Tannins and related compounds. XLVIII Rhubarb. 7 Isolation and characterization of new dimeric and trimeric procyanidins.
Abstract
Together with the known flavan-3-ols and procyanidins, a new procyanidin dimer (11) and several new trimers (14, 15, 16, 20, 22, 24 and 26) have been isolated from high-quality rhubarb ( ?? ?? ?? ). On the basis of chemical and spectroscopic data, the structures of these compounds were characterized as procyanidin B-5 3, 3'-di-O-gallate (11), procyanidin C-1 3', 3''-di-O-gallate (14), procyanidin C-1 3, 3', 3''-tri-O-gallate (15), 3-O-galloylepicatechin-(4β→6)-3-O-galloylepicatechin-(4β→8)-3-O-galloylepicatechin (20), 3-O-galloylepicatechin-(4β→6)-3-O-galloylepicatechin-(4β→6)-3-O-galloylepicatechin (22), 3-O-galloylepicatechin-(4β→6)-3-O-galloylepicatechin-(4β→8)-catechin (26), 3-O-galloylepicatechin-(4β→8)-3-O-galloylepicatechin-(4β→8)-catechin (16) and 3-O-galloylepicatechin-(4β→8)-3-O-galloylepicatechin-(4β→6)-catechin (24).