Bridged nucleic acid

A bridged nucleic acid (BNA) is a modified RNA nucleotide. They are sometimes also referred to as constrained or inaccessible RNA molecules. BNA monomers can contain a five-membered, six-membered or even a seven-membered bridged structure with a "fixed" C₃'-endo sugar puckering.^[1] The bridge is synthetically incorporated at the 2', 4'-position of the ribose to afford a 2', 4'-BNA monomer. The monomers can be incorporated into oligonucleotide polymeric structures using standard phosphoramidite chemistry. BNAs are structurally rigid oligo-nucleotides with increased binding affinities and stability.