Deep-sea natural products

Bonnevillamides, Linear Heptapeptides Isolated from a Great Salt Lake-Derived Streptomyces sp

Streptomyces sp. GSL-6B was isolated from sediment collected from the Great Salt Lake and investigation of its organic extract led to the isolation of three new linear heptapeptides, bonnevillamides A (1), B (2), and C (3). The bonnevillamides represent a new class of linear peptides featuring unprecedented non-proteinogenic amino acids. All three peptides contain the newly characterized bonnevillic acid moiety (3-(3,5-dichloro-4-methoxyphenyl)-2-hydroxyacrylic acid), as well as a heavily modified proline residue. Moreover, in bonnevillamide A, the terminal proline residue found in bonnevillamides B and C is replaced with 4-methyl-azetidine-2-carboxylic acid methyl ester. The structures of the three heptapeptides were elucidated by NMR, high-resolution electrospray ionization mass spectroscopy (HRESIMS), and LC-MS/MS, and the absolute configuration of all proteinogenic amino acid residues were determined by advanced Marfey’s method. Bonnevillamides A, B and C were evaluated for their effects on zebrafish embryo development. All three heptapeptides were shown to modulate heart growth and cardiac function, with bonnevillamide B having the most pronounced effect.

35 Years of Marine Natural Product Research in Sweden: Cool Molecules and Models from Cold Waters

Currents efforts in marine biodiscovery have essentially focused on temperate to tropical shallow water organisms. With more than 6000 species of marine plants and animals, the Kosterfjord area has the richest marine biodiversity in Swedish waters, but it remains understudied. The overall objective of our marine pharmacognosy research is to explore and reveal the pharmacological potential of organisms from this poorly explored region. More generally, we wish to understand aspects of structure-activity relationships of chemical interactions in cold-water marine environment (shallow and deep). Our strategy is based on ecologically guided search for compounds through studies of physiology and organism interactions coupled to identification of bioactive molecules guided by especially in vivo assays. The research programme originated in the beginning of the 1980s with a broad screening of Swedish marine organisms using both in vitro and in vivo assays, resulting in isolation and identification of several different bioactive molecules. Two congenerous cyclopeptides, i.e. barettin and 8,9-dihydrobarettin, were isolated from the deep-sea sponge Geodia barretti, and structurally elucidated, guided by their antifouling activity and their affinity to a selection of human serotonin receptors. To optimize the activity a number of analogues of barettin were synthezised and tested for antifouling activity. Within the EU project BlueGenics, two larger homologous peptides, barrettides A and B, were isolated from G. baretti. Also, metabolic fingerprinting combined with sponge systematics was used to further study deep-sea natural product diversity in the genus Geodia. Finally, the chemical property space model 'ChemGPS-NP' has been developed and used in our research group, enabling a more efficient use of obtained compounds and exploration of possible biological activities and targets. Another approach is the broad application of phylogenetic frameworks, which can be used in prediction of where-in which organisms-to search for novel molecules or better sources of known molecules in marine organisms. In a further perspective, the deeper understanding of evolution and development of life on Earth can also provide answers to why marine organisms produce specific molecules.

Deep Sea Actinomycetes and Their Secondary Metabolites

Deep sea is a unique and extreme environment. It is a hot spot for hunting marine actinomycetes resources and secondary metabolites. The novel deep sea actinomycete species reported from 2006 to 2016 including 21 species under 13 genera with the maximum number from Microbacterium, followed by Dermacoccus, Streptomyces and Verrucosispora, and one novel species for the other 9 genera. Eight genera of actinomycetes were reported to produce secondary metabolites, among which Streptomyces is the richest producer. Most of the compounds produced by the deep sea actinomycetes presented antimicrobial and anti-cancer cell activities. Gene clusters related to biosynthesis of desotamide, heronamide, and lobophorin have been identified from the deep sea derived Streptomyces.

Discovery of Antimycin-Type Depsipeptides from a wbl Gene Mutant Strain of Deepsea-Derived Streptomyces somaliensis SCSIO ZH66 and Their Effects on Pro-inflammatory Cytokine Production

Deepsea microbes are a rich source of novel bioactive compounds, which have developed unique genetic systems as well as biosynthetic pathways compared with those of terrestrial microbes in order to survive in extreme living environment. However, a large variety of deepsea-microbial secondary metabolic pathways remain “cryptic” under the normal laboratory conditions. Manipulation of global regulators is one of the effective approaches for triggering the production of cryptic secondary metabolites. In this study, by combination of various chromatographic purification process, we obtained somalimycin (1), a new antimycin-type depsipeptide, with an unusual substitution of 3-aminosalicylate instead of conserved 3-formamidosalicylate moiety, along with two known (2 and 3) analogs from the ΔwblA_so mutant strain of deepsea-derived Streptomyces somaliensis SCSIO ZH66. The structures of 1–3 were elucidated on the basis of extensive spectroscopic analyses including LC-MS and NMR. In the evaluation of potent anti-inflammatory activity, compound 2 exhibited strong inhibitory activity on the IL-5 production in ovalbumin-stimulated splenocytes with IC₅₀ value of 0.57 μM, while 1 and 3 displayed mild effect (>10 μM), which might be attributed to their different side-chain substitutions. Moreover, compounds 1–3 showed very weak cytotoxicity against human umbilical vein endothelial cells with LD₅₀ values of 62.6, 34.6, and 192.9 μM, respectively, which were far over their IL-5 inhibitory activity. These results indicated that these compounds have good potential for further use in anti-inflammatory drug development.

Antifungal peptidic compound from the deep-sea bacterium Aneurinibacillus sp. YR247

Aneurinibacillus: sp. YR247 was newly isolated from the deep-sea sediment inside the Calyptogena community at a depth of 1171 m in Sagami Bay. The strain exhibited antifungal activity against the filamentous fungus Aspergillus brasiliensis NBRC9455. A crude extract prepared from the YR247 cells by ethanol extraction exhibited broad antimicrobial activities. The antifungal compound is stable at 4-70 °C and pH 2.0-12.0. After treatment with proteinase K, the antifungal activity was not detected, indicating that the antifungal compound of strain YR247 is a peptidic compound. Electrospray ionization mass spectrometry of the purified antifungal compound indicated that the peptidic compound has an average molecular weight of 1167.9. The molecular weight of the antifungal compound from strain YR247 is different from those of antimicrobial peptides produced by the related Aneurinibacillus and Bacillus bacteria. The antifungal peptidic compound from the deep-sea bacterium Aneurinibacillus sp. YR247 may be useful as a biocontrol agent.

Brevianamides and Mycophenolic Acid Derivatives from the Deep-Sea-Derived Fungus Penicillium brevicompactum DFFSCS025

Four new compounds (1–4), including two brevianamides and two mycochromenic acid derivatives along with six known compounds were isolated from the deep-sea-derived fungus Penicillium brevicompactum DFFSCS025. Their structures were elucidated by spectroscopic analysis. Moreover, the absolute configurations of 1 and 2 were determined by quantum chemical calculations of the electronic circular dichroism (ECD) spectra. Compound 9 showed moderate cytotoxicity against human colon cancer HCT116 cell line with IC₅₀ value of 15.6 μM. In addition, 3 and 5 had significant antifouling activity against Bugula neritina larval settlement with EC₅₀ values of 13.7 and 22.6 μM, respectively. The NMR data of 6, 8, and 9 were assigned for the first time.

Cold-water marine natural products, 2006 to 2016

This is an update report on marine natural products isolated from cold-water organisms in the last decade, following the previous review that covered the literature up to 2005. Emphasis is on structural assignments and biological activity.

Biscogniauxone, a New Isopyrrolonaphthoquinone Compound from the Fungus Biscogniauxia mediterranea Isolated from Deep-Sea Sediments

The properties and the production of new metabolites from the fungal strain LF657 isolated from the Herodotes Deep (2800 m depth) in the Mediterranean Sea are reported in this study. The new isolate was identified as Biscogniauxia mediterranea based on ITS1-5.8S-ITS2 and 28S rRNA gene sequences. A new isopyrrolonaphthoquinone with inhibitory activity against glycogen synthase kinase (GSK-3β) was isolated from this fungus. This is the first report of this class of compounds from a fungus isolated from a deep-sea sediment, as well as from a Biscogniauxia species.

Marine-Derived Pharmaceuticals - Challenges and Opportunities

Marine biosphere is the largest one of the earth and harbors an enormous number of different organisms. Living conditions differ fundamentally from those in terrestrial environment. The production of specific secondary metabolites is an important adaption mechanism of marine organisms to survive in the sea. These metabolites possess biological activities which make them interesting as possible drugs for human. The review presents sources, chemistry, production and pharmacology of FDA approved marine derived pharmaceuticals arranged according to their therapeutic indication. Four of the presently seven approved drugs are used for the treatment of cancer. Each another one is applicated for treatment of viral diseases, chronic pain and to lower triglyceride level in blood. Some other products are of interest in diagnostic and as experimental tools. Besides, this article describes challenges in drug development from marine sources, especially the supply problem.

Exopisiod B and farylhydrazone C, two new alkaloids from the Antarctic-derived fungus Penicillium sp. HDN14-431

Two new compounds, exopisiod B (1) and farylhydrazone C (2), together with two known compounds (3-4), were isolated from the Antarctic-derived fungus Penicillium sp. HDN14-431. Their structures including absolute configurations were elucidated by spectroscopic methods and TDDFT ECD calculations. The cytotoxicity and antimicrobial activities of all compounds were tested.

Total syntheses of (±)-spiroindimicins B and C enabled by a late-stage Schöllkopf-Magnus-Barton-Zard (SMBZ) reaction

The spiroindimicins are a family of structurally unprecedented alkaloids isolated from the deep-sea-derived marine actinomycete Streptomyces sp. SCSIO 03032. The total syntheses of (±)-spiroindimicins B and C are disclosed, the first of any member of this family. Central to the successful strategy was installing the spirocentre using a mild intramolecular Heck reaction, the assembly of a pentacyclic spirobisindole by Fischer indolization and a late-stage Schöllkopf-Magnus-Barton-Zard (SMBZ) reaction to construct the trisubstituted pyrrole.

Antifungal New Oxepine-Containing Alkaloids and Xanthones from the Deep-Sea-Derived Fungus Aspergillus versicolor SCSIO 05879

Phytopathogenic fungi remain a continuous and huge threat in the agricultural fields. The agrochemical industry has made great development of the use of microbial natural products, which has been regarded as an effective strategy against phytopathogenic fungi. Antifungal bioassay-directed fractionation was used to isolate two new oxepine-containing alkaloids (1 and 2), two new 4-aryl-quinolin-2-one alkaloids (3 and 4), and four new prenylated xanthones (5-8) from the deep-sea-derived fungus Aspergillus versicolor SCSIO 05879. Extensive NMR spectroscopic analysis, quantum mechanical calculations, and X-ray single-crystal diffraction were used to elucidate their structures, including their absolute configurations. Versicoloids A and B, versicone A, and cottoquinazoline A showed antifungal activities against three phytopathogenic fungi. The antifungal activities of these bioactive compounds strongly depend on the fungal species. Especially versicoloids A and B showed strong fungicidal effect (MIC of 1.6 μg/mL) against Colletotrichum acutatum, compared with that of the positive control cycloheximide (MIC of 6.4 μg/mL). The results of antifungal experiments indicated that versicoloids A and B may be regarded as candidate agents of antifungal agrochemicals.

Leveraging ecological theory to guide natural product discovery

Technological improvements have accelerated natural product (NP) discovery and engineering to the point that systematic genome mining for new molecules is on the horizon. NP biosynthetic potential is not equally distributed across organisms, environments, or microbial life histories, but instead is enriched in a number of prolific clades. Also, NPs are not equally abundant in nature; some are quite common and others markedly rare. Armed with this knowledge, random ‘fishing expeditions’ for new NPs are increasingly harder to justify. Understanding the ecological and evolutionary pressures that drive the non-uniform distribution of NP biosynthesis provides a rational framework for the targeted isolation of strains enriched in new NP potential. Additionally, ecological theory leads to testable hypotheses regarding the roles of NPs in shaping ecosystems. Here we review several recent strain prioritization practices and discuss the ecological and evolutionary underpinnings for each. Finally, we offer perspectives on leveraging microbial ecology and evolutionary biology for future NP discovery.

Aspertetranones A-D, Putative Meroterpenoids from the Marine Algal-Associated Fungus Aspergillus sp. ZL0-1b14

Aspertetranones A-D (1-4), four new highly oxygenated putative rearranged triketide-sesquiterpenoid meroterpenes, were isolated from the marine algal-associated fungus Aspergillus sp. ZL0-1b14. On the basis of a comprehensive spectroscopic analysis, the planar structures of aspertetranones were determined to possess an unusual skeleton in the terpenoid part. The relative and absolute configurations of the aspertetranones were assigned on the basis of NOESY analysis, X-ray crystallography, and circular dichroism spectroscopy. Compounds 1-4 were evaluated for anti-inflammatory activity in LPS-stimulated RAW264.7 macrophages. Aspertetranone D exhibited an inhibitory effect against IL-6 production with 69% inhibition at 40 μM.

Concise Total Synthesis of Aplysinellamides A and B

Concise and efficient total syntheses of bromotyrosine-derived metabolites aplysinellamides A and B, isolated from Australian marine sponge Aplysinella sp., have been accomplished in seven steps. A condensation between cinnamic acid and Boc-D-lysine methyl ester was applied to form the amide skeleton as a key step.

3-Nitroasterric Acid Derivatives from an Antarctic Sponge-Derived Pseudogymnoascus sp. Fungus

Four new nitroasterric acid derivatives, pseudogymnoascins A-C (1-3) and 3-nitroasterric acid (4), along with the two known compounds questin and pyriculamide, were obtained from the cultures of a Pseudogymnoascus sp. fungus isolated from an Antarctic marine sponge belonging to the genus Hymeniacidon. The structures of the new compounds were determined by extensive NMR and MS analyses. These compounds are the first nitro derivatives of the known fungal metabolite asterric acid. Several asterric acid derivatives isolated from other fungal strains have shown antibacterial and antifungal activities. However, the new compounds described in this work were inactive against a panel of bacteria and fungi (MIC > 64 μg/mL).

New polyphenols from a deep sea Spiromastix sp. Fungus, and their antibacterial activities

Eleven new polyphenols namely spiromastols A–K (1–11) were isolated from the fermentation broth of a deep sea-derived fungus Spiromastix sp. MCCC 3A00308. Their structures were determined by extensive NMR data and mass spectroscopic analysis in association with chemical conversion. The structures are classified as diphenyl ethers, diphenyl esters and isocoumarin derivatives, while the n-propyl group in the analogues is rarely found in natural products. Compounds 1–3 exhibited potent inhibitory effects against a panel of bacterial strains, including Xanthomanes vesicatoria, Pseudomonas lachrymans, Agrobacterium tumefaciens, Ralstonia solanacearum, Bacillus thuringensis, Staphylococcus aureus and Bacillus subtilis, with minimal inhibitory concentration (MIC) values ranging from 0.25 to 4 µg/mL. The structure-activity relationships are discussed, while the polychlorinated analogues 1–3 are assumed to be a promising structural model for further development as antibacterial agents.

Cytotoxic and antibacterial angucycline- and prodigiosin-analogues from the deep-sea derived Streptomyces sp. SCSIO 11594

Two new C-glycoside angucyclines, marangucycline A (1) and marangucycline B (2), along with three known compounds, dehydroxyaquayamycin (3), undecylprodigiosin (4) and metacycloprodigiosin (5), have been identified as products of the deep-sea sediment strain Streptomyces sp. SCSIO 11594. New structures were elucidated on the basis of HRESIMS, 1D and 2D NMR analyses and comparisons to previously reported datasets. Compounds 2 and 4 displayed in vitro cytotoxicity against four cancer cell lines A594, CNE2, HepG2, MCF-7 superior to those obtained with cisplatin, the positive control. Notably, compound 2 bearing a keto-sugar displayed significant cytotoxicity against cancer cell lines with IC50 values ranging from 0.24 to 0.56 μM; An IC50 value of 3.67 μM was found when using non-cancerous hepatic cell line HL7702, demonstrating the cancer cell selectivity of 2. Compounds 1-3 were proved to have weak antibacterial activities against Enterococcus faecalis ATCC29212 with an MIC value of 64.0 μg/mL. Moreover, 3 displayed selective antibacterial activity against methicillin-resistant Staphylococcus epidermidis shhs-E1 with an MIC value of 16.0 μg/mL.

The Kolumbo submarine volcano of Santorini island is a large pool of bacterial strains with antimicrobial activity

Microbes in hydrothermal vents with their unique secondary metabolism may represent an untapped potential source of new natural products. In this study, samples were collected from the hydrothermal field of Kolumbo submarine volcano in the Aegean Sea, in order to isolate bacteria with antimicrobial activity. Eight hundred and thirty-two aerobic heterotrophic bacteria were isolated and then differentiated through BOX-PCR analysis at the strain level into 230 genomic fingerprints, which were screened against 13 different type strains (pathogenic and nonpathogenic) of Gram-positive, Gram-negative bacteria and fungi. Forty-two out of 176 bioactive-producing genotypes (76 %) exhibited antimicrobial activity against at least four different type strains and were selected for 16S rDNA sequencing and screening for nonribosomal peptide (NRPS) and polyketide (PKS) synthases genes. The isolates were assigned to genus Bacillus and Proteobacteria, and 20 strains harbored either NRPS, PKS type I or both genes. This is the first report on the diversity of culturable mesophilic bacteria associated with antimicrobial activity from Kolumbo area; the extremely high proportion of antimicrobial-producing strains suggested that this unique environment may represent a potential reservoir of novel bioactive compounds.

Cytotoxic polyketides from the deep-sea-derived fungus Engyodontium album DFFSCS021

Eight new chromones, engyodontiumones A-H (1-8), and three new phenol derivatives (9-11) together with eight known polyketides (12-19) were isolated from the deep-sea-derived fungus Engyodontium album DFFSCS021. Their structures were identified by extensive spectroscopic analysis. Compounds 8 and 16 showed significant selective cytotoxicity against human histiocytic lymphoma U937 cell line with IC50 values of 4.9 and 8.8 μM, respectively. In addition, this is the first time to report that 8, 15 and 16 had mild antibacterial activity against Escherichia coli and Bacillus subtilis, and 15 showed potent antilarval activity against barnacle Balanus amphitrite larval settlement.

Recent advances in deep-sea natural products

Covering: 2009 to 2013. This review covers the 188 novel marine natural products described since 2008, from deep-water (50->5000 m) marine fauna including bryozoa, chordata, cnidaria, echinodermata, microorganisms, mollusca and porifera. The structures of the new compounds and details of the source organism, depth of collection and country of origin are presented, along with any relevant biological activities of the metabolites. Where reported, synthetic studies on the deep-sea natural products have also been included. Most strikingly, 75% of the compounds were reported to possess bioactivity, with almost half exhibiting low micromolar cytotoxicity towards a range of human cancer cell lines, along with a significant increase in the number of microbial deep-sea natural products reported.

Marine sponge derived natural products between 2001 and 2010: trends and opportunities for discovery of bioactives

Marine sponges belonging to the phylum Porifera (Metazoa), evolutionarily the oldest animals are the single best source of marine natural products. The present review presents a comprehensive overview of the source, taxonomy, country of origin or geographical position, chemical class, and biological activity of sponge-derived new natural products discovered between 2001 and 2010. The data has been analyzed with a view to gaining an outlook on the future trends and opportunities in the search for new compounds and their sources from marine sponges.

Global reductions in seafloor biomass in response to climate change

Seafloor organisms are vital for healthy marine ecosystems, contributing to elemental cycling, benthic remineralization, and ultimately sequestration of carbon. Deep-sea life is primarily reliant on the export flux of particulate organic carbon from the surface ocean for food, but most ocean biogeochemistry models predict global decreases in export flux resulting from 21st century anthropogenically induced warming. Here we show that decadal-to-century scale changes in carbon export associated with climate change lead to an estimated 5.2% decrease in future (2091-2100) global open ocean benthic biomass under RCP8.5 (reduction of 5.2 Mt C) compared with contemporary conditions (2006-2015). Our projections use multi-model mean export flux estimates from eight fully coupled earth system models, which contributed to the Coupled Model Intercomparison Project Phase 5, that have been forced by high and low representative concentration pathways (RCP8.5 and 4.5, respectively). These export flux estimates are used in conjunction with published empirical relationships to predict changes in benthic biomass. The polar oceans and some upwelling areas may experience increases in benthic biomass, but most other regions show decreases, with up to 38% reductions in parts of the northeast Atlantic. Our analysis projects a future ocean with smaller sized infaunal benthos, potentially reducing energy transfer rates though benthic multicellular food webs. More than 80% of potential deep-water biodiversity hotspots known around the world, including canyons, seamounts, and cold-water coral reefs, are projected to experience negative changes in biomass. These major reductions in biomass may lead to widespread change in benthic ecosystems and the functions and services they provide.

Nine new and five known polyketides derived from a deep sea-sourced Aspergillus sp. 16-02-1

Nine new C₉ polyketides, named aspiketolactonol (1), aspilactonols A–F (2–7), aspyronol (9) and epiaspinonediol (11), were isolated together with five known polyketides, (S)-2-(2′-hydroxyethyl)-4-methyl-γ-butyrolactone (8), dihydroaspyrone (10), aspinotriol A (12), aspinotriol B (13) and chaetoquadrin F (14), from the secondary metabolites of an Aspergillus sp. 16-02-1 that was isolated from a deep-sea sediment sample. Structures of the new compounds, including their absolute configurations, were determined by spectroscopic methods, especially the 2D NMR, circular dichroism (CD), Mo₂-induced CD and Mosher’s ¹H NMR analyses. Compound 8 was isolated from natural sources for the first time, and the possible biosynthetic pathways for 1–14 were also proposed and discussed. Compounds 1–14 inhibited human cancer cell lines, K562, HL-60, HeLa and BGC-823, to varying extents.

Shagenes A and B, new tricyclic sesquiterpenes produced by an undescribed Antarctic octocoral

The isolation and characterization of two new tricyclic sesquiterpenoids, shagenes A (1) and B (2) are presented. These compounds were isolated from an undescribed soft coral collected from the Scotia Arc in the Southern Ocean. One- and two-dimensional NMR spectroscopy and mass spectrometry provided the data necessary to characterize the compounds and their relative stereochemical configurations. Exploration of the bioactivity of shagenes A and B found 1 active against the visceral leishmaniasis causing parasite, Leishmania donovani, with no cytotoxicity against the mammalian host.

Spiromastixones A-O, antibacterial chlorodepsidones from a deep-sea-derived Spiromastix sp. fungus

Fifteen new depsidone-based analogues named spiromastixones A-O (1-15) were isolated from the fermentation broth of a deep-sea Spiromastix sp. fungus. Their structures were elucidated on the basis of extensive NMR and mass spectroscopic analysis in association with chemical conversion. Spiromastixones A-O are classified into two subtypes based on the orientation of ring C relative to ring A, while the n-propyl substituents on rings A and C are rarely seen in natural products. Most analogues are substituted by various numbers of chlorine atoms. All compounds exhibited significant inhibition against Gram-positive bacteria including Staphylococcus aureus, Bacillus thuringiensis, and Bacillus subtilis with MIC values ranging from 0.125 to 8.0 μg/mL. In addition, compounds 6-10 displayed potent inhibitory effects against methicillin-resistant bacterial strains of S. aureus (MRSA) and S. epidermidis (MRSE), while 10 also inhibited the growth of the vancomycin-resistant bacteria Enterococcus faecalis and E. faecium (VRE). The structure-activity relationships are discussed.

New fatty acids from the Red Sea sponge Mycale euplectellioides

Chemical investigation of the Red Sea sponge Mycale euplectellioides afforded two new compounds; hexacosa-(6Z,10Z)-dienoic acid methyl ester (1) and hexacosa-(6Z,10Z)-dienoic acid (2), along with two known compounds: icosa-(8Z,11Z)-dienoic acid methyl ester (3) and β-sitosterol (4). The structures were elucidated by the interpretation of their spectral data. The total methanol extract (TME) of the sponge exhibited potent antimicrobial activity against the different strains at a concentration of 100 mg/mL. All tested fractions did not exhibit any activity against Serratia marcescens and tested fungal strains. The TME and different fractions displayed anti-inflammatory and antipyretic activities at doses of 100 and 200 mg/kg compared with indomethacin (8 mg). The TME exhibited a remarkable hepato-protective effect in CCl4-induced liver damage compared with silymarin. Furthermore, compounds 1 and 2 displayed weak activity against A549 non-small cell lung cancer, the U373 glioblastoma and the PC-3 prostate cancer cell lines.

Indole-based alkaloids from deep-sea bacterium Shewanella piezotolerans with antitumor activities

Chromatographic separation of a crude extract obtained from a fermentation broth of a chemically unknown bacterium Shewanella piezotolerans WP3 collected in deep-sea yielded three new indole alkaloids namely shewanellines A (1a), B (1b) and C (2), together with 12 known indole alkaloids. The structures were unambiguously elucidated on the basis of 1D and 2D NMR ((1)H, (13)C, COSY, HMBC, HSQC and NOESY) in association with MS and CD data. Compounds 1-4, 7, 9 and 11-14 were selected for the evaluation of their cytotoxic activities against human tumor cell lines HL-60 and BEL-7402, whereas compounds 2, 4 and 9 exhibited significant inhibition toward HL-60.

Concise synthesis of didebromohamacanthin A and demethylaplysinopsine: addition of ethylenediamine and guanidine derivatives to the pyrrole-amino acid diketopiperazines in oxidative conditions

Oxidative nucleophilic addition of ethylenediamine and guanidine derivatives to pyrrole-amino acid diketopiperazines was shown to provide substituted 5,6-dihydro-2(1H)-piperazinones, quinoxalinones, and 2-aminoimidazolones. On the basis of this methodology, a concise approach to natural products didebromohamacanthin A and demethylaplysinopsine has been demonstrated.

Recent advances in deep-sea natural products

Review of deep-sea natural products covering the five-year period 2009–2013.

Marine Bi-, Bis-, and Trisindole Alkaloids

This chapter, covering the chemistry literature up until June 2013 and comprising 142 references, records the chemical structures of 130 bi-, bis-, and trisindole alkaloids isolated from a plethora of marine phyla including bacteria, algae, bryozoans, sponges, mollusks, hard corals, and ascidians. While the vast majority of bisindoles have been isolated from marine sponges, biindoles are more commonly found in red algae species than sponges. Trisindoles are far less common than bisindoles in the marine environment and have been limited to two species of sponge and a single species of marine microbe. Antimicrobial activity and cytotoxicity dominate the bioactivities explored for selected members of this family of alkaloids. Synthetic approaches to 28 natural products are presented in 33 schemes, and in the absence of any in vivo biosynthetic studies, the putative biosyntheses of eight bisindole metabolites are presented.

Induction of apoptosis in cancer cell lines by the Red Sea brine pool bacterial extracts

BACKGROUND

Marine microorganisms are considered to be an important source of bioactive molecules against various diseases and have great potential to increase the number of lead molecules in clinical trials. Progress in novel microbial culturing techniques as well as greater accessibility to unique oceanic habitats has placed the marine environment as a new frontier in the field of natural product drug discovery.

METHODS

A total of 24 microbial extracts from deep-sea brine pools in the Red Sea have been evaluated for their anticancer potential against three human cancer cell lines. Downstream analysis of these six most potent extracts was done using various biological assays, such as Caspase-3/7 activity, mitochondrial membrane potential (MMP), PARP-1 cleavage and expression of γH2Ax, Caspase-8 and -9 using western blotting.

RESULTS

In general, most of the microbial extracts were found to be cytotoxic against one or more cancer cell lines with cell line specific activities. Out of the 13 most active microbial extracts, six extracts were able to induce significantly higher apoptosis (>70%) in cancer cells. Mechanism level studies revealed that extracts from Chromohalobacter salexigens (P3-86A and P3-86B(2)) followed the sequence of events of apoptotic pathway involving MMP disruption, caspase-3/7 activity, caspase-8 cleavage, PARP-1 cleavage and Phosphatidylserine (PS) exposure, whereas another Chromohalobacter salexigens extract (K30) induced caspase-9 mediated apoptosis. The extracts from Halomonas meridiana (P3-37B), Chromohalobacter israelensis (K18) and Idiomarina loihiensis (P3-37C) were unable to induce any change in MMP in HeLa cancer cells, and thus suggested mitochondria-independent apoptosis induction. However, further detection of a PARP-1 cleavage product, and the observed changes in caspase-8 and -9 suggested the involvement of caspase-mediated apoptotic pathways.

CONCLUSION

Altogether, the study offers novel findings regarding the anticancer potential of several halophilic bacterial species inhabiting the Red Sea (at the depth of 1500-2500 m), which constitute valuable candidates for further isolation and characterization of bioactive molecules.

Alkaloids from the deep-sea-derived fungus Aspergillus westerdijkiae DFFSCS013

Two new benzodiazepine alkaloids, circumdatins K and L (1, 2), two new prenylated indole alkaloids, 5-chlorosclerotiamide (3) and 10-epi-sclerotiamide (4), and one novel amide, aspergilliamide B (5), together with six known alkaloids were isolated from the deep-sea-derived fungus Aspergillus westerdijkiae DFFSCS013. Their structures were elucidated by extensive spectroscopic analysis. All of the compounds were tested for cytotoxicity toward human carcinoma A549, HL-60, K562, and MCF-7 cell lines.