Efficient asymmetric hydrolysis of styrene oxide by Mung bean epoxide hydrolases in a supercritical CO2/buffer biphasic system

Abstract

The asymmetric hydrolysis of styrene oxide (SO) by Mung bean epoxide hydrolases in a supercritical carbon dioxide (scCO2)/buffer biphasic system was investigated. With the addition of 0.80 M sodium bicarbonate, the yield of (R)-1-phenyl-1,2-ethanediol ((R)-PED) improved from 20.8% to 47.1%. Compared to the case of the aqueous monophasic system, the enantiomer excess (ee) of (R)-PED improved from 81.8% to 91.5%. Under the optimized conditions for the enzymatic reaction, i.e., at a pressure, temperature, SO concentration, and water content of 12 MPa, 40 °C, 80 mM, and 6.0% (v/v), respectively, an (R)-PED yield of 49.2% and ee of 94.1% were achieved. As the water content had a significant effect on the (R)-PED yield and ee, a stepwise reaction method was adopted. When the initial water content was 8.0% (v/v) and 1% (v/v) water was added at intervals of 1 h, the (R)-PED yield and ee reached 49.1% and 97.2%, respectively.