Self-Assembly of Discrete RuII8 Molecular Cages and Their in Vitro Anticancer Activity

Four new octanuclear Ru­(II) cages (OC-1–OC-4) were synthesized from dinuclear p-cymene ruthenium­(II) acceptors [Ru2(μ–η4-C2O4)­(CH3OH)2(η6-p-cymene)2]­(O3SCF3)2 (A1), [Ru2(μ–η4-C6H2O4)­(CH3OH)2(η6-p-cymene)2]­(O3SCF3)2 (A2), [Ru2(dhnq)­(H2O)2(η6-p-cymene)2]­(O3SCF3)2 (A3), and [Ru2(dhtq)­(H2O)2(η6-p-cymene)2]­(O3SCF3)2 (A4) separately with a tetradentate pyridyl ligand (L1) in methanol using coordination-driven self-assembly [L1= N,N,N′,N′-tetra­(pyridin-4-yl)­benzene-1,4-diamine]. The octanuclear cages are fully characterized by various spectroscopic techniques including single-crystal X-ray diffraction analysis of OC-4. The self-assembled cages show strong in vitro anticancer activity against human lung adenocarcinoma A549 and human cervical cancer HeLa cell lines as observed from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Of all the octanuclear cages, OC-3 exhibits remarkable anticancer activity against both cancer cell lines and is more active than that reported for cisplatin. The excellent anticancer activity of OC-3 and OC-4 highlights the importance of the synergistic effects of the spacer component of the dinuclear p-cymene Ru­(II) acceptor clips.