A-type proanthocyanidins from peanut skins

Six A-type proanthocyanidins were isolated from the water-soluble fraction of peanut skins. On the basis of spectral data, reductive cleavage with sodium cyanoborohydride, and chiral HPLC analysis, three new compounds, epicatechin-(2 beta-->O-->7, 4 beta --> 6)-catechin, epicatechin-(2 beta --> O --> 7, 4 beta --> 6)-ent-catechin and epicatechin-(2 beta --> O --> 7, 4 beta --> 6)-ent-epicatechin were unambiguously identified, together with the three known compounds, psoanthocyanidin A-1, proanthocyanidin A-2 and epicatechin-(2 beta-->O-->7, 4 beta-->8)-ent-epicatechin. (13)C NMR chemical shift rules to distinguish between [2-->O-->7, 4-->8] and [2-->O -->7,4-->6] double-linked heptamethyl ethers of A-type proanthocyanidins are proposed. Bioassay experiments showed that these six compounds possess substantial activity against hyaluronidase. (C) 1999 Elsevier Science Ltd. All rights reserved.