text: Chemical structures of BNA monomers containing a bridge at the 2, 4-position of the ribose to afford a 2, 4-BNA monomer as synthesized by Takeshi Imanishi's group. The nature of the bridge can vary for different types of monomers. The 3D structures for A-RNA and B-DNA were used as a template for the design of the BNA monomers. The goal for the design was to find derivatives that possess high binding affinities with complementary RNA and/or DNA strands.
  An increased conformational inflexibility of the sugar moiety in nucleosides (oligonucleotides) results in a gain of high binding affinity with complementary single-stranded RNA and/or double-stranded DNA. The first 2,4-BNA (LNA) monomers were first synthesized by Takeshi Imanishis group in 1997 followed independently by Jesper Wengels group in 1998.
  BNA nucleotides can be incorporated into DNA or RNA oligonucleotides at any desired position. Such oligomers are synthesized chemically and are now commercially available. The bridged ribose conformation enhances base stacking and pre-organizes the backbone of the oligonucleotide significantly increasing their hybridization properties. 
  The incorporation of BNAs into oligonucleotides allows the production of modified synthetic oligonucleotides with 
  equal or higher binding affinity against a DNA or RNA complement with excellent single-mismatch discriminating power;  
  better RNA selective binding; 
  stronger and more sequence selective triplex-forming characters; 
  pronounced higher nuclease resistance, even higher than  Sp-phosphorothioate analogues; and
  good aqueous solubility of the resulting oligonucleotides when compared to regular DNA or RNA oligonucleotides.
  New BNA analogs introduced by Imanishis group were designed by taking the length of the bridged moiety into account. A six-membered bridged structure with a unique structural feature (N-O bond) in the sugar moiety was designed to have a nitrogen atom. This atom improves the formation of duplexes and triplexes by lowering the repulsion between the negatively charged backbone phosphates. These modifications allow to control the affinity towards complementary strands, regulate resistance against nuclease degradation and the synthesis of functional molecules designed for specific applications in genomics. The properties of these analogs were investigated and compared to those of previous 2,4-BNA (LNA) modified oligonucleotides by Imanishis group. Imanishis results show that "2,4'-BNA-modified oligonucleotides with these profiles show great promise for applications in antisense and antigene technologies."