title: Synthesis and backbone conformations of cyclic hexapeptides cyclo-(Xxx-Pro-D-Gln)2.
abstract: The solution syntheses of cyclo-(Xxx-Pro-D-Gln)2, where Xxx = Gly, Ala, Leu, Phe and Val are described. Several routes were examined, the most successful involving the intermediate Z-Xxx-Pro-D-Gln-O-tBu and proceeding to cyclization of H-Xxx-Pro-D-Gln-Xxx-Pro-D-Gln-OH using diphenylphosphoryl azide. The N--H regions of the proton magnetic resonance spectra of aqueous solutions of these peptides were examined, and in the Xxx = Leu and Val peptides an unsymmetrical backbone, presumably with one cis Xxx-Pro peptide bond, was found to be important. Previous reports of cyclo-(Xxx-Pro-D-Yyy)2 peptides have shown only C2-symmetric forms.
mesh_terms: D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D009842:Oligopeptides / Q000138:chemical synthesis*; D010456:Peptides, Cyclic / Q000138:chemical synthesis*; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D007202:Indicators and Reagents; D009842:Oligopeptides; D010456:Peptides, Cyclic