Rearrangement Catechin

WANG H, LYNCH p N, LEWIS J, BOND T and DAVIES A p (1998b) Molecular rearrangements of tea catechins , in Proc of Polyphenol Communications 98, XIXth Intern Conf on Polyphenols, 1-4 September, 1998, Lille, France, 181-2. 

Clark-Levuis, J. W. The relative configuration of catechin and epi-catechin 1,2-rearrangement in the reduction of the diastereoisomers to the same enantiomorph of a propan-l-ol. Proc. chem. Soc. [London] 1959, 388. 

In addition to the effect pH has on the overall reaction rate, it is also important to note the effect of pH on rearrangement reactions of (+)-catechin. At alkaline pH, these secondary rearrangement reactions dominate. Epimerization of (+)-catechin to (-b)-epicatechin is a prominent reaction at pH 9.0. This is not serious in terms of adhesive formulation because it does not alter the reactivity of the aromatic nucleus toward condensation with benzyl alcohols. However, in reactions at pH 10.0 or 11.0, the intramolecular rearrangement to catechinic acid dominates and results in loss of the phloroglucinol functionality. 

Precipitation studies at comparatively high concentrations have shown that proanthocyanidins form complexes with poly(L-proline) as well as with poly(vinylpyrrolidone) (9,W). Figure 2 depicts the repeat units of poly(vinylpyrrolidone y and poly(L-proline). The L-prolyl unit contains one fewer methylene and has the remaining atoms rearranged so that the amide and five-membered ring become parts of the backbone of the chain. The results reported in the proceeding section might lead to the expectation that addition of poly(L-proline) to an aqueous solution of one of the fluorophores would produce 1/1(0) > 1. This expectation is not realized. Poly(L-proline) with M = 60000 does not produce I/l(0) > 1. Instead it quenches the fluorescence. For example, the values of I/l(0) for 3.6 X 10 5 M (+)-catechin in water are 0.75 and 0.41, respectively. 

Scheme 8. Base-catalyzed pyran ring rearrangements of fisetinidol-(4a—>8)- and (4p— 8)-catechin 4-0 (E-ring) methyl ethers (100) and (101) ] 1...

Most of the catechins are unstable in cell culture media, and their spontaneous rearrangement products tend to bind to extracellular matrix. 

Scheme 1 Catechin epimerization and rearrangement in basic medium. (Adapted from Ref. 36.)...

Kiatagrajai P, WeUons JD, Golob L, White JD J. Kinetics of epimerization of (+) catechin and its rearrangement to catechinic acid. Org Chem 1982 47 2910-2912. Kennedy JA, Munro MHG, Powell HKJ, Porter LJ, Foo Y. The protonation reactions of catechin, epicatechin and related compounds. Aust J Chem 1984 38 885-892. 

Until recently, little attention has been given to the reactions of polymeric proanthocyanidins under alkaline conditions. It was known that solution of polymeric procyanidins in base caused a marked decrease in the reactivity of these polymers with aldehyde and that both carbonyl and relatively acidic functions were generated analogous to the rearrangement of catechin to catechinic acid (152, 335). 

Sears K D, Casebier R L, Hergert H L, Stoudt G H, McCandlish L E 1975 The structure of catechinic acid, a base rearrangement product of catechin. J Org Chem 39 3244-3247... 

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