Abstract: Mometasone furoate (MF) is a potent synthetic corticosteroid widely used in the treatment of asthma, skin inflammation, and pruritic diseases. This study discovered six solvates of MF (acetonitrile, methanol, acetone, dichloromethane, ethyl acetate, and tetrahydrofuran solvates), and the crystal structure of the acetonitrile solvate and dichloromethane solvate were successfully resolved using single-crystal X-ray diffraction. Crystal structure analysis showed that the acetonitrile solvate belongs to the same P212121 space group as the known Form I, but its PXRD pattern differs significantly. The dichloromethane solvate belongs to a new space group different from the anhydrous Form I and the hydrate. The MF molecule has an irregular shape with two large rotatable groups, which can form large cavity structures with adjustable sizes during packing, enabling it to accommodate solvent molecules of different sizes and thus form various solvates. The stability of the solvates under different environments and their polymorphic transformations were studied by PXRD. The solvates of dichloromethane, acetonitrile, and ethyl acetate were unstable at room temperature, spontaneously desolvating and converting into a new metastable form, while the solvates of tetrahydrofuran, acetone, and methanol were relatively stable at room temperature. All these solvates and the new metastable forms converted to Form I upon heating.

Key words: Mometasone furoate, Solvate, Polymorph