Institute of Food Chemistry, Technische Universität Braunschweig, Braunschweig, Germany.
J Agric Food Chem. 2011 Jan 12;59(1):62-9. doi: 10.1021/jf1032334. Epub 2010 Dec 8.
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 (1)H 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.
原花青素二聚体和三聚体是生物研究所需的参考化合物，已经通过半合成方法从各种天然来源合成，并通过高速逆流色谱 (HSCCC) 进行纯化。在过去，这些化合物的结构很难阐明，特别是确定黄烷间键的结构。在这里，使用低温（1）H NMR 光谱以及圆二色性（CD）光谱阐明了两种 B 型原花青素二聚体和八种 C 型原花青素三聚体的结构，其中上单元为 (+)-儿茶素 ((+)-C)，而上单元为 (-)-表儿茶素 ((-)-EC)。这是首次使用 NOE 相互作用来表征未衍生的原花青素三聚体中的黄烷间键。对原花青素 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、原花青素 C4 (-)-EC-4β→8-(+)-C-4α→8-(+)-C 和原花青素二聚体 B6 (+)-C-4α→6-(+)-C 和 B8 (+)-C-4α→6-(-)-EC 的结构都进行了呈现。
