Electron-induced single strand break in the nucleotide of 5- and 6-bromouridine. A DFT study

We studied electron-induced O–P bond breakage in 5- and 6-bromo-2′-deoxyuridine 3′,5′-diphosphates at the B3LYP/6-31++G** level of theory. Electron attachment to the 6-bromo derivative causes debromination, resulting in 6-radical that can abstract a hydrogen atom from the sugar residue. For 5-radical, H abstraction and conversion to 6-radical are kinetically prevented, suggesting that the radiosensitizing properties of 5-bromo-2′-deoxyuridine cannot be explained by intranucleotide reaction. The radicals, produced by hydrogen abstraction may undergo breakage at the O–P bond, forming carbonyl compounds. This reaction is thermodynamically favored for the 3′-site. Identification of 3′-ketone in radiolytic experiments with 6-bromo-2′-deoxyuridine labeled DNA would confirm our mechanism.