Biocatalytic reduction of α,β-unsaturated carboxylic acids to allylic alcohols

We have developed robustin vivoandin vitrobiocatalytic systems that enable reduction of alpha,beta-unsaturated carboxylic acids to allylic alcohols and their saturated analogues. These compounds are prevalent scaffolds in many industrial chemicals and pharmaceuticals. A substrate profiling study of a carboxylic acid reductase (CAR) investigating unexplored substrate space, such as benzo-fused (hetero)aromatic carboxylic acids and alpha,beta-unsaturated carboxylic acids, revealed broad substrate tolerance and provided information on the reactivity patterns of these substrates.E. colicells expressing a heterologous CAR were employed as a multi-step hydrogenation catalyst to convert a variety of alpha,beta-unsaturated carboxylic acids to the corresponding saturated primary alcohols, affording up to >99% conversion. This was supported by the broad substrate scope ofE. coliendogenous alcohol dehydrogenase (ADH), as well as the unexpected C = C bond reducing activity ofE. colicells. In addition, a broad range of benzofused (hetero)aromatic carboxylic acids were converted to the corresponding primary alcohols by the recombinantE. colicells. An alternative one-potin vitrotwo-enzyme system, consisting of CAR and glucose dehydrogenase (GDH), demonstrates promiscuous carbonyl reductase activity of GDH towards a wide range of unsaturated aldehydes. Hence, coupling CAR with a GDH-driven NADP(H) recycling system provides access to a variety of (hetero)aromatic primary alcohols and allylic alcohols from the parent carboxylates, in up to >99% conversion. To demonstrate the applicability of these systems in preparative synthesis, we performed 100 mg scale biotransformations for the preparation of indole-3-aldehyde and 3-(naphthalen-1-yl)propan-1-ol using the whole-cell system, and cinnamyl alcohol using thein vitrosystem, affording up to 85% isolated yield.