Peptaibolin

In this study, we investigate the effect of nine noncanonical α,α-dialkyl glycines on the structure, dynamics, and membrane permeation properties of a small peptaibol, peptaibolin. The noncanonical amino acids under study are Aib (α-amino isobutyric acid), Deg (α,α-diethyl glycine), Dpg (α,α-dipropyl glycine), Dibg (α,α-di-isobutyl glycine), Dhg (α,α-dihexyl glycine), DΦg (α,α-diphenyl glycine), Db(z)g (α,α-dibenzyl glycine), Ac6c (α,α-cyclohexyl glycine), and Dmg (α,α-dihydroxymethyl glycine). It is hypothesized that these amino acids are able to induce well-defined secondary structures in peptidomimetics. To investigate this hypothesis, we designed new peptaibolin peptidomimetics by replacing the native Aib positions with a new α,α-dialkyl glycine. We show that Dhg and Ac6c noncanonical amino acids are able to induce α-helix secondary structures of peptaibolin in water, which are not present in the native structure. We also demonstrate that the α,α-dialkyl glycines increase the membrane permeability of peptaibolin in 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) membranes. However, there is no apparent correlation between increased helicity and membrane permeability. In summary, we show that some α,α-dialkyl glycines under study induce the formation of α-helix secondary structures in peptaibolin and promote spontaneous membrane permeation. Our findings increase the knowledge of the membrane permeability and folding of peptides incorporating α,α-dialkyl glycines.

An automated approach to peptaibols using microwave-assisted solid-phase peptide synthesis is demonstrated with a combination of HBTU and acid fluoride mediated couplings for normal and alpha,alpha-dialkylated amino acids, respectively. The method is utilized for the automated synthesis of several full-length peptaibols, including alamethicin, tylopeptin, ampullosporin, bergofungin, cervinin, trikoningin, trichogin, and peptaibolin, reducing both synthesis time and costs significantly as compared to other approaches. Furthermore, the use of noncommercially available reagents is minimized.

Fungal species of genus Sepedonium are rich sources of diverse secondary metabolites (e.g., alkaloids, peptaibols), which exhibit variable biological activities. Herein, two new peptaibols, named ampullosporin F (1) and ampullosporin G (2), together with five known compounds, ampullosporin A (3), peptaibolin (4), chrysosporide (5), c(Trp-Ser) (6) and c(Trp-Ala) (7), have been isolated from the culture of Sepedonium ampullosporum Damon strain KSH534. The structures of 1 and 2 were elucidated based on ESI-HRMSn experiments and intense 1D and 2D NMR analyses. The sequence of ampullosporin F (1) was determined to be Ac-Trp1-Ala2-Aib3-Aib4-Leu5-Aib6-Gln7-Aib8-Aib9-Aib10-GluOMe11-Leu12-Aib13-Gln14-Leuol15, while ampullosporin G (2) differs from 1 by exchanging the position of Gln7 with GluOMe11. Furthermore, the total synthesis of 1 and 2 was carried out on solid-phase to confirm the absolute configuration of all chiral amino acids as L. In addition, ampullosporin F (1) and G (2) showed significant antifungal activity against B. cinerea and P. infestans, but were inactive against S. tritici. Cell viability assays using human prostate (PC-3) and colorectal (HT-29) cancer cells confirmed potent anticancer activities of 1 and 2. Furthermore, a molecular docking study was performed in silico as an attempt to explain the structure-activity correlation of the characteristic ampullosporins (1-3).