LC-MS Identification of the Degradates of NGP1-01 and Subsequent Development of a Routine Stability-Indicating Method of Analysis

Abstract

NGP1-01 (1) is a heterocyclic cage compound with calcium channel blocking activity similar to that of nifedipine. Since no data on the stability or mechanism of degradation of this type of compound are available, the kinetics of degradation and pH stability were investigated. The degradates formed at pH 2, 5, and 9 were separated and identified with LC-MS. Chromatography was performed on a Hypersil phenyl column, 150 × 2.1 mm, flow 0.2 ml/min, mobile phase acetonitrile-0.05 M ammonium acetate pH 4.7, 30/70 for 5 min, then gradient to 65/35 at 10 min. The MS was operated in the electron ionization mode at 70 eV. It was found that pH did not have an influence on the mechanism of degradation, and the same degradates were observed throughout the pH range investigated, namely benzylamine and a heterocyclic keto-alcohol. A method for routine stability-indicating analysis of (1) was developed using a phenyl column (5 μmlm, 250 × 4.6 mm Hypersil) with a mobile phase of acetonitrile-0.01 M ammonium phosphate, 0.3% triethylamine, pH 4.5 60/40. Flow rate was I ml/min, injection volume 20 μmll, and UV detection at 210 nm. The method proved usable over a range of 15-1000 μmlg/ml, with an accuracy of 100.1 ± 0.55% and precision of <2% variance over the stated range. Reliable kinetic studies could be conducted by using this method of analysis.