Triplex-forming oligonucleotides (TFOs) are powerful tools for genomic research. The most stable triplex is formed by the interaction between TFOs and homopurine/homopyrimidine sequences in the target duplex, but the triplex DNA is hampered by one pyrimidine base in the homopurine tract. Previously, we developed novel nucleoside analogues (WNA: W-shaped nucleoside analogues) to recognize pyrimidine/purine inversion sites (TA or CG interrupting sites) and determined two useful WNA analogues, WNA-betaT and WNA-betaC. However, subsequent study showed that the triplex formation using the WNA analogues was dependent on its neighbouring bases of the TFOs. In this study, the new WNA analogues having a different aromatic ring were synthesized to evaluate effects on sequence dependency. It has been found that o-bromo, m-bromo-, and p-cyano-substituted WNA-betaT derivatives are selective to a TA interrupting site to form triplexes with high stability in the sequences where original WNA-betaT could not recognize.
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