A tandem and fully enzymatic procedure for the green resolution of chiral alcohols: acylation and deacylation in non-aqueous media

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.

Biocatalysis in continuous-flow mode: A case-study in the enzymatic kinetic resolution of secondary alcohols via acylation and deacylation reactions mediated by Novozym 435®

Enzymatic kinetic resolution reactions are a well-established way to achieve optically active compounds. When enzymatic reactions are combined to continuous-flow methodologies, other benefits are added, including reproducibility, optimized energy use, minimized waste generation, among others. In this context, we herein report a case study involving lipase-mediated transesterification by acylation and deacylation reactions of secondary alcohols/esters in batch and continuous-flow modes. Acylation reactions were performed with high values of enantiomeric excess (72 up to >99%) and enantioselectivity (E > 200) for both batch and continuous-flow modes. On the other hand, for deacylation reactions using n-butanol as nucleophile, enatiomeric excess ranged between 38 to >99% and E from 6 to >200 were observed for batch mode. For deacylation reactions in continuous-flow mode, results were disappointing, as in some cases, very low or no conversion was observed. Enantiomeric excess ranged from 16 to >99% and enantioselectivity from 5 to >200 were observed. In terms of productivity, continuous-flow mode reactions were superior in both strategies (acylation: r from 1.1 up to 18.1-fold higher, deacylation: 2.8 up to 7.4- fold higher in continuous-flow than in batch mode).