Mechanism of Wine Lactone Formation:  Demonstration of Stereoselective Cyclization and 1,3-Hydride Shift

• Published in: Journal of agricultural and food chemistry Vol. 54; no. 26; pp. 10245 - 10252
• Main Authors: Luan, Fang, Degenhardt, Andreas, Mosandl, Armin, Wüst, Matthias
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 27.12.2006
• Subjects: Biological and medical sciences; chemical reactions; Cyclization; Deuterium; Fermented food industries; food chemistry; Food industries; Fundamental and applied biological sciences. Psychology; gas chromatography; Gas Chromatography-Mass Spectrometry; ion trap tandem mass spectrometry; Isotope Labeling; lactones; Lactones - analysis; Lactones - chemical synthesis; mass spectrometry; multidimensional gas chromatography; stereochemistry; Stereoisomerism; Wine - analysis; wine lactone; wines; Wines and vinegars; Deuterium; Wine; deuterium labeling; Lactone; stereoselective cyclization; Flavor; monoterpenes; ion-trap tandem mass spectrometry; Stereoselectivity; Alcoholic beverage; Gas chromatography; Ion trap; Cyclization; Wine lactone; Monoterpene; 1,3-hydride shift; Formation mechanism; Mass spectrometry; enantioselective gas chromatography
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf0625306

The cyclization mechanism of (E)-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid to wine lactone under acidic aqueous conditions was investigated using the two stereoselectively deuterium-labeled precursors (2E,6R,7Z)-[8-2H]-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid and (2E,7E)-(±)-[8-2H]-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid. A detailed analysis of the generated wine lactone isomers by enantioselective multidimensional gas chromatography (MDGC)/ion trap tandem mass spectrometry demonstrates that the formation of wine lactone proceeds via a nonenzymatic stereoselective cationic cyclization cascade that includes a 1,3-hydride shift. Usually, such mechanisms are features of cyclization reactions that are catalyzed by terpene cyclases. This nonenzymatic conversion of an acyclic precursor to a bicyclic monoterpene under relevant cationic cyclization conditions has rarely been observed and confirms recent suggestions that the precursor itself can provide the chemical functionality required for specific steps in the cyclization cascade. Keywords: Wine lactone; monoterpenes; stereoselective cyclization; 1,3-hydride shift; deuterium labeling; ion-trap tandem mass spectrometry; enantioselective gas chromatography; flavor