Improved enantioselectivity of E. coli BioH in kinetic resolution of methyl (S)-3-cyclohexene-1-carboxylate by combinatorial modulation of steric and aromatic interactions

As a chiral precursor for the important anticoagulant Edoxaban, enantioselective synthesis of (S)-3-cyclohexene-1-carboxylic acid is of great significance. The complicated procedures and generation of massive solid waste discourage its chemical synthesis, and the alternative biocatalysis route calls for an enzyme capable of asymmetric hydrolysis of racemic methyl-3-cyclohexene-1-carboxylate. To this end, we engineered the E. coli esterase BioH for improved S-enantioselectivity via rational design. By combinatorial modulation of steric and aromatic interactions, a positive mutant Mu3 (L24A/W81A/L209A) with relatively high S-selectivity in hydrolyzing racemic methyl-3-cyclohexene-1-carboxylate was obtained, improving the enantiomeric excess from 32.3% (the wild type) to 70.9%. Molecular dynamics simulation was conducted for both (R)- or (S)- complexes of the wild type and Mu3 to provide hints for the mechanism behind the increased S-selectivity. Moreover, the reaction conditions of Mu3 in methyl-3-cyclohexene-1-carboxylate hydrolysis was optimized to improve the conversion rate to 2 folds.