TETRAMERIC PROANTHOCYANIDINS CONTAINING A DOUBLE INTERFLAVANOID (A-TYPE) LINKAGE FROM PAVETTA-OWARIENSIS

Pavetannins C-2 to C-6, five new tetrameric proanthocyanidins containing one or two double inter-flavanoid (A-type) linkages have been isolated from the stem bark of Pavetta owariensis. Spectroscopic investigations and partial acid-catalysed degradation established their structure as epicatechin-(4 beta --> 8,2 beta --> O --> 7)-ent-catechin-(4 beta --> 8)-epicatechin-(4 beta --> 8)-epicatechin, epicatechin-(4 beta --> 8,2 beta --> O --> 7)-ent-epicatechin-(4 alpha --> 8)-ent-epicatechin-(4 alpha --> 8)-epicatechin, epiafielechin-(4 beta --> 8,2 beta --> O --> 7)-epicatechin-(4 beta --> 8)-epicatechin-(4 beta --> 8)-epicatechin, epiafzelechin-(4 beta --> 8,2 beta --> O --> 7)-ent-afielechin-(4 alpha --> 8)-ent-epicatechin-(4 alpha --> 8,2 alpha --> O --> 7)-ent-catechin and epiafzelechin-(4 beta --> 8,2 beta --> O --> 7)-ent-catechin-(4 alpha --> 8)-ent-epicatechin-(4 alpha --> 8,2 beta --> O --> 7)-ent-catechin, respectively. While aesculitannin F is being reported from a plant source for the second time, the remaining tetramers are new natural metabolites.