Studies on the synthesis of a G-rich octaoligoisonucleotide (isoT)(2)(isoG)(4)(isoT)(2) by the phosphotriester approach and its formation of G-quartet structure

The octaoligoisonucleotide (isoT)(2)(isoG)(4)(isoT)(2) (I), consisting of isonucleoside units 6′-O-allyl-4′-deoxy-4′-(nucleobase)-2′,5′-anhydro-l-mannitol, was synthesized by the phosphotriester approach in solution phase. Based on CD spectra and capillary electrophoresis, it was confirmed that iso-oligomer I could form a parallel intermolecular G-quadruplex structure. K(+), Na(+) and Li(+) can prompt the formation of G-quartet structures and stabilize them. The effective order of these cations is K(+) > Na(+) > Li(+).