Characterization of a new component and impurities in josamycin by trap-free two-dimensional liquid chromatography coupled to ion trap time-of-flight mass spectrometry.

Abstract

The toxicities of the impurities of a drug will affect the clinical effects and cause potential health risk; therefore, it is essential to study profiles of the impurities. In this study, a new structural type of component and two acid degradation impurities in josamycin were discovered and characterized for the further improvement of official monographs in pharmacopoeias. The component and acid degradation impurities in josamycin were separated and preliminary characterized by trap-free two-dimensional liquid chromatography coupled to high-resolution ion trap time-of-flight mass spectrometry (2D LC/IT-TOF MS) in both positive and negative electrospray ionization mode. The eluent of each peak from the first dimensional chromatographic system was trapped by a switching valve and subsequently transferred to the second dimensional chromatographic system, which was connected to the mass spectrometer. Full scan MS was firstly conducted to obtain the exact m/z values of the molecules. Then LC/MS/MS and LC/MS/MS/MS experiments were performed on the compounds of interest. A new structural type of component, which was named as josamycin A, and two acid degradation impuritiess, which were identified as impurity I and impurity II, were discovered in josamycin. Their structures and fragmentation pattern were deduced according to MSn data. Furthermore, josamycin A was synthesized and impurity I was separated by preparative HPLC. The structures of josamycin A and the impurities were confirmed by 1 H NMR and 13 C NMR data. Josamycin A was produced when the hydroxyl group on the macrolide of josamycin was oxidized into a carbonyl group. Impurity I and impurity II were produced by the loss of one molecule of acetyl mycaminose from josamycin and josamycin A, respectively. Compared with josamycin, the experimental results showed that josamycin A had a higher antibacterial activity with similar cytotoxicity, while impurity I had no antibacterial activity but a higher cytotoxicity. As a result, the control of impurity I is significant.