o-Quinone trapping by stilbenoids

The reaction of resveratrol, pterostilbene, and piceatannol with 4-methylcatechol quinone and hydroxytyrosol quinone was studied to determine the ability of stilbenoids to trap o-quinones. These reactions produced two types of adducts, which were isolated and characterized by one- and two-dimensional nuclear magnetic resonance spectroscopy and mass spectrometry as dihydrobenzo[b][1,4]dioxins (1) and dihydrobenzofuran-7-ols (2). These compounds were produced rapidly at low/room temperature, and at neutral or slightly acid pH values, by reaction of the ethene linker of the stilbenoid with either the two oxygen atoms or one oxygen atom and the neighbor aromatic carbon of the quinone, respectively. Both compounds are postulated to be produced by an addition reaction via an intermediate zwitterion, which explained the reduced number of isomers produced. In addition, compounds 1 were produced to a higher extent than compounds 2 in spite of the similar apparent activation energies determined for the formation of both types of compounds.