Structure of new anthocyanin-derived wine pigments

Two new malvidin-derived pigments, referred to as A and B, were detected in red wine made from Vitis vinifera grapes (var. Carignane) and characterised. The results reported herein indicate that they are formed by covalent binding of major wine anthocyanins [malvidin 3-monoglucoside and malvidin 3-(6-p-coumaroyl)monoglucoside] with 4-vinylphenol. Synthetic products obtained by reaction between these reagents were shown to be identical with the natural compounds on the basis of their UV-visible, mass and H-1 NMR spectra. Their formation involves cyclisation between C-4 and the hydroxy group at C-5 of the original flavylium moiety and the vinylphenol double bond. Subsequent oxidation leads to pigment A or B. Their structure can yield two flavylium mesomeric forms, one corresponding to the malvidin type and the other to the pelargonidin type. The pigments' colour suggests that the latter is the predominant form under our conditions.