Characterization of solution stress degradation products of aliskiren and prediction of their physicochemical and ADMET properties

Abstract

Forced degradation studies on aliskiren were carried out according to ICH and WHO guidelines. Six degradation products were formed in total in the solution state. Their separation among themselves and from the drug was successfully achieved on a C-18 column utilizing acetonitrile and phosphate buffer (pH 3.0) in the mobile phase, which was run in a gradient mode. To characterize them, a complete mass fragmentation pathway of the drug was first established with the help of MS/TOF and MSⁿ data. This was followed by LC-MS/TOF studies on the degradation products. Some of the degradation products were also isolated and subjected to 1D (¹H, ¹³C and DEPT-135) and 2D (COSY, HSQC and HMBC) NMR studies for confirmation of their structures. An interesting observation was hydrolysis followed by cyclization in case of three degradation products. Also, acetonitrile was found to react with aliskiren, leading to formation of a pseudo degradation product. Additionally, comparative ADMET properties of the drug and degradation products were established using ADMET Predictor™.

Keywords: ADMET Predictor(TM); Aliskiren; Degradation products; LC-MS; MS(n) and NMR.