Side chain–backbone hydrogen bonds in peptides containing glutamic acid residues

Over the last few years x-ray diffraction and nmr investigations have been reported for a variety of natural and synthetic peptides in order to enhance our understanding of the conformation of several amino acid side chains and especially those bearing functional groups such as hydroxyl, sulfhydryl, amide, or carboxylate groups.Only a small amount of data is available for glutamic acid: its crystal structure's2 and that of the complex L-argininehg l ~t a m a t e .~We have now synthesized several peptides containing glutamic acid residues and investigated their conformation in dimethylsulfoxide (DMSO) solution by nmr spectroscopy.The results suggest the existence of an intramolecular hydrogen bond between the ionized y-carboxylate group (COO-) of the side chain of the glutamic acid residue and