Abstract
The glucocorticoide bethamethasone valerate was investigated for polymorphism. The commercially available modification (Form I) and one methanol solvate were characterized by single crystal structure analysis. DTA-TG and DSC investigations reveal that on solvent removal the methanol solvate decomposes into a new polymorphic modification (Form III), which, upon further heating, transforms into another modification (Form II) via melting and recrystallization. The crystal structures of forms II and III were determined by a combination of 13C NMR spectroscopy and X-ray powder diffraction. In all modifications as well as in the methanol solvate differences in the conformation and the packing of the molecules are observed. Solvent mediated conversion experiments reveal that form I represents the thermodynamically stable form at room temperature. Thermomicroscopic, XRPD, and heating rate dependent DSC measurements on forms I–III do not show any interconversion of these forms via the solid. Further DSC measurements indicate both a higher melting point and heat of fusion for form I compared to form II and form III. Therefore, form I should also be the thermodynamically stable form over the whole temperature range and all forms seems to be monotropically related.
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