Structure-guided evolution to improve the catalytic performance of aldo-keto reductase yhdN from Bacillus subtilis for preparing chiral diaryl α-hydroxy amides

Abstract

Optical diaryl α-hydroxy amides are valuable motifs for synthesis of chiral pharmaceuticals. Affected by the two bulky aryl substituents, their preparation by enantioselective carbonyl reduction remains a challenge for biocatalysis. Here an aldo-keto reductase yhdN from Bacillus subtilis was found to possess the catalytic abilities towards the reduction, but with poor activity and stereoselectivity, although the constructed yhdN–GDH whole cells were also used as a biocatalyst. Two stereocomplementary variants, W126F/W21S/A56T and W126A/W21A/P325V, were subsequently obtained by structure-guided evolution, achieving N-phenyl-2-hydroxy-2-phenylacetamide (1b) with conversions of 98.8 ± 1.1 % and 98.3 ± 1.3 %, and e.e. of 99.2 ± 0.8 %_(S) and 97.5 ± 1.0 %_(R) within 3 h, respectively. With the excellent variants in hand, the other chiral diaryl α-hydroxy amides were also successfully prepared. Molecular docking and molecular dynamics (MD) simulations revealed that the mutation of W21 and W126 played a key role to reshape the substrate-binding pocket of yhdN, and the formed π-π/π-alkyl interactions between N-phenyl-2-oxo-2-phenylacetamide (1a) and large- or small-pocket amino acid residues, respectively, could further assist in the corresponding (S)−/(R)-stereoselectivity. An advantage in applicability was also presented for variant–GDH whole-cell catalyst. Here provides another enzyme-catalyzed transformation towards chiral diaryl α-hydroxy amides that are difficult to be accessible.