title: Synthesis and hybridization studies of 2'-amino-alpha-L-LNA and tetracyclic "locked LNA".
abstract: A convergent route to a new class of locked nucleic acids, i.e., 2'-amino-alpha-L-LNA, has been developed. The optimized synthetic route to the corresponding phosphoramidite building block of thymine proceeds in 4% overall yield over 15 steps from the starting diol. Crucial synthetic steps include (a) introduction of a C2-azido group prior to nucleobase coupling, (b) Vorbrüggen glycosylation primarily affording the desired alpha-anomer, (c) separation of alpha-L-ribo- and beta-L-ribo-configured bicyclic nucleosides, and (d) selection of a suitable protecting group to avoid intramolecular Michael addition of the C2'-amino group onto the C6-position. Incorporation of a 2'-amino-alpha-L-LNA monomer into oligodeoxyribonucleotides results in modest changes in thermal stability with complementary DNA, whereas significant increases in thermal stability are observed with RNA complements along with excellent Watson-Crick discrimination. These results, along with the flexibility of the synthetic strategy allowing chemoselective N2'-functionalization at a late stage, render 2'-amino-alpha-L-LNA a promising building block for nucleic acid based nanobiotechnology and therapeutics. A slight modification in strategy facilitated the synthesis of the corresponding phosphoramidite building blocks of Michael adducts, which due to their tetracyclic skeletons exhibit a conformationally restricted furanose ring and glycosidic torsion angle (anti-range). Incorporation of such a "locked LNA" monomer into oligodeoxyribonucleotides results in large decreases in thermal affinity toward DNA/RNA complements.
authors.affiliation: Nucleic Acid Center, Department of Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark.
authors.forename: T Santhosh
authors.initials: TS
authors.lastname: Kumar
authors.forename: Andreas S
authors.initials: AS
authors.lastname: Madsen
authors.forename: Jesper
authors.initials: J
authors.lastname: Wengel
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Hrdlicka
mesh_terms: D015394:Molecular Structure; D013938:Thymidine Monophosphate / Q000031:analogs & derivatives* / Q000138:chemical synthesis
chemical_list: C520121:7-(2-cyanoethoxy(diisopropylamino)phosphinoxy)-1-(4,4'-dimethoxytrityloxymethyl)-5-(9'-fluorenylmethoxycarbonyl)-3-(thymin-1-yl)-2-oxa-5-azabicyclo(2.2.1)heptane; D013938:Thymidine Monophosphate