Cyclo(-Phe-Trp)

A metabolomics/peptidomics and genomics approach, using UPLC-MSE, molecular networking, and genome mining, was used to describe the serrawettin W2 lipopeptide family produced by Serratia marcescens NP2. Seven known serrawettin W2 analogues were structurally elucidated along with 17 new analogues, which varied based on the first (fatty acyl length of C8, C10, C12, or C12:1), fifth (Phe, Tyr, Trp, or Leu/Ile), and sixth (Leu, Ile, or Val) residues. Tandem MS results suggested that the previously classified serrawettin W3 may be an analogue of serrawettin W2, with a putative structure of cyclo(C10H18O2-Leu-Ser-Thr-Leu/Ile-Val). Chiral phase amino acid analysis enabled the distinction between l/d-Leu and l-Ile residues within nine purified compounds. 1H and 13C NMR analyses confirmed the structures of four purified new analogues. Additionally, genome mining was conducted using Serratia genome sequences available on the NCBI database to identify the swrA gene using the antiSMASH software. NRPSpredictor2 predicted the specificity score of the adenylation-domain within swrA with 100% for the first, second, and third modules (Leu-Ser-Thr), 60-70% for the fourth module (Phe/Trp/Tyr/Val), and 70% for the fifth module (Val/Leu/Ile), confirming MSE data. Finally, antibacterial activity was observed for compounds 6 and 11 against a clinical Enterococcus faecium strain.

Urotensin II (U-II) has been known for over 30 years as an important teleost fish hormone, but only recently has it been recognized as the endogenous ligand of a new human G-protein-coupled receptor (GPCR) homologous to the GPR14 orphan receptor from rat. Human U-II was found to be a potent vasoconstrictor, widely distributed in human tissues, possibly contributing to several human cardiovascular diseases. It thus has become a major target of medicinal chemistry research. The common structural feature of U-II peptides from different species is the C-terminal portion, characterized by the disulfide bridged cyclic hexapeptide Cys-Phe-Trp-Lys-Tyr-Cys. The few structure-activity relationship studies reported to date attributed a critical role to this portion, with the Trp-Lys-Tyr motif appearing as the key determinant of U-II bioactivity. Consequently, this shorter cyclic peptide was used as a template for the development of several synthetic analogues, among which a superagonist, termed P5U: H-Asp-cyclo(Pen-Phe-Trp-Lys-Tyr-Cys)-Val-OH. Conformational studies confirmed the important role of hU-II C-terminal cyclic portion, enabling the development of 3D pharmacophore models. These findings should lead to the design of new, potent and selective analogues, acting as agonist or antagonist at the human U-II receptor, finally contributing to a deeper comprehension of the (patho)physiological significance of this peptide.

Cyclic hexapeptide analogues representing the modified retro sequence of the amino acid residues 7-11 of natural somatostatin are known to protect liver cells from phalloidin poisoning. To determine the influence of steric, lipophilic, and charge effects on (a) the conformation of the backbone and the aromatic side chains and (b) the biological response, the side chains of Phe2, Lys4, and Phe6 of cyclo(-D-Pro1-Phe2-Thr3-Lys(Z)4-Trp5-Phe6-), 1a, one of the most active peptides found so far, were modified by various residues. The discussion of conformationally relevant parameters proves that neither backbone conformations nor populations of aromatic side chain rotamers were altered by these substitutions. The potency of these derivatives in a cytoprotection assay varies by at most one order of magnitude (more or less active than the parent peptide 1a). A qualitative evaluation of lipophilic, steric, and charge effects reveals the dominance of lipophilic effects of aromatic residues; the most potent compounds contain aromatic substructures in the side chain of Lys4.