Synthesis and Triple‐Helix‐Stabilization Properties of Branched Oligonucleotides Carrying 8‐Aminoadenine Moieties

The synthesis of several branched oligonucleotides, i.e., of the parallel hairpins 5–8 and the Y‐shaped 9 is described, together with their use in the formation of pyrimidine⋅pyrimidine⋅purine triple helices. Special attention was paid to the optimization of the assembly of the second strand from asymmetric branching molecules. The presence of 8‐aminoadenine moieties in the WatsonCrick purine strand and 2′‐O‐methyl‐RNA in the Hoogsteen pyrimidine strand produced strong stabilization of the triplex.