Crystallographic structure of a helical lipopeptaibol antibiotic analogue

An X-ray diffraction analysis of the [Fmoc(0), TOAC(4,8), Leu-OMe11] analogue of the lipopeptaibol antibiotic trichogin A IV shows that the undecapeptide is folded in a right-handed, mixed alpha/3(10)-helix. The helical molecules are connected in a head-to-tail arrangement along the b-axis through C=O ... H-N intermolecular H-bonding. This packing mode generates a hydrophobic cavity where the Fmoc N-alpha-protecting groups are accommodated. The distances and angles between the nitroxide groups of the two TOAC residues, separated by one turn of the alpha-helix, have been determined.