Antiproliferative Constituents in the Plant 8. Seeds of Rhynchosia volubilis

The MeOH extract of the seeds of Rhynchosia volubilis (Leguminosae) showed antiproliferative activity against human gastric adenocarcinoma [MK-1, 50% growth inhibition (GI50): 25 μg/ml], human uterus carcinoma (HeLa, GI50: 30 μg/ml), and murine melanoma (B16F10, GI50: 8 μg/ml) cells. Bioactivity-guided fractionation resulted in the isolation of gallic acid methylester (1), gallic acid (2), 7-O-galloylcatechin (3), 1,6-di-O-galloylglucose (4), 1-O-galloylglucose (5), and trigalloylgallic acid (6), and their antiproliferative activity was estimated. All showed much stronger inhibition against B16F10 cell growth than against HeLa and MK-1 cell growth. Compound 2 and its tetramer (6) with a free carboxyl group showed higher activity than those which did not have a free carboxyl group. In relation to the gallic acid tetramer (6), two gallic acid dimers (ellagic acid and dehydrodigallic acid) and trimers (tergallic acid dilactone and flavogallonic acid dilactone) were tested for their activity, and compared with those of the isolates

Two New Acylated Flavanone Glycosides from the Leaves and Branches of Phyllanthus emblica

Two new acylated flavanone glycosides, (S)-eriodictyol 7-O-(6″-O-trans-p-coumaroyl)-β-D-glucopyranoside (1) and (S)-eriodictyol 7-O-(6″-O-galloyl)-β-D-glucopyranoside (2) were isolated from the leaves and branches of Phyllanthus emblica together with a new phenolic glycoside, 2-(2-methylbutyryl)phloroglucinol 1-O-(6″-O-β-D-apiofuranosyl)-β-D-glucopyranoside (3), as well as 22 known compounds. Their structures were determined by spectral and chemical methods

Association of Tannins and Related Polyphenols with the Cyclic Peptide Gramicidin S

The association of 10 different tannins and related polyphenols with gramicidin S, a cyclic peptide having a rigid β-turn structure, has been examined using 1H-NMR spectroscopy. In the presence of pentagalloylglucose and epigallocatechin-3-O-gallate, the proton signals due to proline and the adjacent phenylalanine moieties selectively shifted to up field, suggesting a regioselective association with the β-turn structure. The association was also supported by the observation of intermolecular nuclear Overhauser effects between epigallocatechin-3-O-gallate and the peptide. In contrast, ellagitannins, biogenetically derived from pentagalloylglucose, showed small and non-selective chemical shift changes, suggesting that interaction with these tannins is relatively weak. The hydrophobicity of the tannin molecules and the steric hindrance of the interaction site are thought to be important in the association