Synthesis and Properties of 2′,4′-Bridged Nucleic Acids Containing Multiple Heteroatoms in the Bridges

Nucleic acids bridged between 2'- and 4'-positions are attracting much attention because the oligonucleotides bearing these derivatives generally increase in the binding affinity with single stranded RNA and have an increased resistance against nuclease. It is found that their properties are greatly affected by size and composition of the bridge. In particular, introduction of heteroatom into the bridge unit is considered to give an influence on network of surrounding water molecules in formation of nucleic acid complex. Therefore, it would be meaningful to investigate and understand the properties of various 2',4'-bridged nucleic acids. Under such a background, this account focuses on 2',4'-bridged nucleic acids containing multiple heteroatoms in the bridge structures, with five-, six- and seven-membered bridges, have recently been reported by us, and the synthesis, duplex-forming ability with single-stranded nucleic acid and nuclease resistance of their modified oligonucleotides are mainly described.