Structures of dimeric, trimeric, and tetrameric procyanidins from Areca catechu L.

Two procyanidin tetramers, two trimers, and a dimer which is a structural isomer of procyanidin B-1, along with (+)-catechin, (–)-epicatechin, and pro-cyandins A-1, B-1, and B-2, have been isolated pure from the seed of Areca catechu L., and their 1H and 13C n.m.r spectral data, combined with degradative studies on their reaction with toluene-α-thiol, have established that they all, except for procyanidin B-2, have the C(4)-to-C(8)[or C(6)]-linked (–)-epicatechin stereochemistry [C(2), C(3):cis] in the upper units, and the (+)-catechin stereochemistry [C(2), C(3): trans] in the terminal (lower) units.

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