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Multiple conformational equilibria of cyclic octapeptide, cyclo (L-Pro-Sar)4 in solution
International Journal of Peptide and Protein Research
|August 1, 1983
Summary
Cyclo(L-Pro-Sar)4, a cyclic octapeptide, exhibits dynamic conformational changes in solution that are highly dependent on solvent polarity. Nuclear magnetic resonance (NMR) spectroscopy revealed distinct ensembles of conformers in chloroform, acetonitrile, and dimethyl sulfoxide.
Area of Science:
- Biochemistry
- Chemical Physics
- Organic Chemistry
Background:
- Cyclic peptides, particularly those composed of N-substituted amino acids, present unique conformational challenges.
- Understanding the solution behavior of synthetic peptides like Cyclo(L-Pro-Sar)4 is crucial for designing novel peptidomimetics.
Purpose of the Study:
- To investigate the conformational landscape of the synthetic cyclic octapeptide Cyclo(L-Pro-Sar)4 in various solvents.
- To elucidate the influence of solvent polarity on the conformational equilibria of this N-substituted cyclic peptide.
Main Methods:
- 1H- and 13C-nuclear magnetic resonance (NMR) spectroscopy were employed to study the peptide in different solvents.
- Conformational analysis was performed by analyzing NMR data to identify and quantify interconverting conformers.
Main Results:
- Multiple conformational equilibria were observed for Cyclo(L-Pro-Sar)4, varying significantly with solvent polarity.
- In chloroform (CDCl3), three conformers (one C4-symmetric, two C2-symmetric) were identified.
- In acetonitrile (CD3CN), a mixture of three C2-symmetric and one asymmetric conformer was detected, while dimethyl sulfoxide (Me2SO-d6) favored a single C2-symmetric conformer.
Conclusions:
- The conformational behavior of Cyclo(L-Pro-Sar)4 is highly sensitive to the surrounding solvent environment.
- NMR spectroscopy provides powerful insights into the dynamic conformational equilibria of complex cyclic peptides in solution.
- Specific peptide bond configurations (trans/cis) were proposed for predominant conformers in different solvents, highlighting the structural plasticity of this octapeptide.