Synthesis of Responsive Fluorescent Nucleobases 7-(Benzofuran-2-yl)-7-deazahypoxanthine and 7-(Benzofuran-2-yl)-7-deazaguanine Using Cross-coupling Reaction

In order to develop fluorescent guanine analogs having substitutions at the 7-positions, 7-(benzofuran-2-yl)-7-deazahypoxanthine (1a) and 7-(benzofuran-2-yl)-7-deazaguanine (1b), were synthesized from 7-deaza-7-iodohypoxanthine and 7-deaza-7-iodo-2-N-pivaloylguanine via a Suzuki–Miyaura cross-coupling, respectively. Compound 1bshowed strong fluorescence, with higher fluorescent quantum yields in less polar solvents; meanwhile, 1ashowed higher activity in more polar solvents. It is expected that the guanine analogs can be incorporated into nucleosides to develop new fluorescent oligonucleotides.