Exploring the Biocatalytic Scope of a Novel Enantioselective Halohydrin Dehalogenase from an Alphaproteobacterium

A gene encoding halohydrin dehalogenase from an alphaproteobacterium ( Ab HHDH) was identified, cloned and over-expressed in Escherichia coli. Ab HHDH was able to catalyze the stereoselective dehalogenation of prochiral and racemic halohydrins. It showed the highest enantioselectivity in the dehalogenation of 20 mM ( R,S )-2-bromo-1-phenylethanol, which yielded ( S )-2-bromo-1-phenylethanol with 99% ee and 34.5% yield. Moreover, Ab HHDH catalyzed the azidolysis of epoxides with low to moderate ( S )-enantioselectivity. The highest enantioselectivity ( E = 18.6) was observed when ( R,S )-benzyl glycidyl ether was used as the substrate. A sequential kinetic resolution catalyzed by HHDH was employed for the synthesis of chiral 1-chloro-3-phenoxy-2-propanol. We prepared enantiopure ( S )-isomer with a high enantiopurity of ee > 99% and a yield of 30.7% ( E -value: 21.3) by kinetic resolution of 20 mM substrate. The ( S )-isomer with 99% ee readily obtained from 40 to 150 mM ( R,S )-1-chloro-3-phenoxy-2-propanol. Taken together, the results of this study demonstrate the applicability of this HHDH for the production of optically active compounds.