Design, synthesis, and evaluation of a novel bridged nucleic acid, 2′,5′-BNAON, with S-type sugar conformation fixed by N–O linkage

We designed a novel 2′-O,5′-N bridged nucleic acid, 2′,5′-BNAON, whose sugar puckering was fixed to S-type conformation by an N–O linkage. A dimer unit formed from 2′,5′-BNAON-U and thymidine was synthesized via a coupling reaction between a protected 2′,5′-BNAON-U monomer and a thymidine derivative. Introduction of 2′,5′-BNAON-U into DNA was carried out using conventional phosphoramidite chemistry with a DNA synthesizer. The hybridization abilities of 2′,5′-BNAON-U-modified oligonucleotides against DNA or RNA complement were evaluated.