Biflavonoids from the unripe fruits of Clusia paralicola and their antioxidant activity.

Investigation of the green fruits of Clusia paralicola (Clusiaceae) led to the isolation and characterization of two 3,8"-biflavonoids, 2R, 3S, 2"R, 3"R-GB1-7"-O-beta-glucoside (1) and 2R, 3S, 2"R, 3,8"-binaringenin-7"-O-beta-glucoside (2), together with four known compounds: beta-sitosterol, stigmasterol, beta-amyrin, and epicatechin. The structures were established from the IR, LC-ESI-MS and NMR spectral data, including 2D-NMR experiments. The absolute configurations of 1 and 2 were determined by CD spectra. The total extract and the biflavonoids demonstrated significant antioxidant activity in DPPH, ABTS, and betacarotene/linoleic acid tests.