7-(4-Chlorophenyl)-1-hydroxy-5-methylpyrido[3,4-<i>d</i>]pyridazin-4(3<i>H</i>)-one: synthesis, solvatomorphism, <i>in vitro</i> anti-inflammatory and cytotoxic activity studies and <i>in silico</i> analysis

The newly obtained compound 7-(4-chlorophenyl)-1-hydroxy-5-methylpyrido[3,4-d]pyridazin-4(3H)-one (CPM) was crystallized as two new variable solvates, namely, the dimethyl sulfoxide monosolvate, C₁₄H₁₀ClN₃O₂·C₂H₆SO (I), and the sesquisolvate, C₁₄H₁₀ClN₃O₂·1.5C₂H₆SO (II), and their structures were confirmed by single-crystal X-ray diffraction analysis. In previous work, 1-hydroxy-5-methyl-7-phenylpyrido[3,4-d]pyridazin-4(3H)-one (PM) was found to display anticancer activity. In the next step of our studies, we synthesized a new derivative of PM, introducing a Cl atom into the PM structure, obtaining CPM, which showed not only anticancer but also anti-inflammatory activity. CPM and the new semi-products of each step of the synthesis were examined by ¹H NMR, ¹³C NMR and FT-IR spectroscopic analyses, and mass spectrometry. CPM forms (I) and (II) crystallize in the triclinic P1 and monoclinic C2/c space groups, respectively, and differ in the stoichiometry of the CPM and DMSO molecules in the crystal lattice, being 1:1 and 1:1.5 for (I) and (II), respectively. A powder X-ray diffraction analysis was performed only for solvate (I) due to the lack of stability of solvate (II). The potential cytotoxicity of CPM was evaluated against the normal cell lines L929 and RPTEC, as well as the cancer cell lines A172, AGS, CACO-2 and HepG2. The anti-inflammatory activity of CPM was also evaluated using colorimetric assay for the inhibition of COX-1 and COX-2. The same biological tests were carried out for PM to compare the activities of both compounds. The biological studies revealed that CPM does not exhibit more activity than PM. Moreover, in silico analysis of the bioavailability and molecular docking were performed.