Asymmetric synthesis of primary amines catalyzed by thermotolerant fungal reductive aminases

Chem. Sci., 2020, 11, 5052–5057. Juan Mangas-Sanchez, Mahima Sharma, Sebastian C. Cosgrove, Jeremy I. Ramsden, James R. Marshall, Thomas W. Thorpe, Ryan B. Palmer, Gideon Grogan and Nicholas J. Turner

Chiral primary amines are important intermediates in the synthesis of pharmaceutical compounds. Fungal
reductive aminases (RedAms) are NADPH-dependent dehydrogenases that catalyse reductive amination of
a range of ketones with short-chain primary amines supplied in an equimolar ratio to give corresponding
secondary amines. Herein we describe structural and biochemical characterisation as well as synthetic
applications of two RedAms from Neosartorya spp. (NfRedAm and NfisRedAm) that display a distinctive
activity amongst fungal RedAms, namely a superior ability to use ammonia as the amine partner. Using
these enzymes, we demonstrate the synthesis of a broad range of primary amines, with conversions up
to >97% and excellent enantiomeric excess. Temperature-dependent studies showed that these
homologues also possess greater thermal stability compared to other enzymes within this family. Their
synthetic applicability is further demonstrated by the production of several primary and secondary
amines with turnover numbers (TN) up to 14 000 as well as continuous flow reactions, obtaining chiral
amines such as (R)-2-aminohexane in space-time yields up to 8.1 g L-1 h-1. The remarkable features of
NfRedAm and NfisRedAm highlight their potential for wider synthetic application as well as expanding
the biocatalytic toolbox available for chiral amine synthesis.