Search Results (22)

Antimicrobial peptides (AMPs) have emerged as promising candidates in the fight against multidrug-resistant pathogens due to their broad-spectrum antimicrobial activity and low potential for resistance development. However, their clinical application is limited by poor stability and susceptibility to enzymatic degradation. This study aims to address these limitations by synthesizing a series of cyclic hexapeptides using the hydrazide method and evaluating their antimicrobial activity and stability. The hydrazide method facilitated the synthesis of 11 cyclic peptides through a reaction between C-terminal hydrazides and cysteine-containing peptides. Antimicrobial assays showed that Cy-f2 and Cy-f4 exhibited potent inhibitory effects against different kinds of bacteria, including E. coli, Staphylococcus aureus, and S. aureus. Hemolysis assays revealed minimal red blood cell lysis at effective antimicrobial concentrations, indicating good biocompatibility. Stability tests demonstrated improved stability of the cyclic peptides compared to linear counterparts in SGF and 80 °C. In conclusion, the cyclic hexapeptides synthesized in this study demonstrate excellent antimicrobial activity, enhanced stability, and low toxicity, suggesting their potential as new candidates for treating drug-resistant bacterial infections. Full article

Malaria, caused by Plasmodium species and transmitted by Anopheles mosquitoes, continues to pose a significant global health threat. Pipecolisporin, a cyclic hexapeptide isolated from Nigrospora oryzae, has emerged as a promising antimalarial candidate due to its potent biological activity and stability. This study explores the synthesis, antimalarial activity, and computational studies of pipecolisporin, aiming to better understand its therapeutic potential. The peptide was successfully synthesized using Fmoc-based solid-phase peptide synthesis (SPPS) followed by cyclization in solution. The purified compound was characterized using HPLC and mass spectrometry, confirming a molecular ion peak at m/z [M + H]⁺ 692.4131, which matched the calculated mass. Structural verification through ¹H- and ¹³C-NMR demonstrated strong alignment with the natural product. Pipecolisporin exhibited significant antimalarial activity with an IC₅₀ of 26.0 ± 8.49 nM, highlighting its efficacy. In addition to the experimental synthesis, computational studies were conducted to analyze the interaction of pipecolisporin with key malaria-related enzymes, such as dihydrofolate reductase, plasmepsin V, and lactate dehydrogenase. These combined experimental and computational insights into pipecolisporin emphasize the importance of hydrophobic interactions, particularly in membrane penetration and receptor binding, for its antimalarial efficacy. Pipecolisporin represents a promising lead for future antimalarial drug development, with its efficacy, stability, and binding characteristics laying a solid foundation for ongoing research. Full article

Fusarium fungi are widespread pathogens of food crops, primarily associated with the formation of mycotoxins. Therefore, effective mitigation strategies for these toxicogenic microorganisms are required. In this study, the potential of pulsed electric field (PEF) as an advanced technology of increasing use in the food processing industry was investigated to minimize the viability of Fusarium pathogens and to characterize the PEF-induced changes at the metabolomic level. Spores of four Fusarium species (Fusarium culmorum, Fusarium graminearum, Fusarium poae, and Fusarium sporotrichioides) were treated with PEF and cultured on potato dextrose agar (PDA) plates. The viability of the Fusarium species was assessed by counting the colony-forming units, and changes in the mycotoxin content and metabolomic fingerprints were evaluated by using UHPLC-HRMS/MS instrumental analysis. For metabolomic data processing and compound identification, the MS-DIAL (v. 4.80)–MS-CleanR–MS-Finder (v. 3.52) software platform was used. As we found out, both fungal viability and the ability to produce mycotoxins significantly decreased after the PEF treatment for all of the species tested. The metabolomes of the treated and untreated fungi showed statistically significant differences, and PEF-associated biomarkers from the classes oxidized fatty acid derivatives, cyclic hexapeptides, macrolides, pyranocoumarins, carbazoles, and guanidines were identified. Full article

Colorectal cancer (CRC) remains a global health burden, accounting for almost a million deaths annually. Deoxybouvardin (DB), a non-ribosomal peptide originally isolated from Bouvardia ternifolia, has been reported to possess antitumor activity; however, the detailed mechanisms underlying this anticancer activity have not been elucidated. We investigated the anticancer activity of the cyclic hexapeptide, DB, in human CRC HCT116 cells. Cell viability, evaluated by MTT assay, revealed that DB suppressed the growth of both oxaliplatin (Ox)-resistant HCT116 cells (HCT116-OxR) and Ox-sensitive cells in a concentration- and time-dependent manner. Increased reactive oxygen species (ROS) generation was observed in DB-treated CRC cells, and it induced cell cycle arrest at the G2/M phase by regulating p21, p27, cyclin B1, and cdc2 levels. In addition, Western blot analysis revealed that DB activated the phosphorylation of JNK and p38 MAPK in CRC. Furthermore, mitochondrial membrane potential (MMP) was dysregulated by DB, resulting in cytochrome c release and activation of caspases. Taken together, DB exhibited anticancer activity against both Ox-sensitive and Ox-resistant CRC cells by targeting JNK and p38 MAPK, increasing cellular ROS levels, and disrupting MMP. Thus, DB is a potential therapeutic agent for the treatment of Ox-resistant CRC. Full article

Naturally occurring echinocandin B and FR901379 are potent antifungal lipopeptides featuring a cyclic hexapeptide nucleus and a fatty acid side chain. They are the parent compounds of echinocandin drugs for the treatment of severe fungal infections caused by the Candida and Aspergilla species. To minimize hemolytic toxicity, the native fatty acid side chains in these drug molecules are replaced with designer acyl side chains. The deacylation of the N-acyl side chain is, therefore, a crucial step for the development and manufacturing of echinocandin-type antibiotics. Echinocandin E (ECE) is a novel echinocandin congener with enhanced stability generated via the engineering of the biosynthetic machinery of echinocandin B (ECB). In the present study, we report the discovery of the first echinocandin E acylase (ECEA) using the enzyme similarity tool (EST) for enzymatic function mining across protein families. ECEA is derived from Streptomyces sp. SY1965 isolated from a sediment collected from the Mariana Trench. It was cloned and heterologously expressed in S. lividans TK24. The resultant TKecea66 strain showed efficient cleavage activity of the acyl side chain of ECE, showing promising applications in the development of novel echinocandin-type therapeutics. Our results also provide a showcase for harnessing the essentially untapped biodiversity from the hadal ecosystems for the discovery of functional molecules. Full article

Antimicrobial peptides (AMPs) are generally membrane-active compounds that physically disrupt bacterial membranes. Despite extensive research, the precise mode of action of AMPs is still a topic of great debate. This work demonstrates that the initial interaction between the Gram-negative E. coli and AMPs is driven by lipopolysaccharides (LPS) that act as kinetic barriers for the binding of AMPs to the bacterial membrane. A combination of SPR and NMR experiments provide evidence suggesting that cationic AMPs first bind to the negatively charged LPS before reaching a binding place in the lipid bilayer. In the event that the initial LPS-binding is too strong (corresponding to a low dissociation rate), the cationic AMPs cannot effectively get from the LPS to the membrane, and their antimicrobial potency will thus be diminished. On the other hand, the AMPs must also be able to effectively interact with the membrane to exert its activity. The ability of the studied cyclic hexapeptides to bind LPS and to translocate into a lipid membrane is related to the nature of the cationic charge (arginine vs. lysine) and to the distribution of hydrophobicity along the molecule (alternating vs. clumped tryptophan). Full article

Bouvardia ternifolia (Cav.) Schltdl. is a shrub that belongs to the Rubiaceae family and is distributed throughout México; it has been used for its antioxidant, neuroprotective, and anti-inflammatory properties. This work aimed to evaluate the protective effects of B. ternifolia root extracts on the blood-brain barrier and the positive regulation of cytokines IL-1β, IL-6, and TNF-α, and the characterization of compounds present in the dichloromethane (BtD) and hexane (BtH) extracts. Male ICR mice were orally administered with B. ternifolia extracts for 5 days before a single injection of LPS. Administration of BtH and BtD significantly decreased Evans blue leakage into brain tissue by 70% and 68%, respectively. Meloxicam (MX) decreased the concentration of IL-1β by 39.6%; BtM by 53.9%; BtAq by 48.4%; BtD by 31.9%, and BtH by 37.7%. BtH was the only treatment that significantly decreased the concentration of IL-6 by 32.2%. The concentration of TNF-α declined with each of the treatments. The chemical composition of BtD and BtH was characterized by GC–MS, and the cyclic hexapeptide was identified by ¹³C, ¹H NMR, and two-dimension techniques. In the BtD extract, seven compounds were found and in BtH 13 compounds were found. The methanolic (BtM) and aqueous (BtAq) extracts were not subjected to chemical analysis, because they did not show a significant difference in the BBB protection activity. Therefore, the results suggested that the extracts BtD and BtH protect the blood-brain barrier, maintaining stable its selective permeability, thereby preventing LPS from entering the brain tissue. Simultaneously, they modulate the production of IL-1β, IL-6, and TNF-α. It is important to note that this research only evaluated the complete extracts. Full article

Streptomyces lunaelactis strains have been isolated from moonmilk deposits, which are calcium carbonate speleothems used for centuries in traditional medicine for their antimicrobial properties. Genome mining revealed that these strains are a remarkable example of a Streptomyces species with huge heterogeneity regarding their content in biosynthetic gene clusters (BGCs) for specialized metabolite production. BGC 28a is one of the cryptic BGCs that is only carried by a subgroup of S. lunaelactis strains for which in silico analysis predicted the production of nonribosomal peptide antibiotics containing the non-proteogenic amino acid piperazic acid (Piz). Comparative metabolomics of culture extracts of S. lunaelactis strains either holding or not holding BGC 28a combined with MS/MS-guided peptidogenomics and ¹H/¹³C NMR allowed us to identify the cyclic hexapeptide with the amino acid sequence (D-Phe)-(L-HO-Ile)-(D-Piz)-(L-Piz)-(D-Piz)-(L-Piz), called lunaemycin A, as the main compound synthesized by BGC 28a. Molecular networking further identified 18 additional lunaemycins, with 14 of them having their structure elucidated by HRMS/MS. Antimicrobial assays demonstrated a significant bactericidal activity of lunaemycins against Gram-positive bacteria, including multi-drug resistant clinical isolates. Our work demonstrates how an accurate in silico analysis of a cryptic BGC can highly facilitate the identification, the structural elucidation, and the bioactivity of its associated specialized metabolites. Full article

Three novel cyclic hexapeptides, sclerotides C–E (1–3), and a new lipodepsipeptide, scopularide I (4), together with a known cyclic hexapeptide sclerotide A (5), were isolated from fermented rice cultures of a soft coral-derived fungus: Aspergillus sclerotiorum SCSIO 41031. The structures of the new peptides were determined by 1D and 2D NMR spectroscopic analysis, Marfey’s method, ESIMS/MS analysis, and single crystal X-ray diffraction analysis. Scopularide I (4) exhibited acetylcholinesterase inhibitory activity with an IC₅₀ value of 15.6 μM, and weak cytotoxicity against the human nasopharyngeal carcinoma cell line HONE-EBV with IC₅₀ value of 10.1 μM. Full article

Cyanobacteria are microorganisms with photosynthetic mechanisms capable of colonizing several distinct environments worldwide. They can produce a vast spectrum of bioactive compounds with different properties, resulting in an improved adaptative capacity. Their richness in secondary metabolites is related to their unique and diverse metabolic apparatus, such as Non-Ribosomal Peptide Synthetases (NRPSs). One important class of peptides produced by the non-ribosomal pathway is anabaenopeptins. These cyclic hexapeptides demonstrated inhibitory activity towards phosphatases and proteases, which could be related to their toxicity and adaptiveness against zooplankters and crustaceans. Thus, this review aims to identify key features related to anabaenopeptins, including the diversity of their structure, occurrence, the biosynthetic steps for their production, ecological roles, and biotechnological applications. Full article

A novel cyclic antimalarial and antitrypanosome hexapeptide, pipecolisporin (1), was isolated from cultures of Nigrospora oryzae CF-298113, a fungal endophyte isolated from roots of Triticum sp. collected in a traditional agricultural land of Montefrío, Granada, Spain. The structure of this compound, including its absolute configuration, was elucidated by HRMS, 1-D and 2-D NMR spectroscopy, and Marfey’s analysis. This metabolite displayed interesting activity against Plasmodium falciparum and Trypanosoma cruzi, with IC₅₀ values in the micromolar range, and no significant cytotoxicity against the human cancer cell lines A549, A2058, MCF7, MIA PaCa-2, and HepG2. Full article

The rare actinobacterium Amycolatopsis sp. strain 195334CR was found to produce previously undescribed cyclic hexapeptides, which we named amycolatomycin A and B (1 and 2). Their planar structures were determined by high-resolution mass spectrometry as well as extensive 1D and 2D NMR spectroscopy, while the absolute stereochemistry of its amino acids were determined by Marfey’s method. Moreover, 1 and 2 differ by the incorporation of l-Ile and l-allo-Ile, respectively, whose FDVA (Nα-(2,4-Dinitro-5-fluorphenyl)-L-valinamide) derivatives were separated on a C₄ column. Their hallmark in common is a unique 2,6-dichloro-tryptophan amino acid unit. Amycolatomycin A (1) exhibited weak activity against Bacillus subtilis DSM 10 (minimum inhibitory concentration (MIC) = 33.4 µg/mL). Full article

The anticancer activities of Rubia cordifolia and its constituents have been reported earlier, but their influence on the crosstalk of complex cancer-related signaling metabolic pathways (i.e., transcription factors; TF) has not yet been fully investigated. In this study, R. cordifolia root extract was subjected to the cancer signaling assay based bioactivity-guided fractionation, which yielded the following compounds viz., three anthraquinones, namely alizarin (1), purpurin (2), and emodin (3); two lignans, namely eudesmin (4) and compound 5; and two cyclic hexapeptides, namely deoxybouvardin RA-V (6), and a mixture of 6+9 (RA-XXI). The structures of the isolated compounds were determined by NMR spectroscopy and HRESIMS. The isolated compounds 1, 2, 3, 6, and a mixture of 6+9 were tested against a panel of luciferase reporter genes that assesses the activity of a wide-range of cancer-related signaling pathways. In addition, reference anthraquinones viz., chrysophanol (11), danthron (12), quinizarin (13), aloe-emodin (14), and α-lapachone (15) were also tested. Among the tested compounds, the cyclic hexapeptide 6 was found to be very active against several signaling pathways, notably Wnt, Myc, and Notch with IC₅₀ values of 50, 75, and 93 ng/mL, respectively. Whereas, the anthraquinones exhibited very mild or no inhibition against these signaling pathways. Compound 6 being the most active, we tested it for stability in simulated intestinal (SIF) and gastric fluids (SGF), since the stability in biological fluid is a key short-coming of cyclic hexapeptides. The anticancer activity of 6 was found to remain unchanged before and after the treatment of simulated gastric/intestinal fluids, indicating that RA-V was stable. As a result, it could be bioavailable when orally used in therapeutics and possibly a drug candidate for cancer treatment. The mechanism for the preferential inhibition of these pathways and the possible crosstalk effect with other previously reported signaling pathways has been discussed. Full article

The present investigation reports an attempt to synthesize naturally occurring α-cyclic tripeptide cyclo(Gly-l-Pro-l-Glu) 1, [cyclo(GPE)], previously isolated from the Ruegeria strain of bacteria with marine sponge Suberites domuncula. Three linear precursors, Boc-GPE(OBn)₂, Boc-PE(OBn)G and Boc-E(OBn)GP, were synthesized using a solution phase peptide coupling protocol. Although cyclo(GPE) 1 was our original target, all precursors were dimerized and cyclized at 0 °C with high dilution to form corresponding α-cyclic hexapeptide, cyclo(GPE(OBn))₂7, which was then converted to cyclic hexapeptide cyclo(GPE)₂2. Cyclization at higher temperature induced racemization and gave cyclic tripeptide cyclo(GP_DE(OBn)) 9. Structure characteristics of the newly synthesized cyclopeptides were determined using ¹H-NMR, ¹³C-NMR and high-resolution mass spectrometry. The chemical shift values of carbonyls of 2 and 7 are larger than 170 ppm, indicating the formation of a cyclic hexapeptide. Full article

Pasireotide is a multi-receptor ligand somatostatin analogue approved for medical treatment of Cushing’s disease and acromegaly. The liquid-phase total synthesis of pasireotide-a 18-membered cyclic hexapeptide-was achieved by the 3 + 2 + 1 strategy, and the Pro¹-Phe⁶ peptide bond was selected as the final cyclization position. Two key fragments were simply synthesized using N,O-bis(trimethylsilyl)acetamide/N-hydroxysuccinimide ester (BSA/NHS) as coupling agents, and processes of the two key fragments were simple without any chromatographic purification. The current synthesis method is easily scalable and produces the target peptide with an overall yield of 15%. Full article