A new solvate of epalerstat, a drug for diabetic neuropathy.

Epalerstat {systematic name: (5Z)-5-[(2E)-2-methyl-3-phenyl-prop-2-en-1-yl-idene]-4-oxo-2-sulfanyl-idene-1,3-thia-zolidine-3-acetic acid} crystallized as an acetone monosolvate, C15H13NO3S2·C3H6O. In the epalerstat mol-ecule, the methyl-propyl-enediene 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 carb-oxy-lic acid groups of epalerstat mol-ecules 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 mol-ecules are linked to the chain by a C-H⋯O hydrogen bond. Epalerstat acetone monosolvate was found to be isotypic with epalerstat tertra-hydro-furan solvate [Umeda et al. (2017 ▸). Acta Cryst. E73, 941-944].