Tannins and related compounds. Part 13. Isolation and structures of trimeric, tetrameric, and pentameric proanthicyanidins from cinnamon
A proanthocyanidin trimer, two tetramers, and a pentamer have been isolated in their free phenolic forms from cinnamon, the bark of Cinnamomum zeylanicum(Lauraceae). Partial acid-catalysed degradation of these tannins with phenylmethanethiol, in conjunction with 1H- and 13C-n.m.r. analysis, has unequivocally established their structures as epicatechin-(4β→8, 2β→7) epicatechin-(4α→8)-epicatechin (5); epicatechin-(4β→8, 2β→7)-epicatechin-(4α→8)-epicatechin (6); epicatechin-(4β→6)-epicatechin-(4β→, 2β→7)-epicatechin-(4α→8)-epicatechin (7); and epicatechin-(4β→8)-epicatechin-(4β→8)epicatechin-(4β→8, 2β→7)-epicatechin-(4α→8)-epicatechin (8).