Promotion of stable triplex formation by partial incorporation of 2,5-phosphodiester linkages into triplexforming oligonucleotides

Pentadecamer homopyrimidine oligonucleotides containing three or more 2ʹ,5ʹ-phosphodiester linkages in different modes were prepared and used to evaluate the ability as a triplex-forming oligonucleotide (TFO), and it was found that discontinuous replacement of the 3ʹ,5ʹ-phosphodiester linkages in TFO by 2ʹ,5ʹ-linkages significantly stabilizes parallel-motif triplexes.