Peptide Structures of the Alamethicin Sequence: The C‐Terminal α/310 Helical Nonapeptide and Two Pentapeptides with Opposite 310 Helicity

A natural oligopeptide with α‐aminoisobutyric acid residues (Aib), which reduce the conformation space, is alamethicin. This icosapeptide antibiotic, as an ionophoric, membrane pore former, is a model compound for the excitability of nerve membranes. Interesting helical structures have now been discovered in the synthetic segments of such compounds: thus, 2 forms a right‐handed 310 helix; in contrast, 1 forms a left‐handed 310 helix! Previously, only one other 3 helix was known. equation image