Oligomeric proanthocyanidins from mangosteen pericarps

Oligomeric proanthocyanidins were extracted from mangosteen pericarps and fractionated by a Sephadex LH-20 column to give 0.66% yield (dry matter). C-13 and H-1 NMR signals showed the presence of predominantly procyanidins together with a few prodelphinidin units along with small amounts of stereoisomers of afzelechin/epiafzelechin, catechin/epicatechin, and gallocatechin/ epigallocatechin. Depolymerization with benzylmercaptan resulted in epicatechin thioether as the major product, and the mean degree of polymerization was determined to be 6.6. The electron spray ionization-mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectra revealed the dominant B type oligomers with mainly epicatechin units and with a small amount of A type oligomers. The isolated proanthocyanidins are potent peroxyl radical scavengers as evidenced by the high oxygen radical scavenging capacity at 1.7 x 10(4) mu mol TE/g, much higher than that of pine bark and grape seed extracts.