Base-modified fluorescent purine nucleosides and nucleotides for use in oligonucleotide probes

Recent years has witnessed increasing development and exploitation of fluorescence techniques which has been spurred by the discovery, design and synthesis of novel fluorescent molecules. In the realm of nucleic acids, both modest and dramatic structural modification of the nucleobase may engender it with fluorescence. This review focuses on the design, synthesis and applications of purine nucleoside analogs possessing fluorescently modified nucleobases, particularly for detection of nucleic acid sequences or for structural studies on nucleic acids. Thus, fluorescent nucleoside/nucleotide analogs that can be incorporated into oligonucleotides and report changes due to base-pairing/stacking or microenvironmental alterations, such as polarity changes in the grooves, are highlighted. Whenever available, the photophysical mechanism giving rise to the environmental responsiveness of the fluorescent nucleoside/tide is presented.