Use of the bromine isotope ratio in HPLC-ICP-MS and HPLC-ESI-MS analysis of a new drug in development

A combination of inductively coupled plasma mass spectrometry ( ICP- MS) and electrospray ionization mass spectrometry ( ESI- MS) was deployed for the metabolite profiling and metabolite identification of a new antituberculosis compound ( R207910, also known as TMC207) that is currently in drug development. R207910 contains one bromine atom, allowing the detection by ICP- MS. Fluctuations in the Br sensitivity caused by the HPLC gradient were counteracted by the use of species- unspecific isotope dilution. In order to evaluate the method developed, the results obtained were compared with those acquired via radioactivity detection. HPLC- ESI- MS was used for the structural identification of R207910 and its metabolites. The Br-79/Br-81 isotope ratio is also valuable in the search for metabolites in the complex background of endogenous compounds obtained using HPLCESI-MS analyses. Data- dependent scanning using isotope recognition with an ion trap mass spectrometer or processing of Q- Tof data provides HPLC- ICP- MS- like "bromatograms". The combination of accurate mass measurements and the fragmentation behavior in the MS2 spectra obtained using the Q- Tof Ultima mass spectrometer or MSn spectra acquired using the LTQ- Orbitrap allowed structural characterization of the main metabolites of R207910 in methanolic dog and rat faeces extracts taken 0 - 24 h post- dose.