TRIPLEX FORMATION BY AN OLIGONUCLEOTIDE CONTAINING THE NOVEL MODIFIED NUCLEOSIDE 2'-DEOXY-N4-PHENYLCARBAMOYLCYTIDINE

2′-Deoxy-N4-phenylcarbamoylcytidine (Pc) was designed for triplex recognition of the cytosine{guanine base pair at physiological pH values to assist in the development of triplex-forming oligomers. Thermal denaturation of a triplex mixture in which the third strand incorporated Pc as a central nucleoside showed that, at pH 6·1, Pc binds selectively—though weakly—to the target cytosine—guanine and also to guanine—cytosine; but the gel mobilities of the same mixtures indicate the possibility of specificity for the target cytosine-guanine base pair at pH values higher than 6·1. The result may provide leads useful in the development of improved triplex-forming oligomers.