Conformational investigation of alpha,beta-dehydropeptides. VII. Conformation of Ac-Pro-deltaAla-NHCH3 and Ac-Pro-(E)-deltaAbu-NHCH3: comparison with (Z)-substituted alpha,beta-dehydropeptides.
The crystal structure and solution conformation of Ac-Pro-deltaAla-NHCH3 and the solution conformation of Ac-Pro-(E)-deltaAbu-NHCH3 were investigated by X-ray diffraction method and NMR, FTIR and CD spectroscopies. Ac-Pro-deltaAla-NHCH3 adopts an extended-coil conformation in the crystalline state, with all-trans peptide bonds and the deltaAla residue being in a C5 form, phi(1)=-71.4(4), psi(1)=-16.8(4), phi(2)= -178.4(3) and psi(2)= 172.4(3) degrees. In inert solvents the peptide also assumes the C5 conformation, but a gamma-turn on the Pro residue cannot be ruled out. In these solvents Ac-Pro-(E)-deltaAbu-NHCH3 accommodates a beta(II)-turn, but a minor conformer with a nearly planar disposition of the CO-NH and C=C bonds (phi(2) approximately 0 degrees) is also present. Previous spectroscopic studies of the (Z)-substituted dehydropeptides Ac-Pro-(Z)-deltaAbu-NHCH3 and Ac-Pro-deltaVal-NHCH3 reveal that both peptides prefer a beta(II)-turn in solution. Comparison of conformations in the family of four Ac-Pro-deltaXaa-NHCH3 peptides let us formulate the following order of their tendency to adopt a beta-turn in solution: (Z)-deltaAbu > (E)-deltaAbu > deltaVal; deltaAla does not. None of the folded structures formed by the four compounds is stable in strongly solvating media.
Pietrzyński
G
G
Department of Organic Chemistry, University of Opole, Poland. gp@uni.opole.pl
Rzeszotarska
B
B
Ciszak
E
E
Lisowski
M
M
Kubica
Z
Z
Boussard
G
G
D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry; D002942:Circular Dichroism; D004151:Dipeptides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D011392:Proline / Q000737:chemistry; D017433:Protein Structure, Secondary; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D004151:Dipeptides; D012997:Solvents; C015102:dehydroalanine; D011392:Proline; D000409:Alanine