Solvent-Mediated Polymorphic Transformation of Famoxadone from Form II to Form I in Several Mixed Solvent Systems

Formation of Hemihydrate Crystal form Overcomes Milling Issue Induced by Exposed Functional Groups on Cleavage Plane for a Y5 Receptor Antagonist of Neuropeptide Y

This study aimed to investigate the crystal forms of an originally designed Y5 receptor antagonist of neuropeptide Y. Polymorphic screening was performed via solvent evaporation and slurry conversion using various solvents. The obtained crystal forms α, β, and γ were characterized by X-ray powder diffraction analysis. Thermal analysis determined that forms α, β, and γ were hemihydrate, metastable and stable forms, respectively; the hemihydrate and the stable forms were candidates. To arrange the particle size, forms α and γ were subjected to jet milling. However, form γ could not be milled because of powder stiction to the apparatus, whereas form α could be. To investigate this mechanism, single-crystal X-ray diffraction analysis was performed. The crystal structure of form γ was characterized by two-dimensional hydrogen bonding between neighboring molecules. This revealed that the functional groups forming hydrogen bonds were exposed on the cleavage plane of form γ. The three-dimensional hydrogen-bonding network with water stabilized the hemihydrate form, α. These results indicate that the hydrogen bondable groups exposed on the cleavage plane of form γ should result in stiction of the powder and adherence to the apparatus. It was concluded that crystal conversion is a method to overcome the milling issue.

[Prediction of the Crystal Growth Mechanism of Aspirin Using Molecular Simulations]

Controlling the physicochemical properties of a drug formulation is important for proper drug efficacy, since in the gastrointestinal tract many drugs undergo dissolution, limiting their efficacy. Factors affecting a drug's physicochemical properties include its crystal habit. Therefore, we predicted the crystal habit by molecular simulation for the purpose of controlling crystal morphology. In this study, we used aspirin as a model compound. By performing simulations based on known crystal structure data, we trained the simulation algorithm to produce the cubic and plate-like morphologies of crystals actually obtained. By these methods, we showed that the crystal plane of the crystal form actually obtained coincides with the characteristic crystal plane obtained by simulation. Furthermore, to consider the influence of the crystallization solvent on crystal growth, we simulated adsorption of solvent molecules on characteristic crystal planes. The difference in adsorption energy of the solvent molecules prevents the aspirin molecules from attaching to the crystal plane. As a result, we concluded that the crystal habit was caused by the difference in growth rate of the crystal plane. By applying the methods developed in this research, the growth of crystal planes can be predicted by molecular simulation, making it possible to efficiently obtain crystal forms with optimal physical properties for drug development. We believe that further development of this approach will lead to dramatic decreases in the cost and duration of drug development.