Identification, Synthesis, and Characterization of Potential Oxidative Impurities of Venetoclax: Application of Meisenheimer Rearrangement.

Venetoclax is a potent BCL-2 inhibitor that is used for the treatment of several blood cancers. During the oxidative stress degradation of venetoclax, we observed the formation of two potential impurities at levels of about 8-10%, which have similar molecular weights. The two impurities were isolated and identified as 4-(3-((1-pyrrolo[2,3-]pyridin-5-yl)oxy)-4-(((3-nitro-4-(((tetrahydro-2-pyran-4-yl)methyl)amino)phenyl)sulfonyl)carbamoyl)phenyl)-1-((4'-chloro-5,5-dimethyl-3,4,5,6-tetrahydro-[1,1'-biphenyl]-2-yl)methyl)piperazine 1-oxide (venetoclax -oxide, ) and 2-((1-pyrrolo[2,3-]pyridin-5-yl)oxy)-4-(4-((4'-chloro-5,5-dimethyl-3,4,5,6-tetrahydro-[1,1'-biphenyl]-2-yl)methoxy)piperazin-1-yl)--((3-nitro-4-(((tetrahydro-2-pyran-4-yl)methyl)amino)phenyl)sulfonyl)benzamide (venetoclax hydroxylamine impurity, ). To confirm these two compounds, we have synthesized each impurity individually and analyzed it by high-performance liquid chromatography, mass spectrometry, H NMR, C NMR, and 2D NMR. VNO was synthesized by the oxidation of venetoclax using -CPBA in dichloromethane to get the required -oxide impurity. After the confirmation of the VNO impurity, the VNO impurity was heated with water at reflux in a sealed tube for 36 h to get the VHA impurity of about 6-8% after 36 h. After thorough analysis, it was confirmed that venetoclax -oxide undergoes [1,2] Meisenheimer rearrangement to form the venetoclax hydroxylamine impurity. These two impurities may be relevant reference standards in manufacturing venetoclax Active Pharmaceutical Ingredient (API) (or) tablets.