Fluorinated RNA molecules, particularly 2′-F RNA, have found a wide range of applications in RNA therapeutics, RNA aptamers, and ribozymes and as 19F NMR probes for elucidating RNA structure. Owing to the instability of 4′-F ribonucleosides, synthesis of 4′-F-modified RNA has long been a challenge.

Recently, Prof. Chuanzheng Zhou’s group has developed a strategy for synthesizing a 4′-F-uridine (^4′FU) phosphoramidite, and they used it to prepare 4′-F RNA successfully. In the context of an RNA strand, ^4′FU, which existed in a North conformation, was reasonably stable and resembled unmodified uridine well. The ¹⁹F NMR signal of ^4′FU was sensitive to RNA secondary structure, with a chemical shift dispersion as large as 4 ppm (compared with <1 ppm for ^2′FU), which makes it a valuable probe for discriminating single-stranded RNA and A-type, B-type, and mismatched duplexes. In addition, they demonstrated that because RNA-processing enzymes treated ^4′FU the same as unmodified uridine, ^4′FU could be used to monitor RNA structural dynamics and enzyme-mediated RNA processing. Taken together, the results indicate that 4′-F RNA represents a probe with wide utility for elucidation of RNA structure and function by means of ¹⁹F NMR spectroscopy.