In this assay, all test compounds effectively reduced the stable radical DPPH to the yellow-coloured diphenylpicrylhydrazine and their scavenging effect was dose-dependent. It was also found that compound 3 possesses the most potent DPPH radical-scavenging activity, with an IC value of 1.5 lg/ml, which was about three-fold more potent than Vitamin E (3 lg/ml) used as positive control. Based on the IC50 values, the potency of DPPH free radical-scavenging activity of the tested flavonoids was in the order of 3 (1.5 lg/ml) > 1 (23 lg/ ml) > 2 (38 lg/ml).
Against the standard substance is vitamin E.