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Free Radic Biol Med. 2018 Aug 20;124:31-39. doi: 10.1016/j.freeradbiomed.2018.05.087. Epub 2018 May 31.

The chemical reactivity of (-)-epicatechin quinone mainly resides in its B-ring.

Author information

1
Department of Pharmacology and Toxicology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, the Netherlands.
2
Zuyd University of Applied Science, Heerlen, the Netherlands.
3
Faculty of Veterinary Medicine, University of Liège, 4000 Liège, Belgium.
4
Department of Pharmacology and Toxicology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, the Netherlands. Electronic address: g.haenen@maastrichtuniversity.nl.

Abstract

As one of the important dietary antioxidants, (-)-epicatechin is a potent reactive oxygen species (ROS) scavenger involved in the redox modulation of the cell. When scavenging ROS, (-)-epicatechin will donate two electrons and become (-)-epicatechin quinone, and thus take over part of the oxidative potential of the ROS. The aim of the study is to determine where this chemical reactivity resides in (-)-epicatechin quinone. When this reactivity is spread out over the entire molecule, i.e. over the AC-ring and B-ring, this will lead to partial epimerization of (-)-epicatechin quinone to (-)-catechin quinone. In our experiments, (-)-epicatechin quinone was generated with tyrosinase. The formation of (-)-epicatechin quinone was confirmed by trapping with GSH, and identification of (-)-epicatechin-GSH adducts. Moreover, (-)-epicatechin quinone could be detected using Q-TOF/MS despite its short half-life. To detect the epimerization, the ability of ascorbate to reduce the unstable flavonoid quinones into the corresponding stable flavonoids was used. The results showed that the reduction of the formed (-)-epicatechin quinone by ascorbate did not result in the formation of an appreciable amount of (-)-catechin. Therefore it can be concluded that the chemical reactivity of (-)-epicatechin quinone mainly resides in its B-ring. This could be corroborated by quantum chemical calculations. Understanding the stabilization of the (-)-epicatechin quinone will help to differentiate between flavonoids and to select the appropriate compound for a specific disorder.

KEYWORDS:

(-)-catechin; (-)-epicatechin; Antioxidant; Epimerization; Quinone

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