Epalrestat tetrahydrofuran monosolvate: crystal structure and phase transition
The title compound, epalrestat {systematic name: (5Z)-5-[(2E)-2-methyl-3-phenylprop-2-en-1-ylidene]-4-oxo-2-sulfanylidene-1,3-thiazolidine-3-acetic acid}, crystallized as a tetrahydrofuran monosolvate, C15H13NO3S2·C4H8O. Epalrestat, an important drug for diabetic neuropathy, has been reported to exist in polymphic, solvated and co-crystal forms. In the molecule reported here, the phenyl ring is inclined to the rhodamine ring by 22.31 (9)°, and the acetic acid group is almost normal to the rhodamine ring, making a dihedral angle of 88.66 (11)°. In the crystal, pairs of O—H...O hydrogen bonds are observed between the carboxylic acid groups of epalerstat molecules, forming inversion dimers with anR22(8) loop. The dimers are linked by pairs of C—H...O hydrogen bonds, forming chains along [101]. The solvate molecules are linked to the chain by a C—H...O(tetrahydrofuran) hydrogen bond. A combination of thermal analysis and powder X-ray diffraction revealed that title compound desolvated into epalerstat Form II. One C atom of the tetrahydrofuran solvate molecule is positionally disordered and has a refined occupancy ratio of 0.527 (18):0.473 (18).