Site-specific modification of amino acids and peptides by aldehyde-alkyne-amine coupling under ambient aqueous conditions.

A highly efficient method for the direct, site-specific functionalization of amino acids and peptides, under ambient conditions, is described. In aqueous, nearly solvent-free conditions, copper(I) chloride catalyzed the aldehyde-alkyne-amine (A(3)) coupling of amino acids to form dipropargylated products in moderate to excellent yields. The propargylamine functionality provides a convenient handle for further structural modifications, demonstrated by a subsequent one-pot deprotection and "click" reaction and a solution-phase peptide coupling.