"2'-deoxy-6-thioguanosine :synthesis of monomer, oligomers and long DNA, and their binding with metal ions

Abstract

The formation of one-dimensional (1D) coordination polymers using thiolated DNA nucleosides and nucleotides with transition metals was investigated. 2’-Deoxy-6- 1 13 thioguanosine was successfully synthesised and characterized by H-NMR, C-NMR, IR, MS and UV spectroscopy. Subsequently, the binding of several transition metal ions to 2’-deoxy-6-thioguanosine and 6-thioguanosine was studied. The binding ratio of thio-monomer with metal ions was shown to be three ligands to one metal in the case of cobalt (II) and nickel (II), whilst in the case of the cadmium (II)-complex with the thio-monomer, the results suggested that a 1D coordination polymer might be formed, although no crystal data was obtained to confirm this structure. Therefore, the oligonucleotides containing the thiolated monomer were synthesised to extend this study. The preparation of thiolated homo-guanosine oligomers involved standard solid phase synthesis of oligo-guanosine followed by on-column conversion of guanosine to 6-thioguanosine. The thiolated reaction was the same as that used for the monomer and yielded 2-, 3-, 4- and 5-mer thio-oligomers in good yield. The thio-oligomers were purified by HPLC and were fully characterized by mass spectrometry and UV. The interaction of thio-oligomers with cadmium (II) ions was investigated. For the dimer and tetramer, the binding ratio was two thio-bases bound to one cadmium, whereas for the trimer and pentamer the binding ratio showed more than one binding species in solution. In order to synthesise a long thiolated DNA polymer, an enzymatic slippage reaction was performed, where a short primer-template of poly (dG)-poly (dC) was 1010 - extended up to 300 bp using Klenow exo polymerase and nucleosides triphosphate (d-tGTP and d-CTP). The addition of cadmium ions to thio-modified DNA suggested a structure resembling M-DNA as coordination polymer is obtained according to UV titration data.