Synthesis of chemical probes to map sulfenic acid modifications on proteins

Cysteine sulfenic acids in proteins can be identified by their ability to form adducts with dimedone, but this reagent imparts no spectral or affinity tag for subsequent analyses of such tagged proteins. Given its similar reactivity toward cysteine sulfenic acids, 1,3-cyclohexadione was synthetically modified to an alcohol derivative and linked to fluorophores based on isatoic acid and 7-methoxycoumarin. The resulting compounds retain full reactivity and specificity toward cysteine sulfenic acids in proteins, allowing for incorporation of the fluorescent label into the protein and tagging it based on its sulfenic acid redox state. Control experiments using dimedone further show the specificity of the reaction of 1,3-diones with protein sulfenic acids in aqueous media. These new compounds provide the basis for an improved method for the detection of protein sulfenic acids.