Synthesis and optical behaviors of 6-seleno-deoxyguanosine.

We have developed a simple method to synthesize 6-seleno-2'-deoxyguanosine (SedG) by selectively replacing the 6-oxygen atom with selenium. This selenium-atom-specific modification (SAM) alters the optical properties of the naturally occurring 2'-deoxyguanosine (dG). Unlike the native dG, the UVabsorption of SedG is significantly influenced by the pH of the aqueous solution. Moreover, SedG is fluorescent at the physiological pH and exhibits pH-dependent fluorescence in aqueous solutions. Furthermore, SedG has noticeable fluorescence in non-aqueous solutions, indicating its sensitivity to environmental changes. This is the first time a fluorescent nucleoside by single-atom alteration has been observed. Fluorescent nucleosides modified by a single atom have great potential as molecular probes with minimal perturbations to investigate nucleoside interactions with proteins, such as membrane-transporter proteins.