Phenolic constituents from Rhopalocnemis phalloides with DPPH radical scavenging activity.

The 80% aqueous acetone extract of the whole plant of Rhopalocnemis phalloides Jungh. (Balanophoraceae) showed obvious radical scavenging activity (SC(50) = 32.1 mug/mL) on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay. Further chemical investigation of the extract led to the isolation of 12 phenolic compounds (1-12). Among these, bis-6,8'-catechinylmethane (2), a flavan-3-ol dimer, was first isolated as a natural product from Rhopalocnemis phalloides. The full NMR assignments of bis-catechinylmethanes (1 and 2) are reported for the first time, on the basis of detailed spectroscopic analysis. The DPPH assay showed that flavan-3-ol dimers (1-3) had remarkable free radical scavenging activity, while flavonoid aglycones (4 and 9) presented stronger activities than those of their glycosides (5-8 and 10).