Large scale synthesis of 2'-amino-LNA thymine and 5-methylcytosine nucleosides.

Thymine intermediate 17 has been synthesized on a multigram scale (50 g, 70 mmol) from starting sugar 1 in 15 steps in an overall yield of 73%, with only 5 purification steps. The key thymine intermediate 18 was obtained from 17 in a single step in 96% yield, whereas the key 5-methylcytosine intermediate 20 was obtained from 17 in 2 steps in 58% yield. This highly efficient large scale route necessitates only 2 and 3 novel steps to obtain N2'-functionalized thymine and 5-methylcytosine amino-LNA phosphoramidites from these key intermediates, respectively.

Synthesis and structural characterization of 2'-fluoro-α-L-RNA-modified oligonucleotides.

We describe the synthesis and binding properties of oligonucleotides that contain one or more 2'-fluoro-α-L-RNA thymine monomer(s). Incorporation of 2'-fluoro-α-L-RNA thymine into oligodeoxynucleotides decreased thermal binding stability slightly upon hybridization with complementary DNA and RNA with the smallest destabilization towards RNA. Thermodynamic data show that the duplex formation with 2'-fluoro-α-L-RNA nucleotides is enthalpically disfavored but entropically favored.

Unlocked nucleic acid (UNA) and UNA derivatives: thermal denaturation studies.

A study on the thermal stability of duplexes formed between unlocked nucleic acid (UNA) modified DNA and RNA oligonucleotides and complementary DNA and RNA is presented. The acyclic UNA monomers are shown to induce a decrease in duplex thermal stability.