Total synthesis of the natural, medium‐length, peptaibol pentadecaibin and study of the chemical features responsible for its membrane activity

Abstract

Peptaibols are naturally-occurring, antimicrobial peptides endowed with well-defined helical conformations and resistance to proteolysis. Both features stem from the presence in their sequence of several, C α -tetrasubstituted, α-aminoisobutyric acid (Aib) residues. Peptaibols interact with biological membranes, usually causing their leakage. All of the peptaibolmembrane interaction mechanisms proposed so far begin with peptide aggregation or accumulation. The long-length alamethicin, the most studied peptaibol, acts by forming pores in the membranes. Conversely, the carpet mechanism has been claimed for shortlength peptaibols, such as trichogin. The mechanism of medium-length peptaibols is far less studied and this is partly due to the difficulties of their synthesis. They are believed to perturb membrane permeability in different ways, depending on the membrane properties. The present work focuses on pentadecaibin, a recently discovered, medium-length peptaibol. In contrast to the majority of its family members, its sequence does not comprise hydroxyprolines or prolines, and its helix is not kinked. A reliable and effective synthesis procedure is described that allowed us to produce also two shorter analogs. By a combination of techniques, we were able to establish a 3D-structure-activity relationship. In particular, the membrane activity of pentadecaibin heavily depends on the presence of three consecutive Aib residues that are responsible for the clear, albeit modest, amphiphilic character of its helix. The shortest analog, devoid of two of these three Aib residues, preserves a well-defined helical conformation, but not its amphipathicity, and loses almost completely the ability to cause membrane leakage. We conclude that pentadecaibin amphiphilicity is probably needed for the peptide ability to perturb model membranes.

Synthesis, Conformational Analysis and Antitumor Activity of the Naturally Occurring Antimicrobial Medium-Length Peptaibol Pentadecaibin and Spin-Labeled Analogs Thereof

“…The synthesis strategy was optimized to obtain spin-labeled pentadecaibin analogs, containing the nitroxidebearing Toac residue, which replaces Aib 1 or Aib 11 . The main goal was to reduce byproduct formation and to shorten the production and purification procedures compared to previous strategies [39,45].…”

“…The synthesis of Toac-containing pentadecaibins foresees the use of unprotected sidechain Gln residues and the of TFFH to couple Toac, as described in the text, and the procedure is similar to that reported in [45]. Briefly, the manual solid phase peptide synthesis was carried out on a Phol-preloaded 2-chlorotrytil resin (loading: 0.4 mmol/g).…”

“…Still, three Aib residues in a row are present at its C-terminus (Table 1). We recently reported the synthesis and 3D structure analysis of the native sequence pentadecaibin [45]. The membrane-disrupting properties of peptaibols represent an attractive feature to target hyperproliferative diseases such as cancer.…”

“…Still, three Aib residues in a row are present at its C-terminus (Table 1). We recently reported the synthesis and 3D structure analysis of the native sequence pentadecaibin [45]. By building on the strategy reported there and on our past experience in the insertion of spin-labeled residues in peptides, we herein report the synthesis of two pentadecaibin analogs in which Aib residues at position 1 or 11 were replaced with Toac.…”

Uncovering the Effects of the Cultivation Condition on Different Forms of Peptaibol’s Emericellipsins Production from an Alkaliphilic Fungus, Emericellopsis alkalina

“…It is known that this group of non-ribosomal peptides is synthesized by micromycetes from the genera Trichoderma, Acremonium, Emericellopsis, and a few others. A producer normally synthesizes a complex of peptaibols, which are structurally homologous compounds that vary in their placement in the peptid chain by one or several amino acids, which also determines differences in bioactivity [15][16][17][18][19][20][21][22]. The discovery of Paib in micromycetes that inhabit cold and saline soils, sea depths, and other extreme environments expands opportunities for generating new antimicrobial drugs [23][24][25].…”