Highly Diastereo‐ and Enantioselective Imine Reductases Engineered for γ‐Piperidinamines Bearing Contiguous Stereocenters

ABSTRACT Imine reductases (IREDs) represent a highly promising class of biocatalysts for the asymmetric synthesis of chiral amines bearing two stereogenic centers. Herein, we report an IRED‐catalyzed asymmetric reductive amination strategy that converts racemic ketones into γ‐piperidinamines with contiguous stereocenters and operates through a pathway consistent with a dynamic kinetic resolution‐asymmetric reductive amination (DKR‐ARA). The wild‐type Ac IRED afforded the 1‐benzyl‐ N ‐cyclopropyl‐3‐methylpiperidin‐4‐amine ( 1a ) in 60.8% conversion, but with only 78.5% enantiomeric excess ( ee cis ) for (3 S ,4 R )‐ 1a and 23.5% ee trans for (3 R ,4 R )‐ 1a , giving an 84:16 diastereomeric ratio ( dr ). To enhance stereoselectivity, we employed a “trans‐drop, enantio‐catch” strategy to reshape the pocket architecture of Ac IRED. The resulting variant Mut‐5 afforded 99.9% ee cis for (3 S ,4 R )‐ 1a and > 99:1 dr , along with a 19‐fold increase in specific activity and a 24.7°C elevation in . Remarkably, at a cumulative substrate loading of 700 mM (142.3 g·L –1 ), Mut‐5 furnished (3 S ,4 R ) −1a with 95% conversion, a space‐time yield (STY) of 208.7 g·L –1 ·d –1 . This strategy not only provided highly efficient imine reductases but also established a robust platform for the atom‐economical synthesis of γ‐piperidinamine building blocks bearing two stereogenic centers.