Haloacetyl and Alkyl Halide Derivatives

The relative reactivity of a-haloacetates toward protein functionalities is sulfhydryl imidazolyl thioether amine. Among halo derivatives the relative reactivity is I Br Cl F, with fluorine being almost unreactive. The a-haloacetamides have the same trend of relative reactivities, but will obviously not create a terminal carboxylate functional group. 

iodoacetate has the highest reactivity toward sulfhydryl cysteine residues and may be directed specifically for—SH modification. If iodoacetate is present in limiting 

Although the primary utility of active halogen compounds is to modify sulfhydryl groups in proteins or other molecules, the reaction is not totally specific. Iodoacetyl (and bromoacetyl) derivatives can react with a number of functional groups within proteins the sulfhydryl group of cysteine, both imidazolyl side chain nitrogens of histidine, the thioether of methionine, and 

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