Septocylindrins A and B:  Peptaibols Produced by the Terrestrial Fungus <i>S</i><i>eptocylindrium</i> sp. LL-Z1518^⊥

Two new peptaibols, septocylindrin A (<b>1</b>) and septocylindrin B (<b>2</b>), related to the well-studied membrane-channel-forming peptaibol alamethicin, were obtained from a terrestrial isolate of the fungus <i>Septocylindrium</i> sp. Both <b>1</b> and <b>2</b> 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 <b>1</b> contains Glu and <b>2</b> contains Gln. The structures of these two peptaibols were determined by extensive NMR and HRMS analysis. The absolute configurations of amino acids present in <b>1</b> were determined using Marfey's methodology. Both compounds were isolated through bioassay-guided fractionation and exhibited significant antibacterial and antifungal activity.