Scavenging Effects of Dihydric and Polyhydric Phenols on Superoxide Anion Radicals, Studied by Electron Spin Resonance Spectrometry

Abstract

We investigated the scavenging effects of dihydric, trihydric phenols and related polyphenols on superoxide anion radicals (O2 ) generated from the hypoxanthine-xanthine oxidase system by ESR (electron spin resonance) spin trapping technique using 5,5-dimethyl- l-pyrroline-N-oxide (DMPO) as a trapping reagent. The O2 scavenging activities of non-substituted dihydric phenols were in the order of pyrocatechol»hydroquinone» resorcinol. Trihydric phenols, pyrogallol and gallic acid, which have phenolic OH groups at ortho positions, had stronger activities than pyrocatechol; phloroglucinol, on the other hand, which has phenolic OH groups at meta positions, had much weaker effect. Polyhydric phenols like quercetin and hematoxylin, which have catechol groups, had significant O2 scavenging activities. In order to clarify the physico-chemical property of these phenolic compounds which determines their O2 scavenging activities, we investigated the effects of six 4-substituents of pyrocatechol on O2“ scavenging effects. The effects of these substituents were well correlated with their redox potentials, indicating that O2 scavenging activities of catechol derivatives are controlled by their electron donor activities. We also observed the scavenging effects of these phenolic compounds on O2_ from a different source: potassium superoxide (KO2) solubilized in dimethyl sulfoxide by 18-crown-6. ESR analysis in this system revealed that one-electron oxidized products of these compounds were concomitantly formed accompanied by the reduction of O2. The results revealed that phenolic compounds directly react with O2 to form stable radicals, which account for the O2 scavenging activities of the compounds. © 1992, The Pharmaceutical Society of Japan. All rights reserved.