Isolation and Structural Elucidation of Palbociclib's Eight Process-Related Impurities: Two Identified as New Compounds

Palbociclib is the first U.S. Food and Drug Administration-approved cyclin-dependent kinase inhibitor indicated in combination with letrozole for the treatment of breast cancer. Development of a selective method for the determination of any impurities contained in this drug is significantly important to ensure the quality and safety of palbociclib. In this study, a reliable reversed-phase HPLC method for the separation and determination of eight potential impurities was developed and validated. The structures of two new compounds and six other process-related impurities were characterized and confirmed by MS, NMR, and IR. Based on spectral analysis and available knowledge of the synthetic route of palbociclib, these two new compounds were designated as 6-acetyl-8-cyclopentyl-5-methyl-2-{[3-(piperazin-1-yl)pyridin-2yl]amino}pyrido [2,3-d]pyrimidin-7(8H)-one and 6-acetyl-8-cyclopentyl-5-methyl-2-{[5-(4-t-butyloxycarbonyl-)-(piperazin-1-yl)pyridin-2yl]amino}pyrido [2,3-d] pyrimidin-7(8H)-one. The developed method was validated for accuracy, precision, linearity, sensitivity, robustness, and solution stability.