Proanthocyanidins and a phloroglucinol derivative from Rumex acetosa L.

From the ethyl acetate soluble fraction of an acetone-water extract of the aerial parts of Rumex acetosa L (Polygonaceae), a variety of monomeric flavan-3-ols (catechin, epicatechin, epicatechin-3-O-gallate), A- and B-type procyanidins and propelargonidins (15 dimers, 7 trimers, 2 tetramers) were isolated with 5 so far unknown natural products. Dimers: procyanidin B1, B2, B3, B4, B5, B7, A2, epiafzelechin-(4 beta -> 8)-epicatechin, epiafzelechin-(4 beta -> 8)-epicatechin-3-O-gallate (new natural product), epiafzelechin-(4 beta -> 6)-epicatechin-3-O-gallate (new natural product), epiafzelechin-3-O-gallate-(4B -> 8)-epicatechin-3-O-gallate, B2-3,3'-di-O-gallate, B2-3,3'-di-O-gallate, B5-3'-O-gallate, and B5-3,3'-di-O-gallate. Trimers: procyanidin C1, epiafzelechin(40-8)-epicatechin-(4 beta -> 8)-epicatechin (new natural product), epicatechin-(4 beta -> 8)epicatechin-(4 beta -> 8)-catechin, cinnamtannin B1, cinnamtannin B1-3-O-gallate (new natural product), tentatively epicatechin-(2 beta -> 7, 4 beta -> 8)-epiafzelechin-(4 alpha -> 8)-epicatechin (new n atural product), and epicatechin-3-O-gallate-(4 beta -> 8)-epicatechin-3-O-gallate-(4 beta -> 8)-epicatechin-3-O-gallate. Tetramers: procyanidin D1 and parameritannin A1. All compounds were elucidated by ESI-MS, CD spectra, 1D- and 2D-NMR experiments as free phenols or peracetylated derivatives and, in part, after partial acid-catalysed degradation with phloroglucinol. A more abundant proanthocyanidin polymer was also isolated, purified and its chemical composition studied by C-13 NMR. In addition a so far unknown phloroglucinolglycoside (1-O-beta-D-(2,4-dihydroxy-6-methoxyphenyl)-6-O-(4-hydroxy-3,5-dimethoxybenzoyl)-glucopyranoside) was isolated. (C) 2009 Elsevier B.V. All rights reserved.