Determination of Two Potential Genotoxic Impurities in Crisaborole API by UPLC-MS/MS

Background: Atopic dermatitis (AD) is an allergic skin disease that can be inherited. Crisaborole is a specific drug developed to deal with this disease. The compounds of 4-(4- Bromo-3-formyl-phenoxy)-benzonitrile and 4-(4-(4-bromo-3-formylphenoxy)-3- formylphenoxy) benzonitrile are the representative impurities in the synthesis of Crisaborole active pharmaceutical in gradient (API). Owing to the genotoxic impurities that could lead to cancer and gene mutations, it is necessary to develop a simple, efficient, sensitive, and accurate method to detect these impurities. In this study, the 4-(4-Bromo-3-formyl-phenoxy)-benzonitrile and 4-(4-(4- bromo-3-formylphenoxy)-3-formylphenoxy)benzo- nitrile present in Crisaborole API were detected using UPLC-MS/MS. Methods: The separation was made on a ZORBAX Eclipse XDB-Pheny column (4.6 mm ×75mm, 3.5 μm) with the mobile phase of acetonitrile solution containing 0.1% trifluoroacetic acid (A) and water containing 0.1% formic acid (B) in gradient elution mode. Quantification was performed using positive ion electrospray ionization (ESI), and the contents of two compounds were determined using the multiple reaction monitoring (MRM) modes. Results: The quantitative analytical method was fully validated with respect to linearity (r > 0.9998), sensitivity, precision, accuracy (the average recovery of two impurities was 84.1% to 90.7%), and robustness. Conclusion: Three batches of samples were detected by UPLC-MS/MS, indicating that the proposed approach was applicable for the quality evaluation of Crisaborole.