The synthesis and characterization of new sulfoxide complexes of ruthenium and their potential as anti-cancer agents

Areas of hypoxia (low O₂ content) within malignant tumours are often resistant to radiotherapy and chemotherapy. Compounds that work in conjunction with radiation or alone are required to remove or define hypoxic areas. The complexes cis-RuCl₂(DMS̲O)₃(DMSO̲) (1) and cis-RuCl₂(TMS̲O)₄ (3) (the figure [in actual abstract] shows the sulfoxide structures) were previously used as precursors for the synthesis of Ru(II)-sulfoxide-nitroimidazole complexes. The structural chemistry and spectroscopic data of Ru/DMSO/TMSO complexes are reviewed. RuCl₂(TMS̲O)₄, previously assigned a Trans geometry, is shown to be cis; two crystal forms are characterized crystallographically. Two bromo-Ru(II) complexes of TMSO, [RuBr₃(TMSO)₄Li]₂ and trans-RuBr₂(TMS̲O)₄, are isolated, and both compounds are subsequently characterized by X-ray crystallography. The dimer contains four kinds of coordinated TMSO ligands: the formulation is best written as [Br₆(TMS̲O)₂Ru₂(μ₂-TMS̲O̲)(μ₃- TMS̲O̲)₂Li₂(TMSO̲̲)₂], and reveals a unique μ₃-type sulfoxide ligand. The dinuclear, mixed valence Ru-sulfoxide complexes Ru₂Cl₅(Et₂SO)₄, Ru₂Cl₅(ⁿPr₂SO)₅ and Ru₂Cl₅(ⁿBu₂SO)₅, and monomeric Ru(III) complexes of ⁿPr₂SO and Ph₂SO are synthesized and characterized spectroscopically. The two Ru(III) complexes are structurally characterized as [H(ⁿPr₂SO̲)₂][trans-RuCl₄(ⁿPr₂SO̲)₂] and mer-RuCl₃(Ph₂SO̲)(Ph₂SO̲)(MeOH). The former complex reveals the presence of a cation containing the strongly hydrogen-bonded ⁿPr₂SO‧‧H‧‧OSⁿPr moiety; the latter complex reveals a coordinated methanol ligand (H-bonded to the O atom of Ph₂S̲O), as well as both sulfur- and oxygen-bonded Ph₂SO ligands. Four ruthenium (II) complexes of chelating sulfoxides are also synthesized and structurally characterized. The data for the complexes trans-RuCl₂(BMSE)₂ (4), cis-RuCl₂(BESE)₂ (5), trans-RuCl₂(BPSE)₂ (6) and cis-RuCl₂(BMSP)₂ (7) reveal in each case only S-bonded sulfoxides. The unit cell of complex 4, in addition, contains a water molecule strongly hydrogen-bonded to two chloride atoms from two different molecules of the complex. Seven of the characterized Ru-sulfoxide complexes (1 - 7) are tested in vitro using Chinese hamster ovary (CHO) cells. The biological data indicate that the complexes accumulate in CHO cells, without hypoxic selectivity. No toxicity is observed at the complex concentrations used (1.0 mM for 1 - 4, 7; 0.50 mM for 5 and 6) despite evidence that all seven complexes bind to DNA. Of some interest, the trans- complexes (2, 4, 6) accumulate in CHO cells and bind to DNA to a greater degree than the cis complexes.Science, Faculty ofChemistry, Department ofGraduat