LNA units present in [R(P)-PS]-(DNA#LNA) chimeras enhance the thermal stability of parallel duplexes and triplexes formed with (2′-OMe)-RNA strands

The results of CD measurements indicate that 2-4 LNA units distributed along 12 nt P-stereodefined phosphorothioate [R(P)-PS]-(DNA#LNA) chimeras impose a C3′-endo conformation on the 2′-deoxyribonucleosides. Under neutral and slightly acidic conditions homopurine [R(p)-PS]-(DNA#LNA) hybridizes with 9–12 nt Hoogsteen-paired (2′-OMe)-RNA strands to form parallel duplexes, which are thermally more stable than the reported earlier analogous complexes containing LNA-free [R(P)-PS]-DNA oligomers (ΔT(m) = 7 °C per LNA unit at pH 5.4). Upon addition of the corresponding Watson–Crick-paired (2′-OMe)-RNA strands, parallel triplexes are formed with further increased thermal stability.