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-(2β→O→7, 4β→6)-catechin, epicatechin-(2β→O→7, 4β→6)-ent-catechin and epicatechin-(2β→O→7, 4β→6)-ent-epicatechin were unambiguously identified, together with the three known compounds, proanthocyanidin A-1, proanthocyanidin A-2 and epicatechin-(2β→O→7, 4β→8)-ent-epicatechin. 13C 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.