Normal phase and reverse phase HPLC-UV-MS analysis of process impurities for rapamycin analog ABT-578: Application to active pharmaceutical ingredient process development

ABT-578, an active pharmaceutical ingredient (API), is a semi-synthetic tetrazole derivative of the fermented polyene macrolide rapamycin. Reverse phase (RP)-HPLC-UV-MS and normal phase (NP)-HPLC-UV-MS methods employing an LC/MSD trap with electrospray ionization (ESI) have been developed to track and map all significant impurities from the synthetic process. Trace-level tracking of key impurities occurring at various process points was achieved using complimentary methodologies, including a stability indicating reverse phase HPLC method capable of separating at least 25 starting materials and process-related impurities from the API (YMC-Pack Phenyl column, UV-MS, 210 nm) and a targeted reverse phase HPLC method capable of separating very polar compounds from crude reaction mixtures (Phenomenex Synergi Polar RP column, UV, 265 nm). In addition, a normal phase HPLC method condition with post-column modifier infusion is described for the separation of epimeric impurities, and analysis of aqueous-sensitive reactive species (YMC-Pack SIL column, UV-MS, 278 nm). Process control strategies were established with these combinations of analytical technologies for impurities analyses to enable a rich understanding of the ABT-578 process.