2',4'-BNA bearing a chiral guanidinopyrrolidine-containing nucleobase with potent ability to recognize the CG base pair in a parallel-motif DNA triplex.

In order to expand the target sequence used in triplex DNA formation, seven novel nucleotide analogues were synthesized and incorporated into triplex-forming oligonucleotides by post-elongation modification approaches. Among them, , equipped with a suitable restricted conformation of sugar and nucleobase moieties, was found to have the highest sequence-selectivity and affinity towards CG base pairs within double-stranded DNA.