Lipopeptaibol metabolites of Tolypocladium geodes:: Total synthesis, preferred conformation, and membrane activity

We have synthesized by solution methods and characterized the lipopeptaibol metabolite LP237-F8 extracted from the fungus Tolypocladium geodes and five selected analogues with the Etn --> Aib or Etn --> Nva replacement at position 8 and/or a triple Gln --> Glu(OMe) replacement at positions 516, and 9 (Etn = Calpha-ethylnorvaline, Aib = alpha-aminoisobutyric acid, Nva = norvaline). Conformation analysis, performed by FT-IR absorption, NMR, and CD techniques, strongly supports the view that the six terminally blocked decapeptides are highly helical in solution. Helix topology and amphiphilic character are responsible for their remarkable membrane activity. At position 8 the combination of high hydrophobicity and Ca tetrasubstitution, as in the Etn-containing LP237-F8 metabolite, has a positive effect on membrane interaction.