Synthesis and properties of nucleic acid duplexes and quadruplexes containing 3'-S-phosphorothiolate linkages

• Main Author: Piperakis, Michael Matthew
• Published: University of Liverpool 2012
• Subjects: 572.85
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569181

3'-Thiopurine 2'-deoxynucleosides have been incorporated into model oligodeoxynucleotides (DONs) thus giving rise to ODNs that consist of the 3- S-phosporothiolate (3'-sp) linkage. Due to the complex chemical manipulations implicated, the preparation of such analogues has been scarcely explored to date. The 3'-thiopurine nucleosides were prepared prior to incorporation into the desired DON sequences by traditional automated 3'---+5' solid-phase phosporamidite chemistry. Two different strategies, one involving neighbouring group participation and the other an in situ oxidation-reduction, were successfully applied for the key C3' epimerisation in deoxyadenosine and deoxyguanosine, respectively. Subsequent UV denaturation studies revealed that the destabilisation effect recorded in DNA/DNA duplexes consisting of a single 3'-sp modified residue on one strand was diminished when more 3'-sp modified residues were incorporated. The destabilisation is expected on the basis that the sugars on the 3'-sp modified and neighbouring residues predominantly adopt the RNA-like North conformation. A surprising stabilisation effect was, moreover, observed for DNA/RNA hybrids containing 3'-sp modifications in the RNA strand. Additionally, when 3'-sp modifications were incorporated into both strands of the homo- or hetero-duplexes, an additive effect was generally exhibited. UV denaturation studies revealed a significant position specific 3'-sp substitution effect when incorporated into G-quadruplexes; the thermal stability of the tetramolecular complex was significantly increased when either of the two central guanines in the G-tract of the sequence was modified. A clear position-dependent substitution effect on the rate of association of the quadruplex was also observed, however, no correlation between the kinetics of association and the recorded thermal stability was realised.