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Abstract:The deprotection step is crucial in order to secure a good quality product in Fmoc solid phase peptide synthesis. 9-Fluorenylmethoxycarbonyl (Fmoc) removal is achieved by a two-step mechanism reaction favored by the use of cyclic secondary amines; however, the efficiency of the reaction could be affected by side reactions and by-product formation. Several aspects have to be taken into consideration when selecting a deprotection reagent: its physicochemical behavior, basicity (pKa) and polarity, concentration, and time of reaction, toxicity and disposability of residues and, finally, availability of reagents. This report presents a comparison of the performance of three strategies for deprotection using microwave-assisted Fmoc peptide synthesis. Four peptide sequences were synthesized using Rink amide resin with a Liberty Blue™ automated synthesizer and 4-methylpiperidine (4MP), piperidine (PP), and piperazine (PZ) as Fmoc removal reagents. In the first instance all three reagents behaved similarly. A detailed analysis showed a correlation between the hydrophobicity and size of the peptide with the yield and purity of the obtained product. The three reagents are interchangeable, and replacement of piperidine could be advantageous regarding toxicity and reagent handling.

The outburst of microbial resistance to antibiotics creates the need for new sources of active compounds for the treatment of pathogenic microorganisms. Marine microalgae are of particular interest in this context because they have developed tolerance and defense strategies to resist the exposure to pathogenic bacteria, viruses, and fungi in the aquatic environment. Although antimicrobial activities have been reported for some microalgae, natural algal bioactive peptides have not been described yet. In this work, acid extracts from the microalga Tetraselmis suecica with antibacterial activity were analyzed, and de novo sequences of peptides were determined. Synthetic peptides and their alanine and lysine analogs allowed identifying key residues and increasing their antibacterial activity. Additionally, it was determined that the localization of positive charges within the peptide sequence influences the secondary structure with tendency to form an alpha helical structure.

Cyanobacteria and microalgae are oxygen-producing photosynthetic unicellular organisms encompassing a great diversity of species, which are able to grow under all types of extreme environments and exposed to a wide variety of predators and microbial pathogens. The antibacterial compounds described for these organisms include alkaloids, fatty acids, indoles, macrolides, peptides, phenols, pigments and terpenes, among others. This review presents an overview of antibacterial peptides isolated from cyanobacteria and microalgae, as well as their synergism and mechanisms of action described so far. Antibacterial cyanopeptides belong to different orders, but mainly from Oscillatoriales and Nostocales. Cyanopeptides have different structures but are mainly cyclic peptides. This vast peptide repertoire includes ribosomal and abundant non-ribosomal peptides, evaluated by standard conventional methodologies against pathogenic Gram-negative and Gram-positive bacteria. The antibacterial activity described for microalgal peptides is considerably scarcer, and limited to protein hydrolysates from two Chlorella species, and few peptides from Tetraselmis suecica. Despite the promising applications of antibacterial peptides and the importance of searching for new natural sources of antibiotics, limitations still persist for their pharmaceutical applications.

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The objectives of this experiment were to (i) determine the efficacy of essential oils of clove (CO) and Lippia alba (EOLA) to induce deep anaesthesia in juvenile specimens (49.0 AE 6.2 g body mass, 16.6 AE 0.8 cm; n = 8 per treatment) of meagre (Argyrosomus regius); and (ii) study the feasibility of these substances, together with 2-phenoxyethanol (2-PHE), as potential sedatives [low concentration: (i) EOLA: 12 mg L À1 ; (ii) CO: 1 mg L À1 ; and (iii) 2-PHE: 33 mgÁL À1 ; n = 8 per treatment] for live fish transport of this species. All test were performed at a constant temperature (18°C). Thus, the main primary stress indicator (plasma cortisol) and secondary factors (plasma metabolites) were evaluated. In addition, growth hormone (GH) mRNA expression was also evaluated in the pituitary gland. The results indicated that EOLA is considered to be effective for deep anaesthesia when the concentration is close to 160 mg L À1 , while CO produces the same effect when lower concentrations are added (40-50 mg L À1 ). Regarding sedative concentrations, a significant~3-fold increase in plasma cortisol levels was detected in the EOLA group when compared to control specimens. In addition, glucose levels were not reduced and significantly increased (~1.6-fold) for 2-PHE in relation to the control fish. None of the anaesthetics promoted a significant difference for GH expression with respect to the control group, but a significant~2-fold increase for 2-PHE treatment with respect to the EOLA exposition was found in this gene expression. Results show that none of the anaesthetics analysed, at least in the ranges of concentrations used in this study (EOLA 12 mg L À1 , CO 1 mg L À1 , 2-PHE 33 mg L À1 ), are recommended for live fish transport, as shown by the absence of inhibition on the stress parameters assessed.