Free radical-scavenging activity of organic extracts and of pure flavonoids of Blumea balsamifera DC leaves

Phytochemical investigation on the leaves of Blumea balsamifera DC resulted in the isolation of 11 flavonoids. Their chemical structures were elucidated by means of elemental analyses and different spectroscopic methods, such as UV, IR, NMR and MS. The free radical scavenging activity of organic extracts of B. balsamifera DC leaves and that of pure flavonoids isolated from the leaves was evaluated using 1,1-diphenyl-2-picrylhydrazyl radical. A dose response curve was plotted for determining SC50 values (the concentrations required to inhibit radical formation by 50%). The antioxidant activities of crude extracts decreased in the order: methanol extract > chloroform extract > pet-ether extract. The antioxidant activities of all compounds tested decreased in the order: quercetin > rhamnetin > luteolin > luteolin-7-methylether > l-ascorbic acid > blumeatin > butylated hydroxyanisole > 5,7,3′,5′-tetrahydroxyflavanone > tamarixetin > butylated hydroxytoluene > α-tocopherol > dihydroquercetin-4′-methylether > dihydroquercetin-7,4′-dimethylether. This result indicates that flavonoid contents of different solvent extracts of B. balsamifera DC leaves were responsible for their antioxidant properties.