NMR Structural Characterization of the Reaction Product between d(GpG) and the Octahedral Antitumor Complex trans-RuCl₂(DMSO)₄

The reaction between the antitumor octahedral complex trans-RuCl₂(DMSO)₄ and d(GpG) leads to the formation of a stable compound characterized by a covalent bifunctional coordination of the bases to the metal center. The structure of the compound has been fully characterized by NMR and molecular modeling studies, showing the presence of two N7-coordinated guanine moieties in a head to head conformation, two dimethyl sulfoxide molecules, and one halogen atom in the coordination sphere of the ruthenium. The glycosidic x angles are essentially in the anti range, the sugar puckering of the 5ʹG is 3ʹ-endo (100% N), whereas that of the 3ʹG is more flexible but mainly in 2ʹ-endo conformation (85% S), the two bases are strongly destacked. The compound shows structural features which are surprisingly similar to those exhibited by the corresponding cisplatin complex, indicating that such a way of interaction with DNA is not exclusive to Pt or to metals with square planar coordination geometries.