2-Aminopurine radicals

Oxidation of Guanine at a Distance in DNA Induced by 2-Aminopurine Radicals... 

Shafirovich V, Dourandin A, Luneva NP, Geacintov NE (2000) The kinetic deuterium isotope effect as a probe of a proton coupled electron transfer mechanism in the oxidation of guanine by 2-aminopurine radicals. J Phys Chem B 104 137-139... 

Shafirovich V, Cadet J, Gasparutto D, Dourandin A, Fluang W, Geacintov NE (2001) Direct spectroscopic observation of 8-oxo-7,8-dihydro-2 -deoxyguanosine radicals in double-stranded DNA generated by one-electron oxidation at a distance by 2-aminopurine radicals. J Phys Chem B 105 586-592... 

The results indicate that C-6 in purine and 2-aminopurine (17) is more reactive than C-8 or C-2, while the primary attack at C-8 in adenine and 6-ethoxypurine (18) indicates that C-8 is more reactive than C-2. The order of reactivity toward a-hydroxyalkyl radicals in the purine system is therefore C-6 > C-8 > C-2. 

Table 2 Deuterium isotope effect on the rate constants of the oxidation of guanine and 8-oxoguanine by 2-aminopurine neutral radicals in double-stranded DNA duplexes (adapted from [11] and [13]) ...

As with other reducing agents, G reacts with 02 (Chap. 10.2) which is the most abundant freely diffusing peroxyl radical. Upon two-photon excitation of a 2-aminopurine-containing ss- and dsODN in air-saturated solutions, photoionization leads to the formation of eaq (and subsequently 02 ) and the 2-amino-purine radical cation oxidizes a neighboring G (leading to G plus H+ Misiaszek et al. 2004). G and 02 react with one another (ssDNA k = 4.1 x 108 dm3 mol-1 s 1 dsDNA 2.7 x 108 dm3 mol-1 sH). In the majority of these events G is reformed, but with an efficiency of 15% Iz and, to a minor extent, 8-oxo-G are formed. The suggested mechanism is shown in Chapter 10.2. 

The related reaction with alkyl nitrites generates purinyl radicals which efficiently abstract halogen from halogenated solvents and this procedure is generally to be preferred for the transformation of aminopurine into halopurine. Comparably, the use of dimethyl disulfide produces methylthiopurines. ... 

Free-radical deoxygenation procedures have been used to convert 6-chlorogua-nosine into 2-aminopurine-2 -deoxyriboside, BusSnH effecting both deoxygenation at C-2 and dechlorination at C-6, and for the synthesis of 2-aza-2 -deoxyinosine (25), which was then incorporated into oligonucleotides. Treatment of the 3, 5 -di-C -acetyl analogue of 14 with acetyl chloride in MeCN gave a chlorocompound, reducible with tributylstannane to the dihydrothymidine derivative 26. ... 

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