Nucleoside and oligonucleotide pyrene conjugates with 1,2,3-triazolyl or ethynyl linkers: synthesis, duplex stability, and fluorescence changes generated by the DNA-dye connector

Fluorescent nucleosides and oligonucleotides functionalized with pyrene were synthesized using 'click' chemistry or the Sonogashira cross-coupling reaction. The dye was connected to position-7 of 7-deaza-2′-deoxyguanosine or to the 2′-deoxyribofuranose moiety. Four different DNA-dye connectors with 1,2,3-triazolyl residues or triple bonds were constructed. Phosphoramidites of the pyrene conjugates (9, 14, 25) were prepared and used in solid-phase synthesis. Short linkers (2, 4) destabilize DNA, while long linkers (1) increased duplex stability. Nucleosides and oligonucleotides with single dye incorporations show linker dependent fluorescence. Linker dependent excimer emission with pyrenes in proximal positions was also observed. A 'superchromophore' formed by the 7-deaza-2′-deoxyguanosine ethynylpyrene conjugate shows strong red shifted fluorescence emission at 495 nm.