Conformational investigation of α,β-dehydropeptides VII*. Conformation of Ac-Pro-ΔAla-NHCH3 and Ac-Pro-(E)-ΔAbu-NHCH3: comparison with (Z)-substituted α,β-dehydropeptides† |
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Authors: | C PIETRZYASKI B RZESZOTARSKA E CISZAK M LISOWSKI Z KUBICA G BOUSSARD |
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Institution: | C. PIETRZY?ASKI,B. RZESZOTARSKA,E. CISZAK,M. LISOWSKI,Z. KUBICA,G. BOUSSARD |
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Abstract: | The crystal structure and solution conformation of Ac-Pro-ΔAla-NHCH3 and the solution conformation of Ac-Pro-(E)-ΔAbu-NHCH3 were investigated by X-ray diffraction method and NMR, FTIR and CD spectroscopies. Ac-Pro-ΔAla-NHCH, adopts an extended-coil conformation in the crystalline state, with all-trans peptide bonds and the ΔAla residue being in a C5 form, φ1=– 71.4(4), ψ1=– 16.8(4), φ2=– 178.4(3) and ψ2= 172.4(3)°. In inert solvents the peptide also assumes the C5 conformation, but a γ-turn on the Pro residue cannot be ruled out. In these solvents Ac-Pro-(E)- ΔAbu-NHCH3 accommodates a βII-turn, but a minor conformer with a nearly planar disposition of the CO—NH and C=C bonds (φ2~0°) is also present. Previous spectroscopic studies of the (Z)-substituted dehydropeptides Ac-Pro-(Z)- ΔAbu-NHCH, and Ac-Pro-ΔVal-NHCH3 reveal that both peptides prefer a βII-turn in solution. Comparison of conformations in the family of four Ac-Pro-ΔXaa-NHCH3 peptides let us formulate the following order of their tendency to adopt a β-turn in solution: (Z)- ΔAbu > (E)- δAbu > ΔVal; ΔAla does not. None of the folded structures formed by the four compounds is stable in strongly solvating media. © Munksgaard 1996. |
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Keywords: | circular dichroism C5 conformation crystal structure dehydroalanine β -dehydrobutyrine β -dehydropeptide conformation infrared spectroscopy nuclear magnetic resonance β -turn |
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