title: The photochemistry of 8-bromo-2'-deoxyadenosine. A direct entry to cyclopurine lesions.
abstract: The UV photolysis of 8-bromo-2'-deoxyadenosine has been investigated in different solvents and in the presence of additives like halide anions. Photolytic cleavage of the C-Br bond leads to formation of the C8 radical. In methanol, subsequent hydrogen abstraction from the solvent is the main radical reaction; however, in water or acetonitrile intramolecular hydrogen abstraction from the sugar moiety, to give the C5' radical, is the major path. This C5' radical undergoes a cyclization reaction on the adenine and gives the aminyl radical. A rate constant of 1.8 x 10(5) s(-1) has been measured by laser flash photolysis in CH(3)CN for this unimolecular process. Product studies from steady-state photolysis in acetonitrile have shown the conversion of 8-bromo-2'-deoxyadenosine to 5',8-cyclo-2'-deoxyadenosine in 65% yield and in a diastereoisomeric ratio (5' R):(5' S)= 1.7. Evidence supporting that the equilibrium Br*+ Br(-)[right left harpoons] Br(2)*(-) plays an important role in this synthetically useful radical cascade is obtained by regulating the relative concentrations of the two reactive oxidizing species.
authors.affiliation: Departamento de Química/Instituto de Tecnologia Química UPV-CSIC, Universidad Politécnica de Valencia, Camino de Vera s/n, E-46022, Valencia, Spain.
authors.forename: Liliana B
authors.initials: LB
authors.lastname: Jimenez
authors.forename: Susana
authors.initials: S
authors.lastname: Encinas
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Miranda
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Navacchia
authors.forename: Chryssostomos
authors.initials: C
authors.lastname: Chatgilialoglu
mesh_terms: D003839:Deoxyadenosines / Q000737:chemistry* / Q000528:radiation effects; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D010777:Photochemistry; D012997:Solvents; D013053:Spectrophotometry
chemical_list: D003839:Deoxyadenosines; D012997:Solvents; C042464:8-bromo-2'-deoxyadenosine