Binding of bis-linked netropsin derivatives in the parallel-stranded hairpin form to DNA

Cis-diammine Pt(II)- bridged bis-netropsin and oligomethylene-bridged bis-netropsin in which two monomers are linked in a tail-to-tail manner bind to the DNA oligomer with the sequence 5'-CCTATATCC-3' in a parallel-stranded hairpin form with a stoichiometry 1:1. The difference circular dichroism (CD) spectra characteristic of binding of these ligands in the hairpin form are similar. They differ from CD patterns obtained for binding to the same duplex of another bis-netropsin in which two netropsin moieties were linked in a head-to-tail manner. This reflects the fact that tail-to-tail and head-to-tail bis-netropsins use parallel and antiparallel side-by-side motifs, respectively, for binding to DNA in the hairpin forms. The binding affinity of cis-diammine Pt(II)-bridged bis-netropsin in the hairpin form to DNA oligomers with nucleotide sequences 5'-CCTATATCC-3' (I), 5'-CCTTAATCC-3' (II), 5'-CCTTATTCC-3' (III), 5'-CCTTTTTCC-3' (IV) and 5'-CCAATTTCC-3' (V) decreases in the order I = II > III > IV > V . The binding of oligomethylene-bridged bis-netropsin in the hairpin form follows a similar hierarchy. An opposite order of sequence preferences is observed for partially bonded monodentate binding mode of the synthetic ligand.