Six impurities were identified in the lab development batches during the course of benzimidazole intermediate (1) synthesis by reverse phase HPLC method. Intermediate 1 is used as a common and advanced intermediate in the synthesis of candesartan and azilsartan. All the impurities were characterized by IR, NMR, LC/MS and CHN analyses, which included an isomer of intermediate 11 (impurity 19), desethyl analogue of 1 (impurity 20), desethoxy analogue of 1 (impurity 21), methyl analogue of 1 (impurity 22), cyanobiphenyl benzimidazole (impurity 25) and cyanobiphenyl derivative of 1 (impurity 26). The synthesis and characterization of these impurities are presented.
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