Profiling of Resveratrol Oligomers, Important Stress Metabolites, Accumulating in the Leaves of Hybrid Vitis vinifera (Merzling x Teroldego) Genotypes Infected with Plasmopara viticola

In the Vitaceae, viniferins represent a relatively restricted group of trans-resveratrol oligomers with antifungal properties, thus enabling plants to cope with pathogen attack. The aim of this study was to perform isolation and structural characterization of the whole class of viniferins accumulating in the leaves of hybrid Vitis vinifera (Merzling × Teroldego) genotypes infected with Plasmopara viticola. Infected leaves of resistant plants were collected 6 days after infection, extracted with methanol, and prepurified by flash chromatography using ENV+ and Toyopearl HW 40S resins. Further fractionation using normal-phase preparative chromatography and then reversed-phase preparative chromatography allowed isolation of 14 peaks. The isolated compounds were identified using advanced mass spectrometry techniques and extensive one-and two-dimensional nuclear magnetic resonance measurements, UV, CD, optical properties, and molecular mechanic calculations. The results demonstrated the presence in infected leaves of seven dimers (six stilbenes and one stilbenoid), of which four were new in grapevine (ampelopsin D, quadrangularin A, E-ω-viniferin, and Z-ω-viniferin), four trimers (three stilbenes and one stilbenoid), of which two (Z-miyabenol C and E-cis-miyabenol C) were new in grapevine, three tetramer stilbenoids, all new in grapevine, isohopeaphenol, ampelopsin H, and a vaticanol C-like isomer. The isolation of a dimer deriving from the condensation of (+)-catechin with trans-caffeic acid also indicated that other preformed phenolics are structurally modified in tissues infected with P. viticola.