FAST-ATOM-BOMBARDMENT AND COLLISIONAL ACTIVATION MASS-SPECTROMETRY AS PROBES FOR THE IDENTIFICATION OF POSITIONAL ISOMERS IN A SERIES OF BENZYLATED GUANOSINES

The mass spectra of a series of 1-, N2-, O6-, 7-, and 8-(p-Y-benzyl)guanosines (where Y = H, CH3, CH3O, Cl, and NO2) were examined in order to identify spectral characteristics that might distinguish these positional isomers. Field desorption and positive chemical ionization (isobutane) spectra were not diagnostic, while both positive and negative ion fast atom bombardment (FAB) spectra provided sufficient information to differentiate among these isomers. Abundant [M + H]+ and [M-H]- ions together with extensive fragmentation were obtained by using a glycerol-N,N-dimethylformamide (1:1 v/v) mixture as FAB matrix. Collision-activated dissociation-mass analyzed ion kinetic energy (CAD-MIKE) spectrometry and kinetic energy release measurements provided additional information for distinguishing members of this series of isomers. Short- and long-term reproducibility of the relative ion abundance was excellent and demonstrated that, of the ionization techniques examined, FAB was the most useful for isomer differentiation.