Co-Crystal Screening of Diclofenac

In the pharmaceutical industry, co-crystals are becoming increasingly valuable as crystalline solids that can offer altered/improved physical properties of an active pharmaceutical ingredient (API) without changing its chemical identity or biological activity. In order to identify new solid forms of diclofenac—an analgesic with extremely poor aqueous solubility for which few co-crystal structures have been determined—a range of pyrazoles, pyridines, and pyrimidines were screened for co-crystal formation using solvent assisted grinding and infrared spectroscopy with an overall success rate of 50%. The crystal structures of three new diclofenac co-crystals are reported herein: (diclofenac)·(2-aminopyrimidine), (diclofenac)·(2-amino-4,6-dimethylpyrimidine), and (diclofenac)·(2-amino-4-chloro-6-methylpyrimidine).