title: Conformational studies of cyclic tetrapeptides. Evidence for a bis gamma-turn conformation for chlamydocin and Ala4-chlamydocin in nonpolar solvents.
abstract: The conformations of chlamydocin and cyclo (Ala-Aib-Phe-D-Pro) (Ala4-chlamydocin) in chloroform have been investigated by nuclear magnetic resonance, infrared and circular dichroism spectroscopy. The data obtained from these experiments establish an all transoid, bis gamma-turn conformation for both compounds in chloroform with the following torsional angles (+/- 20 degrees): Ala4-chlamydocin: Aib, phi + 60 degrees, psi - 50 degrees; omega + 160 degrees; Phe phi - 120 degrees, psi + 120 degrees, omega - 160 degrees; D-Pro phi + 60 degrees, psi - 55 degrees, omega + 160 degrees; Ala phi - 110 degrees, psi + 110 degrees, omega - 160 degrees. Chlamydocin adopts a closely related conformation in neat chloroform. Nuclear Overhauser Effect (NOE) data are utilized to assign amide bond geometries in the cyclic tetrapeptide ring system.
mesh_terms: D000595:Amino Acid Sequence; D002725:Chloroform; D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D010456:Peptides, Cyclic; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D010456:Peptides, Cyclic; C006963:chlamydocin; D002725:Chloroform