NMR and X-ray characterization of a platinum(II) complex with (−)sparteine

A platinum(II) complex containing the diamine (−)sparteine has been synthesized for the first time and fully characterized by 1H and 13C NMR spectroscopy and X-ray crystallography. (−)Sparteine is an alkaloid containing four fused rings and four asymmetric centers of configurations 6R, 7S, 9S, and 11S at the four tertiary carbon atoms. In the cis conformation it can act as a chelating N-donor ligand toward a metal ion. The steric bulkiness of this ligand is such that the Pt–N bond lengths are greater than normal and the angle between the cis-chlorido ligands is well below the theoretical value of 90°. This sparteine complex of platinum appears to be an ideal substrate for investigating the stereochemistry of adducts with nucleotides and DNA. For instance the orientation of a coordinated nucleobase can be determined with precision by monitoring the strength of NOE cross peaks between the sparteine protons pointing toward the metal center and key protons of the coordinated nucleobase(s) (e.g. H8 protons of guanine or adenine).