Procyanidin B2 dimer

Procyanidin B2 (dimer), isolated from loquat leaves, was found to inhibit the 12-0-tetradecanoylphorbol-13-acetate (TPA)-induced activation of Epstein-Barr virus early antigen in Raji cells [108]. Animal studies and cell models suggest that flavonoids act as anticarcinogens through influencing molecular events in the initiation, promotion, and progression stages of cancer [109]. 

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].

Fig. 3.9 ESI mass spectrum of the dimer-rich fraction from Fig. 3.8c showing the procyanidin B2 peak (this eluted at 16.4 min after reverse-phase HPLC separation)...

Mescaline (=Mezcaline 3,4,5-Trimethoxy-phenethylamine) (phenylethylamine) A-Methylmescaline (= A -Methylmezcaline 7 1Methyl-3,4,5-trimethoxy-phenethylamine) (phenylethylamine) Procyanidin B2 (= Epicatechin (4(3 —>8) epicatechin) (procyanidin dimer) Procyanidin B3 (= Catechin (4a—>8) catechin (procyanidin dimer)... 

Figure 2.20 Chromatogram relative to analysis of dimer procyanidins in the skins extract (fraction ethyl acetate from C18 cartridge) (sample volume injected 10p,L). 1. procyanidin Bl, 2. procyanidin B3, 3. procyanidin B2...

Figures 2.21,2.22 and 2.23 show the chromatograms relative to analysis of catechins and procyanidins prior to fractionation in the cartridge, of catechins monomer (fraction diethyl ether) and of procyanidins dimer (fraction ethyl acetate), respectively. As evidenced by Figures 2.20 and 2.23, the main procyanidin in seeds is procyanidin B2, however in skins procyanidin Bl prevails.

Ethyl-linked pigments in wine-like media are also short lived. Francia-Arichia et al. (13) showed that ethyl-linked procyanidin B2-Mv dimers at pH 3.2 in a model solution reached a maximum after 10 days but then declined to negligible levels after 120 days. The rate constants for the formation and disappearance of ethyl-linked pigments formed from other procyanidins show... 

The theoretical yield for a dimer is 50 %, but for procyanidin B2, for example, only 30 % [11,104] or determined by HPLC (high performance liquid chromatography) 13 % [118], respectively, could be obtained. Procyanidins with a higher degree of polymerization produce more anthocyanidin than dimers, because more "upper units" exist which can be converted into carbocations [113]. For a procyanidin polymer with an average degree of polymerization of 9.4 a cyanidin yield of 58 % is reported [113]. 

Diethyl ether is also frequently used to delipidate extracts which are subsequently analyzed by conventional methods [46,55,67,175]. It has been reported that extraction using diethyl ether allows the quantitative removal of monomers from acidified aqueous wood extracts, while dimeric proanthocyanidins remain in the aqueous phase [121]. Recovery studies of (-)-epicatechin and (+)-catechin in synthetic wine solutions only yielded 24 % and 46 %, respectively, of the added amounts. Procyanidin B2, however, could not be detected in the lipophilic layer. Analogous results... 

Recovery studies for (+)-catechin and (-)-epicatechin in synthetic wine solutions performed by HPLC revealed differences between these stereoisomers 79 % (-)-epicatechin was recovered compared to 97 % (+)-catechin [176]. We evaluated the use of ethyl acetate as extraction solvent in the analysis of extracts of hawthorn herb. Four subsequent extractions were performed and determinations were carried out in triplicate. From the total contents only 82 % (-)-epicatechin and 43 % procyanidin Cl could be recovered in the ethyl acetate extracts. The proportions of procyanidins B2 and B5 in the ethyl acetate extracts could not be determined because the peaks in the water phases were superimposed by matrix components. LC-MS (liquid chromatography mass spectrometry) analysis of the water phases however proved the presence of procyanidins B2, B5 and Cl besides other dimeric, trimeric and tetrameric procyanidins (see Fig. (4)).3... 

The B-ring substitution pattern influences the absorbance. Pure prodelphinidin polymers show much lower specific absorption coefficients (El% = 62) than pure procyanidin polymers (E 0/o = 130) [141]. The molar absorption coefficients of dimeric and higher oligomeric procyanidins are similar (see Tab. (8)). The overall UV absorbance of an oligomer approximately amounts to the sum of the absorbances of the monomer units [226,254], However, UV detection of individual procyanidins after chromatographic separation implies that - in this case - molar absorbances depend on structure. In the series (+)-catechin, procyanidin B2, Cl and a tetramer molar absorbances decreased [262], Treutter et al. [154] found lower molar absorbances for dimers with a 2,3-cis stereochemistry (procyanidin B2 and B5) compared to (-)-epicatechin and (+)-catechin which nearly showed identical molar calibration plots. The molar absorbance of the doubly-linked procyanidin A2 was much higher than the ones of the monomers. 

The crude drug of H. perforatum contains approx. 8% of tannins of the proanthocyanidin-type [92]. These proanthocyanidins are constituted of catechin and epicatechin units since acid hydrolysis results exclusively in cyanidin [2]. Melzer isolated and characterised the dimeric procyanidin B2 50, further procyanidins of a higher degree of polymerisation also found were not fully identified [93]. 

HPLC analysis of the development of dimeric and trimeric procyanidins, as well as simple flavanols, extracted from the skins and seeds of red and white grapes, shows that concentrations decrease to a greater or lesser extent, but never increase (de Freitas, 1995). It has been observed that procyanidin B2 is the most common dimer in ripe Merlot and Cabernet Sauvignon (Table 6.11), followed by trimeric Ci. All the dimers are present in the seed extract, whereas procyanidins B4,... 

Stoupi S, Williamson G, Drynan JW, Barron D, Clifford MN. Procyanidin B2 catabolism by human fecal microflora partial characterization of dimeric intermediates. Arch Biochem Biophys. 2010 501 73—78. 

It was reported that esterification of (—)-epicatechin and procyanidin B2 by gallic acid can occur and that these gallate esters are only found in the grape seed extract. Grape seed extract contains oligomer procyanidins made up of dimers or trimers of (+)-catechin and (—)-epicatechin.4-6 The procyanidin dimers are comprised of procyanidins Bl, B2, B3, B4, B5, B6, B7, and B8. There are six procyanidin trimers which include procyanidins Cl and C2. 

Regarding cytotoxic activities, the 3,3 -di-0-gallate derivative of procyanidin B2 was found to be active against human leukemic cells (HL-60) and a melanoma cell line but was inactive toward several other tumor cell lines. Several other galloylated procyanidin dimers were also shown to inhibit the growth of human lung and colon carcinoma cell lines [7, 108]. 

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). 

The content of proanthocyanidins of the procyanidin type in the seeds of red grapes is 2 5 times higher than in the skin. In the seeds it is mainly oligomers with 2-6 flavanol units that are found, in the skin higher oligomers are also present. The main dimer in the skin of grapes is procyanidin Bj, which is epicatechin-(4p 8)-catechin and the major trimer is epicatechin-(4fl 8)-epicatechin-(4p—>8)-catechin. The seeds contain mainly procyanidin B2, which is epicatechin-(4p 8)-epicatechin,and trimer epicatechin-(4p—>8)-epicatechin-(4p 8)-epicatechin (procyanidin Cj). In addition to these compounds, other dimers are found in smaller quantities. 

The B-type procyanidins include a mixture of oligomers and polymers composed of flavan-3-ol units linked mainly through C4 C8 and/or C4 C6 bonds, and represent the dominant class of natural proanthocyanidins. Among the dimers, procyanidins Bl, B2, B3 and B4 (Fig. 2a) are the most frequently occurring in plant tissues. Procyanidin B5 (EC-(4j6 6)-EC), B6 (catechin-(4o 6)-catechin), B7 (EC-(4/3 6)-catechin) and B8 (catechin-(4q 6)-EC) are also widespread (Eig. 2b) [17-19]. 

Monomers, dimers (procyanidin Bl, B2), and oligomers Apples, cherries, berries, grapes, peaches, pears... 

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