An ESI-MS/MS study of copper complexes of resveratrol and its dihydrofuran dimer

Resveratrol (=3,4’,5-trihydroxystilbene) is a polyphenolic compound found in various plants, including grapes, berries and many other dietary sources. Its biological activity has attracted increasing interest in the last few years. Though resveratrol is a well known antioxidant, it can become a prooxidant agent in presence of Cu(II) compounds, eventually leading to the formation of a dihydrofuran dimer . We have studied by ESI(+)-MS techniques the formation of Cu-resveratrol complexes starting from a resveratrol/CuSO4 solution in CH3CN/H2O. Only singly charged species were detected, indicating that in the ESI process the reduction of Cu(II) occurs. Structural features of the detected [Resv+Cu]+, [Resv+Cu+H2O]+ and [2Resv+Cu]+ complexes have been investigated by MS/MS experiments and by calculations at the B3LYP/6-311G(d) level of theory. The spectrum indicated also the formation of a dihydrofuran dimer, whose structure was defined by MS/MS experiments. The fragmentation pattern was equal to that of the known product obtained by galvinoxyl reaction of resveratrol. In order to investigate the structure-reactivity correlation, we have carried out similar studies on a series of synthetic analogues of resveratrol.