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Synthetic agents that bind to DNA and affect its processing are attractive targets in molecular design. Small molecules can regulate specific gene expression [1] and remain at the forefront of clinical application as anticancer and antiviral drugs.[2] Clinical drugs can intercalate (anthracycline antibiotics), [3] minor groove bind (berenil), [4] or form coordination bonds to DNA (cisplatin). [5] To create different spectra of activity and circumvent cross-resistance, it is important to explore drugs that interact with DNA in new and distinct ways.We have previously described synthetic metallo-supramolecular cylinders of a similar size and shape to protein zinc fingers. These tetracationic cylinders contain three bis(pyridylimine) ligand strands wrapped in a helical fashion about two iron(II) centers. The cylinders not only can bind strongly and noncovalently in the major groove of DNA, inducing dramatic and unprecedented intramolecular DNA coiling in natural polymeric DNAs, [2,6] but also can bind at the heart of Y-shaped DNA junctions, an unparalleled and hitherto unexpected mode of DNA recognition. [7] Combining these striking DNA binding features with the fact that ruthenium compounds represent a new and promising class of anticancer drugs [8][9][10] led to the aim of developing a triple-stranded ruthenium cylinder that would be one of the few noncovalent DNA recognition metal compounds studied for its biological activity. This design was still more attractive because of the potential for luminescence (from MLCT states), [11] which might be used to probe the DNA binding. We describe herein the synthesis of the luminescent ruthenium(II) triple-stranded helicate of ligand L (Scheme 1) and explore its DNA binding and activity against cancer cells.Although the synthesis of triple-stranded helicates with labile first-row transition metals is well established, [12] the synthesis of triple-stranded helicates with an inert metal such as ruthenium(II) represents a considerable challenge and prior to this work had not been achieved. Coordinate bond formation with labile metals is reversible and the assembly is under thermodynamic control. With inert metals this is not the case and the metals and ligands can become trapped in alternative polymeric structures that are not pathways to the assembly of the helicate; in illustration we note that of the three isomeric dinuclear double-stranded unsaturated ruthenium(II) helicates we recently described, none has the correct conformation at any of their metal centers needed for triple-helicate formation.[13] It is striking that, despite the great interest in the photophysical and redox properties of ruthenium(II) tris(diimine) centers, [14] no diruthenium(II) triple-stranded helicate has been prepared. [15] To try to prepare the triple-stranded diruthenium(II) complex, we initially explored different ruthenium starting materials ([{Ru(cod)Cl 2 } n ], RuCl 3 , and [Ru(CH 3 CN) 6 ](PF 6 ) 2 ; cod = 1,5-cyclooctodiene), which we heated under reflux with the ligand in a variety of o...

New water-soluble bis(2-phenylazopyridine)ruthenium(II) complexes, all derivatives of the highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha denoting the coordinating pairs Cl, N(py), and N(azo) as cis, trans, cis, respectively) have been developed. The compounds 1,1-cyclobutanedicarboxylatobis(2-phenylazopyridine)ruthenium(II), alpha-[Ru(azpy)(2)(cbdca-O,O')] (1), oxalatobis(2-phenylazopyridine)ruthenium(II), alpha-[Ru(azpy)(2)(ox)] (2), and malonatobis(2-phenylazopyridine)ruthenium(II), alpha-[Ru(azpy)(2)(mal)] (3), have been synthesized and fully characterized. X-ray analyses of 1 and 2 are reported, and compound 1 is the first example in which the cbdca ligand is coordinated to a ruthenium center. The cytotoxicity of this series of water-soluble bis(2-phenylazopyridine) complexes has been determined in A2780 human ovarian carcinoma and A2780cisR, the corresponding cisplatin-resistant cell line. For comparison reasons, the cytotoxicity of the complexes alpha-[Ru(azpy)(2)Cl(2)], alpha-[Ru(azpy)(2)(NO(3))(2)], beta-[Ru(azpy)(2)Cl(2)] (beta indicating the coordinating pairs Cl, N(py), and N(azo) as cis, cis, cis, respectively), and beta-[Ru(azpy)(2)(NO(3))(2)] have been determined in this cell line. All the bis(2-phenylazopyridine)ruthenium(II) compounds display a promising cytotoxicity in the A2780 cell line (IC(50) = 0.9-10 microM), with an activity comparable to that of cisplatin and even higher than the activity of carboplatin. Interestingly, the IC(50) values of this series of ruthenium compounds (except the beta isomeric compounds) are similar in the cisplatin-resistant A2780cisR cell line compared to the normal cell line A2780, suggesting that the activity of these compounds might not be influenced by the multifactorial resistance mechanism that affect platinum anticancer agents.

The synthesis and characterization of alpha-[Ru(azpy)2(NO3)2], 1, are reported (azpy is 2-(phenylazo)pyridine; alpha indicates the isomer in which the coordinating pairs ONO2, N(py), and N(azo) are cis, trans, and cis, respectively). The solid-state structure of 1 has been determined by X-ray crystallography. Crystal data: orthorhombic a = 15.423(5) A, b = 14.034(5) A, c = 10.970(5) A, V = 2374(2) A3, space group P2(1)2(1)2(1) (No. 19), Z = 4, Dcalc = 1.655 g cm-3. The structure refinement converged at R1 = 0.042 and wR2 = 0.118 for 3615 unique reflections and 337 parameters. The octahedral complex shows monodentate coordination of the two nitrate ligands. The Ru-N(azo) bond distances (2.014(4) and 1.960(4) A), slightly shorter than the Ru-N(py) bonds (2.031(4) and 2.059(4) A), agree well with the pi-back-bonding ability of the azo groups. The binding of the DNA-model bases 9-ethylguanine (9egua) and guanosine (guo) to 1 has been studied and compared with previously obtained results for the binding of model bases to the bis(bipyridyl)ruthenium(II) complex. The ligands 9egua and guo appear to form monofunctional adducts, which have been isolated as alpha-[Ru(azpy)2(9egua)Cl]PF6, 2, alpha-[Ru(azpy)2(9egua)(H2O)]-(PF6)2, 3, alpha-[Ru(azpy)2(guo)(H2O)](PF6)2, 4, and alpha-[Ru(azpy)2(guo)Cl]Cl, 5. The orientations of 9egua and guo in these complexes have been determined in detail with the use of 2D NOESY NMR spectroscopy. In 2 and 5, H8 is directly pointed toward the coordinated Cl, whereas, in 3 and 4, H8 is wedged between the pyridine and phenyl rings. The guanine derivatives in the azpy complexes can have more orientations than found for related cis-[Ru(bpy)2Cl2] species. This fluxionality is considered to be important in the binding of the alpha-bis(2-(phenylazo)pyridine)ruthenium(II) complex to DNA. In complex 1, ruthenium is the chiral center and in the binding to guanosine, two diastereoisomers each of adducts 4 and 5 have been clearly identified by NMR spectroscopy.