Late‐Stage Fluorination of Tyrosine Residues in Antiviral Protein Cyanovirin‐N

The applications of fluorinated molecules in chemical biology are rapidly expanding driven by the unique properties of C-F bonds, leading to increased interest in methodologies for controlled introduction of this atom. In this study, we present the first method for late-stage fluorination of tyrosine residues in proteins. Our results demonstrate that electrophilic fluorination using Selectfluor, a stable and non-toxic reagent, offers a straightforward and cost-effective method for labeling Cyanovirin-N (CVN), a 101-amino-acid lectin with effective antiviral activity. Uni- and bidimensional ¹H, ¹³C and ¹⁹F NMR analyses, along with mass spectrometry, revealed chemoselective fluorination of the three tyrosine residues in CVN without affecting its overall structure or mannose-binding affinity. Additionally, we observed that other aromatic amino acids, such as tryptophan, phenylalanine, and histidine, are not fluorinated using this method. These findings advance our understanding of protein fluorination and its applications in studying structure, dynamics, and interactions, as well as other biological utilities.