N-(tert-Butoxycarbonylglycyl-alpha,beta-dehydrophenylalanylglycylphenylalanyl)-4-nitroaniline

In the crystal structure of the tetrapeptide Boc(0)-Gly(1)-Delta Phe(2)-Gly (3)-Phe(4)-p-NA (p-NA is para-nitroaniline), C33H36N6O8, there are two inde pendent molecules differing in conformation in the asymmetric part of the u nit cell. All the amino acids in the peptide are linked trans to each other . The torsion angles in the main chain of both molecules are close to the v alues of the type beta -II turn. Two intramolecular and three intermolecula r N-H . . .O hydrogen bonds stabilize the conformation of each of the molec ules.