Incorporation and Utility of a Responsive Ribonucleoside Analogue in Probing the Conformation of a Viral RNA Motif by Fluorescence and ¹⁹F NMR Spectroscopy

Development of versatile probes that can enable the study of different conformations and recognition properties of therapeutic nucleic acid motifs by complementing biophysical techniques can greatly aid nucleic acid analysis and therapy. Here, we report the design, synthesis and incorporation of an environment‐sensitive ribonucleoside analogue, which serves as a two‐channel biophysical platform to investigate RNA structure and recognition by fluorescence and 19 F NMR spectroscopy techniques. The nucleoside analogue is based on a 5‐fluorobenzofuran‐uracil core and its fluorescence and 19 F NMR chemical shifts are highly sensitive to changes in solvent polarity and viscosity. Notably, the modified ribonucleotide and phosphoramidite substrates can be efficiently incorporated into RNA oligonucleotides (ONs) by in vitro transcription and standard solid‐phase ON synthesis protocol, respectively. Fluorescence and 19 F readouts of the nucleoside incorporated into model RNA ONs are sensitive to the neighbouring base environment. The responsiveness of the probe was aptly utilized in detecting and quantifying the metal ion‐induced conformational change in an internal ribosome entry site RNA motif of hepatitis C virus, which is an important therapeutic target. Taken together, our probe is a good addition to the nucleic acid analysis toolbox with the advantage that it can be used to study nucleic acid conformation and recognition simultaneously by two biophysical techniques.