Hydroxyl Free Radical-Mediated Oxidative Degradation of Quercetin and Morin: A Preliminary Investigation

Quercetin and morin, two flavonol aglycones with a key difference in the B-ring structure, were oxidized by means of hydroxyl free radicals (HFRs), generated through a CuSO4/H2O2 system. For comparison reasons, oxidations with sodium periodate were also undertaken. Oxidations were performed in 70% acetonitrile (MeCN), due to poor solubility of both flavonols in aqueous media, and followed by UV–Vis spectroscopy and reversed-phase high-performance liquid chromatography. Quercetin and morin HFR-oxidation resulted in six and four major products, respectively. Among quercetin and morin degradation products, resorcinol, protocatechuic, 2,4-dihydroxybenzoic, and phloroglucinol carboxylic acids were tentatively identified. It is claimed that cleavage of quercetin and morin with HFRs is mediated by the formation of hemiketals or tautomeric compounds, and proceeds through the same pathway, which does not depend on the B-ring substitution pattern.