Multifunctional biocatalyst for conjugate reduction and reductive amination

Abstract

A major challenge in chemical synthesis is to develop catalytic systems that convert simple molecules to complex high-value products. Often these valuable compounds must be manufactured asymmetrically, as their biochemical properties can differ based on the chirality of the molecule. Of great interest are enantioenriched amine diastereomers, which are prevalent in pharmaceuticals and agrochemicals, 1 yet their preparation often relies on low-e ciency multi-step synthesis. 2 Herein, we report the discovery and characterisation of a multi-functional biocatalyst, which operates using a previously unreported conjugate reduction-reductive amination mechanism. This enzyme (pIR-120), identi ed within a metagenomic imine reductase (IRED) collection 3 and originating from an unclassi ed Pseudomonas species, possesses an unusual active site architecture that facilitates an amine-activated conjugate alkene reduction followed by reductive amination. This enzyme enables the coupling of a broad selection of α,β-unsaturated carbonyls with amines for the e cient preparation of enantioenriched amine diastereomers. Moreover, employing a racemic substrate partner or conjugated dienyl-ketone provides a means of controlling additional stereocentres using the single catalyst. Mechanistic and structural studies have been carried out to delineate the order of individual steps catalysed by pIR-120 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.

Enzymatic N-Allylation of Primary and Secondary Amines Using Renewable Cinnamic Acids Enabled by Bacterial Reductive Aminases

“…The latter feature is particularly important in the light of a recent discovery that a subset of IREDs can catalyze conjugate reduction–reductive amination of enones. 51 …”

Unlocking New Reactivities in Enzymes by Iminium Catalysis

“… Future perspectives of iminium biocatalysis. KRED (ketoreductase), ADH (alcohol dehydrogenase), AlDH (aldehyde dehydrogenase), IRED (imine reductase), RedAm (reductive aminase), EnelRED (multifunctional imine reductase), [100] SOMO (singly occupied molecular orbital).…”

“…Nevertheless, we are confident that the recent development of iminium biocatalysis has just scratched the surface. In addition to using directed evolution for improving existing enzymes, alternative enzymes such as IRED/ RedAm/EnelRED [100,101] and Pictet-Spenglerases [25] where iminium ions are used could be hijacked for substrateassisted iminium catalysis or multicomponent reactions (Figure 7). New reaction patterns based on iminium catalysis will surely be engineered into enzymes.…”

Reductive aminations by imine reductases: from milligrams to tons

“…However, a subsequent screen of the ene–imine substrates against IREDs alone unearthed a surprising promiscuous activity of some enzymes for the reduction of both C C and C N bonds. 79 A screen of 389 IREDs revealed that 44 of the enzymes were competent for the four-electron reduction of the model ene–imine compound 48 ( Scheme 19 ) to the saturated amine 49 with a particular enzyme, termed EneIRED, catalyzing the reaction with 83% conversion and a diastereomeric ratio of 79 : 21. An extension to this observation was that EneIRED also catalyzed the C C bond reduction in cyclohex-2-enone 50 followed by reductive amination using allylamine j, giving N -allylcyclohexylamine 19j with 69% isolated yield, constituting a conjugate reduction-reductive amination reaction (CR-RA).…”

“…An extension to this observation was that EneIRED also catalyzed the C C bond reduction in cyclohex-2-enone 50 followed by reductive amination using allylamine j, giving N -allylcyclohexylamine 19j with 69% isolated yield, constituting a conjugate reduction-reductive amination reaction (CR-RA). 79 No CR products were formed in the absence of the amine substrate, strongly indicating a mechanism whereby the substrate for CR is the condensation product 51 of unsaturated ketone and amine ( Scheme 19 ). Following reduction of 51 using NADPH, release of the intermediate 52 into solution would result in hydrolysis to the saturated ketone, which would then be bound by the IRED, along with the amine, in the active site with NADPH to achieve a reductive amination to give secondary amine product 19j.…”