Structure-Activity Relationship in Radical- Scavenging Reactions of Naturally-Oriented Artepillin C Derivatives

Artepillin C [3-{4-hydroxyl-3,5-bis(3-methyl-2-butenyl)phenyl}- 2(E)-propenoic acid], a major component of Brazilian propolis, and its derivatives efficiently scavenged 2,2-diphenyl-1-picrylhydrazyl radical (DPPH center dot) in deaerated acetonitrile at 298 K. The DPPH center dot-scavenging rate constants determined by the stopped-flow technique indicate that the introduction of the electron-donating groups on the benzene ring significantly decreases the enthalpy of the phenolic O-H bond dissociation, resulting in the enhancement of the radical-scavenging activities of the artepillin C derivatives.