A CHROMATOGRAPHIC AND MASS-SPECTROMETRIC APPROACH FOR THE ANALYSIS OFLIPASE-PRODUCED THIOESTER DERIVATIVES

The synthesis of thioethyl 2-methylpropanoate, butanoate, 3-methylbuta noate, hexanoate, and of thiobutyl propanoate, butanoate, and pentanoa te was achieved via esterification of ethanethiol or butanethiol with short-chain acids using an immobilised lipase from Rhizomucor miehei. High acid conversions were obtained (47% for thiobutyl pentanoate). Th e analysis of educts and products was carried out by reverse-phase liq uid chromatography (HPLC), gas chromatography (GC), GC/mass spectromet ry, and GC/olfactometry. All of the thioesters imparted a similar, oni on-like smell, which remained unchanged on dilution. The thresholds of thioesters derived from the same thiol were loosely correlated with t he size of the acid moiety: the larger the molecular mass the higher t he threshold. Surprisingly, higher odour thresholds were obtained for the branched-chain thioesters than for their linear analogues.