Electrospray Ionization Mass Spectrometry and HPLC Determination of the Products in the Radiolysis of 5-Bromouracil, its Nucleoside and Nucleotide Derivatives

Abstract

Radiolysis of 5-bromouracil (BrUr), 5-bromo-2′-deoxyuridine (BrdU) and 5-bromo-2′-deoxyuridine-5′-monophosphate (BrdUMP) has been studied by high performance liquid chromatography and electrospray ionization mass spectrometry. Production of bromide ions and the complementary uracil, 2-deoxyuridine and 2-deoxyuridine-5′-monophosphate has been quantitatively examined. It is concluded that in the presence of hydroxyl radical scavenger, at pH 6 to 10, BrUr, BrdU and BrdUMP quantitatively react with hydrated electron. In the absence of hydroxyl radical (.OH) scavenger in N₂-saturated solutions the yield of bromide ions is about 5.0, indicating that hydroxyl radicals also significantly react with BrUr, BrdU and BrdUMP to eliminate hydrogen bromide. Results from the radiolysis of 1 mM aqueous solutions of BrdU and BrdUMP suggested that abstraction of hydrogen by uracilyl radicals from the sugar moieties is not important. Our mass spectrometry experiments indicated that uracilyl radicals react with the starting substrate to form dimers. The radiolysis of N₂-saturated solutions of nucleosides and nucleotides suggested that the base radicals formed by.OH addition can react with undamaged reagents to produce dimers.