Plant polyphenol proanthocyanidins

Anthocyanidins from Ricciocarpos natans Proanthocyanidins from Stryphnodendron adstringens Proanthocyanidins from Cassipourea gummiflua Anthocyanins from plants Polyphenols from tea... 

Alai s rich blue-purple color advertises its high content of anthocyanins, a class of plant polyphenols under study as potential anti-disease agents. Five chemically different anthocyanins, particularly cyanidins, and at least a dozen other polyphenols have been isolated, including a high content of proanthocyanidins linked to possible anti-disease effects, such as in bacterial infections, onset of cancer, and inflammation. 

D. Ferreira E. V. Brandt H. van Rensburg R. Bekker R. J. J. Nel, Manipulation of Some Crucial Bonds in the Molecular Backbone of Proanthocyanidins and Related Compounds. In Plant Polyphenols 2 Chemistry, Biology, Pharmacology, Ecology (Basic Life Sciences - Volume 66)] G. G. Gross, R. W. Hemingway, T. Yoshida, Eds. Kluwer Academic/Plenum Publishers New York, 1999 p 163. 

J. P. Steynberg E. V. Brandt M. J. H. Hoffman R. W. Hemingway D. Ferreira, Conformations of Proanthocyanidins. in Plant Polyphenols Synthesis, Properties, Significance (Basic Life Sciences - Volume 59) R. W. Hemingway, P. E. Laks, Eds. Plenum Press New York, 1992, p 501. 

Comparative Aspects of Polyphenol Metabolism - Proanthocyanidins and the complex esters of gallic and hexahydroxydiphenic acid show many structural similarities as plant metaijol i tes. The shape and size of the ester (5) is thus very similar to that of a proanthocyanidin hexamer (1, n = 4). The most striking feature of both structures however s the manner in which free phenolic groups are distributed over the surface of the molecule providing a structure with the inbuilt capacity for multidentate attachment to other species by hydrogen bonding. 

The polyphenols are a series of phytochemicals synthesized by plants. They include the bioflavonoids anthocyanins, coumestanes, flavonoids, isoflavonoids, and stil-benes (Figure 4.1). Each bioflavanoid class is subdivided into other groups, e.g., flavones, flavans, flavanols, flavonols, and flavanones (Figure 4.2). Another class of polyphenol is the oligomeric polyphenols, such as the proanthocyanidins, found in the grape and various berries (black currant, blueberry, etc.). 

Although these same effects could be demonstrated with other polyphenol-enriched berries, the relatively higher concentrations of anthocyanins and proanthocyanidins in aronia simplify sourcing these polyphenols to one plant. 

It is well known that tea contains catechins besides caffeine. Although catechins are widely distributed in the plant kingdom, the catechin monomers in many plants coexist with larger amounts of dimeric to polymeric proanthocyanidins, which are comprised of catechin units connected by C-C bonds. However, the polyphenol composition of C. sinensis is unique, and mainly comprised of four monomeric catechins—(-)-epicatechin (1), (-)-epigallocatechin (2) and their galloyl esters. 

Procyanidins are the most widely distributed members of the class of polyphenolic compounds known as proanthocyanidins (synonyms oligoflavanoids, condensed polyphenols, condensed tannins). Proanthocyanidins are colorless compounds, occurring predominantly in woody or herbaceous plants. They got their name from the characteristic hydrolyzation reaction they undergo in acidic medium which yields colored anthocyanidins. Proanthocyanidins consist of flavonoid precursors, which are commonly linked by carbon-carbon bonds at C4—>C8 or C4—>C6. A variety of different classes are known, depending on the substitution pattern of the monomer units (see Fig. (1)). More details on structures, distribution and general features of this class of compounds can be found in numerous reviews [1-6]. 

There is a general consensus that analysis of fresh material yields results which come closest to the natural distribution pattern in plants. Since this approach is not feasible in most cases suitable preservation procedures must be employed. Advantages and disadvantages of such procedures with respect to polyphenol analysis have been reviewed by several authors [47-49]. The procedure keeping the chemical composition as close as possible to the natural state is lyophilization. A study of the extractability of proanthocyanidins in the bark of several pines (Pinus sp.) showed no difference between freshly collected samples and freeze-dried samples. On the other hand drying at room temperature resulted in an increase in extractability in one sample [50]. Increased extractability after drying at room temperature compared to fresh material has also been... 

Havanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthocyanidins), flavan-4-ols, and flavan-3,4-diols. They arise from plant secondary metabolism through condensation of phenylalanine derived from the shikimate pathway with malonyl-CoA obtained from citrate that is produced by the tricarboxylic acid cycle, leading to the formation of the key precursor in the flavonoids biosynthesis the naringenin chalcone. The exact nature of the molecular species that undergo polymerization and the mechanism of assembly in proanthocyanidins are still unknown. From a structural point of view, flavanols... 

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