Tannins complex

Complex tannins are defined as tannins in which a catechin unit (1.39) is bound glycosidically to either a gallotannin or an ellagitannin unit. As the name implies, the structure of these compounds can be very complex. An example is Acutissimin A (1.99). This is a flavogallonyl unit bound glucosidically to Cl, with an additional three hydrolyzable ester bonds to a D-glucose-derived open-chain polyol. 

This complex tannin is formed during the aging process of red wine, whereby the catechin unit originates from the grapes, and the ellagitannin, in this case vescalagin, originates from the oak barrels. 

Acutissimin A has been shown to be a powerful inhibitor of DNA topo-isomerase II, an enzyme required for the division of cancer cells, and a target for chemotherapeutic drugs (Quideau et al., 2003). Based on these findings, however, it is an overstatement to consider red wine a cancer preventative. Red wine contains other compounds with medicinal activity which will be discussed in more detail in Chapter 7. 

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In the adsorption of some metal ion by tannin adsorbents [16], tannins are widely distributed in nature and have multiple adjacent phenolic hydroxyl groups and exhibit specific chelation ability toward metal ions [17]. According to the chemical stractures of tannins, they can usually be classified into hydrolyzable tannins, condensed tannins and complex tannins. Hydrolyzed tannins yield galhc acid or ellagic acid when hydrolyzed by acid, base or some enzymes [18]. Turkish sumac tannin (hydrolyzable tannin) is illustrated in Fig. 28.1 whose basic stracture is of flavan-3-ols. 

Nonproanthocyanidins with flavan or flavan-3-ol constituent units as well as complex tannins, i.e., polyphenols in which a flavan-3-ol unit is connected to a hydrolyzable tannin through a C—C linkage are discussed in Sections 11.3.3 and 11.3.4, respectively. 

The term, complex tannin, appears to be established as descriptor for the class of polyphenols in which a flavan-3-ol unit, representing a constituent unit of the condensed tannins (proanthocyanidins), is connected to a hydrolyzable (gallo-or ellagi-) tannin through a carbon-carbon linkage. Since the first demonstration of their natural occurrence, a considerable number of these unique secondary metabolites have been reported. " New additions (Table 11.17) to this series of compounds come exclusively from the groups of Nonaka and Nishioka, and Okuda and Yoshida in Japan. 

Tanaka, T. et al., Tannins and related compounds. CXVI. Six new complex tannins, guiajavins, psidinins and psiguavin from the bark of Psidium guajava L., Chem. Pharm. Bull, 40, 2092, 1992. 

Han, L. et al.. Tannins of Stachyurus species. III. Stachyuranins A, B and C, three new complex tannins from Stachyuruspraecox leaves, Chem. Pharm. Bull, 43, 2109, 1995. 

Tannins can be classified in three groups condensed tannins, hydrolysable tannins, and complex tannins (Khanbabaee and Van Ree, 2001). These groups can then be further divided, as shown in Figure 1-3. 

Addition of catechin or epicatechin onto vescalagin yield complex tannin structures called acutissimin and epiacutissimin (Quideau et al. 2003) that have been isolated earlier from Quercus acutissirm. It is worth noting that the isomer of vescalagin (i.e. castalagin) fails to undergo this reaction. 

Fig. 7.2 Subgroups of hydrolyzable tannins gallotannin, ellagitannin, dehydroellagitannin, C-glucosidic ellagitannin and complex tannin.

OKUDA, T., YOSHIDA, T., ASHIDA, M., YAZAKI, K., Tannins oi Casuarina and Stachyurus Species. Part 1. Structures of pedunculagin, casuarictin, strictinin, casuarinin, casuariin, and stachyurin. J. Chem. Soc. Perkin Trans. 1, 1983, 1765-1772. HATANO, T., SHIDA, S., HAN, L., OKUDA, T., Tannins of theaceous plants. III. Camelliatannins A and B, two new complex tannins from Camellia japonica L., Chem. Pharm. Bull, 1991,39, 876-880. 

Examples of complex tannin dimers which have a flavan-3-ol unit attached through C-C linkage to C-1 of a C-glucosidic monomer include anogeissinin (47) and anogeissusins [79]. 

Tanaka, T., Kirihara, S., Nonaka, G., and Nishioka, L, Tannins and related compounds. CXXIV. Five new ellagitannins, Platycaryanins A, B, C, and D, and Platycariin, and a new complex tannin, Strobila-nin, from the fruits and bark of Platycarya strobilacea SIEB. et ZUCC., and biomimetic synthesis of C-glycosidic ellagitannins fromglucopyranose-based ellagitannins, Chem. Pharm. Bull., 41,1708-1716, 1993. 

Complex tannins, also called flavano-ETs or flavono-ETs depending on the flavonoid unit, are hybrid tannins composed of a C-glycosidic ET and a glycosidically linked flavan-3-ol (like catechin or epicatechin), anthocyanin or procyanidin. ... 

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