Nucleobases, Nucleosides and Nucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 257

the lowest dose rate used, not all • CH 2 OH were scavenged by the pyrimidine but
also reacted with one another and with the 1,3Me 2 Ura • CH 2 OH-adduct [reac-
tions (191)-(194)].

In this context, it may be of interest that hydroxymethylation of 1,3Me 2 Ura (and
its derivatives) by the Eu(III)/Eu(II) photoredox system in MeOH affords 5,6-
dihydro-1,3-dimethyl-6-hydroxymethyluracil in close to 100% yield (Ishida et
al. 1985). Apparently, the one-electron-reduced 1,3Me 2 Ura, the O (4)-protonated
1,3Me 2 Ura-4-yl radical, does not undergo sufficiently rapid isomerization into
the thermodynamically more stable 1,3-dimethyl-5-hydro-uracil-5-yl radical
under these conditions. Otherwise, 5,6-dihydro-1,3-dimethyl-5-hydroxymethy-
luracil would have been observed.
In dCyd, the

-posi-
tion must add to C (6) [reaction (195)] that fast that it is not scavenged effectively
by O 2 . An oxidation of the ensuing C (5) radical by O 2 and deamination are fur-
ther likely steps [reaction (196)] to the observed product (Wagner et al. 1999; for
its yield see Table 10.16).

α -hydroxyalkyl radical formed upon • OH attack at the 5 ′