Design, Synthesis, and Properties of 2‘,4‘-BNA^NC: A Bridged Nucleic Acid Analogue

The novel bridged nucleic-acid analogue 2‘,4‘-BNANC (2‘-O,4‘-C-aminomethylene bridged nucleic
acid), containing a six-membered bridged structure with an N−O linkage, was designed and synthesized
efficiently, demonstrating a one-pot intramolecular NC bond-forming key reaction to construct a perhydro-1,2-oxazine ring (11 and 12). Three monomers of 2‘,4‘-BNANC (2‘,4‘-BNANC[NH], [NMe], and [NBn]) were
synthesized and incorporated into oligonucleotides, and their properties were investigated and compared
with those of 2‘,4‘-BNA (LNA)-modified oligonucleotides. Compared to 2‘,4‘-BNA (LNA)-modified oligonucleotides, 2‘,4‘-BNANC congeners were found to possess:  (i) equal or higher binding affinity against an
RNA complement with excellent single-mismatch discriminating power, (ii) much better RNA selective
binding, (iii) stronger and more sequence selective triplex-forming characters, and (iv) immensely higher
nuclease resistance, even higher than the Sp-phosphorthioate analogue. 2‘,4‘-BNANC-modified oligonucleotides with these excellent profiles show great promise for applications in antisense and antigene
technologies.