Synthesis and characterization of ruthenium(ii) complexes with the new ligand2-phenylazopyridine-5-sulfonic acid (Hsazpy): in search for new anticancer agents

Abstract

Isomers of dichlorobis(2-phenylazopyridine)ruthenium(II) [Ru(azpy)₂Cl₂], especially the so-called α isomer, display remarkably high cytotoxicities against human tumor cell lines. Unfortunately, the parent [Ru(azpy)₂Cl₂] compounds are poorly water-soluble. In this paper the synthesis and characterization of the new water-soluble ligand 2-phenylazopyridine-5-sulfonic acid (Hsazpy) is described. Use of this ligand in reaction with RuCl₃ gave two isomers, which were isolated as α- and β-[NEt₄]₂[Ru(sazpy)₂Cl₂]. The compounds have been fully characterized by (2D) NMR spectroscopy. The molecular structure of the α isomer of [NEt₄]₂[Ru(sazpy)₂Cl₂]·2H₂O has been determined by single-crystal structure analysis. The packing in the crystal structure of α-[NEt₄]₂[Ru(sazpy)₂Cl₂]·2H₂O shows an interesting hydrogen-bonding pattern in which two water molecules are involved. One water molecule bridges between a Cl ligand and a SO₃⁻ group within one ruthenium moiety, the other water molecule forms a bridge between two SO₃⁻ groups from two different ruthenium centers, resulting in a chain-like structure. Preliminary evaluation of the cytotoxicity by means of the IC₅₀ value in A2780 cell line classifies α-[NEt₄]₂[Ru(sazpy)₂Cl₂] as non-toxic, but this does not rule out other anticancer activities.