Configurations and Sensory Properties of the Stereoisomers of 2,6-Dimethyl-4-propyl-1,3-oxathiane and 2,4-Dimethyl-6-propyl-1,3-oxathiane.

The heterocyclic compounds 2,6-dimethyl-4-propyl-1,3-oxathiane 1 and 2,4-dimethyl-6-propyl-1,3-oxathiane 2 were obtained by condensing 4-mercapto-2-heptanol and 2-mercapto-4-heptanol, respectively, with acetaldehyde. For both, separation of the eight stereoisomers was achieved via capillary gas chromatography using heptakis(diethyl-tert-butyldimethylsilyl)-ß-cyclodextrin as the chiral stationary phase. Their configurations were assigned by combinations of enzyme-catalyzed kinetic resolutions, HPLC separations, and assessments of NMR data. The odor thresholds and odor qualities of the stereoisomers were determined by capillary gas chromatography/olfactometry. The odor thresholds of the stereoisomers of 2 were generally higher than those of 1. For both oxathianes, the stereoisomers in which all substituents are in equatorial positions showed the highest odor thresholds. Most of the stereoisomers of 1 exhibited pleasant flowery, fruity, or sweet nuances; the stereoisomers of 2 were mainly characterized by descriptors, such as broth, mushroom, or pungent. The data demonstrate the impact of the positions of substituents and their spatial orientations on the sensory properties of 1,3-oxathianes.

Absolute Configurations and Sensory Properties of the Stereoisomers of a Homologous Series (C6-C10) of 2-Mercapto-4-alkanols.

A homologous series (C6-C10) of 2-mercapto-4-alkanols was obtained by the addition of thioacetic acid to the respective alkenones and subsequent reduction with LiAlH4. Gas chromatographic separation of the stereoisomers was achieved using chiral stationary phases. Their absolute configurations were assigned by the correlation of 1H NMR data and enzyme-catalyzed kinetic resolutions. Odor thresholds and odor qualities were determined by capillary gas chromatography/olfactometry. Compared to the odor qualities reported for the isomeric 4-mercapto-2-alkanols, the homologous series of 2-mercapto-4-alkanols lacked fruity, tropical notes. There was no consistent correlation between the configurations and the odor qualities. However, the observed odor thresholds indicated the importance of the configuration of the asymmetric center bearing the hydroxyl group and the alkyl substituent. The length of this alkyl chain is a main driver for the odor properties, ranging from pungent, vegetable to earthy, mushroom notes.