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  • Title: Investigation and structural elucidation of a process related impurity in candesartan cilexetil by LC/ESI-ITMS and NMR.
    Author: Raman B, Sharma BA, Mahale G, Singh D, Kumar A.
    Journal: J Pharm Biomed Anal; 2011 Sep 10; 56(2):256-63. PubMed ID: 21664089.
    Abstract:
    Four impurities were detected in candesartan cilexetil bulk drug samples by HPLC and LC/MS. These impurities were marked as CDC-I, II, III and IV. One of the impurities CDC-II was unknown and has not been reported previously. An optimized method using liquid chromatography coupled with electrospray ionization ion trap mass spectrometry (LC/ESI-ITMS) in positive ion mode has been developed to carry out structural identification of unknown impurity. Based on mass spectrometric data and synthetic specifics the structure of CDC-II was proposed as 2-ethoxy-1-[[2'-(1-ethyl-1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-1H-benzimidazole-7-carboxylic acid ethyl ester. The impurity was isolated by semi-preparative HPLC and structure was confirmed by NMR spectroscopy. The plausible mechanism for the formation of impurities is also discussed.
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