Kinetic Resolution of Racemic Amines to Enantiopure (S)-amines by a Biocatalytic Cascade Employing Amine Dehydrogenase and Alanine Dehydrogenase

Yumi Won,Sanghan Yoon,Amol D Pagar,Sharad Sarak,Hyungdon Yun,Taresh P Khobragade,Hyunwoo Jeon,Mahesh D Patil

doi:10.3390/catal9070600

Abstract

Amine dehydrogenases (AmDHs) efficiently catalyze the NAD(P)H-dependent asymmetric reductive amination of prochiral carbonyl substrates with high enantioselectivity. AmDH-catalyzed oxidative deamination can also be used for the kinetic resolution of racemic amines to obtain enantiopure amines. In the present study, kinetic resolution was carried out using a coupled-enzyme cascade consisting of AmDH and alanine dehydrogenase (AlaDH). AlaDH efficiently catalyzed the conversion of pyruvate to alanine, thus recycling the nicotinamide cofactors and driving the reaction forward. The ee values obtained for the kinetic resolution of 25 and 50 mM rac-α-methylbenzylamine using the purified enzymatic systems were only 54 and 43%, respectively. The use of whole-cells apparently reduced the substrate/product inhibition, and the use of only 30 and 40 mgDCW/mL of whole-cells co-expressing AmDH and AlaDH efficiently resolved 100 mM of rac-2-aminoheptane and rac-α-methylbenzylamine into the corresponding enantiopure (S)-amines. Furthermore, the applicability of the reaction protocol demonstrated herein was also successfully tested for the efficient kinetic resolution of wide range of racemic amines.

Highlights

Enantiopure chiral amines are important precursors of numerous small molecule pharmaceuticals, agrochemicals and fine chemicals
In order to explore the applicability of Amine dehydrogenases (AmDHs) for the kinetic resolution, the oxidative deamination potential of AmDHs was evaluated toward various racemic amines (Figure 2A)
The analysis of kinetic resolution of racemic amines to their enantiopure (S)-amines was performed as previously reported [32,33]. Since their generation by protein engineering strategies from L-amino acid dehydrogenase parent scaffolds, amine dehydrogenases have been used for the reductive amination of prochiral ketone to chiral amines

Summary

Introduction

Enantiopure chiral amines are important precursors of numerous small molecule pharmaceuticals, agrochemicals and fine chemicals. It has been estimated that more than one third of the 200 most prescribed small molecule drugs contain chiral amine precursors [1,2,3]. The asymmetric synthesis of amines from prochiral carbonyls and ammonia has been acknowledged as one of the most highly desired transformations industrially by the ACS Green Chemistry Institute Pharmaceutical. The increasing demand for enantiomerically pure compounds and the simultaneous imposition of environmental restrictions by many countries necessitates the effective integration of traditional chemical syntheses with biocatalytic ‘greener’ methods [5,6,7,8,9]. Traditional organo-catalytic methods for the synthesis of chiral amines use toxic intermediates and require environmentally harsh conditions. The purification of toxic metals is warranted, which complicates the synthetic methods and its cost [10,11,12]

Methods

Results

Conclusion