Synthesis and DNA duplex recognition of a triplex-forming oligonucleotide with an ureido-substituted 4-phenylimidazole nucleoside

A 4-(3-n-butylureidophenyl)imidazole nucleoside was successfully incorporated into a triplex-forming oligonucleotide (TFO). Binding affinity and base pair selectivity of the TFO containing this non-natural nucleoside were studied with various duplex targets containing all four possible Watson–Crick base pairs opposite the nucleoside analog in the third strand. Triplex thermal stabilities indicate that the synthetic nucleoside acts as a universal base in binding to all four possible Watson–Crick base pairs with moderate affinity but poor selectivity. Based on an analysis of its binding thermodynamics, this can be rationalized by the absence of strong specific interactions and more favorable entropic contributions upon triplex formation.