Improving Enantioselectivity of Candida parapsilosis for Deracemization of (R,S)-1-phenyl-1,2-ethanediol by Addition of Alcohols during Cell Cultivation

(R,S)-1-phenyl-1,2-ethanediol (PED) was deracemized to the corresponding (S)-enantiomer by using whole cells of the Candida parapsilosis as a biocatalytic system. To improve enantioselectivity of Candida parapsilosis, a new method was developed by the addition of alcohols or ketones during cell cultivation. The results showed that there were little effect caused by addition of diols, middle-chain alcohols and ketones, but there were increases in cell mass, enantiomeric excess and yield by addition of short-chain (C1～C4) alcohols such as ethanol (EtOH) especially. Effects of the phase and concentration of added ethanol during cell cultivation on enantioselectivity of the cells were also investigated. When cultivation continued for 16 h under the condition of 0.1% (-) ethanol, the cell mass increased by 10% and the relative enzyme activity increased by 30%. Meanwhile, the conversion of 105 mmol/L R,S-PED to S-PED with the cells cultured under this condition, an improvement of enantiomeric excess from 91% to 99% and a yield up to 92% were achieved.