Efficient Biocatalytic Synthesis of (R)-2-Chloro-1-(3,4-difluorophenyl)ethanol by the Short-Chain Dehydrogenase PpKR8 from Paraburkholderia phymatum STM815

Bioreductions catalyzed by ketoreductases play an important role in the synthesis of chiral alcohols. However, the synthesis of (R)-2-chloro-1-(3,4-difluorophenyl)ethanol (24b), an important chiral intermediate for the synthesis of the anticoagulant ticagrelor, poses significant challenges in terms of high substrate concentration requirements that limit its production. In this study, a novel NADH-dependent, short-chain dehydrogenase, PpKR8, from Paraburkholderia phymatum STM815, exhibited excellent enantioselectivity and high activity for the production of (R)-CFPL (24b) through the reduction of 2-chloro-1-(3,4difluorophenyl)ethanone (24a). The coexpression of PpKR8 and glucose dehydrogenase from Bacillus subtilis in Escherichia coli allowed up to 300 g/L (1.57 M) CFPO (24a) to be completely converted into 24b with 99.9% enantiomeric excess and a high space-time yield (728 g/(L day)). Substrate specificity assays demonstrated a broad substrate spectrum for PpKR8, which included 35 alpha/beta-ketoesters, aromatic ketones, and heterocyclic ketones. Moreover, three additional optically pure chiral alcohols that are used as important drug intermediates were synthesized at high substrate concentrations (150-330 g/L), demonstrating the excellent industrial potential of PpKR8-mediated bioreductions.