Chiral analysis of cis-2-methyl-4-propyl-1,3-oxathiane and identification of cis-2,4,4,6-tetramethyl-1,3-oxathiane in wine

Abstract

cis-2-Methyl-4-propyl-1,3-oxathiane (cis-2-MPO), arising from 3-sulfanylhexan-1-ol (3-SH) and acetaldehyde, was recently identified in wine, but the enantiomeric distribution was unknown. Such information could reveal influences on wine aroma, given the impact of chirality on odorant molecules. Herein, a stable isotope dilution assay employing headspace solid-phase microextraction with chiral gas chromatography–mass spectrometry was developed, validated, and applied to a selection of wines. Studies with (3R)-3-SH revealed the elution order of the cis-2-MPO enantiomers and the concentrations of (2R,4S)-2-MPO and (2S,4R)-2-MPO in the studied wines ranged from undetected to 250 ng/L and 303 ng/L, respectively. Strong positive correlations were found between (3R)-3-SH and (2S,4R)-2-MPO (r = 0.654), and (3S)-3-SH and (2R,4S)-2-MPO (r = 0.860). Additionally, cis- 2,4,4,6-tetramethyl-1,3-oxathiane, constituted from acetaldehyde and 4-methyl-4-sulfanylpentan-2-ol (4- MSPOH), was identified in wine for the first time. This new 1,3-oxathiane, which presents a novel fate for 4- MSPOH, was detected in wines as a single enantiomer at up to 28 ng/L.