title: A simplified and efficient route to 2'-O, 4'-C-methylene-linked bicyclic ribonucleosides (locked nucleic acid).
abstract: A novel efficient method for the synthesis of locked nucleic acid (LNA) monomers is described. The LNA 5',3'-diols containing thymine, 4-N-acetyl- and 4-N-benzoylcytosine, 6-N-benzoyladenine, and 2-N-isobutyrylguanine as nucleobases were prepared via convergent syntheses. The method is based on the use of the common sugar intermediate 1,2-di-O-acetyl-3-O-benzyl-4-C-methanesulfonoxymethyl-5-O-methanesulfonyl-D-erythro-pentofuranose (8) that easily can be prepared from D-glucose in multigram scale. Four different nucleobases were stereoselectively coupled to 8 using a modified Vorbrüggen procedure to give the corresponding 4'-C-branched nucleoside derivatives. Subsequent ring closing furnished the protected LNA nucleosides. The 5'-O-mesyl groups were efficiently displaced by nucleophilic substitution using sodium benzoate. Saponification of the 5'-benzoates followed by catalytic removal of the 3'-O-benzyl groups afforded the free LNA diols. The exocyclic amino groups of adenosine and cytidine were selectively acylated to give 4-N-acetyl- or 4-N-benzoyl-LNA-C and 6-N-benzoyl-LNA-A. The isobutyryl group of guanine was retained during the preparation of 2-N-isobutyryl-LNA-G. The LNA-T diol and base-protected LNA diols can be directly converted into LNA-phosphoramidites for automated chemical synthesis of LNA containing oligonucleotides.
authors.affiliation: Exiqon A/S, Department of Chemistry, Bygstubben 9, DK-2950 Vedbaek, Denmark. koshkin@exiqon.com
authors.forename: A A
authors.initials: AA
authors.lastname: Koshkin
authors.forename: J
authors.initials: J
authors.lastname: Fensholdt
authors.forename: H M
authors.initials: HM
authors.lastname: Pfundheller
authors.forename: C
authors.initials: C
authors.lastname: Lomholt
mesh_terms: D002851:Chromatography, High Pressure Liquid; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D009696:Nucleic Acids / Q000737:chemistry*; D012263:Ribonucleosides / Q000138:chemical synthesis*
chemical_list: D007202:Indicators and Reagents; D009696:Nucleic Acids; D012263:Ribonucleosides