The organic-synthetic potential of recombinant Ene reductases: Substrate-Scope Evaluation and Process Optimization

Abstract

In this study an evaluation of the synthetic potential of a broad range of recombinant ene reductases was performed. In detail, a library of 23 ene reductases was used to screen the C=C reduction of 21 activated alkenes from different compound classes as substrates. The chosen set of substrates comprises nitroalkenes with an aryl substituent at the β-position and a methyl substituent at the α- or β-position, α,β-unsaturated carboxylic acids and their esters with and without substituents at the β-position, a range of cyclic α,β-unsaturated ketones with different ring sizes and substitution patterns and one α,β-unsaturated boronic acid. After we obtained insight into the substrate scope, several biotransformations were prioritised and further investigated in a screening of 41 reaction parameters (which included chaotropic and kosmotropic salts, polyols, buffer solutions, amino acids and organic solvents) towards their impact on the activity and enantioselectivity of the applied ene reductases. Under the optimised conditions, selected reduction processes were performed on an increased lab scale (up to 30 mL) with up to 10% substrate concentration, which led in general to both high conversion and (if chiral products were formed) enantioselectivity. Comprehensive screening: A detailed screening of 23 recombinant ene reductases for the reduction of 21 activated alkenes is performed as well as a subsequent study of the influence of 41 reaction parameters towards the enzyme activity and selectivity of selected reactions. In addition, a range of biocatalytic reductions on an increased laboratory scale are performed with substrate concentrations between 5 and 100 gL -1. EWG=Electron-withdrawing group.