Copper(II)-mediated biomimetic oxidation of quercetin: generation of a naturally occurring oxidation product and evaluation of its in vitro antioxidant properties

摘要

Quercetin was oxidized with CuSO4 in aqueous acetonitrile, a reaction that has been previously shown to generate products that were detected in polyphenol oxidase and peroxidase-catalysed oxidation of quercetin. The major oxidation product was isolated and characterized by means of 1H-NMR and LC-MS, as 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxybenzofuran-3(2H)-one. This compound is a natural polyphenol reported to occur in the outer dry layers of onion bulbs. Its in vitro antioxidant properties were evaluated in comparison with the parent molecule and other natural polyphenols, employing three representative tests and the alterations in the activity observed were discussed on the basis of structure–activity relationships.