Pure and Applied Chemistry

Abstract: RNA molecules play essential roles in biological processes and are evolving as important targets for therapeutic intervention. Small molecules that specifically bind unique RNA sites and prevent the formation of functional RNA folds or RNA-protein complexes can modulate cell functions and can become of therapeutic potential. To explore such recognition events and to fabricate discovery assays, effective biophysical tools need to be advanced. When carefully designed, new fluorescent nucleosides can serve an unparalleled role in such studies. Our criteria for "ideal" fluorescent nucleoside analogs include: (a) high structural similarity to the native nucleobases to faithfully mimic their size and shape, as well as hybridization and recognition properties; (b) red-shifted absorption bands; (c) red-shifted emission band (preferably in the visible); (d) a reasonable emission quantum efficiency; and, importantly, (e) sensitivity of their photophysical parameters to changes in the microenvironment. Our program, aimed at the development of new emissive isomorphic nucleoside analogs, has yielded several useful nucleobases. Selected analogs were implemented in fluorescence-based assays. This overview presents the motivation for this work by introducing RNA-ligand interactions and discusses the design and synthesis of fluorescent isosteric nucleobase analogs and their utilization for the fabrication of "real-time" fluorescence-based biophysical assays.