Gas Phase Rearrangement Of Aromatic Amide Compounds And Structural Identification Of Unknown Impurities In Two Kinds Of APIs

Mass spectrometry is a vital tool to achieve structural analysis of compounds with speed and sensitivity. Study of the fragmentation reactions of ions has always been the focus of mass spectrometry. These researches have not only expanded the understanding of gas phase chemical reactions but also been helpful to explain some special fragmentation behavior of the analytes. The high-performance liquid chromatography coupled with electrospray ionization mass spectrometry technology (HPLC-ESI-MSn), which can get a rapid chromatographic analysis of a large number of components in the mixture as well as the molecular structural information, has become an irreplaceable method for drug analysis. In this paper, the rearrangement reactions of N-phenylbenzamide compounds were studied by tandem mass spectrometry and the structures of trace impurities in bulk drug α-tocopherol nicotinate and unknown impurities in bulk fluoroquinolonic acid had been identified using HPLC-ESI-MSn combined with NMR experiments.Part Ⅰ Study of the rearrangement reactions of N-phenylbenzamides by tandem mass spectrometry. In negative ion mode, the CO loss and generation of phenolate anion were observed and the mechanisms were elucidated to be Smiles rearrangement reactions initiated by nitrogen and oxygen of the amide bond, respectively. In positive ion mode, protonation at the ortho carbon of the aniline ring induced a nucleophilic substitution reaction of the oxygen of amide bond, giving rise to a benzonitrile loss. This rearrangement reaction can only proceed when the aniline ring is substituted by a strong electron donating group (e.g. OH, NH2, OCH3, or NHCOPh) at the meta position. High resolution mass spectrometry, deuterium experiments and theoretical calculations were performed to confirm the proposed mechanism.Part Ⅱ Characterization of the trace impurities in bulk drug α-tocopherol nicotinate by HPLC-ESI-MSn. The contents and molecular weights of two trace impurities had been obtained by HPLC-ESI-MS. Structural information of impurity1and impurity2were analyzed by tandem mass spectrometry and high resolution mass spectrometry. Impurity1is isomeric with a-tocopherol nicotinate and confirmed by NMR technologies. Impurity2was proved to be a-tocopherol benzenesulfonate,which was generated from the reactant benzenesulfonyl chloride. The fragmentation mechanisms of impurities and a-tocopherol nicotinate were proposed.Part III Structural identification of the unknown impurities in bulk fluoroquinolonic acid. A high-performance liquid chromatography method was first developed to suit the requirements in HPLC-ESI-MSn experiment. According to the synthesis of fluoroquinolonic acid, the possible structures of unknown impurities were proposed and verified by high-resolution mass spectrometry and NMR technologies. The fragmentation reactions of fluoroquinolonic acid and the unknown impurities were also studied by tandem mass spectrometry in negative ion mode.In addition, the gas-phase fragmentation reactions of quasi-molecular ions and applications of HPLC-ESI-MSn in drug analysis were reviewed briefly.