Analysis and Sensory Evaluation of the Stereoisomers of a Homologous Series (C5-C10) of 4-Mercapto-2-alkanols.

A homologous series of 4-mercapto-2-alkanols (C5-C10) was used to investigate the impact of the stereochemistry on the sensory properties of a class of naturally occurring polyfunctional thiols having a 1,3-oxygen-sulfur functionality. Stereoisomers were obtained via syntheses of racemic mixtures and subsequent lipase-catalyzed kinetic resolutions. Analytical separations of the stereoisomers were achieved by capillary gas chromatography (GC) using chiral stationary phases. The absolute configurations were assigned via NMR analysis. Sensory evaluations by means of GC/olfactometry revealed odor threshold minima for the medium-chain homologues (C7-C9) of the 4-mercapto-2-alkanol stereoisomers. Except for the C5 homologue, the lowest odor thresholds were determined for the (2R,4R)-configured stereoisomers. The variability in odor qualities was mainly determined by the chain length. None of the 4-mercapto-2-alkanol stereoisomers showed consistent odor qualities for all homologues.