C9 CONFORMATION OF N-(N-ALPHA-[(TERT-BUTYLOXY)-CARBONYL]-L-ALANYL)-N,N'-DICYCLOHEXYLUREA IN SOLID AND SOLUTION

An X-ray diffraction study was carried out on a single crystal of N-{N(alpha)-[(tert.-butyloxy)-carbonyl]-L-alanyl}-N,N'-dicyclohexylurea belonging to the tetragonal space group P4(1)2(1)2, having cell dimensions a = b = 10.102(3) angstrom, c = 46.067(7) angstrom, V = 4701.2 angstrom3, Z = 8. The crystal structure was solved by direct methods and refined to an R value of 0.056 for 1602 unique reflections with I > 2.5 sigma(I). Crystal structure analysis shows the presence of an intramolecular N-H ... O = C H-bond stabilizing the molecule in a folded form similar to that of a beta-turn, forming a nine-membered ring. IR and H-1-NMR studies in CDCl3 solution confirm the stable folded conformation found in the crystalline state, as well as the existence of N-H ... O = C H-bonds in the title compound, as in peptides.