Use of ferrocene scaffolds as pendant groups in hairpin-type pyrrole-imidazole polyamide molecules showing sequence-selective binding to DNA duplexes

[reaction: see text] The synthesis and properties of new conjugate molecules, Fc-PIA, composed of ferrocene (Fc) and pyrrole-imidazole polyamides (PIA) are reported. As a PIA sequence, we chose Im-Py-Im/Py-Im-Py considering its future application to the SNPs detection of genes having a GCG/CGC sequence. Two types of Fc-containing linkers, i.e., ferrocene-1,1'-dicarboxamide and ferrocenecarboxamide, were designed, and several Fc-PIPA molecules having these linkers were synthesized. Titration studies by use of circular dichroism revealed that the carboxamide-type Fc-PIA could bind to the target DNA with an association constant of 10(7) M(-1). In contrast, ferrocene dicarboxamide-type compounds have slightly weaker affinity for the target DNA. However, the affinity could be recovered by replacing one of the pyrrole residues with beta-alanine. We carried out the CV measurement and observed quasi-irreversible oxidation of the ferrocene moieties in the Fc-PIA compounds. These properties of Fc-PIA indicate the potential usefulness of these molecules in electrochemical detection of genes.