Structural characterization of a A-type linked trimeric anthocyanin derived pigment occurring in a young Port wine.

A new trimeric flavylium derivative pigment was detected for the first time in a young Port wine and structurally characterised using both API-LC ESI MS/MS and NMR techniques. Its structure comprises a malvidin-3-glucoside molecule (terminal unit) linked to two units of flavans (extension units) involving two A-type linkages (C4→C8 and C7-O-C2 ether linkages). The energies of the minimized geometries for all four conformations of this compound were calculated and comparing the structures of all isomers, it was verified that the binding mode (α or β) between the first and second anthocyanin unit does not have a key role in the compound stability. However, for isomers 1 and 2 where the interaction between the second and third anthocyanin units occurs by a "β" mode in opposition to the "α" mode verified in isomers 3 and 4, revealed a higher stability. The presence of these compounds in red wines is thought to result from their extraction from grape skin during fermentation, as the presence of these trimeric pigments was detected in a grape skin extract by API-LC ESI MS/MS spectrometry.