A Planar Catechin Analogue as a Promising Antioxidant with Reduced Prooxidant Activity

Abstract

A planar catechin analogue (1H2), in which catechol and chroman moieties in (+)-catechin are constrained to be coplanar, is an efficient radical scavenger compared to the native catechin, and are nearly as effective as quercetin, a strong radical scavenger. The dianion (1(2-)) of 1H2 produced by the reaction of 1H2 with 2 equiv of tetramethylammonium methoxide reduced molecular oxygen (O2) to generate superoxide anion (O2*-). The resulting radical anion (1*-) from 1H2 underwent intramolecular proton transfer to give an o-semiquinone radical anion form of 1*-, which shows a characteristic ESR spectrum with g value of 2.0048. Although the same mechanism has also been shown for (+)-catechin, the rate constant of electron transfer (ket) from 1(2-) to O2 is about a half of that reported for (+)-catechin, indicating that the electron transfer from 1(2-) to O2 is slower than that from (+)-catechin dianion to O2. Together with efficient protection against DNA strand breakage induced by the Fenton reaction, the small ket value for 1H2 implies that, in physiologically relevant systems, there is less of a possibility of generating oxygen radicals responsible for prooxidant activity with 1H2 than that with (+)-catechin. The strong radical scavenging ability and less-efficient generation of O2*- suggest that the planar catechin analogue may be useful for the prevention and/or treatment of free-radical-associated diseases.

A Planar Catechin Analogue as a New Type of Synthetic Antioxidant

“…The one electron-transfer reaction from dianion to molecular oxygen proceeds to form O2 -. The same reaction is also shown by the dianion (PCA 2-) of PCA, forming O 2 -by electron-transfer oxidation from PCA 2-to O2 as conˆrmed by a low-temperature ESR (23). A characteristic ESR g// value of 2.070 due to O2 -, together with an ESR g// value of 2.050 for protonated O2 -(HO2  ) was observed for an O2-saturated MeCN solution of PCA and 2 equiv of MeO -at 77 K, as shown in Fig.…”

Importance of Proton-Coupled Electron Transfer from Natural Phenolic Compounds in Superoxide Scavenging

“…It is also accepted that oxidation of Cat 2− to produce Cat a ·− is are generated via an electron transfer oxidation of Cat 2− by molecular oxygen. 44,45) Therefore, the proton and electron are transferred in one kinetic step corresponding to following the diagonal of the rectangle in Fig. 4a, labeled concerted PCET, avoiding generation of the high-energy intermediates.…”

Effect of Egyptian Propolis on the Susceptibility of LDL to Oxidative Modification and its Antiviral Activity with Special Emphasis on Chemical Composition

“…Electron spin resonance (ESR) spectroscopy can provide direct evidence of the formation of free radicals in chemical and biological reactions. Because ESR generates signals only in molecules with unpaired electrons, it is very selective and can be used even in situations where thousands of other compounds are present (Fukuhara et al, 2003). Some authors demonstrated such results of free radical scavenging activities of propolis and some plants were examined using ESR spectroscopy (Scheller et al, 1990;Rapta et al, 1995;Cal- Scheller et al (1990) stated that the DPPH signal intensity was inversely related to the concentration of the ethanolic extract of propolis (EEP) and due to the reaction time.…”