The crystal structure and the conformational analysis of carbobenzoxyl-L-leucyl-p-nitrophenyl ester

Abstract

Carbobenzoxy-L-leucyl-p-nitrophenyl ester crystallizes in space group P212121 with a= 8"498, b= 9"40j and c=25"217 A. 1398 independent reflexions were collected on a Philips automatic diffractometer. The structure was solved by direct methods, and refined isotropically by full-matrix least-squares calculations. The final R is 0.105. The molecule assumes a 'folded-back' conformation in the crystal, the folding occurring at the Leu residue. The two parts of the molecule departing from the Leu residue are in the extended conformation. The OC-NH group deviates significantly from planarity. The molecules are held together by hydrogen bonds and dipole-dipole and van der Waals interactions. The prediction of the conformational analysis, particularly for the fragment containing the Leu residue, is in accordance with the actual structure.

Understanding α-amino acid chemistry from X-ray diffraction structures

“…The dihedral angle between the two aromatic rings is about 90", a very different spatial relationship compared to that of Z-L-Leu-ONP, . 53 The geometry of the NG, group, including the distance-dependent angular deformation, is the same as that of NP,. The (aromatic) C1-02 bond is…”

The crystal structures of two cyclic polyurethane oligomers, cyclobisurethane and cyclotetraurethane

“…1, 3, and 4 were plotted with program ORTEP (Johnson, 1965) on the Univac 1108 computer at Carnegie-Mellon University. Table 5 lists the hydrogen-bonding parameters, which compare favorably with those of other urethane structures (Bracher & Small, 1967;Ganis, Avitabile, Migdal & Goodman, 1971;Adams & Small, 1973;Gieren, Hoppe & Fleischmann, 1973;Coiro, Mazza & Mignucci, 1974), and those of cyclic amides (Northolt, 1970;Northolt & Alexander, 1968).…”