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Although cyclic peptide structures are usually investigated as highly constrained scaffolds, cyclic antimicrobial peptides of natural origin often feature flexible residues. Hereby we report our findings concerning a structure-activity study conducted on a model sequence by replacing a glycine residue with a variety of flexible residues (i.e. ω-amino and α,ω-diamino acids). The resulting library has been tested for antimicrobial activity against a wide range of clinically relevant pathogens as well as for toxicity to red blood cells. Circular dichroism and molecular modelling have been used to study changes in conformation. Increments as high as 16-fold in antimicrobial activity (as effective as lipidation) and >2-fold in haemolytic EC 50 values were observed. Interestingly, secondary structures can be stabilized by increasing, rather than decreasing, ring flexibility. [ABSTRACT FROM AUTHOR]

A convenient strategy for the on-resin synthesis of macrocyclic peptides (3- to 13-mers) via intramolecular halide substitution by a diamino acid is described. The method is compatible with standard Fmoc/tBu SPPS and affords a tail-to-side-chain macrocyclic peptide featuring an endocyclic secondary amine. This functional group is still reactive toward acylation, allowing for the continuation of the synthesis. An application to the synthesis of lipidated cyclic and bicyclic antimicrobial peptides is presented. [ABSTRACT FROM AUTHOR]

Abstract: The UDP-3-O-[(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase (LpxC) is a promising target for the development of novel antibiotic substances against multidrug-resistant Gram-negative bacteria. The C-aryl glycoside 3 was designed as conformationally constrained analogue of the potent LpxC-inhibitor CHIR-090. The chiral pool synthesis of 3 started with d-mannose. The C-aryl glycoside 8 was synthesized stereoselectively by nucleophilic attack of 4-iodine-substituted phenyllithium and subsequent reduction with Et3SiH. The ester 10 was obtained in a one-pot diol cleavage, CrO3 oxidation, and esterification. A Sonogashira reaction of the aryl iodide 11 led to the alkyne 17 which was transformed with H2NOH into the hydroxamic acid 3. [Copyright &y& Elsevier]

Multidrug-resistant bacteria are a global health problem. One of the last-resort antibiotics against Gram-negative bacteria is the cyclic lipopeptide colistin, displaying a flexible linker with a fatty acid moiety. The aim of the present project was to investigate the effect on antimicrobial activity of introducing fatty acid moieties of different lengths and in different positions in a cyclic peptide, S3(B), containing a flexible linker. The lipidated analogues of S3(B) were synthesized by 9-fluorenylmethoxycarbonyl (Fmoc) solid-phase peptide synthesis. Following assembly of the linear peptide by Fmoc solid-phase peptide synthesis, on-resin head-to-tail cyclization and fatty acid acylation were performed. The antimicrobial activity was determined against the ESKAPE pathogens, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli. Furthermore, hemolytic activity was determined against human erythrocytes. A total of 18 cyclic lipopeptides were synthesized and characterized. It was found that introduction of fatty acids in positions next to the flexible linker was more strongly linked to antimicrobial activity. The fatty acid length altered the overall hydrophobicity, which was the driving force for both high antimicrobial and hemolytic activity. Peptides became highly hemolytic when carbon-chain length exceeded 10 (i.e., C10), overlapping with the optimum for antimicrobial activity (i.e., C8–C12). The most promising candidate (C8)5 showed antimicrobial activity corresponding to that of S3(B), but with an improved hemolytic profile. Finally, (C8)5 was further investigated in a time-kill experiment. [ABSTRACT FROM AUTHOR]

Preliminary data on age, growth and diet of bluespotted cornetfish Fistularia commersonii Rüppell, 1838 (Fistulariidae) in the central Mediterranean Sea are provided. In the study area, this invasive Lessepsian fish showed piscivorous behaviour, focusing mainly on labrids, clupeids and sparids. Prey composition suggests that bluespotted cornetfish explores various habitats for hunting. Prey fishes were mainly juveniles and their size showed positive correlation with predator size. Estimated by vertebrae readings, ages of bluespotted cornetfish, having sizes from 73.0 to 107.5 cm total length, ranged from 2 to 4 years; these are the first estimates of age for this species. The parameters of von Bertalanffy growth curves were L∞ = 102.39 cm, k = 0.49 year-1, t0 = -0.57 years. The analysis of growth rates indicates that bluespotted cornetfish is a fast-growing species. Growth performance index was Φ' = 3.71, and weight-length relationship, W = 0.0001 x TL3.372 (R2 = 0.857), described positive allometric growth of F. commersonii. [ABSTRACT FROM AUTHOR]

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper. [ABSTRACT FROM AUTHOR]

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) constitutes an emerging health problem for companion animals in veterinary medicine. Therefore, discovery of novel antimicrobial agents for treatment of Staphylococcus-associated canine infections is urgently needed to reduce use of human antibiotics in veterinary medicine. In the present work, we characterized the antimicrobial activity of the peptoid D2 against S. pseudintermedius and Pseudomonas aeruginosa, which is another common integumentary pathogen in dogs. Furthermore, we performed a structure–activity relationship study of D2, which included 19 peptide/peptoid analogs. Our best compound D2D, an all d-peptide analogue, showed potent minimum inhibitory concentrations (MICs) against canine S. pseudintermedius (2–4 µg/mL) and P. aeruginosa (4 µg/mL) isolates as well as other selected dog pathogens (2–16 µg/mL). Time–kill assays demonstrated that D2D was able to inhibit MRSP in 30 min at 1× MIC, significantly faster than D2. Our results suggest that at high concentrations D2D is rapidly lysing the bacterial membrane while D2 is inhibiting macromolecular synthesis. We probed the mechanism of action at sub-MIC concentrations of D2, D2D, the l-peptide analog and its retro analog by a macromolecular biosynthesis assay and fluorescence spectroscopy. Our data suggest that at sub-MIC concentrations D2D is membrane inactive and primarily works by cell wall inhibition, while the other compounds mainly act on the bacterial membrane. [ABSTRACT FROM AUTHOR]