Solid-state characterization and amorphous form identification in a small molecule

Amorphous form and its characterization using a wide variety of analytical techniques have been known for decades. However, there is no single superior method because of similarities between crystalline mesophases and amorphous forms. The aim of the present study was to characterize and identify solid-state of CKD-519, a new cholesteryl ester transfer protein inhibitor, using a combination of analytical techniques. CKD-519 was analyzed via scanning electron microscope, thermogravimetric/differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), hot-stage polarized light microscopy (HSPLM), and variable temperature x-ray powder diffraction (VT-XRPD). Endothermic shifts in the baseline before and after the peak with no mass change were observed via TG/DTA and conventional DSC. Enthalpy recovery experiments and modulated-temperature DSC (MDSC) measurement revealed enthalpy recovery superimposed on glass transition. The absence of birefringence in HSPLM micrographs as well as the glass transition and presence of diffuse scattering (halo) in the VT-XRPD pattern of micron-sized particles up to 200 µm indicate that CKD-519 exists in an amorphous form. This combination of analytical techniques may be used to distinguish amorphous forms from crystalline mesophases.