Development of a Challenging Salt Formation Step for a Phosphate API

The development of a final API step involving salt formation is described. Challenging properties of this system include: (1) the free base API has low solubility in most organic solvents; (2) residual solvent is difficult to reduce below desired limits; (3) salt disproportionaton occurs at mild temperatures. A process that addresses these challenges was developed, generating API with desired physical properties.