Procyanidins monomeric units

Another membrane property physically affected by flavonoids is the surface potential. Working with liposomes composed of PC and PS, we found that (—)-epicatechin and certain procyanidins (dimer to hexamer) decreased liposome surface potential. This effect relied on both, procyanidin concentration and number of monomeric units [Verstraeten et al., 2003]. On the other hand, when liposomes were composed exclusively of PC, it was found that (—)-epi-catechin dimers Al and B2, and the trimers A and C2 increased liposome surface potential in a concentration-dependent manner [Verstraeten et al.,... 

Condensed T. are polymers in which the monomeric unit is a phenolic flavan, usually a flavan-3-ol, and in which the flavan units are link by 4 8 (C-C) bonds. Many higher oligomers and polymers of Proanthocyanidins (see) are therefore condensed vegetable T. An example is the procyanidin polymer from the seed coat of sorghum (Fig.). SynAesis of condensed T by hiomimetic condensation reactions has been reported. The condensation sequence is initiated by flavan-3-oIs acting as nucleophiles, and fla-van-3,4- ols as potential 4-carbenium ions [J.XBetha et al. Phytochemistry 21 (1982) 1289-1294 CL Hartisch H. Kolodziej Phytochemistry 42 (1996) 191—198]. 

The proanthocyanidins form a considerable portion of the tannins found in wine and in particular contribute heavily to the color and flavor of red wines. Proanthocyanidins are high-molecular-weight polymers formed from flavan-3-ol monomeric unit (i.e., (+)-catechin and (—)-epicatechin). Oxidative condensation occurs between carbon C-4 of the heterocycle C ring and carbons C-6 or C-8 of the attached aromatic A rings (Fig. 72.3) [15]. The procyanidins B1-B4 are the most... 

Common dimers such as procyanidin B1 (PBl) and procyanidin B2 (PB2) are also present in grape skins. Colorless flavanols include C and EC, the monomeric units of proanthocyanidins. Proanthocyanidins, also known as condensed tannins, are characterized by polymerization degree (PD) ranging mainly between 3 and 11, but varying up to 17 or more (Iriti and Faoro 2006). 

Monomeric flavanols yield dimeric, higher oligomeric and polymeric procyanidins (proanthocyanidins) of several types. The link between the monomeric units is usually in position C-4 of the... 

Flavonoids represent one class of bioactive compounds that may have multiple beneficial effects on several chronic diseases [3-4]. Cocoa represents an example of a potentially rich dietary source of flavonoids. High concentrations of flavonoids are present in certain cocoas, predominately as the flavanol monomers (-)-epicatechin (epicatechin) and (+)-catechin (catechin), and as oligomers of these monomeric base units which are known as the procyanidins (Figure 1) [5]. Other potential rich dietary sources of flavonoids include tea, wine, grape juice, apples, onions and certain nuts. 

Studies on the stability of procyanidins oligomers isolated from Theobroma cacao L. has shown that these compounds are unstable under acidic conditions and decompose to epicatechin monomeric and dimeric units, but also to other oligomeric units [81]. 

It has also been observed that proanthocyanidins normally accumulate in plant tissue as polymers rather than lower oligomers (dimers or trimers). This implies that the major biosynthetic route is directed toward the synthesis of proanthocyanidin units to form those polymers, in contrast to the formation of lesser amounts of monomeric flavan-3-ols. For instance, the total production of epicatechin, including that present as monomer and as a terminal (B) unit in the polymers, is only 10% that of epicatechin-4 procyanidin units, in the tannins extracted from the unripe fruits of Chaenomeles chinensis (L. J. Porter, unpublished observations). 

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