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

<div><p>The fragmentation of patterns of moxifloxacin, 2-N-methylated moxifloxacin (analog <b>1</b>), and 1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-3-quinolinecarboxylic acid (analog <b>2</b>) 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 <b>1</b> were similar, the relative abundances of products varied greatly. Comparison of the relative abundances of the product ions that lost CO<sub>2</sub> or H<sub>2</sub>O 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.</p> </div>