Currently, the search for new alternatives to conventional antibiotics to combat bacterial resistance is an urgent task, as many microorganisms threaten human health due to increasing bacterial resistance to traditional medicines. Thus, new molecules such as antimicrobial peptides have emerged as promising alternatives because of their low induction of resistance and broad spectrum of action. In this context, in the past few years, our research group has synthesized and characterized a peptide derived from the C-terminal region of the Lys⁴⁹ PLA₂-like BthTX-I, named p-BthTX-I. After several studies, the peptide (p-BthTX-I)₂K was proposed as the molecule with the most considerable biotechnological potential. As such, the present work aimed to evaluate whether the modifications made on the peptide (p-BthTX-I)₂K can be applied to other molecules originating from the C-terminal region of PLA₂-like Lys⁴⁹ from snake venoms. The peptides were obtained through the solid-phase peptide synthesis technique, and biochemical and functional characterization was carried out using dichroism techniques, mass spectrometry, antimicrobial activity against ESKAPE strains, hemolytic activity, and permeabilization of lipid vesicles. The antimicrobial activity of the peptides was promising, especially for the peptides (p-AppK)₂K and (p-ACL)₂K, which demonstrated activity against all strains that were tested, surpassing the model molecule (p-BthTX-I)₂K in most cases and maintaining low hemolytic activity. The modifications initially proposed for the (p-BthTX-I)₂K peptide were shown to apply to other peptides derived from Lys⁴⁹ PLA₂-like from snake venoms, showing promising results for antimicrobial activity. Future assays comparing the activity of the dimers obtained through this strategy with the monomers of these peptides should be carried out.

Polyalthic acid (PA) is a diterpene found in copaiba oil. As a continuation of our work with PA, we synthesized PA analogs and investigated their antibacterial effects on preformed biofilms of Staphylococcus epidermidis and determined the minimal inhibitory concentration (MIC) of the best analogs against planktonic bacterial cells. There was no difference in activity between the amides 2a and 2b and their corresponding amines 3a and 3b regarding their ability to eradicate biofilm. PA analogs 2a and 3a were able to significantly eradicate the preformed biofilm of S. epidermidis and were active against all the Gram-positive bacteria tested (Enterococcus faecalis, Enterococcus faecium, S. epidermidis, Staphylococcus aureus), with different MIC depending on the microorganism. Therefore, PA analogs 2a and 3a are of interest for further in vitro and in vivo testing to develop formulations for antibiotic drugs against Gram-positive bacteria.

Antimicrobial peptides such as Melittin exhibit potent broad-spectrum activity but are limited by high cytotoxicity. The rational design of bioinspired Melittin-derived analogues represents a promising strategy to reduce toxicity while maintaining antimicrobial efficacy. In this study, Melittin and analogues (TT-1, FKW, and WKW) were synthesized using solid-phase peptide synthesis (SPPS) and characterized for biological and biophysical essays. Antimicrobial and hemolytic activity, serum stability, secondary structure, and membrane interaction were analysed. FKW and WKW exhibited broad-spectrum antimicrobial activity, with minimum inhibitory concentration (MIC) as low as 8 and 16 µg/mL against Staphylococcus aureus and Enterococcus faecium. Both analogues also showed improved activity against Klebsiella pneumoniae (32 µg/mL) and Pseudomonas aeruginosa (128 and 256 µg/mL for FKW and WKW, respectively) compared to Melittin (64 and 512 µg/mL). In terms of cytotoxicity, FKW and WKW showed significantly reduced hemolytic activity, with HC₅₀ values of 264.8 µg/mL and 237.2 µg/mL, respectively, resulting in improved selectivity indexes relative to Melittin (HC₅₀ of 7.9 µg/mL). In liposomes, both adopt α-helical structures and cause disruption via pore formation or detergent-like mechanisms. TT-1 showed minimal toxicity but weak antimicrobial activity (MIC > 256 µg/mL). Although FKW and WKW exhibited limited serum stability (half-lives of 2.2 and 1.5 h), their degradation may reduce systemic toxicity. Overall, these analogues demonstrate an improved balance between antimicrobial activity and safety.

Background: Peptides are promising tools in medicine for viral, bacterial, and parasitic infections. MAP1 and MAP2 are peptides with antimicrobial activity. Aiming to increase selectivity, enhance antimicrobial activity, and reduce its cytotoxicity, two bioconjugates (GVL1-MAP2 and GVL1-MAP1) with the guanidine derivative group in the N-terminus position were synthesized. Methods: The peptides and bioconjugates were synthesized by SPPS. The biological activity and inhibition of the CPB enzyme were evaluated. Results: Antileishmanial activity was evaluated, and the bioconjugates exhibited higher activity in both the promastigote and amastigote forms than isolated GVL1 and peptides alone. Discussion: GVL1-MAP2 bioconjugate demonstrated not only the greatest activity against L. amazonensis in the promastigote (IC₅₀ = 3.2 μM) and amastigote (IC₅₀ = 0.6 μM) forms but also prevented the parasite from infecting new host cells, reducing the infection rate by 3-fold compared to the untreated control. Similar results were obtained in L. infantum, with IC₅₀ = 2.5 and 1.0 μM for promastigote and amastigote forms, respectively. In active serum, GVL1-MAP2 continued to show high activity. GVL1-MAP2 also showed bactericidal activity against most strains tested. The bioconjugate GVL1-MAP2 showed lower cytotoxicity than GVL1-MAP1 and amphotericin B in macrophages. Permeabilization studies and enzyme inhibition revealed that the peptide acts via at least two distinct mechanisms, with the primary mechanism targeting the membrane and inner targets as an inhibitor of the CPB enzyme. Conclusions: These data demonstrated that the synthesis of bioconjugates can be a tool for the development of bactericidal and antileishmanial compounds with improved potency and selectivity.