A Bifunctional Enzyme for a Michael Addition-Oxidation Sequence

Significance

A biocatalytic hydration-oxidation sequence of α,β-unsaturated carbonyl compounds is reported. The enzyme, a Michael ­hydratase-alcohol dehydrogenase (MhyADH) from Alicycliphilus denitrificans, enabled the efficient Michael addition of water to suitable acceptor molecules. Moreover, in the presence of a biocompatible electron acceptor, such as methylene blue or dichlorophenol indophenol, the oxidation to the dicarbonyl compound could also be catalyzed by the same enzyme. The biocatalytic system tolerated aldehydes and ketones equally well. The enantioselectivity of the enzyme could be demonstrated, as upon incubation of the biocatalyst with an enantiomerically pure (R) versus the racemic alcohol substrate the former was oxidized at higher rate.