Water-Soluble Mixed-Ligand Ruthenium(II) and Osmium(II) Arene Complexes with High Antiproliferative Activity

The synthesis of ruthenium(II) and osmium(II) arene complexes of the general formula [(eta(6)-p-cymene)-M(oxine)(Hazole)]X, where M = Ru, Os; oxine = deprotonated 8-hydroxyquinoline, and Hazole = azole heterocycle, i.e., pyrazole (Hpz), indazole (Hind), imidazole (Him), benzimidazole (Hbzim), or 5,6-dimethylbenzimidazole (Hdmbzim); X = CF3SO3-, PF6-, or Cl-, combining ligands involved in metal-based complexes that are currently in clinical development, is reported. The compounds have been comprehensively characterized by elemental analysis, ESI mass spectrometry, spectroscopy (IR, UV-vis, NMR), and X-ray crystallography. The synthesis of these complexes was performed in order to achieve a balance between aqueous solubility and lipophilicity. The ruthenium(II) and osmium(II) compounds exhibit excellent cytotoxic effects in the tumor cell lines CH1 and SW480, with IC50 values ranging from 3.3 to 9.4 mu M. As expected, the compounds are water soluble and show no evidence of hydrolysis or ligand exchange in aqueous media, which makes them noteworthy candidates for further development. The complexes [(eta(6)-p-cymene)M(oxine)(Hazole)](+) do not react with DNA purine bases, even if the latter are present in excess. However, the complex [(eta(6)-p-cymene)Os(oxine)Cl] reacts with 9-methyladenine (meade) to for m [(eta(6)-p-Cymene)Os(oxine)meade](+), which was isolated and characterized by X-ray diffraction as a hexafluorophosphate salt.