Cationic Pentaheteroaryls as Selective G-Quadruplex Ligands by Solvent-Free Microwave-Assisted Synthesis

A solvent-free and microwave-assisted synthesis of several water soluble acyclic penta-heteroaryls containing 1,2,4-oxadiazole moieties (1–7) has been achieved with good yields. Their binding interactions with DNA quadruplex structures were thoroughly investigated by FRET melting, fluorescent intercalator displacement assay (G4-FID) and CD spectroscopy. Among the G-quadruplexes considered, attention was focused on telomeric repeats together with the proto-oncogenic c-kit sequences and the c-myc oncogene promoter. Compound 1, and to a lesser extent 2 and 5, preferentially stabilise an antiparallel structure of the telomeric DNA motif, and exhibit an opposite binding behaviour to structurally related polyoxazole (TOxaPy), and do not bind duplex DNA. The efficiency and selectivity of the binding process was remarkably controlled by the structure of the solubilising moieties.