Fragmentation patterns of novel dispirocyclopiperazinium dibromides with strong analgesic activity under electrospray ionization tandem mass spectrometry conditions.

The fragmentation patterns of a series of dispirocyclopiperazinium dibromides with strong analgesic activity are analyzed by positive ion electrospray ionization mass spectrometry in conjunction with tandem mass spectrometry (ESI-MS(n)). Instead of the parent molecular ions, the fragment ions M-Br are detected as characteristic double peaks and usually the base peaks. Meanwhile, the fragment ions M-2Br are unique for this series of diquaternary ammonium dibromides and show high intensity. Besides the common fragmentation patterns around the carbonyl group, elimination of hydrogen bromide from M--Br ions is another important pathway. Following the elimination, an interesting rearrangement takes place in the unsaturated spirocyclopiperazine and transforms it into a dihydropyrrole structure, whose fragmentations are similar to its precursor ion in the succeeding steps.