Formamidopyrimidines

R = R = R" = Me). These hydrates readily undergo acid hydrolysis to give (substituted) 4-formamidopyrimidine-5-aldehyde. 

One-electron oxidation of the adenine moiety of DNA and 2 -deoxyadenos-ine (dAdo) (45) gives rise to related purine radical cations 46 that may undergo either hydration to generate 8-hydroxy-7,8-dihydroadenyl radicals (47) or deprotonation to give rise to the 6-aminyl radicals 50. The formation of 8-oxo-7,8-dihydro-2 -deoxyadenosine (8-oxodAdo) (48) and 4,6-diamino-5-formamidopyrimidine (FapyAde) (49) is likely explained in terms of oxidation and reduction of 8-hydroxy-7,8-dihydroadenyl precursor radicals 47, respectively [90]. Another modified nucleoside that was found to be generated upon type I mediated one-electron oxidation of 45 by photoexcited riboflavin and menadione is 2 -deoxyinosine (51) [29]. The latter nucleoside is likely to arise from deamination of 6-aminyl radicals (50). Overall, the yield of formation of 8-oxodAdo 48 and FapyAde 49 upon one-electron oxidation of DNA is about 10-fold-lower than that of 8-oxodGuo 44 and FapyGua 43, similar to OH radical mediated reactions [91]. 

This enzyme catalyzes the release of formamidopyrimid-ines from methylated, alkali-treated DNA. The enzyme will also act on unmethylated formamidopyrimidine derivatives of both adenine and guanine. See also Formam-idomethyluracil-DNA Glycosidase... 

Greenberg MM, Hantosi Z, Wiederholt CJ, Rithner CD (2001) Studies on N4-(2-deoxy-D-pentofura-nosyl)-4,6-diamino-5-formamidopyrimidine (FAPYdA) and N6(2-deoxy-D-pentofuranosyl)-6-diamino-5-formamido-4-hydroxyprimidine (FAPYdG). Biochemistry 40 15856-15861 Greenstock CL, Dunlop I (1973) Pulse radiolysis studies of nitrofurans Chemical radiosensitization. Radiat Res 56 428-440... 

Raoul S, Cadet J (1996) Photosensitized reaction of 8-oxo-7,8-dihydro-2 -deoxyguanosine Identification of 1-(2-deoxy-p-D-erytftro-pentofuranosyl)cyanuric add as the major singlet oxygen oxidation product. J Am Chem Soc 118 1892-1898 Raoul S, Bardet M, Cadet J (1995) y Irradiation of 2 -deoxyadenosine in oxygen-free aqueous solutions Identification and conformational features of formamidopyrimidine nucleoside derivatives. Chem Res Toxicol 8 924-933... 

Diamino-5-formamidopyrimidine (in general also with respect to dAdo, Ado and DNA)... 

Fig. 4.6.2. Examples of oxidative G damage (Gox) with formamidopyrimidine (Fapy-dG), 8-oxoguanine (8-oxo-dG), oxazolone (dOz), or imidazolone (dlz) structure.

With oxygen-free atmospheres, attack at the 8-position is followed by degradation to 5-formamidopyrimidines (71).126,127 The complexity of this reaction is shown by the fact that adenine gives, in addition to the 5-formamidopyrimidine, some 8-oxoadenine128 and small amounts of hypoxanthine, produced by oxo displacement of the amino group. 

Figure 22.5. Representatives of the major oxidative base damage. The 8-oxoguanine is also known as 8-hydroxyguanine due to isomerization. FaPy-G, 2,6-diamino-4-hydroxy-5-formamidopyrimidine FaPy-A, 2,6-diamino-5-formamidopyrimidine.

Removes oxidized and ring-opened purines including 8-oxoG and formamidopyrimidine... 

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