STUDY OF 8-BROMO-2'-DEOXYNOSINE BY PHOTOCHEMICAL AND RADIOLYTIC METHODS.

LILIANA B. JIMENEZ; SUSANA ENCINAS; MIGUEL A. MIRANDA; MARIALUISA RUSSO; MILA D'ANGELANTONIO; QUINTO G. MULAZZANI; CHRYSSOSTOMOS CHATGILIALOGLU

Aix-les-Bains, France

Congreso; 11th Congress of the European Society for Photobiology.; 2005

European Society of Photobiology

When the DNA is exposed to ionising radiation or under particular chemical reactions are formed products of descomposition as 5?,8-cyclopurines. From a mechanistic point of view, it was verified that the C5? radical initially generated by hydrogen abstraction, intramolecularly attacks the aromatic ring of the base moiety to form these cyclopurines as the final products of oxidation.1The 8-bromo-2?-deoxyadenosine (1) and 8-bromo-2?-deoxyguanosine (2), have recently been studied by photochemical and radiolytic methods.2 Employing pulse radiolysis, it was found that 1 produces the 2?-deoxyadenosin-5?-yl radical followed by a cyclisation generating the corresponding aminyl radical (precursor of cyclopurines) with a rate constant of 1,6 x 105 s-1. On the other hand, 2 captures electron forming the radical anion that undergoes protonation at C8 to afford the one-electron oxidized 2?-deoxyguanosine.Also, analysing in steady-state photolysis it was found that cyclisation process is the major pathway for 1, were observed (5?R) and (5?S) isomers of 5?-8-ciclo-2?-deoxyadenosine, whereas for the 2 predominates the reduction producing 2?-deoxyguanosine.Following with 8-bromo-2?-deoxypurines studies it was proposed to synthesize a new halodeoxypurine, the 8-bromo-2?-deoxyinosine, and to study the influence, as the activation method as nature purine, on the generation and reactivity of the 2?-deoxyinosin-5?-yl radical R1. In order to analyse this radical are used pulsed and continuous radiolysis as well as steady-state and time resolved photolysis. At a transient level, formation of the cyclised aminyl radical was observed from R1, whose reactivity was analysed towards Fe(CN)63-, methylviologen and molecular oxygen. Furthermore, studying final products of steady-state photolysis and continuous radiolysis was evidenced formation of the two 5´-8-cyclo-2?-deoxyinosine isomers together with the 5?-carboxaldehyde-2?-deoxyinosine.