'Sulfo-click' for ligation as well as for site-specific conjugation with peptides, fluorophores, and metal chelators.

The 'sulfo-click' reaction, which is a chemoselective amidation reaction involving the reaction of an aminoethane sulfonyl azide with a thio acid, encompasses a new approach for ligation and conjugation. Detailed protocols are provided for decorating biologically active peptides or dendrimers with biophysical tags, fluorescent probes, metal chelators, and small peptides by using this reaction as a novel, metal-free 'sulfo-click' approach.