PROANTHOCYANIDINS WITH (-EPICATECHIN UNITS FROM BYRSONIMA-CRASSIFOLIABARK())

Two new procyanidin trimers (3-O-galloyl-(+)-epicatechin-[4 alpha-->8] -3-O-galloyl-(+)-epicatechin-[4 alpha --> 8]-(+)-epicatechin and 3-O-g alloyl-(-)-epicatechin-[4 beta --> 8]-3-O-galloyl-(+)-epicatechin-[4 a lpha --> 8]-(+)-epicatechin), together with four new dimers (3-O-gallo yl-(+)-epicatechin-[4 alpha --> 8]-3-0-galloyl-(+)-epicatechin, 3-O-ga lloyl-(+)-epicatechin-[4 alpha --> 8]-(+)-epicatechin, (+)-epicatechin -[4 alpha --> 8]-3-0-galloyl-(+)-epicatechin, (+)-epicatechin-[4 alpha --> 6]-(+)-epicatechin), one known dimer ((+)-epicatechin-[4 alpha -- > 8]-(+)-epicatechin), three known monomers ((+)-epicatechin, 3-O-gall oyl-(+)-epicatechin, catechin) and gallic acid were isolated from Byrs onima crassifolia bark, which is used medicinally by the Mire Indians (Oaxaca, Mexico). The new compounds were characterized by spectroscopi c methods, as well as by thiolytic degradation with toluene-alpha-thio l and structural elucidation of the cleavage products by H-1 NMR and O R measurements. Bonding positions of dimeric compounds were determined by H-1 NMR spectroscopy of their peracetate derivatives. The backbone of the isolated compounds consisted mainly of flavan-3-ol units with the 2S-configuration which so far have been rarely found in nature. Th e enantiomeric purity of (+)-epicatechin, (+)-epicatechin-[4 alpha --> 8]-(+)-epicatechin and (+)-epicatechin-[4 alpha --> 6](+)-epicatechin was checked by HPLC on a chiral cyclodextrin column.