Time-of-Flight Secondary Ion Mass Spectrometry of Isomeric O-Alkylthymidines

Positive ion mass spectra of the title compounds and their parent molecule, thymidine, show prominent [M + H]+ and [M + Na]∗ ions, as well as base fragment ions resulting from cleavage of the N-glycosyl bond. In the case of alkylated nucleosides the base fragments can undergo further elimination of an alkene. In the negative ion spectra the prominent ions for all nucleosides are B− and NCO−. Molecular mass can be verified for thymidine by a prominent [M - H]− ion, which is not, or barely, detectable for the alkylated molecules. In addition, the NCO− ion produces a prominent [M + 41]− adduct with a (dT - H)• radical, but not with the alkylated species. Trends in the relative abundances of the ions are discussed.