The photochemistry of 8-bromo-2'-deoxyadenosine. A direct entry to cyclopurine lesions.

LILIANA B. JIMENEZ

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2004 vol. 3 p. 1042 - 1042

1474-905X

he 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 intramol. 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 const. of 1.8  105 s-1 has been measured by laser flash photolysis in CH3CN for this unimol. 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 equil. Br + Br- .dblharw. Br2- plays an important role in this synthetically useful radical cascade is