Polymorphic behavior of an NK1 receptor antagonist

Area of Science:

• Pharmaceutical Sciences
• Solid-State Chemistry

Background:

• Polymorphism significantly impacts drug properties, including solubility, stability, and bioavailability.
• Understanding the polymorphic landscape of active pharmaceutical ingredients (APIs) is crucial for drug development.

Purpose of the Study:

• To discover and characterize anhydrous polymorphic forms of an NK1 receptor antagonist, Compound A.
• To investigate the solid-phase transformations and relative stabilities of these polymorphs under varying temperatures.

Main Methods:

• Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for thermal characterization.
• X-ray powder diffraction (XRPD) and solid-state NMR spectroscopy (SSNMR) for structural analysis.
• Hot stage XRPD, temperature-modulated SSNMR, and hot stage optical microscopy for studying polymorphic transformations.

Main Results:

• Four anhydrous polymorphic forms (I, II, III, and IV) of Compound A were identified.
• Forms I and II are stable at room temperature, while Forms III and IV are stable at elevated temperatures.
• Solubility studies of Forms I and II in tert-butyl acetate were performed, establishing their relative stability. Thermodynamic transformation temperatures were estimated.
• A novel conversion route from the more stable Form I to the less stable Form II at room temperature was observed.

Conclusions:

• Compound A exhibits complex polymorphism with distinct anhydrous forms stable at different temperature ranges.
• The characterization and understanding of these polymorphic transformations are essential for controlling the solid-state properties of Compound A.
• Further studies are warranted to explore the implications of these findings on the pharmaceutical development of NK1 receptor antagonists.