Radical scavenging and xanthine oxidase inhibitory activity of phenolic compounds from Bridelia ferruginea stem bark

Bridelia ferruginea Benth. (Euphorbiaceae) is a subtropical medicinal plant widely used in traditional African medicine against various diseases. incl uding rheumatic pains. Seven of its constituents (3-O-methylquercetin (1), 3,7,3'.4'-tetra-O-methylquercetin (rutisin, 2), myricetin (3), 3',4',5'-tri -O-methylmyricetin (ferrugin, 4), 3,3'.4'.5'-tetra-O-methylmyricretin (5), quercetin 3-O-glucoside (6), and a biflavanol gallocatechin-[4'-O-7]-epigal locatechin (7)) have been evaluated in-vitro in the xanthine-xanthine oxida se enzymatic system for inhibition of xanthine oxidase and radical scavengi ng activity. Results indicated that compounds 1, 3, 4 and 6 exhibited, at d ifferent levels, xanthine oxidase inhibiting and superoxide scavenging acti vity at micromolarconcentrations, whereas compound 7 showed scavenging acti vity only. Compounds 2 and 5 were inactive in both cases. Study of the stru cture-activity relationship demonstrated that for flavonoids the xanthine o xidase inhibitory activity was reduced by methylation of the hydroxyl funct ionality at C-3 and in rings A and B. These results may partly explain and support the use of B. ferruginea stem bark for the treatment of rheumatic p ains in traditional medicine.