Investigation on the in vitro antioxidant capacity of methanol extract, fractions and flavones from Oroxylum indicum Linn bark

ABSTRACT Antioxidants from natural sources hold high values regarding their indispensible roles in the development of nutraceuticals, pharmaceuticals and cosmetic products. Oroxylum indicum L. is a common medicinal plant with a wide range of therapeutic properties, including a notable antioxidant potency that was reported, yet has not been subjected to more detailed studies. The present study evaluated the potency of Oroxylum indicum methanol stem bark extract, along with its hexane, ethyl acetate, methanol fractions, three flavones including baicalein, oroxylin A and chrysin using DPPH assay. In terms of IC50 values, the crude extract (65,48 μg/mL) exhibited moderate inhibitory activity which was as half potent as that of its ethyl acetate fraction (32,94 μg/mL). This fraction was also superior to the methanol and hexane fractions, as their IC50 were 57,19 and 137,95 μg/mL respectively. Remarkably, a yellow powdery sub-fraction consisted of isolated compounds showed powerful activity (32,89 μg/mL) compared to those of its components, revealing the intriguing effect of synergism while giving evidence for the theory of structure-activity relationship between some flavones and their antioxidant capability. Perpetual search for new radical scavenging agents in Oroxylum indicum is emboldened considering its partially exploited potential in this study.