Enzyme Optimization and Process Development for a Scalable Synthesis of (R)-2-Methoxymandelic Acid

The rational protein engineering of wild type BCJ2315 nitrilase and its use in the development of a one-pot, enantioselective, dynamic kinetic resolution for (R)-2-methoxymandelic acid is reported. Through a combination of molecular docking and B-factor analyses, a focused library of mutants was identified and screened to improve nitrilase selectivity, activity, and stability. Initial optimization revealed that the addition of sodium bisulfite prevented enzyme deactivation by the aldehyde starting material, removing the need to isolate the cyanohydrin and allowing for development of a one-pot process for mutant screening. Further optimization of the process with the preferred mutants revealed subtle interactions between temperature, pH, substrate loading, and enzyme source which ultimately led to development of a suitable lyophilized whole cell process for scale-up, affording (R)-2-methoxymandelic acid in 97% ee and 70% isolated yield on multigram scale.