Testacosides A-D, glycoglycerolipids produced by Microbacterium testaceum isolated from Tedania brasiliensis

Marine bacteria living in association with marine sponges have proven to be a reliable source of biologically active secondary metabolites. However, no studies have yet reported natural products from Microbacterium testaceum spp. We herein report the isolation of a M. testaceum strain from the sponge Tedania brasiliensis. Molecular networking analysis of bioactive pre-fractionated extracts from culture media of M. testaceum enabled the discovery of testacosides A-D. Analysis of spectroscopic data and chemical derivatizations allowed the identification of testacosides A-D as glycoglycerolipids bearing a 1-[α-glucopyranosyl-(1 → 3)-(α-mannopyranosyl)]-glycerol moiety connected to 12-methyltetradecanoic acid for testacoside A (1), 14-methylpentadecanoic acid for testacoside B (2), and 14-methylhexadecanoic acid for testacosides C (3) and D (4). The absolute configuration of the monosaccharide residues was determined by 1H-NMR analysis of the respective diastereomeric thiazolidine derivatives. This is the first report of natural products isolated from cultures of M. testaceum. KEY POINTS: • The first report of metabolites produced by Microbacterium testaceum. • 1-[α-Glucopyranosyl-(1 → 3)-(α-mannopyranosyl)]-glycerol lipids isolated and identified. • Microbacterium testaceum strain isolated from the sponge Tedania brasiliensis.

Metabolomics approach to understand molecular mechanisms involved in fungal pathogen-citrus pathosystems

Citrus is a crucial crop with a significant economic impact globally. However, postharvest decay caused by fungal pathogens poses a considerable threat, leading to substantial financial losses. Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii and Phyllosticta citricarpa are the main fungal pathogens, causing green mold, blue mold, sour rot and citrus black spot diseases, respectively. The use of chemical fungicides as a control strategy in citrus raises concerns about food and environmental safety. Therefore, understanding the molecular basis of host-pathogen interactions is essential to find safer alternatives. This review highlights the potential of the metabolomics approach in the search for bioactive compounds involved in the pathogen-citrus interaction, and how the integration of metabolomics and genomics contributes to the understanding of secondary metabolites associated with fungal virulence and the fungal infection mechanisms. Our goal is to provide a pipeline combining metabolomics and genomics that can effectively guide researchers to perform studies aiming to contribute to the understanding of the fundamental chemical and biochemical aspects of pathogen-host interactions, in order to effectively develop new alternatives for fungal diseases in citrus cultivation. We intend to inspire the scientific community to question unexplored biological systems, and to employ diverse analytical approaches and metabolomics techniques to address outstanding questions about the non-studied pathosystems from a chemical biology perspective.

Improvement of Targeted Fungi Secondary Metabolite Production Using a Systematic Experimental Design and Chemometrics Analysis

Fungi are well-known producers of chemically diverse and biologically active secondary metabolites. However, their production yields through fermentation may hamper structural analysis and biological activity downstream investigations. Herein, a systematic experimental design that varies multiple cultivation parameters, followed by chemometrics analysis on HPLC-UV-MS or UHPLC-HRMS/MS data, is presented to enhance the production yield of fungal natural products. The overall procedure typically requires 3-4 months of work when first developed, and up to 3 months as a routine procedure.

Phomactinine, the First Nitrogen-Bearing Phomactin, Produced by Biatriospora sp. CBMAI 1333

Metabolomics analyses and improvement of growth conditions were applied toward diversification of phomactin terpenoids by the fungus Biatriospora sp. CBMAI 1333. Visualization of molecular networking results on Gephi assisted the observation of phomactin diversification and guided the isolation of new phomactin variants by applying a modified version of chemometrics based on a fractional factorial design. Consequentially, the first nitrogen-bearing phomactin, phomactinine (1), with a new rearranged carbon skeleton, was isolated and identified. The strategy combining metabolomics and chemometrics can be extended to include bioassay potency, structure novelty, and metabolic diversification connected or not to genomic analyses.

Polyketide- and Terpenoid-Derived Metabolites Produced by a Marine-Derived Fungus, Peroneutypa sp

Bioassay-guided investigation of the EtOAc-soluble extract of a culture of the marine-derived fungus Peroneutypa sp. M16 led to the isolation of seven new polyketide- and terpenoid-derived metabolites (1, 2, 4-8), along with known polyketides (3, 9-13). Structures of compounds 1, 2, and 4-8 were established by analysis of spectroscopic data. Absolute configurations of compounds 1, 2, 4, 6, 7, and 8 were determined by the comparison of experimental ECD spectra with calculated CD data. Compound 5 exhibited moderate antiplasmodial activity against both chloroquine-sensitive and -resistant strains of Plasmodium falciparum.

Discovery of lead natural products for developing pan-SARS-CoV-2 therapeutics

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global public health crisis. The reduced efficacy of therapeutic monoclonal antibodies against emerging SARS-CoV-2 variants of concern (VOCs), such as omicron BA.5 subvariants, has underlined the need to explore a novel spectrum of antivirals that are effective against existing and evolving SARS-CoV-2 VOCs. To address the need for novel therapeutic options, we applied cell-based high-content screening to a library of natural products (NPs) obtained from plants, fungi, bacteria, and marine sponges, which represent a considerable diversity of chemical scaffolds. The antiviral effect of 373 NPs was evaluated using the mNeonGreen (mNG) reporter SARS-CoV-2 virus in a lung epithelial cell line (Calu-3). The screening identified 26 NPs with half-maximal effective concentrations (EC50) below 50 μM against mNG-SARS-CoV-2; 16 of these had EC50 values below 10 μM and three NPs (holyrine A, alotaketal C, and bafilomycin D) had EC50 values in the nanomolar range. We demonstrated the pan-SARS-CoV-2 activity of these three lead antivirals against SARS-CoV-2 highly transmissible Omicron subvariants (BA.5, BA.2 and BA.1) and highly pathogenic Delta VOCs in human Calu-3 lung cells. Notably, holyrine A, alotaketal C, and bafilomycin D, are potent nanomolar inhibitors of SARS-CoV-2 Omicron subvariants BA.5 and BA.2. The pan-SARS-CoV-2 activity of alotaketal C [protein kinase C (PKC) activator] and bafilomycin D (V-ATPase inhibitor) suggest that these two NPs are acting as host-directed antivirals (HDAs). Future research should explore whether PKC regulation impacts human susceptibility to and the severity of SARS-CoV-2 infection, and it should confirm the important role of human V-ATPase in the VOC lifecycle. Interestingly, we observed a synergistic action of bafilomycin D and N-0385 (a highly potent inhibitor of human TMPRSS2 protease) against Omicron subvariant BA.2 in human Calu-3 lung cells, which suggests that these two highly potent HDAs are targeting two different mechanisms of SARS-CoV-2 entry. Overall, our study provides insight into the potential of NPs with highly diverse chemical structures as valuable inspirational starting points for developing pan-SARS-CoV-2 therapeutics and for unravelling potential host factors and pathways regulating SARS-CoV-2 VOC infection including emerging omicron BA.5 subvariants.

Metabolomics Reveals a 26-Membered Macrolactone Produced by Endophytic Colletotrichum spp. from Alcatrazes Island, Brazil

Comparative metabolomics analysis of nonphytotoxic endophytic Colletotrichum spp. isolated from Anthurium alcatrazense endemic to Alcatrazes island (Brazil) and phytopathogenic Colletotrichum spp. isolated from the mainland of Brazil revealed significant differences in chemical composition. Examination of endophytic Colletotrichum spp. from Alcatrazes island led to the discovery of a 26-member macrolactone, colletotrichumolide (1), containing a phosphatidyl choline side chain. Further examination of the phytopathogenic strains from the mainland identified a family of phytopathogenic metabolites not present in the nonpathogenic island-derived strains, suggesting that geographical isolation could influence the secondary metabolism of fungal strains.

Sponges present a core prokaryotic community stable across Tropical Western Atlantic

Sponges are among the earliest lineages of metazoans, with first fossil records dated back to 890 million years ago. All sponge species present associations with microorganisms to some extension, which influence sponges' survival and adaptation. Sponge species can be divided into two categories, Low Microbial Abundance and High Microbial Abundance, depending on the abundance of the microbial community that they host. Monanchora arbuscula (a Low Microbial Abundance sponge species) and Xestospongia muta (a High Microbial Abundance sponge species) are sponges with widespread distribution in the Tropical Western Atlantic. Despite previous studies on the major features of these species, little is known whether M. arcuscula and X. muta prokaryotic communities are stable across vast geographic regions. We obtained a total of ~9.26 million 16S rRNA gene Illumina sequences for M. arbuscula samples collected at seven locations and for X. muta samples collected at three locations, corresponding to five ecoregions of the Caribbean and the Southwestern Atlantic (N = 105, 39 from M. arcuscula and 66 from X. muta). These samples reflected different ecological strategies for prokaryotic communities assembly, since the core prokaryotic communities of M. arbuscula are more heterotrophic and shared with different sources (corals, sponges, seawater, sediments), while X. muta has more significant photosynthetic prokaryotic communities, mainly outsourced from other sponges. Results of M. arbuscula and X. muta prokaryotic communities analysis demonstrate that both sponge species have core prokaryotic communities stable across a vast geographic area (> 8000 km), and the world's most notable coastal marine biogeographic filter, the Amazon River Mouth, in spite of the significant differences found among transient prokaryotic communities of both sponge species.

Feature-Based Molecular Networking Discovery of Bromopyrrole Alkaloids from the Marine Sponge Agelas dispar

Investigation of the marine sponge Agelas dispar MeOH fractions using feature-based molecular networking, dereplication, and isolation led to the discovery of new bromopyrrole-derived metabolites. An in-house library of bromopyrrole alkaloids previously isolated from A. dispar and Dictyonella sp. was utilized, along with the investigation of an MS/MS fragmentation of these compounds. Our strategy led to the isolation and identification of the disparamides A-C (1-3), with a novel carbon skeleton. Additionally, new dispyrins B-F (4-8) and nagelamides H2 and H3 (9 and 10) and known nagelamide H (11), citrinamine B (12), ageliferin (13), bromoageliferin (14), and dibromoageliferin (15) were also isolated and identified by analysis of spectroscopic data. Analysis of MS/MS fragmentation data and molecular networking analysis indicated the presence of hymenidin (16), oroidin (17), dispacamide (18), monobromodispacamide (19), keramadine (20), longamide B (21), methyl ester of longamide B (22), hanishin (23), methyl ester of 3-debromolongamide B (24), and 3-debromohanishin (25). Antibacterial activity of ageliferin (13), bromoageliferin (14), and dibromoageliferin (15) was evaluated against susceptible and multi-drug-resistant ESKAPE pathogenic bacteria Klabsiella pneumoniae, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterococcus faecalis. Dibromoageliferin (15) displayed the most potent antimicrobial activity against all tested susceptible and MDR strains. Compounds 13-15 presented no significant hemolytic activity up to 100 μM.

Comparative study of composition of methanolic extracts of the paratoid gland secretions (PGS) of Rhinella jimi (cururu toad) from northeastern Brazil: Gender, seasonality and geographic occurrence

Toads belonging to the Bufonidae family have a pair of paratoid glands that store highly toxic a biological secretion with varied chemical composition, that act as a chemical defense against microbial infections and predators. The paratoid gland secretion (PGS) of bufonids is rich in bioactive steroids, alkaloids, proteins, bufadienolides and bufotoxins. In the present investigation we performed a systematic analysis of the chemical profile of PGS obtained from the Bufonidae toad Rhinella jimi ("Cururu" toad) collected at three different regions of Piauí state, Northeastern Brazil. Our aim was to investigate the PGS variation related to the season of animals collection, geographic distribution and gender of the animals. The methanolic extracts of PGS were analyzed by UPLC-QToF-MS/MS. Principal component analysis (PCA) were applied to the data set obtained by the UPLC-QToF-MS/MS analyses. Among 23 compounds identified, dehydrobufotenine, suberoyl arginine, 3-(N-suberoyl-argininyl) telocinobufagin, 3-(N-suberoyl-argininyl) marinobufagin, telocinobufagin, marinobufagin and 3-(N-suberoyl-argininyl) bufalin were detected in all PGS. Minimal variations in the composition of paratoid secretions of R. jimi were observed related to distinct geographical and seasonal parameters. R. jimi female animals presented the most diverse chemical composition in its PGS. With this comparative study, unprecedented for the species, it was possible to observe that the secretions of the paratoid glands produced by R. jimi from different regions of the state of Piauí, at different times of the year, presented consistent chemical composition, with discrete particularities in the number and nature chemistry of its constituents.

Absolute configuration of cytotoxic anthraquinones from a Brazilian cave soil-derived fungus, Aspergillus sp. SDC28

Microbial strains isolated from extreme and understudied environments, such as caves, are still poorly investigated for the production of bioactive secondary metabolites. Investigation of the ethyl acetate extract from the growth medium produced by the soil-derived fungus Aspergillus sp. SDC28, isolated from a Brazilian cave, yielded two anthraquinones: versicolorin C (1) and versiconol (2). The complete assignment of nuclear magnetic resonance and mass spectroscopic data of 1 and 2 was performed for the first time. Moreover, the yet unreported absolute configuration of both compounds was unambiguously established by analysis of experimental and theoretical electronic circular dichroism data. Vibrational circular dichroism was also applied to confirm the absolute stereochemistry of 2. Compounds 1 and 2 showed cytotoxic activity against human ovarian cancer cells (OVCAR3).

Isolation of Water-Soluble Metabolites from Marine Invertebrates and Microorganisms

The isolation of pure organic compounds from biological sources, reaction media, or other complex molecular matrixes is the first step to overcome before further biological and chemical investigations. While the isolation of chemicals soluble in organic solvents is commonly accomplished, the isolation of water-soluble organic compounds is less often addressed. We present here a simple method for the isolation of water-soluble organic compounds, using adsorptive macroporous resins and reversed-phase chromatography.

Microbiome associated with the tetrodotoxin-bearing anuran Brachycephalus pitanga

The genus Brachycephalus includes small species of aposematic anurans known as microendemic, occurring in the mountains of the Atlantic Forest. Brachycephalus ephippium, B. nodoterga and B. pernix have been reported to contain the neurotoxin tetrodotoxin in skin and viscera. The biological conservation of several Brachycephalus species is currently threatened by climate change, deforestation, and the pandemic caused by the fungus Batrachochytrium dendrobatidis (Bd). Despite the well-known importance of amphibians' associated bacteria in the defensive role against pathogens, there is still a poor understanding of amphibian microbiome composition. The present study investigated the composition of B. pitanga microbial community and the presence of TTX in the host and in cultures of bacterial isolates, using a combination of metagenomics, bacterial culture isolation, mass spectrometry and metabolomic analyses. Results of culture-dependent and -independent analyses characterized the microbial communities associated with the skin and viscera of B. pitanga. Mass spectrometry analysis indicated the presence of TTX in host tissues, while bacterial production of TTX was not observed under the experimental conditions used in this investigation. This is the first report confirming the occurrence of TTX in B. pitanga.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

A Family of Nonribosomal Peptides Modulate Collective Behavior in Pseudovibrio Bacteria Isolated from Marine Sponges*

Although swarming motility and biofilms are opposed collective behaviors, both contribute to bacterial survival and host colonization. Pseudovibrio bacteria have attracted attention because they are part of the microbiome of healthy marine sponges. Two-thirds of Pseudovibrio genomes contain a member of a nonribosomal peptide synthetase-polyketide synthase gene cluster family, which is also found sporadically in Pseudomonas pathogens of insects and plants. After developing reverse genetics for Pseudovibrio, we isolated heptapeptides with an ureido linkage and related nonadepsipeptides we termed pseudovibriamides A and B, respectively. A combination of genetics and imaging mass spectrometry experiments showed heptapetides were excreted, promoting motility and reducing biofilm formation. In contrast to lipopeptides widely known to affect motility/biofilms, pseudovibriamides are not surfactants. Our results expand current knowledge on metabolites mediating bacterial collective behavior.

Early Oxidative Transformations During the Biosynthesis of Terrein and Related Natural Products

The mycotoxin terrein is derived from the C₁₀‐precursor 6‐hydroxymellein (6‐HM) via an oxidative ring contraction. Although the corresponding biosynthetic gene cluster (BGC) has been identified, details of the enzymatic oxidative transformations are lacking. Combining heterologous expression and in vitro studies we show that the flavin‐dependent monooxygenase (FMO) TerC catalyzes the initial oxidative decarboxylation of 6‐HM. The reactive intermediate is further hydroxylated by the second FMO TerD to yield a highly oxygenated aromatic species, but further reconstitution of the pathway was hampered. A related BGC was identified in the marine‐derived Roussoella sp. DLM33 and confirmed by heterologous expression. These studies demonstrate that the biosynthetic pathways of terrein and related (polychlorinated) congeners diverge after oxidative decarboxylation of the lactone precursor that is catalyzed by a conserved FMO and further indicate that early dehydration of the side chain is an essential step.

Post-synthetic functionalization of tryptophan protected peptide sequences through indole (C-2) photocatalytic alkylation

We report a selective, mild, and efficient C-H functionalization of tryptophan and tryptophan-containing peptides with activated α-bromo-carbonyl compounds under visible-light irradiation. The protocol efficiency is outlined by the wide substrate scope and excellent tolerance of sensitive functional groups present in the amino acid side chains. The method can be successfully extended to access pharmaco-peptide conjugate scaffolds.

Metabolomics Reveals Minor Tambjamines in a Marine Invertebrate Food Chain

Metabolomics analysis detected tambjamine alkaloids in aqueous and EtOAc extracts of the marine invertebrates Virididentula dentata, Tambja stegosauriformis, Tambja brasiliensis, and Roboastra ernsti. Among several tambjamines, the new amino acid derivatives tambjamines M-O (17-19) were identified by Marfey's advanced analysis, UPLC-MS/MS analyses, and total synthesis. The tambjamine diversity increased from the bryozoan V. dentata to its nudibranch predators T. stegosauriformis and T. brasiliensis and attained a higher diversity in R. ernsti, the nudibranch that preys upon T. stegosauriformis and T. brasiliensis. The total tambjamine content also increases among the trophic levels, probably due to biomagnification. Tambjamines A (1), C (3), and D (4) are the major metabolites in the tissues of V. dentata, T. stegosauriformis, T. brasiliensis, and R. ernsti and are likely the main chemical defenses of these marine invertebrates.

The bacterial and fungal communities associated with Anthurium ssp. leaves: Insights into plant endemism and microbe association

It is known that different plant species select specific microbes to live inside their tissues in a process determined by the host genotype, phenotype and geographic location, which can introduce discussion on plant endemism and the assembly of specific microbial communities. Herein, we report the results of an investigation relating the geographic distribution of plant species and the composition of microbial communities associated with plant hosts. The bacterial and fungal community associated with Anthurium plant leaves was mapped to assess the diversity and ecology of the endophytic community associated with Anthurium spp. collected on islands and on the Brazilian mainland. Twenty-six Anthurium specimens were surveyed, distributed throughout the São Paulo state coastline, including Alcatrazes Island, some coastal islands and distinct mainland environments. Bacterial and fungal endophytes were obtained from the leaves of A. alcatrazense, A. loefgrenii, A. penthaphyllum, A. urvellianum and A. intermedium and subjected to massive bacterial 16S rRNA and fungal ITS sequencing. The results indicated that A. alcatrazense, endemic to Alcatrazes Island, hosted a specific bacterial community structure, while its fungal community was similar to that of Anthurium species from other locations. Betaproteobacteria showed a high differential occurrence in A. alcatrazense. Some groups of fungi were found mainly inhabiting A. loefgrenii plants. While Alphaproteobacteria, Gammaproteobacteria, Actinobacteria and Sordariomycetes, Dothiodeomycetes and Tremellomycetes composed the core microbial community among Anthurium plants. The results suggest crucial role for the bacterial communities to endemic plants, while endophytic fungal diversity is less specifically distributed among endemic and nonendemic plant species.

Batzelladine D and norbatzelladine L purified from marine sponge Monanchora arbuscula induce the reversal of fluconazole

ATP-Binding Cassette (ABC) transporters are the main class of transmembrane transporters involved in pathogenic fungal resistance against chemotherapeutic agents. Herein we report results which show that batzelladine D (1) and norbatzelladine L (2) reverse the fluconazole resistance phenotype mediated by Pdr5p transporter on Saccharomyces cerevisiae. Both alkaloids were able to chemosensitize the Pdr5p-overexpressing strain by synergistic interaction with fluconazole. Both compounds also showed an inhibitory effect on the catalytic activity and on the intracellular accumulation of rhodamine 6G, and did not show significant in vitro mammalian cells toxicity.

The chemistry and biology of guanidine secondary metabolites

Covering: 2017-2019Guanidine natural products isolated from microorganisms, marine invertebrates and terrestrial plants, amphibians and spiders, represented by non-ribosomal peptides, guanidine-bearing polyketides, alkaloids, terpenoids and shikimic acid derived, are the subject of this review. The topics include the discovery of new metabolites, total synthesis of natural guanidine compounds, biological activity and mechanism-of-action, biosynthesis and ecological functions.

Antiproliferative Flavanoid Dimers Isolated from Brazilian Red Propolis

Herein reported are results of the chemical and biological investigation of red propolis collected at the Brazilian Northeast coastline. New propolones A-D (1-4), with a 3-{3-[(2-phenylbenzofuran-3-yl)methyl]phenyl}chromane skeleton; propolonones A-C (5-7), with a 3-[3-(3-benzylbenzofuran-2-yl)phenyl]chromane skeleton; and propolol A (8), with a 6-(3-benzylbenzofuran-2-yl)-3-phenylchromane skeleton, were isolated as constituents of Brazilian red propolis by cytotoxicity-guided assays and structurally identified by analysis of their spectroscopic data. Propolone B (2) and propolonone A (5) display significant cytotoxic activities against an ovarian cancer cell line expressing a multiple drug resistance phenotype when compared with doxorubicin.

Merulinic acid C overcomes gentamicin resistance in Enterococcus faecium

Enterococci are gram-positive, widespread nosocomial pathogens that in recent years have developed resistance to various commonly employed antibiotics. Since finding new infection-control agents based on secondary metabolites from organisms has proved successful for decades, natural products are potentially useful sources of compounds with activity against enterococci. Herein are reported the results of a natural product library screening based on a whole-cell assay against a gram-positive model organism, which led to the isolation of a series of anacardic acids identified by analysis of their spectroscopic data and by chemical derivatizations. Merulinic acid C was identified as the most active anacardic acid derivative obtained against antibiotic-resistant enterococci. Fluorescence microscopy analyses showed that merulinic acid C targets the bacterial membrane without affecting the peptidoglycan and causes rapid cellular ATP leakage from cells. Merulinic acid C was shown to be synergistic with gentamicin against Enterococcus faecium, indicating that this compound could inspire the development of new antibiotic combinations effective against drug-resistant pathogens.

New tetrodotoxin analogs in Brazilian pufferfishes tissues and microbiome

While tetrodotoxin (TTX) is commonly found in pufferfish tissues, it is unclear if bacterial symbionts isolated from pufferfish tissues can produce TTX. In this investigation, UPLC qTOF-MS/MS analysis of tissue extracts obtained from Sphoeroides spengleri and Canthigaster figuereidoi identified TTX in their composition, indicating their consumption is unsafe. UPLC qTOF-MS/MS analysis coupled with Molecular Networking indicated new TTX analogs (methyl-TTX, TTX-acetate, hydroxypropyl-TTX and glycerol-TTX). Bacterial extracts from sixteen strains revealed a compound with a [M+H]⁺ ion at m/z 320.1088, identical to TTX. However, TTX itself was not detected in these cultures by UPLC-MS/MS. Neurotoxicity of Vibrio A665 purified fraction 2 (with precursor [M+H]⁺ ion at m/z 320.1088) was significant in human neural stem cells (hNSCs), but the Na_v blockage activity was not confirmed by the veratridine/ouabain essays, indicating a possible difference in the mechanism of action between the bacterium A665 purified fraction 2 and TTX. Vibrios symbionts of pufferfish point out involving in the production of TTX precursors.

Water-Soluble Glutamic Acid Derivatives Produced in Culture by Penicillium solitum IS1-A from King George Island, Maritime Antarctica

A new method of screening was developed to generate 770 organic and water-soluble fractions from extracts of nine species of marine sponges, from the growth media of 18 species of marine-derived fungi, and from the growth media of 13 species of endophytic fungi. The screening results indicated that water-soluble fractions displayed significant bioactivity in cytotoxic, antibiotic, anti-Leishmania, anti-Trypanosoma cruzi, and inhibition of proteasome assays. Purification of water-soluble fractions from the growth medium of Penicillium solitum IS1-A provided the new glutamic acid derivatives solitumine A (1), solitumine B (2), and solitumidines A-D (3-6). The structures of compounds 1-6 have been established by analysis of spectroscopic data, chemical derivatizations, and vibrational circular dichroism calculations. Although no biological activity could be observed for compounds 1-6, the new structures reported for 1-6 indicate that the investigation of water-soluble natural products represents a relevant strategy in finding new secondary metabolites.

Unveiling sequential late-stage methyltransferase reactions in the meleagrin/oxaline biosynthetic pathway

Antimicrobial and anti-proliferative meleagrin and oxaline are roquefortine C-derived alkaloids produced by fungi of the genus Penicillium. Tandem O-methylations complete the biosynthesis of oxaline from glandicoline B through meleagrin. Currently, little is known about the role of these methylation patterns in the bioactivity profile of meleagrin and oxaline. To establish the structural and mechanistic basis of methylation in these pathways, crystal structures were determined for two late-stage methyltransferases in the oxaline and meleagrin gene clusters from Penicillium oxalicum and Penicillium chrysogenum. The homologous enzymes OxaG and RoqN were shown to catalyze penultimate hydroxylamine O-methylation to generate meleagrin in vitro. Crystal structures of these enzymes in the presence of methyl donor S-adenosylmethionine revealed an open active site, which lacks an apparent base indicating that catalysis is driven by proximity effects. OxaC was shown to methylate meleagrin to form oxaline in vitro, the terminal pathway product. Crystal structures of OxaC in a pseudo-Michaelis complex containing sinefungin and meleagrin, and in a product complex containing S-adenosyl-homocysteine and oxaline, reveal key active site residues with His313 serving as a base that is activated by Glu369. These data provide structural insights into the enzymatic methylation of these alkaloids that include a rare hydroxylamine oxygen acceptor, and can be used to guide future efforts towards selective derivatization and structural diversification and establishing the role of methylation in bioactivity.

Synthesis of 4-alkoxy-N-substituted-1,8-naphthalimides

The present work deals with two improved methods for the synthesis of 4-alkoxy- N-alkyl-1,8-naphthalimides from 4-nitro- N-alkyl-1,8-naphthalimides employing in situ generation of the alkoxylating agent in the alcoholic saturated solution of alkaline metal carbonates.

Approaches for the isolation and identification of hydrophilic, light-sensitive, volatile and minor natural products

Water-soluble, volatile, minor and photosensitive natural products are yet poorly known, and this review discusses the literature reporting the isolation strategies for some of these metabolites.

Bromopyrrole Alkaloid Inhibitors of the Proteasome Isolated from a Dictyonella sp. Marine Sponge Collected at the Amazon River Mouth

The new pyrrole-imidazole and pyrrole-guanidine alkaloids 4-debromooroidin (1), 4-debromougibohlin (2), 5-debromougibohlin (3), and 5-bromopalau'amine (4), along with the known hymenidin (5) and (+)-monobromoisophakellin (6), have been isolated from a Dictyonella sp. marine sponge, collected at the Amazon River mouth. The bromine-substitution pattern observed for compounds 1, 2 and 4 is unusual among bromopyrrole alkaloids isolated from marine sponges. The 20S proteasome inhibitory activities of compounds 1-6 have been recorded, with 5-bromopalau'amine (4) being the most active in this series.

Microbial and Functional Biodiversity Patterns in Sponges that Accumulate Bromopyrrole Alkaloids Suggest Horizontal Gene Transfer of Halogenase Genes

Marine sponge holobionts harbor complex microbial communities whose members may be the true producers of secondary metabolites accumulated by sponges. Bromopyrrole alkaloids constitute a typical class of secondary metabolites isolated from sponges that very often display biological activities. Bromine incorporation into secondary metabolites can be catalyzed by either halogenases or haloperoxidases. The diversity of the metagenomes of sponge holobiont species containing bromopyrrole alkaloids (Agelas spp. and Tedania brasiliensis) as well as holobionts devoid of bromopyrrole alkaloids spanning in a vast biogeographic region (approx. Seven thousand km) was studied. The origin and specificity of the detected halogenases was also investigated. The holobionts Agelas spp. and T. brasiliensis did not share microbial halogenases, suggesting a species-specific pattern. Bacteria of diverse phylogenetic origins encoding halogenase genes were found to be more abundant in bromopyrrole-containing sponges. The sponge holobionts (e.g., Agelas spp.) with the greatest number of sequences related to clustered, interspaced, short, palindromic repeats (CRISPRs) exhibited the fewest phage halogenases, suggesting a possible mechanism of protection from phage infection by the sponge host. This study highlights the potential of phages to transport halogenases horizontally across host sponges, particularly in more permissive holobiont hosts, such as Tedania spp.

Isolation, Derivative Synthesis, and Structure-Activity Relationships of Antiparasitic Bromopyrrole Alkaloids from the Marine Sponge Tedania brasiliensis

The isolation and identification of a series of new pseudoceratidine (1) derivatives from the sponge Tedania brasiliensis enabled the evaluation of their antiparasitic activity against Plasmodium falciparum, Leishmania (Leishmania) amazonensis, Leishmania (Leishmania) infantum, and Trypanosoma cruzi, the causative agents of malaria, cutaneous leishmaniasis, visceral leishmaniasis, and Chagas disease, respectively. The new 3-debromopseudoceratidine (4), 20-debromopseudoceratidine (5), 4-bromopseudoceratidine (6), 19-bromopseudoceratidine (7), and 4,19-dibromopseudoceratidine (8) are reported. New tedamides A-D (9-12), with an unprecedented 4-bromo-4-methoxy-5-oxo-4,5-dihydro-1H-pyrrole-2-carboxamide moiety, are also described. Compounds 4 and 5, 6 and 7, 9 and 10, and 11 and 12 have been isolated as pairs of inseparable structural isomers differing in their sites of bromination or oxidation. Tedamides 9+10 and 11+12 were obtained as optically active pairs, indicating an enzymatic formation rather than an artifactual origin. N12-Acetylpseudoceratidine (2) and N12-formylpseudoceratidine (3) were obtained by derivatization of pseudoceratidine (1). The antiparasitic activity of pseudoceratidine (1) led us to synthesize 23 derivatives (16, 17, 20, 21, 23, 25, 27-29, 31, 33, 35, 38, 39, 42, 43, 46, 47, 50, and 51) with variations in the polyamine chain and aromatic moiety in sufficient amounts for biological evaluation in antiparasitic assays. The measured antimalarial activity of pseudoceratidine (1) and derivatives 4, 5, 16, 23, 25, 31, and 50 provided an initial SAR evaluation of these compounds as potential leads for antiparasitics against Leishmania amastigotes and against P. falciparum. The results obtained indicate that pseudoceratidine represents a promising scaffold for the development of new antimalarial drugs.

Quantitative Detection of Active Vibrios Associated with White Plague Disease in Mussismilia braziliensis Corals

Over recent decades several coral diseases have been reported as a significant threat to coral reef ecosystems causing the decline of corals cover and diversity around the world. The development of techniques that improve the ability to detect and quantify microbial agents involved in coral disease will aid in the elucidation of disease cause, facilitating coral disease detection and diagnosis, identification and pathogen monitoring, pathogen sources, vectors, and reservoirs. The genus Vibrio is known to harbor pathogenic strains to marine organisms. One of the best-characterized coral pathogens is Vibrio coralliilyticus, an aetilogic agent of White Plague Disease (WPD). We used Mussismilia coral tissue (healthy and diseased specimens) to develop a rapid reproducible detection system for vibrios based on RT-QPCR and SYBR chemistry. We were able to detect total vibrios in expressed RNA targeting the 16S rRNA gene at 5.23 × 10⁶ copies/μg RNA and V. coralliilyticus targeting the pyrH gene at 5.10 × 10³ copies/μg RNA in coral tissue. Detection of V. coralliilyticus in diseased and in healthy samples suggests that WPD in the Abrolhos Bank may be caused by a consortium of microorganism and not only a single pathogen. We developed a more practical and economic system compared with probe uses for the real-time detection and quantification of vibrios from coral tissues by using the 16S rRNA and pyrH gene. This qPCR assay is a reliable tool for the monitoring of coral pathogens, and can be useful to prevent, control, or reduce impacts in this ecosystem.

Rearranged Terpenoids from the Marine Sponge Darwinella cf. oxeata and Its Predator, the Nudibranch Felimida grahami

Marine sponges are a rich source of terpenoids with rearranged spongian carbon skeletons. Investigation of extracts from the sponge Darwinella cf. oxeata yielded four new rearranged diterpenoids, oxeatine (2) and oxeatamides H-J (3-5), as well as the known metabolites oxeatamide A (6), oxeatamide A methyl ester (7), and membranolide (1). Oxeatine (2) has a new heterocyclic skeleton, while oxeatamide J (5) has an N-methyl urea group included in a γ-lactam moiety. UPLC-QTOF analysis of the extract obtained from the mantle of the nudibranch Felimida grahami indicated the presence of 1 and 4.

Cultures of the Marine Bacterium Pseudovibrio denitrificans Ab134 Produce Bromotyrosine-Derived Alkaloids Previously Only Isolated from Marine Sponges

Herein we report the isolation and spectroscopic identification of fistularin-3 (1), 11-hydroxyaerothionin (2), and verongidoic acid (3), as well as the UPLC-HRMS detection of aerothionin (4), homopurpuroceratic acid B (5), purealidin L (6), and aplysinamisine II (7), from cultures of the marine bacterium Pseudovibrio denitrificans Ab134, isolated from tissues of the marine sponge Arenosclera brasiliensis. These results unambiguously demonstrate for the first time that bromotyrosine-derived alkaloids that were previously isolated only from Verongida sponges can be biosynthesized by a marine bacterium.

The chemistry and biology of guanidine natural products

The chemistry and biology of natural guanidines isolated from microbial culture media, from marine invertebrates, as well as from terrestrial plants and animals, are reviewed.

Analogues of Marine Guanidine Alkaloids Are in Vitro Effective against Trypanosoma cruzi and Selectively Eliminate Leishmania (L.) infantum Intracellular Amastigotes

Synthetic analogues of marine sponge guanidine alkaloids showed in vitro antiparasitic activity against Leishmania (L.) infantum and Trypanosoma cruzi. Guanidines 10 and 11 presented the highest selectivity index when tested against Leishmania. The antiparasitic activity of 10 and 11 was investigated in host cells and in parasites. Both compounds induced depolarization of mitochondrial membrane potential, upregulation of reactive oxygen species levels, and increased plasma membrane permeability in Leishmania parasites. Immunomodulatory assays suggested an NO-independent effect of guanidines 10 and 11 on macrophages. The same compounds also promoted anti-inflammatory activity in L. (L.) infantum-infected macrophages cocultived with splenocytes, reducing the production of cytokines MCP-1 and IFN-γ. Guanidines 10 and 11 affect the bioenergetic metabolism of Leishmania, with selective elimination of parasites via a host-independent mechanism.

Condensation of Macrocyclic Polyketides Produced by Penicillium sp. DRF2 with Mercaptopyruvate Represents a New Fungal Detoxification Pathway

Application of a refined procedure of experimental design and chemometric analysis to improve the production of curvularin-related polyketides by a marine-derived Penicillium sp. DRF2 resulted in the isolation and identification of cyclothiocurvularins 6-8 and cyclosulfoxicurvularins 10 and 11, novel curvularins condensed with a mercaptolactate residue. Two additional new curvularins, 3 and 4, are also reported. The structures of the sulfur-bearing curvularins were unambiguously established by analysis of spectroscopic data and by X-ray diffraction analysis. Analysis of stable isotope feeding experiments with [U-(13)C3(15)N]-l-cysteine confirmed the presence of the 2-hydroxy-3-mercaptopropanoic acid residue in 6-8 and the oxidized sulfoxide in 10 and 11. Cyclothiocurvularins A (6) and B (7) are formed by spontaneous reaction between 10,11-dehydrocurvularin (2) and mercaptopyruvate (12) obtained by transamination of cysteine. High ratios of [U-(13)C3(15)N]-l-cysteine incorporation into cyclothiocurvularin B (7), the isolation of two diastereomers of cyclothiocurvularins, the lack of cytotoxicity of cyclothiocurvularin B (7) and its methyl ester (8), and the spontaneous formation of cyclothiocurvularins from 10,11-dehydrocurvularin and mercaptopyruvate provide evidence that the formation of cyclothiocurvularins may well correspond to a 10,11-dehydrocurvularin detoxification process by Penicillium sp. DRF2.

The chemistry and biology of guanidine natural products

The present review discusses the isolation, structure determination, synthesis, biosynthesis and biological activities of secondary metabolites bearing a guanidine group.

Structure and Biogenesis of Roussoellatide, a Dichlorinated Polyketide from the Marine-Derived Fungus Roussoella sp. DLM33

The structure of the fungal metabolite roussoellatide (1) has been established by spectroscopic and X-ray diffraction analyses. Results from feeding experiments with [1-(13)C]acetate, [2-(13)C]acetate, and [1,2-(13)C]acetate were consistent with a biosynthetic pathway to the unprecedented skeleton of 1 involving Favorskii rearrangements in separate pentaketides, subsequently joined via an intermolecular Diels-Alder reaction.

Anti-parasitic Guanidine and Pyrimidine Alkaloids from the Marine Sponge Monanchora arbuscula

HPLC-UV-ELSD-MS-guided fractionation of the anti-parasitic extract obtained from the marine sponge Monanchora arbuscula, collected off the southeastern coast of Brazil, led to the isolation of a series of guanidine and pyrimidine alkaloids. The pyrimidines monalidine A (1) and arbusculidine A (7), as well as the guanidine alkaloids batzellamide A (8) and hemibatzelladines 9-11, represent new minor constituents that were identified by analysis of spectroscopic data. The total synthesis of monalidine A confirmed its structure. Arbusculidine A (7), related to the ptilocaulin/mirabilin/netamine family of tricyclic guanidine alkaloids, is the first in this family to possess a benzene ring. Batzellamide A (8) and hemibatzelladines 9-11 represent new carbon skeletons that are related to the batzelladines. Evaluation of the anti-parasitic activity of the major known metabolites, batzelladines D (12), F (13), L (14), and nor-L (15), as well as of synthetic monalidine A (1), against Trypanosoma cruzi and Leishmania infantum is also reported, along with a detailed investigation of parasite cell-death pathways promoted by batzelladine L (14) and norbatzelladine L (15).

The marine-derived fungus Tinctoporellus sp. CBMAI 1061 degrades the dye Remazol Brilliant Blue R producing anthraquinones and unique tremulane sesquiterpenes

Conversion of RBBR dye to anthraquinones by the fungusTinctoporellussp., also producing novel tremulene terpenes.

Total synthesis and isolation of citrinalin and cyclopiamine congeners

Many natural products that contain basic nitrogen atoms--for example alkaloids like morphine and quinine-have the potential to treat a broad range of human diseases. However, the presence of a nitrogen atom in a target molecule can complicate its chemical synthesis because of the basicity of nitrogen atoms and their susceptibility to oxidation. Obtaining such compounds by chemical synthesis can be further complicated by the presence of multiple nitrogen atoms, but it can be done by the selective introduction and removal of functional groups that mitigate basicity. Here we use such a strategy to complete the chemical syntheses of citrinalin B and cyclopiamine B. The chemical connections that have been realized as a result of these syntheses, in addition to the isolation of both 17-hydroxycitrinalin B and citrinalin C (which contains a bicyclo[2.2.2]diazaoctane structural unit) through carbon-13 feeding studies, support the existence of a common bicyclo[2.2.2]diazaoctane-containing biogenetic precursor to these compounds, as has been proposed previously.

Diversity and antimicrobial potential of culturable heterotrophic bacteria associated with the endemic marine sponge Arenosclera brasiliensis

Marine sponges are the oldest Metazoa, very often presenting a complex microbial consortium. Such is the case of the marine sponge Arenosclera brasiliensis, endemic to Rio de Janeiro State, Brazil. In this investigation we characterized the diversity of some of the culturable heterotrophic bacteria living in association with A. brasiliensis and determined their antimicrobial activity. The genera Endozoicomonas (N = 32), Bacillus (N = 26), Shewanella (N = 17), Pseudovibrio (N = 12), and Ruegeria (N = 8) were dominant among the recovered isolates, corresponding to 97% of all isolates. Approximately one third of the isolates living in association with A. brasiliensis produced antibiotics that inhibited the growth of Bacillus subtilis, suggesting that bacteria associated with this sponge play a role in its health.

Antifungal Activity of Metabolites from the Marine Sponges Amphimedon sp. and Monanchora arbuscula against Aspergillus flavus Strains Isolated from Peanuts (Arachis hypogaea)

Contamination of preharvest and stored peanuts ( Arachis hypogaea L.) by aflatoxigenic strains of Aspergillus flavus is an important economical and food safety problem in many tropical and subtropical areas of the world. The present investigation reports the antifungal activity of a halitoxins/amphitoxins enriched extract obtained from the sponge Amphimedon sp. (HAEEAsp), and of batzelladine L isolated from the sponge Monanchora arbuscula on Aspergillus flavus isolated from stored peanuts. A PCR system directed against the ITS region and aflatoxin biosynthetic pathway genes of A. flavus was applied for identification of aflatoxin producing strains. The HAEEAsp extract and batzelladine L showed minimal inhibitory concentration (MIC) in the range between 1.9 to 15.6 μg/mL and between 1.9 to 7.8 μg/mL, respectively. The minimal fungicide concentration (MFC) of HAEEAsp extract and batzelladine L was in the range between 3.9 to 31.3 μg/mL and 3.9 to 15.6 μg/mL, respectively. These results indicate that these marine alkaloids may be further explored for the development of potential lead compounds active against aflatoxigenic fungi.