Locked nucleic acid; a novel class of nucleic acid analogues. LNA monomers are bicyclic compounds that are structurally similar to RNA nucleosides; the term LNA refers to the observation that the furanose ring conformation is restricted in LNA by a methylene linker that connects the 2'O position to the 4'-C position. Therefore, all nucleic acids that contain one or more LNA modifications are called LNA. Duplexes formed with either DNA or RNA have a very high thermal stability (approximately 3°C to 8°C per modified base higher).