Peroxyl Radicals - Free-Radical-Induced DNA Damage and Its Repair - page 159

In competition with O 2 -addition [reaction (25)], the -alkylperoxide species

may undergo radical-induced cleavage of the peroxide function [reaction (26);
Bloodworth et al. 1984; Phulkar et al. 1990].
In allylperoxyl radicals, allylic rearrangement leads to the 1,3-migration of
the peroxyl function, with the corresponding shift of the double bond [reaction
(28); Schenck et al. 1958].

β

Evidence has been adduced that for many such systems, the apparently obvious
cyclic intermediate 1,2-dioxanyl is not realized in the course of this rearrange-
ment: an O 2 -allylradical pair is postulated instead (Beckwith et al. 1989; Porter
et al. 1994). Nevertheless, this cyclic structure has been invoked in the gas phase
(Lodhi and Walker 1991; Bozzelli and Dean 1993), and an exothermicity of 96 kJ
mol − 1 has been computed for the formation of the cyclic intermediate relative to
the level of allyl plus O 2 (Bozzelli and Dean 1993).
In DNA free-radical chemistry allylperoxyl radicals play a major role in the
free-radical-induced oxidation of Thy. Thus far, this kind of rearrangement has
not yet been observed (but also not especially looked for) in this system.

8.6
Intramolecular and Intermolecular H-Abstraction Reactions

The H-abstraction reactions of peroxyl radicals are related to ET discussed above,
as in both cases the same final product is formed, a hydroperoxide. Mechanisti-
cally, these two processes are, of course, different. Hydrogen-abstraction reac-
tions by peroxyl radical, including HO 2 • , are common (cf. the autoxidation of
polyunsaturated lipids;Hasegawa and Patterson 1978; Patterson and Hasegawa
1978; Patterson 1981; Porter et al. 1981; Gebicki and Bielski 1981; Barclay et al.
1989; Zhu and Sevilla 1990; Aikens and Dix 1991; Simic et al. 1992). This H-ab-
straction reaction may occur intra molecularly as well as inter molecularly [cf.
reactions (29) and (30)].