Microwave-Assisted Synthesis of 2,2′-Azopyridine-Labeled Amines, Amino Acids, and Peptides

A microwave-assisted procedure for labeling amines, amino acids, and peptides with 2,2′-azopyridines (2,2′-AzPy) is described using the corresponding 2,2′-azopyridine-diacylbenzotriazoles. The efficiency of the procedure is proven by the generation of three constitutionally isomeric sets of 2,2′-AzPy-X,X′-labeled amino conjugates (where X = 4, 5, 6) including amines, amino acids, and peptides. Microwave-assisted synthesis conditions provide good to excellent yields in less than 15 minutes with retention of original chirality. A trans -to- cis isomerization of the 2,2′-azopyridine-labeled amino conjugate upon laser irradiation at 325 nm is visualized with UV and NMR spectroscopy.