The synthesis of 2'-amino-LNA (the 2'-amino derivative of locked nucleic acid) has opened up a number of exciting possibilities with respect to modified nucleic acids. While maintaining the excellent duplex stability inferred by LNA-type oligonucleotides, the nitrogen in the 2'-position of 2'-amino-LNA monomers provides an excellent handle for functionalisation. Herein, the synthesis of amino acid functionalised 2'-amino-LNA derivatives is described. Following ON synthesis, a glycyl unit attached to the N2'-position of 2'-amino-LNA monomers was further acylated with a variety of amino acids. On binding to DNA/RNA complements, the modified ONs induce a marked increase in thermal stability, which is particularly apparent in a buffer system with a low salt concentration. The increase in thermal stability is thought to be caused, at least in part, by decreased electrostatic repulsion between the negatively charged phosphate backbones when positively charged amino acid residues are appended. Upon incorporation of more than one 2'-amino-LNA modification, the effects are found to be nearly additive. For comparison, 2'-amino-LNA derivatives modified with uncharged groups have been synthesised and their effect on duplex thermal stability likewise investigated.

3′-Deoxy-4′-azaribonucleosides (15a-d) were synthesized starting from the commercially available (4R)-trans-4-hydroxy-L-proline 7. From biological evaluations, 15b and 15d emerged as potent inhibitors of HCV replication on a replicon assay. These findings demonstrate that synthesized pyrrolidine nucleosides represent a new template for antiviral or other biological studies and could be considered for novel combination therapy against HCV infection using nucleoside inhibitors and non-nucleoside inhibitors of HCV NS5B.

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