Oxidation-derived metabolites sustain the antioxidant network of quercetin.

Quercetin is a widely consumed dietary flavonoid and nutraceutical with diverse biological activities, yet the mechanisms underlying its potent antioxidant effects remain incompletely understood. This study aims to examine the hypothesis that quercetin's antioxidant efficacy is associated with a unique coordinating network in which radical-derived oxidation metabolites retain reducing capacity, supporting successive scavenging reactions and potentially contributing to selected regulatory pathways. To investigate this hypothesis, oxidation metabolites were first generated using 2,2-diphenyl-1-picrylhydrazyl as a readily monitored and well-controlled radical oxidant. The reaction mixture was separated using an Agilent 1290 Infinity ultrahigh-performance liquid chromatography system with a water-acetonitrile gradient. Metabolites of interest were then characterized using a quadrupole time-of-flight tandem mass spectrometer in negative-ion mode and annotated based on [M-H]⁻ and fragmentation patterns. Electronic-structure and thermodynamic calculations based on density functional theory (DFT) were performed to evaluate frontier molecular orbitals and the mechanistic feasibility of the common antioxidant pathways. These results indicate that these metabolites can retain, and in some cases exceed the radical-scavenging capacity of the parent molecule. Network pharmacology analysis and molecular docking further suggest that these metabolites potentially engage a substantial portion of quercetin's core regulatory targets and may contribute to its broader biological effects. Notably, among these metabolites, 2-benzoyl-2-hydroxy-3(2H)-benzofuranones emerged as promise. Explanatorily, time-dependent density functional theory (TD-DFT) analysis further suggested that the formation of successively reactive metabolites may be facilitated by the characteristic excited-state intramolecular proton-transfer mechanism of flavonols. These findings warrant further investigation of oxidation metabolites within quercetin's antioxidant network.