Synthesis, preferred conformation, and membrane activity of medium-length peptaibiotics: tylopeptin B.

The solid-phase synthesis and full chemical characterization of the medium-length (14-amino acid residues) peptaibol with antibiotic properties of tylopeptin B, originally extracted from the fruiting body of the mushroom Tylopilus neofelleus, are described. These data are accompanied by the results on the solution-phase synthesis via the segment condensation approach of a selected, side-chain protected, analog. A solution conformational analysis, performed by the combined use of FTIR absorption, circular dichroism, and 2D-NMR (the latter technique coupled to molecular dynamics calculations), favors the conclusion that the 3D-structure of tylopeptin B is largely helical with a preference for the alpha- or the 3(10)-helix type depending upon the nature of the solvent. Helix topology and (partial) amphiphilic character are responsible for the observed membrane-modifying properties of this peptaibiotic.