Biocatalytic Access to 1,4-Diazepanes via Imine Reductase-Catalyzed Intramolecular Asymmetric Reductive Amination
Zefei Xu, Peiyuan Yao, Xiang Sheng, Jinlong Li, Jianjiong Li, Shanshan Yu, Jinhui Feng, Qiaqing Wu, Dunming Zhu
Abstract
An enzymatic intramolecular asymmetric reductive amination has been developed for the synthesis of chiral 1,4-diazepanes. Several enantiocomplementary IREDs were identified for the synthesis of (R)- and (S)-5-chloro-2-(5-methyl-1,4-diazepan-1-yl)benzo[d]oxazole with high enantioselectivity. The catalytic efficiency of (R)-selective IRED from Leishmania major (IR1) and (S)-selective IRED from Micromonospora echinaurantiaca (IR25) was 0.027 and 0.962 s–1 mM–1, respectively. To further improve the catalytic efficiency of IR1, its double mutant Y194F/D232H was identified by saturation mutagenesis and iterative combinatorial mutagenesis, which exhibited 61-fold in the catalytic efficiency relative to that of wild-type enzyme. The density functional calculations and molecular dynamics simulations provided some insights into the molecular basis for the improved activity of mutant Y194F/D232H. Furthermore, Y194F/D232H and IR25 were applied to access a range of different substituted 1,4-diazepanes with high enantiomeric excess (from 93 to >99%). This study offers an effective method for construction of chiral 1,4-diazepanes of pharmaceutical importance via imine reductase-catalyzed intramolecular reductive amination of the corresponding aminoketones.