Procyanidin dimers and trimers from grape seeds

Fractionation of a grape (Vitis vinifera) seed extract yielded various natural procyanidin dimers and trimers isolated and identified for the first time in grapes: procyanidin dimers B5 [epicatechin-(4β → 6)-epicatechin], B6 [catechin-(4α → 6)-catechin] and B8 [catechin-(4α → 6)-epicatechin]; four procyanidin trimers [epicatechin-(4β → 6)-epicatechin-(4β → 8)-epicatechin], [epicatechin-(4β → 8)-epicatechin-(4β → 6)-catechin], [epicatechin-(4β → 8)-epicatechin-(4β → 6)-epicatechin], [epicatechin-(4β → 6)-epicatechin-(4β → 8)-catechin] along with five galloyl procyanidins: B2 3-O-gallate, B1 3-O-gallate, B4 3′-O-gallate, B2 3,3′-di-O-gallate and [epicatechin-(4β → 8)-epicatechin 3-O-gallate-(4β → 8)-catechin]. The presence of (+)-catechin, (−)-epicatechin, (−)-epicatechin 3-O-gallate, procyanidins dimers B1, B2, B3, B4, B7, B2 3′-O-gallate and procyanidin trimers C1 and [epicatechin-(4β → 8)-epicatechin-(4β → 8)-catechin] was also confirmed. The structures of all these compounds were elucidated by enzymatic hydrolysis, complete acid hydrolysis, partial acid-catalysed degradation with phloroglucinol and phenylmethanethiol, FABMS and 1H NMR. Separation of procyanidins and of their phloroglucinol or phenylmethanethiol adducts was achieved by TLC on silica plates and HPLC.