Palladium and platinum 3,5-diacetyl-1,2,4-triazol bis(thiosemicarbazones): Chemistry, cytotoxic activity and structure–activity relationships

The preparation of platinum(II) complexes derived from 3,5-diacetyl-1,2,4-triazol bis(4-phenylthiosemicarbazone) (H5L1), 3,5-diacetyl-1,2,4-triazol bis(thiosemicarbazone) (H7L2), 3,5-diacetyl-1,2,4-triazol bis(4-methylthiosemicarbazone) (H5L3) and 3,5-diacetyl-1,2,4-triazol bis(4-ethylthiosemicarbazone) (H5L3) is described. The new complexes [Pt(μ-H3L1)]2, [Pt(μ-H5L2)]2, [Pt(μ-H3L3)]2 and [Pt(μ-H3L4)]2 have been characterized by elemental analyses, fast atom bombardment mass spectrometry (FAB+) and spectroscopic studies. The crystal and molecular structure of compounds [Pt(μ-H3L1)]2, parent ligand H5L1 and [Pt(μ-H3L3)]2 have been determined by single crystal X-ray diffraction. The ligands coordinate, in a dideprotonate form to the platinum ions in a new tridentate fashion (NNS) and S-brigding bonding modes. Thus the molecular units of the platinum complexes are stacked as dimers. The testing of the cytotoxic activity of the synthesized compounds together with their palladium analogues against human A2780 and A2780cisR epithelial ovarian carcinoma cells lines suggests that the compounds may be endowed with important antitumor properties since they show IC50 values in a micromolar range similar to those of cisplatin. The structure and antitumor activity relationships of platinum and palladium complexes are also discussed.