Determination and characterization of process impurities in Tolvaptan drug substance

An accurate and sensitive reverse phased liquid chromatographic method was developed for the determination of three process impurities in Tolvaptan (TPN) drug substance. Structural confirmation and characterization of these three process impurities was carried out by using proton and carbon magnetic resonance spectroscopy (PMR, CMR) and Liquid chromatography coupled with mass spectrometry (LC-MS). Based on the spectroscopic studies three unknown process impurities were characterized as (4-Amino-2-methylphenyl)(7-chloro-5-hydroxy-2,3,4,5-tetrahydro-1H-1-benzo[b]azepin-1-yl)methanone (TPNRC01) 7-Chloro-1-[2-methyl-4-[(2-methyl benzoyl)amino]benzoyl]-5-oxo-2,3,4,5-tetrahydro-1H-1-benzazepine (TPNRC02) and 4-[(5-Hydroxy-2,3,4,5-tetrahydro-1H-1-benzazepin-1-yl)carbonyl]-3-methylphenyl-2-methylbenzamide (TPNRC03) . The newly developed method was validated according to ICH guidelines considering three process impurities to demonstrate specificity, precision, linearity and accuracy of the method. The Limit of detection for the three process impurities were 0.0005, 0.0008 and 0.0005 mg mL-1 respectively and limit of quantitation detection for the three process impurities were 0.0015, 0.0016 and 0.0016 mg mL-1 respectively. The newly developed method was found to be highly efficient, selective, sensitive and accurate.