Proanthocyanidins with (+)-epicatechin units from Byrsonima crassifolia bark

Two new procyanidin trimers (3-O-galloyl-( + )-epicatechin-[4α → 8]-3-O-galloyl-( + )-epicatechin-[4α → 8]-( + )-epicatechin and 3-O-galloyl-( − )-epicatechin-[4β → 8]-3-O-galloyl-( + )-epicatechin-[4α → 8]-( + )-epicatechin), together with four new dimers (3-O-galloyl-( + )-epicatechin-[4α → 8]-3-O-galloyl-( + )-epicatechin, 3-O-galloyl-( + )-epicatechin-[4α → 8]-( + )-epicatechin, ( + )-epicatechin-[4α → 8]-3-O-galloyl-( + )-epicatechin, ( + )-epicatechin-[4α → 6]-( + )-epicatechin), one known dimer (( + )-epicatechin-[4α → 8]-( + )-epicatechin), three known monomers (( + )-epicatechin, 3-O-galloyl-( + )-epicatechin, catechin) and gallic acid were isolated from Byrsonima crassifolia bark, which is used medicinally by the Mixe Indians (Oaxaca, Mexico). The new compounds were characterized by spectroscopic methods, as well as by thiolytic degradation with toluene-α-thiol and structural elucidation of the cleavage products by ¹H NMR and OR measurements. Bonding positions of dimeric compounds were determined by ¹H 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. The enantiomeric purity of ( + )-epicatechin, ( + )-epicatechin-[4α → 8]-( + )-epicatechin and ( + )-epicatechin-[4α → 6]-( + )-epicatechin was checked by HPLC on a chiral cyclodextrin column.