The photochemistry of 8-bromo-2'-deoxyadenosine. A direct entry to cyclopurine lesions.
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.
Jimenez
Liliana B
LB
Departamento de Química/Instituto de Tecnologia Química UPV-CSIC, Universidad Politécnica de Valencia, Camino de Vera s/n, E-46022, Valencia, Spain.
Encinas
Susana
S
Miranda
Miguel A
MA
Navacchia
Maria Luisa
ML
Chatgilialoglu
Chryssostomos
C
D003839:Deoxyadenosines / Q000737:chemistry* / Q000528:radiation effects; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D010777:Photochemistry; D012997:Solvents; D013053:Spectrophotometry
D003839:Deoxyadenosines; D012997:Solvents; C042464:8-bromo-2'-deoxyadenosine