Ajothiolanes: 3,4-Dimethylthiolane Natural Products from Garlic (Allium sativum)

• Published in: Journal of agricultural and food chemistry Vol. 66; no. 39; pp. 10193 - 10204
• Main Authors: Block, Eric, Dethier, Bérénice, Bechand, Benjamin, Cotelesage, Julien J. H, George, Graham N, Goto, Kei, Pickering, Ingrid J, Mendoza Rengifo, Emerita, Sheridan, Robert, Sneeden, Eileen Y, Vogt, Linda
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 03.10.2018
• Subjects: 3,4-dimethylthiolanes; ajothiolane; Allium cepa; Allium fistulosum; Allium sativum; BASIC BIOLOGICAL SCIENCES; DART-MS; garlic; INADEQUATE NMR; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; naturally occurring thiolanes; onion; sulfenic acids; thiolane-2-ol; UPLC; X-ray absorption spectroscopy; garlic; Allium cepa; ajothiolane; onion; INADEQUATE NMR; thiolane-2-ol; DART-MS; sulfenic acids; 3,4-dimethylthiolanes; UPLC; naturally occurring thiolanes; X-ray absorption spectroscopy; Allium sativum; Allium fistulosum
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/acs.jafc.8b03638

Stereoisomers of 5-(2-allylsulfinyl)-3,4-dimethylthiolane-2-ol, a family of 3,4-dimethylthiolanes of formula C9H16O2S2 we name ajothiolanes, were isolated from garlic (Allium sativum) macerates and characterized by a variety of analytical and spectroscopic techniques, including ultraperformance liquid chromatography (UPLC), direct analysis in real time-mass spectrometry (DART-MS), and liquid chromatography–tandem mass spectrometry (LC-MS/MS). Ajothiolanes were found to be spectroscopically identical to a family of previously described compounds named garlicnins B1–4 (C9H16O2S2), whose structures we demonstrate have been misassigned. 2D 13C–13C NMR incredible natural abundance double quantum transfer experiments (INADEQUATE) were used to disprove the claim of nine contiguous carbons in these compounds, while X-ray absorption spectroscopy (XAS) along with computational modeling was used to disprove the claim that these compounds were thiolanesulfenic acids. On the basis of the similarity of their NMR spectra to those of the ajothiolanes, we propose that the structures of previously described, biologically active onionins A1–3 (C9H16O2S2), from extracts of onion (Allium cepa) and Allium fistulosum, and garlicnin A (C12H20O2S4), from garlic extracts, should also be reassigned, in each case as isomeric mixtures of 5-substituted-3,4-dimethylthiolane-2-ols. We conclude that 3,4-dimethylthiolanes may be a common motif in Allium chemistry. Finally, we show that another garlic extract component, garlicnin D (C7H12O2S3), claimed to have an unprecedented structure, is in fact a known compound from garlic with a structure different from that proposed, namely, 2­(E)-3-(methylsulfinyl)-2-propenyl 2-propenyl disulfide.