Selecting compound 97-9-G4 as lead compound, a series of bispiperazinittm salts 5a-h were designed, synthesized and evaluated for their analgesic activities. The results show that phenylethyl group of 97-9-G4 is a crucial pharmacophore; the intro- duction of electron-withdrawing group on benzene ring is favorable to the activity.
The fragmentation patterns of a series of dispirocyclopiperazinium dibromides with strong analgesic activity during positive ion electrospray ionization mass spectrometry were analyzed. The [M-Br]^＋ 2 ions showed the characteristic isotopic peaks and were assigned as the molecular ions. The loss of a 44 Dalton unit from 2 produced ion 3 [M-Br-44]^＋ and the loss of HBr from 2 formed ion 4. Besides, the carbamates 1d-1e produced extra ions [M-2Br-33]^＋. The related fragmentation mechanisms were proposed.
