Spectroscopically labeled peptaibiotic analogs: the 4-nitrophenylalanine infrared absorption probe inserted at different positions into trichogin GA IV

A set of three analogs of the 10-residue, membrane-active lipopeptaibiotic trichogin GA IV, labeled with the promising 4-nitrophenylalanine IR absorption probe for local polarity, was synthesized by the solid-phase methodology, chromatographically purified, and extensively characterized. A single residue modification was inserted near the N-terminus, in the central region, or at the C-terminus. A solution conformational analysis, carried out by FT-IR absorption, CD, and 2D-NMR combined with molecular dynamics calculations, indicates that the mono-labeled analogs maintain the overall helical properties of the parent compound. Membrane permeabilization measurements and antimicrobial tests revealed that they possess membrane-modifying properties and in vitro antibacterial activities analogous to those of the natural lipopeptaibiotic. Our IR absorption and attenuated total reflectance investigations in various environments, from which water was excluded for solubility reasons, showed that the 1350 cm1 4-nitrobenzyl band is a reporter group of rather limited sensitivity.