N-Butylamine as an alternative amine donor for the stereoselective biocatalytic transamination of ketones

Abstract

Formal reductive amination has been a main focus of biocatalysis research in recent times. Among the enzymes able to perform this transformation, pyridoxal-5′-phosphate-dependent transaminases have shown the greatest promise in terms of extensive substrate scope and industrial application. Despite concerted research efforts in this area, there exist relatively few options regarding efficient amino donor co-substrates capable of allowing high conversion and atom efficiency with stable enzyme systems. Herein we describe the implementation of the recently described spuC gene, coding for a putrescine transaminase, exploiting its unusual amine donor tolerance to allow use of inexpensive and readily-available n-butylamine as an alternative to traditional methods. Via the integration of SpuC homologues with tandem co-product removal and cofactor regeneration enzymes, high conversion could be achieved with just 1.5 equivalents of the amine with products displaying excellent enantiopurity.