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Structure Elucidation of Procyanidin Oligomers by Low-Temperature 1H NMR Spectroscopy
- Esatbeyoglu, Tuba, Jaschok-Kentner, Beate, Wray, Victor, Winterhalter, Peter
- Journal of agricultural and food chemistry 2011 v.59 no.1 pp. 62–69
- catechin, chemical structure, countercurrent chromatography, epicatechin, nuclear magnetic resonance spectroscopy, procyanidins
- Procyanidin dimers and trimers, needed as reference compounds for biological studies, have been synthesized from various natural sources using a semisynthetic approach and purified by high-speed countercurrent chromatography (HSCCC). In the past, it has been difficult to elucidate the structure of these compounds, especially the determination of the interflavanoid bond. Here, the structure of two B-type procyanidin dimers, with (+)-catechin ((+)-C) in the upper unit, and eight C-type procyanidin trimers, with (−)-epicatechin ((−)-EC) in the upper unit, have been elucidated using low-temperature 1H NMR spectroscopy, as well as circular dichroism (CD) spectroscopy. This is the first time NOE interactions have been used to characterize the interflavanoid linkage in underivatized procyanidin trimers. Complete analyses of procyanidin C1 (−)-EC-4β→8-(−)-EC-4β→8-(−)-EC, (−)-EC-4β→8-(−)-EC-4β→8-(+)-C, (−)-EC-4β→6-(−)-EC-4β→8-(−)-EC, (−)-EC-4β→6-(−)-EC-4β→8-(+)-C, (−)-EC-4β→8-(−)-EC-4β→6-(−)-EC, (−)-EC-4β→8-(−)-EC-4β→6-(+)-C, (−)-EC-4β→8-(+)-C-4α→8-(−)-EC, procyanidin C4 (−)-EC-4β→8-(+)-C-4α→8-(+)-C, and procyanidin dimers B6 (+)-C-4α→6-(+)-C and B8 (+)-C-4α→6-(−)-EC are presented.