Engineering of Candida glabrata Ketoreductase 1 for Asymmetric Reduction of α-Halo Ketones

Enantiopure halohydrins, which are important building blocks for pharmaceutical agents, could be synthesized by biocatalytic reduction of alpha-halo ketones using ketoreductases. In this study, Candida glabrata ketoreductase 1 (CgKR1) variants with >99% stereoselectivity toward alpha-halo ketones, such as 2-chloroacetophenone, 2-chloro-4'-fluoroacetophenone, and 2-bromoacetophenone, were obtained through engineering of CgKR1 at residues Phe92 and Tyr208. Interestingly, asymmetric reduction of these a-halo ketones by all the variants of CgKR1 followed anti-Prelog's rule, which is rarely found in natural ketoreductases. Moreover, the biocatalytic processes for reduction of these aromatic alpha-halo ketones with high substrate loading were achieved by coexpression of glucose dehydrogenase (GDH) for NADPH regeneration, indicating the potential of practical applications of these variants.