A Multidisciplinary Investigation to Determine the Structure and Source of Dimeric Impurities in AMG 517 Drug Substance

In the initial scale-up batches of the experimental drug substance AMG 517, a pair of unexpected impurities was observed by HPLC. Analysis of data from initial LC-MS experiments indicated the presence of two dimer-like molecules. One impurity had an additional sulfur atom incorporated into its structure relative to the other impurity. Isolation of the impurities was performed, and further structural elucidation experiments were conducted with high-resolution LC-MS and 2D NMR. The dimeric structures were confirmed, with one of the impurities having an unexpected C-S-C linkage. Based on the synthetic route of AMG 517, it was unlikely that these impurities were generated during the last two steps of the process. Stress studies on the enriched impurities were carried out to further confirm the existence of the C-S-C linkage in the benzothiazole portion of AMG 517. Further investigation revealed that these two dimeric impurities originated from existing impurities in the AMG 517 starting material, N-acetyl benzothiazole. The characterization of these two dimeric impurities allowed for better quality control of new batches of the N-acetyl benzothiazole starting material. As a result, subsequent batches of AMG 517 contained no reportable levels of these two impuritie

Synthesis and evaluation of novel polymeric stationary phases for capillary liquid chromatography and electrochromatography.

The stationary phase is at the heart of chromatographic separation techniques. In the pursuit of higher separation efficiency and resolving power, methods for the synthesis of novel polymeric stationary phases were developed. These stationary phases were evaluated using microscale separation techniques that have inherent high efficiency: open-tubular liquid chromatography (OT-LC), open-tubular capillary electrochromatography (OT-CEC), and packed column capillary electrochromatography (PC-CEC). A new technique was developed for the in situ synthesis of thin film polymer stationary phases inside small diameter fused silica capillaries. This technique allows the use of readily available and inexpensive polyimide jacketed capillaries, and provides greater control over the experimental conditions compared to other similar techniques. The versatility of the monomers—methacrylates—made it possible to employ the same basic experimental setups and conditions for the syntheses of various types of stationary phases that were used in reverse phase, ion exchange, and chiral separations. Detailed studies were conducted on the effects of various experimental parameters on the chromatographic performance of these stationary phases. High efficiency and resolution were achieved without extensive optimization of the separation conditions. One particular type of polymer studied herein is of great interest: molecular imprinted polymer (MIP). Methods were developed for the synthesis of MIPs in two formats: as bonded thin films inside fused silica capillaries, and as uniform-sized polymer particles. These MIPs were tested using chromatographic methods for chiral separation and screening of library compounds. The physical properties of these materials were also characterized by scanning electron microscopy and particle size distribution experiments