Methylated catechins

Ring contraction was also noted on acetolysis of 3-tosyltetra-O- methyl-(+)-catechin the 2,3-dihydrobenzo[Z> ]furan formed can be oxidized to the benzo[f>]furan (Scheme 105) (66JCS(C)634). The 2-phenylbenzo[6]furan and its 2,3-dihydro derivative are degradation products of lignin and as such have been investigated extensively. 

The structure of 8-bromotetra-0-methyl-(+)-catechin (161) has been determined. The conformation of the heterocyclic ring in the crystal is between a C-2, C-3 half-chair and a C-2 sofa arrangement. The 2R,1R absolute configuration of (-l-)-catechin is confirmed (78CC695). 

Maeda-Yamamoto, M., Nagai, H., Suzuki, Y., Ema, K., Kanda, E., and Mitsuda, H. 2005. Changes in O-methylated catechin and chemical component contents of Beni-fuuki green tea (Camellia sinensis L.) beverage under various extraction conditions. Food Sci. Technol. Res. 11 248-53. 

Many other flavonic compounds have been reported to exhibit an interesting antiulcer effect mecyadanol, (+)-cyanidanol-3, (+)-catechin, 3-0-methyl-(+)-catechin, 3-methoxy-5,7,3 ,4 -tetrahydroxyflavan, apigenin-7,4 -diorthomethylether, hesperidin, and amentoflavone [118-121],... 

Fronczec, F.R., R.W. Hemingway, G.W. McGraw, J.P. Steynberg, C.A. Helper, and W.L. Mattice Crystal Structure, Conformational Analysis, and Molecular Dynamics of Tetra-0-methyl-(+)-catechin. Biopolymers, 33, 275 (1993). 

Methyl catechin glucuronide Methyl catechin sulfate... 

Catechin glucuronide Epicatechin glucuronide Methyl catechin glucuronide Trimer... 

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. 

Apart from these in vivo applications, a coculture system on hepatic cells was also reported for assaying the bioactivity of a procyanidin extract. In this report, different procyanidin metabolites were identified, these being catechin and epicatechin in its sulfate forms methyl-catechin and methyl-epicatechin in its sulfate forms epicatechin glucuronide, methyl-catechin, and methyl-epicatechin in its glucuronide forms and the aglycones catechin and epicatechin, epicatechin in its gallate forms, dimer and trimer [38]. 

Recently, a new strategy based on successive and seleetive protections of the various phenol functions present on flavan-3-ols has allowed synthesis of a whole family of methylated catechin analogues. These materials appear particularly useful for the development of a new analytical tool allowing the identification of all flavan-3-ol metabolites, for the study of their chemical reactivity, and thus for understanding the mechanism by which these methylated flavan-3-ols behave as antioxidants. 

Indeed, with these selectively methylated catechin analogues, it has been possible to determine thermodynamic constants (redox potentials, pKa) and to study the intrinsic reactivity of each catechin moiety. Each moiety, the A- or B-ring, presents its own reactivity whereas the A-ring is more specifically involved in H-atom transfer, the B-ring is specifically involved in electron transfer. These results lead to a new interpretation of the antioxidant properties of these molecules since B-ring of flavan-3-ols has been shown to be the active moiety of the molecule [12], the antioxidant activity involves mainly an electron transfer and not only an H-atom transfer as is so often proposed. 

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