Free Radical Scavenging Activity of Kielmeyera variabilis (Clusiaceae)

As part of our ongoing research on antioxidant agents from Brazilian flora, we screened the free radical scavenging activity of two extracts and eight fractions of Kielmeyera variabilis (Clusiaceae) using DPPH center dot (2,2-diphenyl-1-picrylhydrazyl-hydrate) and ABTS(center dot+) [2,2'-azinobis(3-ethylenebenzothiazoline-6-sulfonic acid)] colorimetric assays. The ethyl acetate and n-butanol fractions of the leaves of K. variabilis displayed the strongest activity (IC50 of 3.5 +/- 0.3 and 4.4 +/- 0.2 mu g mL(-1) for DPPH center dot and 6.6 +/- 0.4 and 3.1 +/- 0.1 mu g mL(-1) for ABTS(center dot+), respectively). Chromatographic fractionation of the most potent fractions led to identification of three flavonols with previously described antioxidant activity, quercitrin (1), quercetin-3-O-beta-glucoside (3), and quercetin-3-O-beta-galactoside (4), and of one biflavone, podocarpusflavone A (2). This is the first time that the presence of these flavonoids in Kielmeyera variabilis has been reported.