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

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Abstract
A planar catechin analogue (1H(2)), 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 1H(2) produced by the reaction of 1 H-2 with 2 equiv of tetramethylammonium methoxide reduced molecular oxygen (O-2) to generate superoxide anion (O-2(.-)). The resulting radical anion (1(.-)) from 1H(2) 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 M-catechin, the rate constant of electron transfer (k(et)) from 1(2-) to O-2 is about a half of that reported for (+)-catechin, indicating that the electron transfer from 1(2-) to O-2 is slower than that from (+)-catechin dianion to O-2. Together with efficient protection against DNA strand breakage induced by the Fenton reaction, the small k(et) value for 1H(2) implies that, in physiologically relevant systems, there is less of a possibility of generating oxygen radicals responsible for prooxidant activity with 1H(2) than that with (+)catechin. The strong radical scavenging ability and less-efficient generation Of O-2(.-) suggest that the planar catechin analogue may be useful for the prevention and/or treatment of free-radical-associated diseases.