Stress Degradation Studies of Anagliptin, Development of Validated Stability Indicating Method, Degradation Kinetics Study, Identification and Isolation of Degradation Products

A gradient-specific stability indicating HPLC method was developed and validated for the determination of the antidiabetic agent anagliptin in laboratory mixtures. Reversed-phase chromatography was performed using a Shimadzu LC-20 AD pump (binary), Shimadzu PDA M-20A diode array detector, and Waters Symmetry C-18 column (150 × 4.6 mm, 3.5 µm) maintained at a column oven temperature of 40 °C with UV detection at 247 nm. A gradient program was run at flow rate of 1 mL min−1. Mobile phase A consisted of a mixture of acetate buffer(10 mm) pH 5/methanol/acetonitrile in the ratio of 90:5:5. Mobile phase B consisted of a mixture of acetate buffer (10 mm) pH 5/methanol/acetonitrile in the ratio of 50:25:25. The method was validated according International Conference of Harmonization (ICH) guidelines. Linearity was observed in the concentration range of 10–120 µg/mL with regression coefficient r2(0.999). The LOD was found to be 7.8 µg/mL and LOQ was found to be 22.68 µg/mL. Anagliptin was subjected to stresses such as acidic, alkali, oxidation, photolysis, and thermal conditions. The proposed method was validated as per ICH guidelines and was found to be accurate, precise, and specific. The drug showed significant degradation in alkaline and oxidative conditions. Alkaline and oxidative degradation followed first-order kinetics. Degradation rate constant and half-lives were determined. Degradation products in alkaline and oxidative conditions were identified by LC–MS. One major degradation product was isolated from each condition by preparative HPLC. These degradation products were characterized by 1H NMR, 13C NMR, DEPT, D2O exchange, MS/MS, HRMS, and IR techniques. From the spectral data the alkaline degradation product was characterized as 1-{2-[1-(2-methylpyrazolo[1,5-a]pyrimidine-6-carboxamido)-methyl-propan-2-yl-amino]acetyl}pyrrolidine-2-carboxamide. The oxidative degradation product was characterized as N-[2-({2-[(2S)-2-cyanopyrrolidin-1-yl]-2-oxoethyl}amino)-2-methylpropyl]-2-methylpyrazolo-[1,5-a]pyrimidine-N-oxido-6-carboxamide.