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 [MBr] + are detected as characteristic double peaks and usually the base peaks. Meanwhile, the fragment ions [M2Br] 2+ 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 [MBr] + 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. Copyright © 2004 John Wiley & Sons, Ltd.