Multifunctional biocatalyst for conjugate reduction and reductive amination

Chiral amine diastereomers are ubiquitous in pharmaceuticals and agrochemicals,1 yet their preparation often relies on low-efficiency multi-step synthesis.2 These valuable compounds must be manufactured asymmetrically, as their biochemical properties can differ based on the chirality of the molecule. Herein, we report the discovery and characterisation of a multi-functional biocatalyst for amine synthesis, which operates using a previously unreported mechanism. This enzyme (EneIRED), identified within a metagenomic imine reductase (IRED) collection3 and originating from an unclassified Pseudomonas species, possesses an unusual active site architecture that facilitates amine-activated conjugate alkene reduction followed by reductive amination. This enzyme can couple a broad selection of α,β-unsaturated carbonyls with amines for the efficient preparation of chiral amine diastereomers baring up to three stereocentres. Mechanistic and structural studies have been carried out to delineate the order of individual steps catalysed by EneIRED which have led to a proposal for the overall catalytic cycle. This work shows that the IRED family can serve as a platform for facilitating the discovery of further enzymatic activities for application in synthetic biology and organic synthesis.