Identification of Novel Bacterial Members of the Imine Reductase Enzyme Family that Perform Reductive Amination

Reductive amination of carbonyl compounds constitutes one of the most efficient ways to rapidly construct chiral and achiral amine frameworks. Imine reductase (IRED) biocatalysts represent a versatile family of enzymes for amine synthesis via NADPH mediated imine reduction. The reductive aminases (RedAms) are a sub-family of IREDs which have recently been shown to catalyse imine formation as well as imine reduction. Herein, a diverse library of novel enzymes were expressed and screened as cell-free lysates for their ability to facilitate reductive amination, in order to expand the known suite of biocatalysts for this transformation and to identify more enzymes with potential industrial applications. A range of ketones and amines were examined and enzymes were identified that were capable of accepting benzylamine, pyrrolidine, ammonia and aniline. Amine equivalents as low as 2.5 were employed to afford up to >99% conversion and for chiral products, up to >98% e.e. could be achieved. Preparative-scale reactions were conducted with low amine equivalents (1.5 or 2.0) of methylamine, allylamine and pyrrolidine, achieving up to >99% conversion and 76% isolated yield.