Synthesis, structure and in vitro antiproliferative effects of alkyne-linked 1,2,4-thiadiazole hybrids including erlotinib- and ferrocene-containing derivatives.

Chemotherapy is an indispensable tool to treat cancer, therefore, the development of new drugs that can treat cancer with minimal side effects and lead to more favorable prognoses is of crucial importance. A series of eleven novel 1,2,4-thiadiazoles bearing erlotinib (a known anticancer agent), phenylethynyl, ferrocenyl, and/or ferrocenethynyl moieties were synthesized in this work and characterized by NMR, IR and mass spectroscopies. The solid-phase structures were determined by single-crystal X-ray diffraction. Partial isomerisation of bis(erlotinib)-1,2,4-thiadiazole into its 1,3,4-thiadiazole isomer, leading to the isolation of a 3 : 2 isomer mixture, was observed and a plausible mechanism for isomerisation is suggested. The in vitro cytostatic effect and the long-term cytotoxicity of these thiadiazole-hybrids, as well as that of erlotinib, 3,5-dichloro-1,2,4-thiadiazole and 3,5-diiodo-1,2,4-thiadiazole were investigated against A2058 human melanoma, HepG2 human hepatocellular carcinoma, U87 human glioma, A431 human epidermoid carcinoma, and PC-3 human prostatic adenocarcinoma cell lines. Interestingly, erlotinib did not exhibit a significant cytostatic effect against these cancer cell lines. 1,2,4-Thiadiazole hybrids bearing one erlotinib moiety or both an iodine and a ferrocenethynyl group, as well as 3,5-diiodo-1,2,4-thiadiazole demonstrated good to moderate cytostatic effects. Among the synthesized 1,2,4-thiadiazole hybrids, the isomer mixture of bis-erlotinib substituted 1,2,4- and 1,3,4-thiadiazoles showed the most potent activity. This isomer mixture was proven to be the most effective in long-term cytotoxicity, too. 3,5-Diiodo-1,2,4-thiadiazole and its hybrid with one erlotinib fragment were also highly active against A431 and PC-3 proliferation. These novel compounds may serve as new leads for further study of their antiproliferative properties.

Crystal structure and Hirshfeld surface analysis of 3-(4-meth-oxy-phen-yl)-1-methyl-4-phenyl-1H-pyrazolo-[3,4-d]pyrimidine.

In the title mol-ecule, C19H16N4O, the planar pyrazolo-pyrimidine moiety is inclined to the attached phenyl rings by 35.42 (4) and 54.51 (6)°. In the crystal, adjacent mol-ecules are linked into chains parallel to [110] and [10] by C-H⋯O and C-H⋯N hydrogen bonds. Additional C-H⋯π(ring) inter-actions lead to the formation of the final three-dimensional network structure. The Hirshfeld surface analysis of the title compound suggests that the most significant contributions to the crystal packing are from H⋯H (48.2%), C⋯H/H⋯C (23.9%) and N⋯H/H⋯N (17.4%) contacts.

Crystal structure and Hirshfeld surface analysis of 5-[(5-nitro-1H-indazol-1-yl)meth-yl]-3-phenyl-4,5-di-hydro-isoxazole.

In the title compound, C17H14N4O3, the indazole unit is planar to within 0.0171 (10) Šand makes dihedral angles of 6.50 (6) and 6.79 (4)°, respectively, with the nitro and pendant phenyl groups. The conformation of the oxazole ring is best described as an envelope. In the crystal, oblique stacks along the a-axis direction are formed by π-π stacking inter-actions between the indazole unit and the pendant phenyl rings of adjacent mol-ecules. The stacks are linked into pairs through C-H⋯O hydrogen bonds. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (36.3%), O⋯H/H⋯O (23.4%), C⋯H/H⋯C (13.4%) and N⋯H/H⋯N (11.4%) inter-actions.

Crystal structure of triethyl 2-(5-nitro-2H-indazol-2-yl)propane-1,2,3-tri-carboxyl-ate.

In the title compound, C19H23N3O8, the 5-nitro-2H-indazol-2-yl unit is almost planar, with the maximum deviation from the mean plane being 0.024 (2) Å. The fused-ring system is nearly perpendicular to the three carboxyl-ate groups, with dihedral angles of 90.0 (3), 83.8 (1) and 80.4 (1)°. The ethyl groups attached to both ends of the propane chain are each disordered over two sets of sites, with site-occupancy ratios of 0.425 (17):0.575 (17) and 0.302 (15):0.698 (15). In the crystal, mol-ecules are linked by pairs of C-H⋯N hydrogen bonds, forming inversion dimers. The dimers are further linked by C-H⋯O hydrogen bonds, forming a three-dimensional network.