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The N‐Terminal Nonapeptide of Cephaibols A and C: A Naturally Occurring Example of Mismatched Helical Screw‐Sense Control
Author(s) -
Orcel Ugo,
De Poli Matteo,
De Zotti Marta,
Clayden Jonathan
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201302648
Subject(s) - diastereomer , stereochemistry , conformational isomerism , residue (chemistry) , peptide , chemistry , circular dichroism , terminal (telecommunication) , nuclear magnetic resonance spectroscopy , right handed , pentapeptide repeat , crystallography , physics , molecule , biochemistry , organic chemistry , telecommunications , computer science , nuclear physics , neutrino
The N‐terminal nonapeptide domain of the fungal nonribosomal peptide antibiotics cephaibol A and cephaibol C (AcPheAib 4 LeuIvaGly‐ Aib) is reported to adopt a right‐handed helical conformation in the crystalline state. However, this conformation is at odds with the left‐handed helicity observed in solution in related synthetic oligomers capped with Ac‐ L ‐PheAib 4 fragments. We report the synthesis of four diastereoisomers of the cephaibol N‐terminal nonapeptide, and show by NMR and CD spectroscopy that the peptide containing the chiral amino acids Phe and Leu in the naturally occurring relative configuration exists in solution as an interconverting mixture of helical screw‐sense conformers. In contrast, the nonapeptide containing the unnatural relative configuration at Phe and Leu adopts a single, stable helical screw‐sense, which is left handed when the N‐terminal Phe residue is L and right‐handed when the N‐terminal Phe residue is D .