Synthesis and characterization of DNA quadruplexes containing T-Tetrads formed by bunch-oligonucleotides

The solid phase syntheses of the bunch oligonucleotides 1 and 2 based on the sequences of the natural oligodeoxynucleotides (ODNs) d(TG 2TG2C) (3) and d(CG2TG2T) (4), respectively, attached to a non-nudeotidic tetrabranched linker, are reported. Bunch-ODNs 1 and 2 were shown to form more stable monomolecular parallel G-quadruplexes I and II when compared with their tetramolecular counterparts [d(TG2TG2C)]4 (III) and [d(CG 2TG2T)]4 (IV), respectively. The structure and stability of all the synthesized complexes have been investigated by circular dichroism (CD), CD thermal denaturation experiments, and 1H-NMR (nuclear magnetic resonance) experiments at variable temperatures. Particularly, the spectroscopic data confirmed that 1 adopts a T-tetrad containing parallel-stranded quadruplex structure I as in the tetramolecular complex III.