High Sensitivity Detection of a Solubility Limiting Surface Transformation of Drug Particles by DNP SENS

Abstract

We investigate the presence of a surface species for the active pharmaceutical ingredient (API) AZD9496 with dynamic nuclear polarization surface enhanced nuclear spectroscopy (DNP SENS). We show that using DNP we can elucidate the presence of an amorphous form of the API at the surface of crystalline particles of the salt form. The amorphous form of the API has distinguishable ¹³C chemical shifts when compared to the salt form under various acidic conditions. The predominant form in frozen particles of AZD9496 is the salt, and we provide evidence to suggest that the amorphous layer at the surface is mainly made up of the dissociated free form.

Keywords: Active pharmaceutical ingredient (API); Amorphous forms; Chemical stability; Crystallinity; Drug particles; Dynamic nuclear polarization surface enhanced spectroscopy (DNP SENS); Nuclear magnetic resonance (NMR); Surface chemistry.