Metal-free and pH-controlled introduction of azides in proteins

Conversion of amines into azides using imidazole-1-sulfonyl azide as a diazotransfer reagent has proven to be a straightforward way to introduce targetable handles into proteins. We explored whether less toxic and milder conditions than described before could be applied. It was shown that the aqueous diazotransfer proceeds without adding Cu(II) not only at pH 11 but also at pH 8.5. The diazotransfer was shown to be selective towards a single amine.