Modification of Methionine and Cysteine

Chemical groups that specifically react with carboxylic acids are limited in variety. In aqueous solutions, the carboxylate functionality displays rather low nucleophilicity. For this reason, it is unreactive with the great majority of bioconjugate reagents which couple through a nucleophilic addition process. 

Several important chemistries, however, have been developed that allow conjugation through a carboxylate group. The following sections briefly describe these reactions. 

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