Development of an enzymatic process for the synthesis of (1S)-2-chloro-1-(3, 4-difluorophenyl) ethanol, the key intermediate of ticagrelor

Asymmetric bioreductions catalyzed by ketoreductases have shown considerable potential in the synthesis of chiral alcohols. However, the synthesis routes of (1S)-2-chloro-1-(3, 4-difluorophenyl) ethanol ((S)-CFPL), a key chiral intermediate in the synthesis of ticagrelor, still pose significant challenges in term of unsatisfactory substrate loading and production cycle. In this study, a structure-guided rational design was applied to a ketoreductase from Candida glabrata (CgKR1) for the asymmetric reduction of the ketone precursor 2-chloro-1-(3, 4-difluorophenyl) ethanone (CFPO). A number of mutants were obtained with remarkably improved activity and inversed stereoselectivity compared with CgKR1-WT. In particular, F92V/Y208T mutant and F92T/Y208V mutant exhibited strict S-stereoselectivity and extremely high catalytic activity for CFPO. In addition, CFPO with the concentration of 200 g/L can be completely converted into (S)-CFPL on a preparative scale (5.0 g, 92.8% isolated yield) in 4 h through optimizing some parameters in the reduction process, delivering a high space-time yield (STY) of 1200 g L−1 day−1. This study not only provides insight into the relationship between the structure and function of CgKR1, but also establishes an efficient enzymatic process for the biocatalytic synthesis of crucial chiral intermediate (S)-CFPL of ticagrelor.