGD as a catalyst is simple, and does not require the addition of GDH or the isolation of th e enzymes, it is highly advantageous for the practical synthesis of (R)-CHB E.