Two New Polymorphic Cocrystals of Zafirlukast: Preparation, Crystal Structure, and Stability Relations

Two new cocrystals of zafirlukast with piperazine, existing in five different solid forms, have been discovered during a cocrystal screening. The crystal structure of one of these forms has been determined by single crystal X-ray diffraction, and the stability landscape of the crystalline forms of the new cocrystal has been studied. In the present article, we extend the knowledge about the solid state of this important pharmaceutical drug for the treatment of asthma by reporting the crystal structures of two new solvates (acetonitrile and butanol) and the elusive anhydrous Form X, which have been solved by single crystal X-ray diffraction.