A new solvate of epalerstat, a drug for diabetic neuropathy

Epalerstat {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 an acetone monosolvate, C₁₅H₁₃NO₃S₂·C₃H₆O. In the epalerstat molecule, the methylpropylenediene moiety is inclined to the phenyl ring and the five-membered rhodamine ring by 21.4 (4) and 4.7 (4)°, respectively. In addition, the acetic acid moiety is found to be almost normal to the rhodamine ring, making a dihedral angle of 85.1 (2)°. In the crystal, a pair of O - H⋯O hydrogen bonds between the carboxylic acid groups of epalerstat molecules form inversion dimers with an R₂²(8) loop. The dimers are linked by pairs of C - H⋯O hydrogen bonds, enclosing R₂²(20) loops, forming chains propagating along the [101] direction. In addition, the acetone molecules are linked to the chain by a C - H⋯O hydrogen bond. Epalerstat acetone monosolvate was found to be isotypic with epalerstat tertrahydrofuran solvate [Umeda et al. (2017). Acta Cryst. E73, 941-944].