Near-perfect kinetic resolution of racemic p-chlorostyrene oxide by SIEH1, a novel epoxide hydrolase from Solanum lycopersicum with extremely high enantioselectivity

摘要

An open reading frame of sleh1, a gene encoding for a novel epoxide hydrolase from Solarium lycopersicum (SlEH1), was amplified by RT-PCR and expressed in E. coli BL21(DE3). The substrate spectrum assay showed that E. coli/sleh1 had EH activities towards all tested substrates except for racemic (rac-) 5a, and the highest enantiomeric ratio (E > 200) towards rac-2a, retaining (R)-2a with 99.1% ee(s) and 49.2% yield(s) and affording (R)-2b with 89.8% ee(p) and 46.7% yield(p). Besides, E. coli/sleh1 also hydrolyzed of rac-7a-9a with moderate regioselectivities, producing (S)- or (R)-7b-9b with 40.5-51.3% ee(p) and 69.4-75.2% yield(p). The pH optimum and stability of the purified SIEH1 were 7.5 and at a range of 6.5-8.5, and it was thermostable at or below 40 degrees C. Its catalytic efficiency (k(cat)(s)/K-m(s) = 7.49 mM(-1) s(-1)) for (S)-2a was much higher than that for (R)-2a. The gram-scale kinetic resolution of 150 mM rac-2a was carried out by E. coli/sleh1 at 20 degrees C for 8 h, producing (R)-2a with 98.2% ee(s) and 45.3% overall yield s after purification by silica gel column chromatography. Furthermore, the source of extremely high enantioselectivity of SlEH1 towards rac-2a was analyzed by molecular docking simulations. (C) 2019 Published by Elsevier B.V.