Peptaibol antibiotics: Conformational preferences of synthetic emerimicin fragments

Abstract

Abstract The ir absorption and CD conformational analyses of solutions of the protected 2–9 fragment of the peptaibol antibiotics emerimicins III and IV \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} (Aib_3 \rlap{--} )L - Val - Gly - L - Leu\rlap{--} (Aib_2 \rlap{--} ) $\end{document} and related short sequences are consistent with the presence of a right‐handed α‐helix for the octapeptide, while the tri‐, tetra‐, and pentapeptides adopt a 3 10 ‐helix, either right‐ or left‐handed, depending on the amino acid sequences. The structural preferences of solid‐state \documentclass{article}\pagestyle{empty}\begin{document}$ Z\rlap{--} (Aib_3 \rlap{--} )L - Val - OMe $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ Z\rlap{--} (Aib_3 \rlap{--} )L - Val - Gly - OMe $\end{document} have been determined by x‐ray diffraction. In accord with the solution data, incipient 3 10 ‐helices, formed by two and three β‐turns, have been found for the tetra‐ and pentapeptides, respectively. The tetrapeptide helix has the left‐handed screw sense, while that of the pentapetide is right‐handed, thus confirming the conclusions of the CD analysis of the solution.