Design of a nonnatural deoxyribonucleoside for recognition of GC base pairs by oligonucleotide-directed triple helix formation

Oligodeoxyribonucleotides bearing nucleoside 1-(2-deoxy-beta-D-ribofuranosyl)-3-methyl-5-amino-1H-pyrazolo (4,3-d)pyrimidin-7-ones exhibited low pH sensitivity and contained nonnatural bases that featured guanine-cytosine (GC) base pair binding without protonation in a pyrimidine triple-helix pattern. The nucleoside facilitated the binding of double-helical DNA groups with GC base pairs via oligonucleotide-directed triple-helix formation. Moreover, the nucleoside promoted the binding of more purine sequences which improved its recognition of GC base pairs.