Effects of Functional Groups and Sugar Composition of Quercetin Derivatives on Their Radical Scavenging Properties

Quercetin derivatives are widespread in the plant kingdom and exhibit various biological actions. The aim of this study was to investigate the structure–activity relationships of quercetin derivatives, with a focus on the influence of functional groups and sugar composition on their antioxidant capacity. A series of quercetin derivatives were therefore prepared and assessed for their DPPH radical scavenging properties. Isoquercetin O-gallates were more potent radical scavengers than quercetin. The systematic analysis highlights the importance of the distribution of hydroxy substituents in isoquercetin O-gallates to their potency.