Polymorph screening and study of the structure of crystalline forms of phenyltetrahydroquinolinedione derivative with TRPA1-antagonistic activity

Introduction. 7-(2-chlorophenyl)-4-(4-methyl-1,3-thiazol-5-yl)-4,6,7,8-tetrahydroquinoline-2,5(1H,3H)-dione is a new selective TRPA1 antagonist, which can become a promising analgesic and anti-inflammatory drug of a new generation. To develop its solid dosage form, it is necessary to determine its characteristics that can affect the critical quality attributes of the final product. Polymorphic modification of an active substance is one of these parameters. Objective: to screen for phenyltetrahydroquinolinedione derivative polymorphs and to study their structure using diffraction methods of analysis. Material and methods. X-ray powder diffraction was carried out on a Bruker D8 Discover diffractometer equipped with a nickel filter and a position-sensitive detector. The calculations were carried out using the DIFFRAC.SUITE EVA and TOPAS 4.2 software. The survey was carried out using the Bragg-Brentano geometry, in the reflection mode. Single crystals of polymorphic modifications were obtained by crystallization from various organic solvents and their mixtures. X-ray diffraction analysis was performed on a single-crystal X-ray diffractometer Xcalibur-3. Single-crystal structures were deciphered by a direct method using the SHELXTL software package. Results. The results of X-ray powder diffraction showed the presence of several crystalline phases in the native API sample; however, the results did not allow us to identify specific polymorphs. As a result of polymorph screening, several single crystals suitable for X-ray diffraction analysis were obtained from various solvents. The evaluation of the obtained samples showed no differences in the solubility of the polymorphs. It was found that orthorhombic modification I crystallizes from ethanol, while triclinic modification II crystallizes from methanol, isopropanol, acetone, acetone/acetonitrile or THF/acetonitrile mixtures. Differences in the molecular structure of the resulting polymorphs and their packing in crystals have been described. Conclusion. The identified API polymorphic modifications can be further evaluated in order to select a polymorph for the development of a solid dosage form based on it.