Nucleobases, Nucleosides and Nucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 238

FAPY-A has been found at 2% of • OH and that of 8-oxo-A at 5% (Vieira and
Steenken 1990 ; Vieira et a l. 1993). In t he presence of Fe (CN) 6 3− , the 8-oxo-A yield
is raised to 18% and that of FAPY-A is now < 0.2%. It is not yet understood why
the balance (based on

30% C (8)- • OH-adduct) is that poor.
FAPY-A is not stable in aqueous solution. It rapidly isomerizes and eventually
is fully hydrolyzed [reactions (116)−(122); Raoul et al. 1995].

∼

With FAPY-A derived from dAMP, where the pyranose forms cannot play a role,
an anomeric ratio of

= 1.33 develops after 6 h, while the deglycosylation half-
life is 103 h at 37 °C (Greenberg et al. 2001). The deglycosylation of FAPY-G de-
rived from dGMP is even slower.
The reactions of • OH-induced radicals of purine deoxyribonucleosides with
nitroxyl radicals (for rate constants, see Brustad et al. 1972) have been studied
with, for example, TAN, and it has been observed that the FAPY-products are no
longer formed to a significant extent, and in the case of dAdo the formation of
8-oxo-A is enhanced (Berger and Cadet 1983b). This further supports the oxidiz-
ing properties of the nitroxyl radicals, although the formation of an adduct as
an intermediate is very likely, considering that in the case of pyrimidine-derived
radicals stable adducts have been observed (Cadet et al. 1979).
The attack of • OH at the C (2) position of dAdo is of little importance (see
above), and it is thus not surprising that 2-hydroxy-dAdo is only a minor prod-
uct (Frelon et al. 2002).
Fluorescent material is formed in the reaction of • OH with Ade, and it as been
suggested that dimers may contribute to the as yet not fully characterized mate-
rial (Yamamoto et al. 1985).
In the reaction of peroxynitrite with dGuo 4,5-dihydro-5-hydroxy-4-(nitro-
sooxy)-2

β / α

-deoxyguanosine has been reported to be formed (Douki et al. 1996)
besides 8-oxo-G and Z (Douki and Cadet 1996) as well as 8-nitroguanine (Douki
et al. 1996; Burney et al. 1999).

′