Process for preparing optically active glycidate esters

This invention relates to a method for the production of (2R,3S)-3-(4-methoxyphenyl)glycidic acids and esters thereof, which are synthetic intermediates for the production of the calcium antagonist diltiazem. The method involves the stereoselective enzymatic ester hydrolysis of racemic trans-3-(4-methoxyphenyl)glycidic acid ester to yield the resolved (2R,3S) compound as the ester. Membrane reactor methods and apparatus for the conduct of this enzymatic resolution process are also disclosed herein, as is the use of bisulfite anion in the aqueous reaction phase as a means of minimizing the inhibitory effect of an aldehyde reaction by-product on the reaction's progress. The benefits of selected solvent systems from which may be obtained highly resolved ester product are also disclosed. These enriched organic solutions may be used in subsequent transformations. Alternatively, optically pure product may be obtained directly therefrom.