Anders E. Håkansson

The Eight Stereoisomers of LNA (Locked Nucleic Acid): A Remarkable Family of Strong RNA Binding Molecules

The authors evaluated the RNA binding of all eight possible stereoisomers of LNA. Synthesis of qa-l-xylo-LNAq has been accomplished and the remaining four stereoisomers, all enantiomers of the four synthesized diastereoisomers, are indirectly evaluated by hybridization studies. The remarkable binding affinities and specificities obtained for LNA and a-l-LNA, both in a fully and in a partly modified context, establish these mols. as unique nucleic acid mimics. A strong impetus for this research has been, and continues to be, the therapeutic promises of the antisense strategy. [on SciFinder (R)]

LNA (locked nucleic acid) and the diastereoisomeric alpha-L-LNA: conformational tuning and high-affinity recognition of DNA/RNA targets.

The remarkable binding properties of LNA (Locked Nucleic Acid) and α-L-LNA (the α-L-ribo configured diastereoisomer of LNA) are summarized, and hybridization results for LNA/2′-O-Me-RNA chimera and LNAs with a “dangling” nucleotide are introduced. In addition, results from NMR investigations on the furanose conformations of the individual nucleotide monomers in different duplexes are presented. All these data are discussed with focus on the importance of conformational steering of unmodified nucleotides in partly modified LNA and α-L-LNA sequences in relation to the unprecedented binding properties of LNA and α-L-LNA.

α‐L‐LNA (α‐L‐ribo Configured Locked Nucleic Acid) Recognition of DNA: An NMR Spectroscopic Study

We have used NMR and CD spectroscopy to study and characterise two α-L-LNA:DNA duplexes, a nonamer that incorporates three α-L-LNA nucleotides and a decamer that incorporates four α-L-LNA nucleotides, in which α-L-LNA is α-L-ribo-configured locked nucleic acid. Both duplexes adopt right-handed helical conformations and form normal Watson–Crick base pairing with all nucleobases in the anti conformation. Deoxyribose conformations were determined from measurements of scalar coupling constants in the sugar rings, and for the decamer duplex, distance information was derived from 1H–1H NOE measurements. In general, the deoxyriboses in both of the α-L-LNA:DNA duplexes adopt S-type (B-type structure) sugar puckers, that is the inclusion of the modified α-L-LNA nucleotides does not perturb the local native B-like double-stranded DNA (dsDNA) structure. The CD spectra of the duplexes confirm these findings, as these display B-type characteristic features that allow us to characterise the overall duplex type as B-like. The 1H–1H NOE distances which were determined for the decamer duplex were employed in a simulated annealing protocol to generate a model structure for this duplex, thus allowing a more detailed inspection of the impact of the α-L-ribo-configured nucleotides. In this structure, it is evident that the malleable DNA backbone rearranges in the vicinity of the modified nucleotides in order to accommodate them and present their nucleobases in a geometry suitable for Watson–Crick base pairing.

The adenine derivative of α-L-LNA (α-L-ribo configured locked nucleic acid): Synthesis and high-affinity hybridization towards DNA, RNA, LNA and α-L-LNA complementary sequences

Synthesis of a 9-mer α-l-LNA (α-l-ribo configured locked nucleic acid) containing three 9-(2-O,4-C-methylene-α-l-ribofuranosyl)adenine nucleotide monomer(s) has been accomplished. The work involved synthesis of the bicyclic adenine nucleoside via a condensation reaction between l-threo-pentofuranose derivative 1 and 6-N-benzoyladenine followed by C2′-epimerization. Hybridization studies demonstrated very strong duplex formation with 9-mer complementary DNA, RNA, LNA and α-l-LNA target sequences.

LNA stereoisomers: xylo-LNA (β-D-xylo configured locked nucleic acid) and α-L-LNA (α-L-ribo configured locked nucleic acid)

Synthesis of xylo-LNA containing one 2′-O,4′-C-methylene-β-D-xylofuranosyl thymine nucleotide monomer and α-L-LNAs containing one or four 2′-O,4′-C-methylene-α-L-ribofuranosyl thymine nucleotide monomer(s) has been accomplished using phosphoramidite chemistry with pyridine hydrochloride as activator; oligothymidylate α-L-LNA displays strongly enhanced affinity towards complementary RNA.

High-affinity nucleic acid recognition using ‘LNA’ (locked nucleic acid, β-D-ribo configured LNA), ‘xylo-LNA’ (β-D-xylo configured LNA) or ‘α-L-LNA’ (α-L-ribo configured LNA)

Remarkably strong binding affinities towards complementary single stranded DNA and RNA were obtained for 10- and 14-mer LNAs (locked nucleic acids) containing diastereoisomeric β-D-ribo, β-D-xylo or α-L-ribo configured LNA thymine monomers; a possible relevance of these results in relation to nucleic acid evolution is discussed.