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

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.

Delocalization of the Unpaired Electron in the Quercetin Radical: Comparison of Experimental ESR Data with DFT Calculations

“…It is generally accepted that this is due to the delocalization of the UE in the extensive π-system of Q • . Despite its pivotal role in the antioxidant activity of Q, research on the exact delocalization of the UE in Q • is rare and not conclusive [6,[8][9][10]. This prompted us to elaborate on this by combing experimentally obtained spin resonance spectroscopy (ESR) results with theoretical quantum calculation of the delocalization of the UE in Q • , while also examining some structurally closely related radicals, and comparing our results to previously reported data.…”

ABTS/PP Decolorization Assay of Antioxidant Capacity Reaction Pathways

“…Many structure-activity relationship studies showed much greater importance of the catechol-like B-ring of flavonoids for antioxidant activity manifestation [1,75,77,84] and the kinetic study of free-radical-scavenging action of flavonoids, and catechin in particular indicated that the activities of 5-and 7-OH groups at A-ring were rather weak and even almost negligible, whereas 3 -and 4 -OH groups at B-ring were highly reactive, suggesting that the o-dihydroxyl (catechol) structure in the B-ring is the obvious radical target site for flavonoids as well [85,86]. Finally, the examination of catechin, epicatechin, and their metabolites' radical-scavenging potency demonstrated that a free catechol moiety in the B-ring is presumably the most important for the direct antioxidant activity and apparently leads to the formation of epicatechin quinone [87,88].…”

Inhibitory Effect and Mechanism of Action of Quercetin and Quercetin Diels-Alder anti-Dimer on Erastin-Induced Ferroptosis in Bone Marrow-Derived Mesenchymal Stem Cells

“…From the perspective of redox chemistry, quercetin ortho-quinone is virtually an oxidized form of quercetin. The ortho-quinone moiety can be achieved through catechol oxidation by multiple pathways, including electron-transfer (ET) plus proton-transfer (PT) [75][76][77][78], hydrogen-abstraction [79][80][81], the ET pathway alone [82][83][84], or even enzymatic oxidation [25,26]. Therefore, it is very difficult for quercetin ortho-quinone to be further oxidized, suggesting that quercetin ortho-quinone is a weak antioxidant [79].…”