Fragmentation of Moxifloxacin and Its Analogs by Electrospray Ionization Time-of-Flight Mass Spectrometry

The fragmentation of patterns of moxifloxacin, 2-N-methylated moxifloxacin (analog 1), and 1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-3-quinolinecarboxylic acid (analog 2) were investigated by electrospray ionization quadrupole time-of-flight tandem mass spectrometry in the positive-ion mode. Many unusual ions were detected in the tandem mass spectra of moxifloxacin. Although the structures of moxifloxacin and analog 1 were similar, the relative abundances of products varied greatly. Comparison of the relative abundances of the product ions that lost CO2 or H2O and complementary product ions resulting from sequential four-membered hydrogen rearrangement showed that the differences were related to the protonation sites. The loss of HF, probably though the formation of an ion/neutral complex, is of scientific interest. The identities of the major product ions were confirmed by deuterium-labeling experiments that demonstrated an unusual loss of a deuterium atom. The major differences in fragmentation patterns were compared to previous reports in the literature.