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Reactivity of wine polyphenols under oxidation conditions: Hemisynthesis of adducts between grape catechins or oak ellagitannins and odoriferous thiols
- Petit, Emilie, Jacquet, Rémi, Pouységu, Laurent, Deffieux, Denis, Quideau, Stéphane
- Tetrahedron 2019 v.75 no.5 pp. 551-560
- Lewis acids, aqueous solutions, barrels, bottles, catechin, chemical structure, ferric chloride, grapes, oxidants, oxidation, polyphenols, pyrogallol, quinones, thiols, wines
- The reasons for the loss of characteristic odoriferous thiols during the aging of wine in oak-made barrels and subsequent storage in bottles have been in part attributed to covalent capture of these thiols by polyphenolic wine components that are dehydrogenated into electrophilic ortho-quinones upon wine oxygenation. Herein, FeCl3 was used as oxidant in oxygen-deprived aqueous solutions to dehydrogenate grape (epi)catechins and oak ellagitannins in the presence of two typical odoriferous thiols, 2-furanmethanethiol (2FMT) and 3-sulfanylhexan-1-ol (3SH). The preparative-scale conditions used enabled the isolation of six novel 2FMT-bearing (epi)catechin derivatives, three known 3SH-bearing catechin derivatives (the structures of two of those were revised to be strictly derived from 1,6-conjugate addition), three novel 2FMT-bearing castalagin derivatives, and one novel 3SH-bearing castalagin derivative. The structures of these castalagin-based thio-adducts revealed that the capture of thiols by the different dehydrogenated pyrogallol rings of castalagin starts at ring IV, then ring III, and finally ring V.