Tuning the Efficacy of Ruthenium(II)-Arene (RAPTA) Antitumor Compounds with Fluorinated Arene Ligands

A series of compounds of general formula [Ru(η6-fluoroarene)(pta)Cl2] (fluoroarene = C6H5F, C6H5CF3, and 1,4-C6H4CH3F; pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane) have been prepared and characterized spectroscopically. Additionally, X-ray diffraction was employed to characterize two of the complexes and the corresponding precursors, i.e., [Ru(acac)2(η4-cod)] and Ru(η6-fluoroarene)(η4-cod)] (cod = cycloocta-1,5-diene). The solubility, pKa’s, and the stability toward hydrolysis of the [Ru(η6-fluoroarene)(pta)Cl2] complexes were studied, and DFT calculations were performed to assist in rationalizing the observed properties at a molecular level. The cytotoxicities of the pta-based compounds were evaluated in A2780 ovarian cancer cells, and the observed activities were correlated to the above-mentioned properties. The rate of hydrolysis of the Ru−Cl bonds in the C6H5CF3 derivative was found to increase significantly at low pH, which represents a possible method of tumor targeting based on the reduced pH of this particular cellular environment.