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Cystine peptides. Spectroscopic studies on the conformations of a cyclic pentapeptide disulfide

R. Kishore, S. Raghothama, P. Balaram

Open publisher page 5 citations

Abstract

The model cyclic pentapeptide disulfide Boc‐Cys‐Ala‐Aib‐Gly‐Cys‐NHMe 1, has been synthesized. 1H n.m.r. studies in (CD3)2SO and CDCl3‐(CD3)2SO mixtures establish the solvent exposed nature of the Cys(l) and Aib NH groups, while a moderate degree of shielding is observed for the other four NH groups. Nuclear Overhauser effects between Cα1H and Ni+1H protons provide evidence for extended or semi‐extended conformations (ø ± 130° ± 30°) at the Cys(l), Ala(2), Gly(4) and Cys(5) residues. The n.m.r. results are supportive of an intramolecular antiparallel β‐sheet conformation at these residues, nucleated by a γ‐turn centered at Aib(3). This conformation is not stabilized by strong transannular hydrogen bonds. CD studies establish solvent dependent structural changes of the disulfide linkage in methanol‐dioxane mixtures. An unusual CD pattern is observed for the peptide chromophore.

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What this paper is about

The model cyclic pentapeptide disulfide Boc‐Cys‐Ala‐Aib‐Gly‐Cys‐NHMe 1, has been synthesized. 1H n.m.r. studies in (CD3)2SO and CDCl3‐(CD3)2SO mixtures establish the solvent exposed nature of the Cys(l) and Aib NH groups, while a moderate degree of shielding is observed for the other four NH groups. Nuclear Overhauser effects between Cα1H and Ni+1H protons provide evidence for extended or semi‐extended conformations (ø ± 130° ± 30°) at the Cys(l), Ala(2), Gly(4) and Cys(5) residues. The n.m.r. results are supportive of an intramolecular antiparallel β‐sheet conformation at these residues, nucleated by a γ‐turn centered at Aib(3). This conformation is not stabilized by strong transannular hydrogen bonds. CD studies establish solvent dependent structural changes of the disulfide linkage in methanol‐dioxane mixtures. An unusual CD pattern is observed for the peptide chromophore.

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Available abstract

The model cyclic pentapeptide disulfide Boc‐Cys‐Ala‐Aib‐Gly‐Cys‐NHMe 1, has been synthesized. 1H n.m.r. studies in (CD3)2SO and CDCl3‐(CD3)2SO mixtures establish the solvent exposed nature of the Cys(l) and Aib NH groups, while a moderate degree of shielding is observed for the other four NH groups. Nuclear Overhauser effects between Cα1H and Ni+1H protons provide evidence for extended or semi‐extended conformations (ø ± 130° ± 30°) at the Cys(l), Ala(2), Gly(4) and Cys(5) residues. The n.m.r. results are supportive of an intramolecular antiparallel β‐sheet conformation at these residues, nucleated by a γ‐turn centered at Aib(3). This conformation is not stabilized by strong transannular hydrogen bonds. CD studies establish solvent dependent structural changes of the disulfide linkage in methanol‐dioxane mixtures. An unusual CD pattern is observed for the peptide chromophore.

Key concepts: Chemistry, Pentapeptide repeat, Antiparallel (mathematics), Intramolecular force, Peptide, Stereochemistry, Cysteine, Cyclic peptide

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