Catechin autoxidation

Hathway, D.E., 1958a, Autoxidation of polyphenols. IV. Oxidative degradation of the catechin autoxidative polymer, J. Chem. 

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

Fig. 1. Amperometric monitoring of the autoxidation of epigallocatechin gallete in the presence of (A) 0, (B) 2.0, (C) 5.0, (D) 10, (E) 20, and (F) 50 pm CuCl2. The measurements were performed in 0.1 M Tris buffer (pH 9.0) with a Clark type oxygen electrode at 28 °C. The epigallocatechin gallate concentration was fixed at 50 pm. The catechin stock solution was injected into the test solution at t = 0. The inset shows the (initial) steady-state autoxidation rate as a function of Cu2+ concentration. Reprinted from Biochimica et Biophysica Acta, vol. 1569, Mochizuki, M. Yamazaki, S. Kano, K. Ikeda,T., Kinetic analysis and mechanistic aspects of autoxidation of catechins, p. 35, Copyright (2002), with permission from Elsevier Science.

Mochizuki et al. also demonstrated that the uncatalyzed autoxidation of catechins is suppressed in the presence of a sufficient amount of borate buffer (44). This was interpreted by considering the adduct formation between borate ion and the catechins. The oxidation resumes on addition of Cu(II) in the presence of the borate ions. This may indicate that Cu(II) forms more stable complex(es) with the catechins than the borate ion, but direct oxidation of the catechin-borate complex by Cu(II) cannot be excluded either. 

Sun, W. and Miller, J.M., Tandem mass spectrometry of the B-type procyanidins in wine and B-type dehydrodicatechins in an autoxidation mixture of (+)-catechin and (-)-epicatechin, J. Mass Spectrom., 38, 438, 2003. 

Hathway, D. E., Seakins, J. W. T. (1957). Autoxidation of polyphenols. Part III. Autox-idation in neutral aqueous solutions of flavans related to catechin.7. Chem. Soc., 300, 1562-1566. 

Hathway DE, Seakins JWT. Autoxidation of polyphenols. Part in. Autoxidation in neutral aqueous solution of flavans related to catechin. J Chem Soc 1957 1562-1566. Yoshida K, Ikeda Y, Tsukamoto G. Japanese Patent 1982 120584. 

Catechin was aerobically subjected to an oxidative coupling by plant polyphenol oxidase (PPO) to give polymers [35], whose analytical properties were similar to those obtained by autoxidation with hydrogen peroxide [36] and to tannins extracted from Acacia catechu. The main reaction sequence involves formation of o-quinone, followed by the coupUng of this unstable intermediate. 

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