Epicatechin dimers

Figure 1. Chemical structures of flavanols and a cocoa (-)-epicatechin dimer. Higher molecular weight procyanidins typically oligomerize through the 4 -8 bond.

Ionisation constants of vitisin A and the various ethyl-linked malvidin-3-glucose / catechin / epicatechin dimers were determined by high voltage paper electrophoresis (HVPE) using chromatography paper (Chr. 1,. Whatman, England) as previously reported (28). All relative mobilities (Rm) were compared to anionic standards orange G and xylene cyanol. Fructose was used as... 

The sample pretreatment used to determine procyanidins and their metabolites in plasma samples (from rats) is off-line solid-phase extraction (SPE) with hydrophilic-lipophilic balanced (HLB) copolymer. Both cartridges (60 mg) [31,32] and microelution SPE plates (pSPEs) (2 mg) [33,36,37] have been used as the device format. For the analysis of tissues (also from rats), such as the liver, brain, aorta artery, and adipose tissue, these were first freeze-dried and then pretreated by off-line Ll.F. (with the solution made up of methanol, water, and phosphoric acid) followed by pSPE [35-37]. The use of two sample pretreatments (LLE and pSPE) is due to the complexity of the tissue sample compared with the biofluid plasma sample. The extraction recoveries (%Rs) for determining the procyanidins catechin, epicatechin, dimer B2, and trimer in the plasma samples by pSPE [33] and SPE [31] were higher... 

Catechin, epicatechin, dimer Bj, trimer 0.2% Acetic acid Acetonitrile HSST3 (100x2.1 1.8 pm) mm, Rat plasma Off-line SPE 65-102 3-800 10-980 [31] 0 n -<... 

The quantification of procyanidins is complex due to the lack of commercial pro-cyanidin standards. At present, only monomers (catechin and epicatechin), dimers... 

The reported LODs and LOQs for procyanidins (catechin, epicatechin, dimer, and trimer) in plasma samples that were lower than 4 and 10 nM, except for the trimers, which were 800 and 980 nM, respectively, using the off-line SPE-UHPLC-MS/MS [31], Similar results were obtained when the off-line iSPE-UHPLC-MS/ MS was used to analyze these procyanidin compounds in the biological sample [33]. This demonstrated the high capacity of the pSPE sample pretreatment technique, where the LODs and LOQs were similar in comparison with SPE. In contrast, the preconcentration factor obtained in SPE was 10, in comparison with obtained in pSPE, which was 3.5. 

Then, different procyanidin metabolites were generated, these being catechin and epicatechin in its glucuronide forms, catechin and epicatechin in its sulfate forms, methyl-catechin and methyl-epicatechin in its glucuronide forms, and methyl-calechin and methyl-epicatechin in its sulfate forms [31-33,35-39], In some studies, the aglycones, catechin, epicatechin, dimer, and trimer were also identified [31,33,35,36]. The main metabolites generated from the procyanidin-rich extract intake are shown in Table 14.3. 

The approach we have found to be most useful for the isolation and purification of Type 1 or 2 proanthocyanidin polymers is extraction from plant tissue with acetone-water mixtures (25, 37), separation of the monomers and lower oligomers from the resulting aqueous solution with ethyl acetate, adsorption on Sephadex LH-20 of the aqueous solution diluted with an equal volume of methanol and washing with the same solvent to eliminate impurities. The polymer is then displaced with acetone-water to yield freeze-dried analytically pure material (25). In the case of procyanidins, the ethyl acetate fraction contains monomers (catechin or epicatechin), dimers, trimers, and some tetramers, whereas the LH-20 fractions contain tetramers, on up to genuinely polymeric species. 

Catechin, epicatechin, dimer B2, dimer B5, trimer Cl, tetramer D... 

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