Septocylindrins A and B:  Peptaibols Produced by the Terrestrial Fungus Septocylindrium sp. LL-Z1518

Two new peptaibols, septocylindrin A (1) and septocylindrin B (2), related to the well-studied membrane-channel-forming peptaibol alamethicin, were obtained from a terrestrial isolate of the fungus Septocylindrium sp. Both 1 and 2 are linear 19-amino acid peptides with a modified phenylalanine C-terminus. Analysis of the HRMS data indicated that they differ only in the 18th residue, where 1 contains Glu and 2 contains Gln. The structures of these two peptaibols were determined by extensive NMR and HRMS analysis. The absolute configurations of amino acids present in 1 were determined using Marfey's methodology. Both compounds were isolated through bioassay-guided fractionation and exhibited significant antibacterial and antifungal activity.