The highly electrophilic character of 4-chloro-7-nitrobenzofurazan and possible consequences for its applications as a protein-labelling reagent

4-Chloro-7-nitrobenzofurazan possesses at least one highly electrophilic centre (C-6) that is much more reactive towards nucleophiles than position C-4, the irreversible alkylating site of this reagent. Possible consequences of the electrophilic character of 4-chloro-7-nitrobenzofurazan for its application as a protein-labelling reagent are discussed.