Selective labeling of amino acid residues introduces site-specific modifications into protein sidechains, which can serve as chemical tools to probe biological pathways and/or protein structural dynamics. Near-isosteric modifications have the potential for non-invasive labeling methods that preserve the native properties of proteins by substituting specific functional groups of similar shape and size. The fluorination of amino acid residues is one example, in which hydrogen in a carbon-hydrogen (C-H) bond is replaced by fluorine in a carbon-fluorine (C-F) bond .