Resolution of esters of phenylglycine with (+)-tartaric acid

The methyl, ethyl, and isopropyl esters of DL-phenylglycine are resolved with 1 mol. equiv. of (+)-tartaric acid aqueous alcohols to give the D-ester hydrogen (+)-tartrate salts in up to 42% yield (or 84% based on the D-content of the DL-esters). The L-salts in the filtrates from the resolutions are racemised in ethanol containing polar co-solvents. The resolution and racemisation stages may be combined so that ethyl DL-phenylglycinate undergoes a second-order asymmetric transformation to give ethyl D-phenylglycinate hydrogen (+)-tartrate in up to 65% yield. The resolved salts are hydrolysed to D-phenylglycine in up to 90% yield.