Liliana B. Jimenez, S. Encinas, M. Miranda
Nov 1, 2004
Citations
0
Influential Citations
21
Citations
Journal
Photochemical & Photobiological Sciences
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 × 10^5 s^−1 has been measured by laser flash photolysis in CH_3CN 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^− ⇌ 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.