Synthesis, characterization and thermal analysis of ursolic acid solid forms

This study performed a solid‐state characterization of ursolic acid (UA) crystalline forms, a poorly water‐soluble triterpene with anticancer activity. Two new polymorphs (form I, II), two new solvates (propanol and isopropanol solvates), and a known ethanol solvate were determined and elucidated using a combination of multi‐techniques, including X‐ray single crystal and powder diffraction, Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A colorless single crystal of UA was grown from a propanol solution, and its crystalline structure was determined through X‐ray single crystal diffraction. It was determined that the propanol solvate was crystallized in the orthorhombic space group P 2 1 2 1 2 1 with unit‐cell parameters a = 7.17200 (8) Å, b = 12.24100 (16) Å, c = 33.8950 (4) Å and Z = 4. The ethanol solvate and propanol solvate were isomorphous crystals. The results of the thermal analysis demonstrate that form I is a meta‐stable form, while form II is a stable form that is monotropically related.