A limited screen of several commercially-available and internally-produced lipases and esterases identified porcine liver esterase as a suitable biocatalyst for the enantioselective hydrolysis of a diester into its (S)-ester acid with high optical purity (99%). This (S)-ester acid is a precursor to an experimental growth hormone secretagogue. After identifying xanthan gum as the best emulsifier and optimizing the reaction conditions, hydrolysis rates of 1 g/l.h and final (S)-ester acid (ee >99%) titers of about 8.5 g/l were routinely achieved. This process supported the production of preparative amounts of optically pure (S)-ester (ee >99%) with a high reaction yield of 82%, Upon purification, the (S)-ester was successfully used in the subsequent synthetic steps to yield the growth hormone secretagogue.