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.

Keywords: Aldo-keto reductase; Asymmetric carbonyl reduction; Chiral diaryl α-hydroxy amides; Structure-guided evolution.