Dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium Salts

Abstract

Water-soluble reagents were prepared by converting 2-hydroxy-5-nitrobenzyl halides into corresponding dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium salts. The resulting salts were found to selectively modify tryptophan and cysteine when added to amino acids in aqueous solutions. N-Acetyltryptophan, glycyltryptophan, and tryptophanylglycine appeared equal to tryptophan in reactivity with the sulfonium chloride; comparable reactivity was observed with chymotrypsin. Although the sulfonium salts are rapidly hydrolyzed in neutral and alkaline solutions, aqueous solutions at pH 3 are relatively stable. Thus, in contrast to 2-hydroxy-5-nitrobenzyl bromide, an aqueous solution of dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium chloride can be used to modify proteins.