Spermidine as a potential biosynthetic precursor to the 1,5-diazabicyclo[4:3:o]nonene residue in the efrapeptins

Conformational properties of secondary amino acids: replacement of pipecolic acid by N-methyl-l-alanine in efrapeptin C

The efrapeptins, a family of naturally occurring peptides with inhibitory activities against ATPases, contain several α,α-disubstituted α-amino acids such as α-aminoisobutyric acid (Aib) or isovaline (Iva) besides pipecolic acid (Pip), β-Ala, Leu, Gly, and a C-terminal heterocyclic residue. Secondary α-amino acids such as proline are known to stabilize discrete conformations in peptides. A similar influence is ascribed to N-alkyl α-amino acids. We synthesized two efrapeptin C analogs with replacement of Pip by N-methyl-L-alanine (MeAla) using a combination of solid- and solution-phase techniques in a fragment-condensation strategy to compare the conformational bias of both secondary amino acids. The solution conformation was investigated by vibrational circular dichroism (VCD) to probe whether the analogs adopt a 310 -helical conformation. The MeAla-containing analogs [MeAla(1,3) ]efrapeptin C and [MeAla(1,3,11) ]efrapeptin C inhibit ATP hydrolysis by the A3 B3 complex of A1 A0 -ATP synthase from Methanosarcina mazei Gö1.

Synthesis, and structural and biological studies of efrapeptin C analogues

A series of analogues of efrapeptin C (1), with variations in the central tripeptide epitope (positions 6-8), were prepared by a combination of solid- and solution-phase peptide syntheses. The conformations of the modified compounds 2-6 were investigated by circular-dichroism (CD) spectroscopy to differentiate between 3(10)- and alpha-helical secondary structures. The inhibitory activities of the new compounds towards F(1)-ATPase from E. coli were determined. The modified congeners 3-5 were less active by one order of magnitude compared to 1 (K(i) 10 microM), and 6 was completely inactive. Our experiments demonstrate that the flexible, central tripeptide epitope, comprising positions 6-8 in 1, is crucial for molecular recognition, even slight sequence modifications being hardly tolerated.

New Sequences, Constituents, and Producers of Peptaibiotics: An Updated Review

To date, 18 genera of imperfect and ascomycetous fungi have been recognized to produce ca. 700 individual sequences of peptaibiotics. These are linear polypeptide antibiotics which i) have a molecular weight between 500 and 2,200 Dalton, thus containing 5-21 residues; ii) show a high content of alpha-aminoisobutyric acid; iii) are characterized by the presence of other nonproteinogenic amino acids and/or lipoamino acids; iv) possess an acylated N-terminus, and v) have a C-terminal residue that, in most of them, consists of a free or acetylated amide-bonded 1,2-amino alcohol, but might also be an amine, amide, free amino acid, 2,5-dioxopiperazine, or sugar alcohol. From April 2003 until present, ca. 300 new individual sequences of peptaibiotics have been published in the literature, but most of them have not yet been included in databases. To summarize these new sequences and novel constituents, as well as to introduce fungal species hitherto unknown as producers of peptaibiotics, the relevant literature is reviewed. Furthermore, ecophysiological and taxonomic aspects of the producing fungi are discussed.