Bio-organic applications of mass spectrometry. Part 6. Selective deprotection of nucleotides by fast atom bombardment mass spectrometry

Abstract

The fully protected nucleoside S-methyl O-2,4-dichlorophenyl phosphorothioates (2) and (3) undergo selective removal of the protecting groups when exposed, in liquid matrices, to 9.5 KeV Xe bombardment. Dimethoxytrityl and 9-phenylxanthen-9-yl cations are formed when the reactivity of the protonated species is examined, while solvolytic removal of the 2,4-dichlorophenyl protecting group afforded the nucleosides phosphodiester anions (6) and (8) as a result of matrix-substrate interaction in the energized condensed phase. The same substrates are competitively demethylated at the sulphur atom when thioglycerol is present in the solvation sphere of the reactants. Anions (6) and (8), desorbed into the gas phase by fast atom bombardment of their triethylammonium salts, displayed the same metastable ion kinetic energy spectra as those produced from nucleotides (2) and (3) by applying the same methodology.