A catechin analogue in which the geometry was constrained to be planar was synthesized. The planar catechin showed excellent radical-scavenging ability, comparable to that of quercetin, and efficient protection against DNA strand breakage induced by the Fenton reaction.
A kinetic study of a hydrogen-transfer reaction from (+)-catechin (1) to galvinoxyl radical (G•) has been
performed using UV−vis spectroscopy in the presence of Mg(ClO4)2 in deaerated acetonitrile (MeCN). The
rate constants of hydrogen transfer from 1 to G• determined from the decay of the absorbance at 428 nm due
to G• increase significantly with an increase in the concentration of Mg2+. The kinetics of hydrogen transfer
from 1 to cumylperoxyl radical has also been examined in propionitrile (EtCN) at low temperature with use
of ESR. The decay rate of cumylperoxyl radical in the presence of 1 was also accelerated by the presence of
scandium triflate [Sc(OTf)3 (OTf = OSO2CF3)]. These results indicate that the hydrogen-transfer reaction of
(+)-catechin proceeds via electron transfer from 1 to oxyl radicals followed by proton transfer rather than via
a one-step hydrogen atom transfer. The coordination of metal ions to the one-electron reduced anions may
stabilize the product, resulting in the acceleration of electron transfer.
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