4- (3-Tosyl-2- (tosylmethyl) propanoyl) benzoic acid

4- (3-Tosyl-2- (tosylmethyl) propanoyl) benzoic acid (Bis-sulfone Acid) is a strong covalent linker featuring a free carboxylic acid and two tosyl groups. Each tosyl group can be displaced by thiol or amine nucleophiles via a Michael addition, and the inclusion of two on this molecule allow this reaction to proceed twice. This may be used to “staple” two reduced cysteine residues on a given protein to reform disulfide bridges. The carboxylic acid is free to react to form amides or esters.