Cyclic Naphthalene Diimide with a Ferrocene Moiety as a Redox-Active Tetraplex-DNA Ligand

Cyclic naphthalene diimides (cNDIs), with a ferrocene moiety (cFNDs) and different linker lengths between the ferrocene and cNDI moieties, were designed and synthesized as redox‐active, tetraplex‐DNA ligands. Intramolecular stacking was observed between ferrocene and the NDI planes, which could affect the binding properties for G‐quadruplexes. Interestingly, the circular dichroism spectrum of one of these compounds clearly shows new Cotton effects around 320–380 and 240 nm, which can be considered a direct evidence of intramolecular stacking of ferrocene and the NDI. Regarding recognition of hybrid G‐quadruplexes, the less rigid structures (longer linkers) show higher binding affinity (106 M−1 order of magnitude). All new compounds show higher selectivity for G4 during electrochemical detection than noncyclic FND derivatives, which further identifies the redox‐active potentiality of the cFNDs. Two of the three compounds tested even show preferential inhibition of cell growth in cancer cells over normal cells in a low concentration range, highlighting the potential for bioapplications of these cFNDs