Proanthocyanidins, occurrence

Rasmussen, S.E. et al.. Dietary proanthocyanidins Occurrence, dietary intake, bioavailability, and protection against cardiovascular disease. Mol. Nutr. Food Res., 49, 159, 2005. 

Proanthocyanidins are an important group of di- to oligomeric flavonoids in plants. Four proanthocyanidins (procyanidin B3, prodelphinidin B4, ECG-(4 8)-ECG and GC-(4 8)-EGCG) were determined quantitatively in tea. The amounts in fresh tea leaves were between 1 and 2 g/kg per compound (Nakabayashi, 1991). The occurrence of proanthocyanidins may serve as a criterion for the differentiation between fermented and non-fermented teas (Kiehne et al, 1997). 

The occurrence in some plants of secondary metabolites characterized by an 0-heterocyclic structure and exhibiting antimicrobial properties is a well-known phenomenon [2,8-10]. Among them, catechins and proanthocyanidins are two classes of compounds exhibiting antimicrobial properties towards both prokaryotic and eukaryotic microorganisms. Yet, despite the large number of studies published so far, the real potentialities and limitations given by the use of this class of molecules as antiviral or antimicrobial (antibacterial, antimycotic, antiprotozoal) agents have not been critically evaluated. The present chapter represents an overview of the re-... 

Santos-Buelga, C. and Scalbert, A., Proanthocyanidins and tannin-like compounds — nature, occurrence, dietary intake and effects on nutrition and health, J. Sci. Food Agric., 80, 1094, 2000. 

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. 

Prior, R.L. Gu, L. 2005. Occurrence and biological significance of proanthocyanidins in the American diet. Phytochem. 66 2264-2280. 

Evidence of such adducts in wine fractions has been provided, as detailed in Chapter 9A. These include F-A+ (Alcalde-Eon et al. 2006 Boido et al. 2006) and F-A-A+ (Alcalde-Eon et al. 2006) adducts based on different flavanol and anthocyanin units and (F) -A+ adducts deriving from different flavanols monomers and oligomers (Hayasaka and Kennedy 2003). Proanthocyanidins arising from these reactions cannot be distinguished from those extracted from grapes. However, detection of F-A+ adducts without prior fractionation (Morel-Salmi et al. 2006) confirmed the occurrence of the acid-catalyzed interflavanic bond breaking process in wines. 

The profisetinidins are the most important proanthocyanidins of commerce, constituting the bulk of wattle Acacia meamsii) and quebracho Schinopsis species) tannins. Their natural occurrence, general synthesis protocols, and chemical transformations, especially under basic conditions, were comprehensively reviewed in Ferreira et al.l Ferreira and Li," Porter, Hemingway, and Ferreira and Bekker. ... 

The natural occurrence of promelacacinidins was until recently restricted to the heartwoods of Prosopis glandulosa and Acacia melanoxylon The first proteracacinidin analogues were indeed identified as recently as 1994 200 g considerable number of these two classes of proanthocyanidins have been isolated ftom three... 

Flavan-3,4-diols are now thought to be of limited natural occurrence whereas dimeric proanthocyanidins are widely distributed in nature. Weinges has characterized four dimeric procyanidins B-1 to B-4 (45)-(48). Of these procyanidins B-3 (dimeric catechin) is present in barley and malt [50] and procyanidins B-1, B-2, B-3, and B-4 are present in hops [51]. 

Biosynthesis Chemical reactions Flavan-3,4-diols Flavan-3-ols Flavan-4-ols Flavanols Occurrence Proanthocyanidins Stmctural features... 

The significance of flavan-3,4-diols in plants rests primarily on their probable role as precursors of the polymeric proanthocyanidins. Co-occurrence of the 5-deoxy compounds - i.e., quibourtacacidins, mollisacacidins, and robinetinidins - with the related proanthocyanidins in Acacia species and the ready synthesis of naturally occurring proanthocyanidins from reactions of these flavan-3,4-diols with catechin under mild acidic conditions constitutes heavy but not definitive evidence for this thesis (31, 315-317). 

The profisetinidins in the Anacardiaceae are of unusual structure as they consist of flavanoid units with a IS rather than the normal 2R configuration (see Sect. 7.6). This situation is rare in the proanthocyanidins and only a few other instances are known the widespread occurrence of e z epicatechin and ent-epicatechin-4 procyanidins in monocotyledonous plants (29), and the presence of ezz epicatechin in Polygonum multiflorum (93) and Uncaria gambir (95). Ent-catechin has been isolated from Polygonum multiflorum (93) and Rhaphiolepsis umbellata (91) - as the 7-O-glucoside and 3-O-gallate, respectively. 

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