Semi-rational design of an imine reductase for asymmetric synthesis of alkylated S-4-azepanamines

Although imine reductase (IRED)-catalyzed reductive amination is promising for the synthesis of alkylated chiral amines, precisely regulating the stereoselectivity of IRED remains a great challenge. Herein, focusing on the residues directly in contact with the ketone moiety, we applied structure-guided semi-rational design to obtain the triple-mutant I149Y/L200H/W234K. This mutant showed high stereoselectivity, of up to >99% (S), toward reductive amination of N-Boc-4-oxo-azepane and different amines, and to the best of our knowledge is the first biocatalyst developed for asymmetric synthesis of chiral azepane-4-amines.