Synthesis and Characterization of Ruthenium-Paraphenylene-Cyclopentadienyl Full-Sandwich Complexes: Cytotoxic Activity against A549 Lung Cancer Cell Line and DNA Binding Properties

Novel full-sandwich (eta 5-Cp)-Ru-paraphenylene complexes with the general formula [(eta 5-Cp)nRu(eta 6-L)](PF6)n where n = 1-3 and L = biphenyl, p-terphenyl and p-quaterphenyl, were synthesized and characterized by means of spectroscopic and analytical techniques. The structures of the complexes [(eta 5-Cp)Ru(eta 6-biphenyl)](PF6) (1), [(eta 5-Cp)Ru(eta 6-terphenyl)](PF6) (3) and [(eta 5-Cp)2Ru(eta 6-terphenyl)](PF6)2 (4) was determined by X-ray single crystal methods. The interaction of the complexes [(eta 5-Cp)Ru(eta 6-quaterphenyl)]Cl, (6)Cl, and [(eta 5-Cp)2Ru(eta 6-quaterphenyl)]Cl2, (7)Cl2, with the DNA duplex d(5 '-CGCGAATTCGCG-3 ')2 was studied using NMR techniques. The results showed that both complexes interacted non-specifically with both the minor and major grooves of the helix. Specifically, (6)Cl exhibited partial binding through intercalation between the T7 and T8 bases of the sequence without disrupting the C-G and A-T hydrogen bonds. Fluorometric determination of the complexes' binding constants revealed a significant influence of the number of connected phenyl rings in the paraphenylene ligand (L) on the binding affinity of their complexes with the d(5 '-CGCGAATTCGCG-3 ')2. The complexes (6)Cl and (7)Cl2 were found to be highly cytotoxic against the A549 lung cancer cell line, with complex (6) being more effective than (7) (IC50 for (6)Cl: 17.45 +/- 2.1 mu M, IC50 for (7)Cl2: 65.83 +/- 1.8 mu M) and with a selectivity index (SI) (SI for (6)Cl: 1.1 and SI for (7)Cl2: 4.8).