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(2)TG(2)C) (3) and d(CG(2)TG(2)T) (4), respectively, attached to a non-nucleotidic tetrabranched linker, are reported. Bunch-ODNs 1 and 2 were shown to form more stable monomolecular parallel G-quadruplexes I and H when compared with their tetramolecular counterparts [d(TG(2)TG(2)C)](4) (III) and [d(CG(2)TG(2)T)](4) (IV), respectively. The structure and stability of all the synthesized complexes have been investigated by circular dichroism (CD), CD thermal denaturation experiments, and H-1-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. (c) 2005 Wiley Periodicals, Inc.