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 were analyzed by positive ion electrospray ionization mass spectrometry in conjunction with tandem mass spectrometry (ESI-MSn). The [C2+Br-](+) ions showed the characteristic isotopic peaks with high intensity. In each of their MS2 spectra, only the [C2+Br--HBr](+) ion peak was observable. Further analysis indicated that a selective rearrangement occurred in the unsaturated spirocyclopiperazine ring to achieve dihydropyrrole moiety. Meanwhile, the [C](2+) ions were unique and always the base peaks. The ions [C2+Br-](+) and [C](2+) were formed from the equilibrium of precursor molecules I in solution, and the latter ions could not be observed in the MS2 spectra of ions [C2+Br-](+). The related fragmentation mechanisms were proposed. (C) 2004 Elsevier B.V. All rights reserved.