Epicatechin oligomers

Besides their free-radical trapping properties, flavonoids can interfere with the capacity of oxidants to reach the bilayer. A study from our laboratory demonstrated that the adsorption of water-soluble ( )-epicatechin oligomers (dimer to hexamer) to membranes prevents lipid oxidation initiated by the azocompound 2,2 -azobis (2,4-dimethylvaleronitrile), (AMVN), a hydrophobic molecule that upon its incorporation into the bilayer decomposes yielding peroxyl radicals [Verstraeten et al., 2003], In this case, given that the oxidant... 

The LC/MS does not allow separation and identification of oligomers higher than pentamers because the number of diastereoisomers is large and their separation is not possible. By having positive-ion MALDI-TOF in the reflectron mode, determination of (+)-catechin, (-)-epicatechin oligomers, and their galloylated derivatives up to a heptamer in grape seed extracts as sodium adducts [M+Na]+ is possible... 

Galloylated epicatechin oligomers, e.g., galoylated (-)-epicatechin 4,8-trimer (158)... 

Fig. 2.115. Mass chromatograms of catechin monomers (m/z 289) and procyanidin oligomers (dimer through hexamers m/z 577 to 1729). C, ( + )-catechin, EC, ( — )-epicatechin, and PB2, procyanidin B2 as identified by the retention times of authentic standard. Reprinted with permission from J. Wollgast et al. [256].

The location of the interflavanyl bond in dimers and oligomers is denoted within parentheses as in carbohydrates. The orientation of the interflavanyl bond at C-4 is denoted as a or (3 as in the lUPAC rules. Thus, the familiar procyanidin B-1 (5) is named epicatechin-(4(3 8)-catechin, the analogous prodelphinidin (6) is named epigallocatechin-(4(3 —> 8)-catechin, and the 2S analog (7) is named e t-catechin-(4(3 6)-e t-epiafzelechin. 

Condensed tannins (= proanthocyanidins) unlike hydrolysable tannins, condensed tannins are polymeric flavans that are not readily hydrolysable. They often consist of molecules of catechin and epicatechin joined by carbon-carbon bonds. Hence catechin and epicatechin are referred to as monomers oligomers containing 2-4 (epi)catechin units are referred to as oligomeric procyanidins (OPC). 

The phenolics ( + )catechin and (— )epicatechin are common flavanols in several fruits (128). Apples and pears contain other phenolic compounds such as quinic, shikimic, chlorogenic, and caffeic acids (39). Durkee and Poapst (162) reported that the two major phenolic constituents of core tissues and seeds of McIntosh apples were chlorogenic acid and phloridzin. After hydrolysis of extracts from core tissues, the identified phenolics were phloretin, caffeic acid, p-coumaric acid, phloretic acid, and trace amounts of ferulic acid. Studies have shown that apple leucoanthocyanins yield catechin, epicatechin, cyanidin, and pelargonidin after hydrolysis (163, 164). Van Buren et al. (164) also reported that a purified leucoanthocyanin from apples was either a dimer or oligomer containing ( —) epicatechin, and 5,7,3, 4 -flavin-3,4-diol. 

Procyanidins. Catechin (Fluka) and epicatechin (ex. cacao beans) were recrystallized and dried before use. The oligomers epicatechin-(4/ — 8)-epicatechin and [epicatechin-(4/ — 8)]3-epicatechin were obtained from the ethyl acetate sol-... 

Figure 2. An example of a hexameric homo-oligomer of epicatechin, containing one (4/ — 6) and four (4/ —>8) interflavanoid linkages. = 3,4-dihydroxyphenyl.

Results obtained with colorimetric methods are highly empirical. Estimations of total PAs are often expressed as catechin or epicatechin equivalents, which make the data difficult to interpret and compare across different samples. Qualitative data such as subunit structures, interflavan bond types, and proportions of oligomers with different degrees of polymerization - is not available with any of these non-chromatographic methods. 

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. 

The unripe apples were homogenized in potassium pyrosulfite solution, and the mixture was allowed to stand for 1 day. The supernatant was centrifuged and filtered with a glass filter funnel. The filtrate was apphed to adsorption chromatography, and the ACT fraction was evaporated and lyophilized. Purified ACTs were a mixture of monomer (catechin and/or epicatechin) and oligomers from dimers to pentadecamers, as shown in Fig. 2. 

---