Enantioconvergent hydrolysis of racemic epoxides at elevated concentrations in Tween-20/phosphate buffer by the corresponding epoxide hydrolases

Abstract

For effectively actualizing the gram-scale preparation of (R)-phenyl-1,2-ethanediol (PED) via the enantioconvergent hydrolysis of racemic (rac-) styrene oxide (SO) at elevated concentration using whole-cell of E. coli/sleh2, the reaction media were constructed by adding non-ionic surfactants, organic solvents, and deep eutectic solvents into phosphate buffer, respectively. After screening, using conversion ratio (c) of rac-SO as the main criterion, the most suitable reaction medium, 30% (v/v) Tween-20/phosphate buffer (50 mM, pH 7.0), was identified, where the c of 400 mM rac-SO was elevated to > 99% from 62.1% in phosphate buffer. The scale-up enantioconvergent hydrolysis of 400 mM rac-SO was carried out in 50 mL Tween-20/aqueous buffer using 200 mg/mL wet cells of E. coli/sleh2 at 20 °C for 8 h, affording (R)-PED with 96.2% eep and 97.2% yield. The experimental results demonstrated that the identified medium can alleviate the inhibition of (R)-PED on the EH activity of E. coli/sleh2. Furthermore, this medium was also applied to the hydrolytic reactions of 300 mM rac-m-nitrostyrene oxide (mNSO) and m-chlorostyrene oxide (mCSO) using the corresponding E. coli/rpehL360C and /pveh1Z6, respectively. The c values of rac-mNSO and mCSO were increased to over 99% from 72.4% and 52.1% in phosphate buffer.