Institute of Food Chemistry, Technische Universitat Braunschweig, Schleinitzstrasse, Braunschweig, Germany.
J Agric Food Chem. 2010 Apr 28;58(8):5147-53. doi: 10.1021/jf904354n.
A semisynthetic approach has been used for the preparative formation of dimeric procyanidins B1, B2, B5, and B7. As starting material for the semisynthesis, polymeric procyanidins from black chokeberry were applied. These polymers were found to consist almost exclusively of (-)-epicatechin units. Under acidic conditions the interflavanoid linkages of the polymeric procyanidins are cleaved and the liberated (-)-epicatechin can react with nucleophiles, such as (+)-catechin or (-)-epicatechin. In this way, the polymeric procyanidins are degraded while dimeric procyanidins are formed. During this reaction only dimeric procyanidins are formed that contain (-)-epicatechin in the upper unit, that is, B1 [(-)-EC-4beta-->8-(+)-C)], B2 [(-)-EC-4beta-->8-(-)-EC], B5 [(-)-EC-4beta-->6-(-)-EC], and B7 [(-)-EC-4beta-->6-(+)-C]. The reaction mixtures of the semisynthesis can be successfully fractionated with high-speed countercurrent chromatography (HSCCC), and it is possible to isolate pure procyanidins B1, B2, B5, and B7 on a preparative scale.
半合成方法已被用于制备二聚原花青素 B1、B2、B5 和 B7。半合成的起始材料是黑果越桔的聚合原花青素。这些聚合物几乎完全由（-）-表儿茶素单元组成。在酸性条件下，聚合原花青素的间黄烷键被切断，释放出的（-）-表儿茶素可以与亲核试剂（如（+）-儿茶素或（-）-表儿茶素）反应。通过这种方式，聚合原花青素被降解，同时形成二聚原花青素。在这个反应中，只有含有（-）-表儿茶素在上单元的二聚原花青素形成，即 B1[（-）-EC-4β→8-（+）-C)]、B2[（-）-EC-4β→8-（-）-EC)]、B5[（-）-EC-4β→6-（-）-EC)]和 B7[（-）-EC-4β→6-（+）-C)]。半合成的反应混合物可以用高速逆流色谱（HSCCC）成功地进行分离，并且可以在制备规模上分离出纯的原花青素 B1、B2、B5 和 B7。
