Identification and Characterization of Belumosudil Degradation Impurities Using the LC–MS/MS Method and Its Validation

ABSTRACT For the treatment of chronic graft‐versus‐host disease (cGVHD), belumosudil (BSL) used as an important therapeutic agent. The stability study of BSL mainly emphasizes the identification and quantification of degradation products formed under different stress conditions such as hydrolysis (acidic, basic, and neutral), oxidation, photolysis, and thermal degradation according to ICH guidelines. In this study, BSL has demonstrated significant deterioration in acidic and basic hydrolysis as well as oxidative stress conditions, while it remains stable in neutral hydrolysis, photolytic, and thermal stress conditions. An LC–MS/MS method for the detection and quantification of BSL degradation products was developed and validated in accordance with ICH Q2 (R1). By using a 25‐min gradient program and an Ascentis Express‐F5 column (150 × 4.6 mm, 5 μm), this method effectively separated the analyte from its degradation impurities. Moreover, exposure of BSL to oxidative, basic, and acidic conditions resulted in four different degradation products. The formed degradation compounds were identified by using mass spectral data, and plausible fragmentation patterns were proposed by using mass data. This validated stability‐indicating assay method confirms its appropriateness for routine analysis and stability investigations of BSL.