Tannins and related compounds. XXXIII. Isolation and characterization of procyanidins in Dioscorea cirrhosa Lour.

Dimeric, trimeric and tetrameric procyanidins have been isolated, together with (+)-catechin (1) and (-)-epicatechin (2), from the tubers of Dioscorea cirrhosa LOUR. (Dioscoreaceae). By comparisons of the physical and spectral data, the dimers (3-5), trimers (6-8) and tetramer (9) were identified as procyanidins obtained previously. The structures of two other trimers (10 and 11) were established by acid-catalyzed thiolytic degradation, while the formation of the tetramer (12) by condensation of the 4-carbocation of 1 with 6, in conjunction with 1H- and 13C-nuclear magnetic resonance examinations, established the structure of 12.

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