Nearly perfect kinetic resolution of racemic o-nitrostyrene oxide by AuEH2, a microsomal epoxide hydrolase from Aspergillus usamii, with high enantio- and regio-selectivity.

Only a few known epoxide hydrolases (EHs) displayed activity towards o-nitrostyrene oxide (4a), presumably owing to the large steric hindrance caused by o-nitro substituent. Therefore, excavating EHs with high activity and enantio- and/or regio-selectivity towards racemic (rac-) 4a is essential but challenging. Here, AuEH2 from Aspergillus usamii was expressed in E. coli BL21(DE3). E. coli/Aueh2, an E. coli transformant expressing AuEH2, possessed EH activities of 16.2-184 U/g wet cell towards rac-styrene oxide (1a) and its derivatives (2a-13a), and the largest enantiomeric ratio of 96 towards rac-4a. The regioselectivity coefficients, β and β, of AuEH2 were determined to be 99.2% and 98.9%, suggesting that it regiopreferentially attacks the C in the oxirane rings of (R)- and (S)-4a. Then, the nearly perfect kinetic resolution of 20 mM rac-4a in pure water was carried out using 20 mg/mL wet cells of E. coli/Aueh2 at 25 °C for 50 min, retaining (S)-4a with over 99% ee and 48.9% yield, while producing (R)-o-nitrophenyl-1,2-ethanediol (4b) with 95.3% ee and 49.8% yield. To elucidate the molecular mechanism of AuEH2 with high enantiopreference for (R)-4a, its crystal structure was solved by X-ray diffraction and the molecular docking of AuEH2 with (R)- or (S)-4a was simulated.