Stereoselective synthesis of a key chiral intermediate of (S)-Rivastigmine by AKR-GDH recombinant whole cells.

Herein, three aldo/ketoreductases (AKRs) were obtained and used to prepare N- ethyl-methyl-carbamic acid-3-[(1S)-hydroxy-ethyl]-phenyl ester ((S)-NEMCA-HEPE), which is a key intermediate of (S)-Rivastigmine. To avoid the usage of extra cofactors, the recombinant whole-cells containing AKRs and glucose dehydrogenase (GDH) were constructed and applied in the reduction reaction. The excellent conversion of 83.3% and enantiomeric excess (e.e.p ) of 99.9% for (S)-NEMCA-HEPE was obtained when the recombinant whole cell (iolS-GDH) was selected as a catalyst. Additional introduction of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4 ) in the whole cell-catalyzed reaction system, the reaction rates can be further enhanced, and the reaction conversion can be increased to 98.3% only in 1 h. The analysis of flow cytometry (FCM) and ultraviolet spectrum shows that [BMIm]BF4 can greatly enhance the whole cell-catalyzed reaction activities by affecting the permeability of cell membrane. This study provided a low-cost and efficient process for preparation of (S)-NEMCA-HEPE with high optical purity.