“…Consequently enzymes concerned with the metabolism and action of cyclic nucleotides are important pharmacological targets. Application of qualitative fastatom bombardment (FAB) mass spectrometry (MS) with mass-analysed ion kinetic energy (MIKE) spectrum scanning has proved invaluable in the identification of endogenous cyclic nucleotides 1-3 and of their analogues 4,5 and derivatives, 6-8 by virtue of the characteristic fragmentations 9,10 observed in the MIKE spectra obtained after collisionally-induced dissociation (CID) of the protonated molecule in the FAB mass spectrum. The advantage of softionization methods such as FAB is the production of cyclic nucleotide mass spectra without a requirement for derivatization and, combined with CID/MIKE analysis, this permits the differentiation of the 3',5'-cyclic nucleotides, 9,10 which are the biochemical second messengers, from the 2',3'-cyclic nucleotide isomers, which are merely intermediates of nucleic acid catabolism.…”