Isolation and structural characterization of Imipramine hydrochloride degradation impurities and development of stability-indicating UPLC method

Abstract

A novel, high-throughput, reverse phase-ultra performance liquid chromatographic (RP-UPLC) method has been developed for the quantification of Imipramine and its related impurities in drug substance. The stability-indicating capability of the developed method is demonstrated using forced degradation samples from stress conditions such as hydrolysis, oxidation, thermal and photolytic degradation. During forced degradation it has been observed significant degradation of drug substance in acid hydrolysis and oxidative conditions. Two of the major degradation impurities are isolated using semi preparative HPLC, and the structures are elucidated using ¹HNMR, ¹³CNMR, 2D NMR (COESY, HSQC, HMBC) and mass spectral data. Based on the complete spectral analysis, these two degradation impurities are designated as 10-(3-(dimethylamino)propyl)acridin-9(10H)-one (acid hydrolysis) and 3-(10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl)-N,N-dimethylpropan-1-amineoxide (oxidative degradation). The separation of known impurities and degradation impurities are accomplished using a YMC TriArt C₁₈ stationary phase with 100 mm length and 1.9 µm particle size in short run time (10 min). The developed method employs a linear gradient elution with ammonium acetate buffer, and mixture of acetonitrile and methanol as mobile phase, and is validated in accordance with International Conference on Harmonization requirements.