Asymmetric Reduction of Ethyl 4-Chloro-3-Oxobutanoate to Ethyl 4-Chloro-3-Hydroxybutanoate by Yeast Cells in Aqueous Phase

The asymmetric reduction of ethyl 4-chloro-3-oxobutanoate (COBE) to optically active ethyl 4-chloro-3-hydroxybutanoate (CHBE) catalyzed by yeast cells in aqueous phase was investigated. The reduction was conducted in Tris-HCl buffer, and the concentrations of COBE and CHBE and the optical purity of product were determined by capillary GC and HPLC equipped with a chiralcel OB column, respectively. The product was mainly D-(S)-CHBE. Both the yield and the stereo-selectivity of CHBE were higher for the reaction. However, the product was mainly R-CHBE when the initial concentration of COBE was low, and the product was mainly S-CHBE when the initial concentration of COBE was higher. The CHBE had a few of inhibition effects on the reaction. In the COBE reduction, a co-substrate was required to regenerate the NAD(P)H. Ethanol, isopropanol and secondary butyl alcohol as the co-substrate were advantageous to the stereo-selectivity of S-CHBE, but glucose as the co-substrate could achieve higher yield. The higher temperature and pH 8 0 were favorable to the production of S-CHBE. The cells in logarithmic growth phase and cultured under anaerobic condition were also favorable to the stereo-selectivity of S-CHBE. 92% for yield and 90% for ee of S-CHBE were obtained respectively under appropriate reaction conditions.