Thorectidiol A Isolated from the Marine Sponge Dactylospongia elegans Disrupts Interactions of the SARS-CoV-2 Spike Receptor Binding Domain with the Host ACE2 Receptor.

Thorectidiols isolated from the marine sponge Dactylospongia elegans (family Thorectidae, order Dictyoceratida) collected in Papua New Guinea are a family of symmetrical and unsymmetrical dimeric biphenyl meroterpenoid stereoisomers presumed to be products of oxidative phenol coupling of a co-occurring racemic monomer, thorectidol (3). One member of the family, thorectidiol A (1), has been isolated in its natural form, and its structure has been elucidated by analysis of NMR, MS, and ECD data. Acetylation of the sponge extract facilitated isolation of additional thorectidiol diacetate stereoisomers and the isolation of the racemic monomer thorectidol acetate (6). Racemic thorectidiol A (1) showed selective inhibition of the SARS-CoV-2 spike receptor binding domain (RBD) interaction with the host ACE2 receptor with an IC50 = 1.0 ± 0.7 µM.

Natural Products Produced in Culture by Biosynthetically Talented Salinispora arenicola Strains Isolated from Northeastern and South Pacific Marine Sediments.

Laboratory cultures of two 'biosynthetically talented' bacterial strains harvested from tropical and temperate Pacific Ocean sediment habitats were examined for the production of new natural products. Cultures of the tropical Salinispora arenicola strain RJA3005, harvested from a PNG marine sediment, produced salinorcinol (3) and salinacetamide (4), which had previously been reported as products of engineered and mutated strains of Amycolatopsis mediterranei, but had not been found before as natural products. An S. arenicola strain RJA4486, harvested from marine sediment collected in the temperate ocean waters off British Columbia, produced the new aminoquinone polyketide salinisporamine (5). Natural products 3, 4, and 5 are putative shunt products of the widely distributed rifamycin biosynthetic pathway.

Accessing chemical diversity from the uncultivated symbionts of small marine animals.

Chemistry drives many biological interactions between the microbiota and host animals, yet it is often challenging to identify the chemicals involved. This poses a problem, as such small molecules are excellent sources of potential pharmaceuticals, pretested by nature for animal compatibility. We discovered anti-HIV compounds from small, marine tunicates from the Eastern Fields of Papua New Guinea. Tunicates are a reservoir for new bioactive chemicals, yet their small size often impedes identification or even detection of the chemicals within. We solved this problem by combining chemistry, metagenomics, and synthetic biology to directly identify and synthesize the natural products. We show that these anti-HIV compounds, the divamides, are a novel family of lanthipeptides produced by symbiotic bacteria living in the tunicate. Neighboring animal colonies contain structurally related divamides that differ starkly in their biological properties, suggesting a role for biosynthetic plasticity in a native context wherein biological interactions take place.

Structures of Nahuoic Acids B-E Produced in Culture by a Streptomyces sp. Isolated from a Marine Sediment and Evidence for the Inhibition of the Histone Methyl Transferase SETD8 in Human Cancer Cells by Nahuoic Acid A.

Nahuoic acids A-E (1-5) have been isolated from laboratory cultures of a Streptomyces sp. obtained from a tropical marine sediment. The structures of the new polyketides 2-5 were elucidated by analysis of spectroscopic data of the natural products and the chemical derivatives 6 and 7. Nahuoic acids 1-5 are in vitro inhibitors of the histone methyltransferase SETD8, and nahuoic acid A (1) and its pentaacetate derivative 8 inhibit the proliferation of several cancer cells lines in vitro with modest potency. At the IC50 for cancer cell proliferation, nahuoic acid A (1) showed selective inhibition of SETD8 in U2OS osteosarcoma cells that reflect its selectivity against a panel of pure histone methyl transferases. A cell cycle analysis revealed that the cellular toxicity of nahuoic acid A (1) is likely linked to its ability to inhibit SETD8 activity.

Single-molecule inhibition of human kinesin by adociasulfate-13 and -14 from the sponge Cladocroce aculeata.

Two merotriterpenoid hydroquinone sulfates designated adociasulfate-13 (1) and adociasulfate-14 (2) were purified from Cladocroce aculeata (Chalinidae) along with adociasulfate-8. All three compounds were found to inhibit microtubule-stimulated ATPase activity of kinesin at 15 µM by blocking both the binding of microtubules and the processive motion of kinesin along microtubules. These findings directly show that substitution of the 5'-sulfate in 1 for a glycolic acid moiety in 2 maintains kinesin inhibition. Nomarski imaging and bead diffusion assays in the presence of adociasulfates showed no signs of either free-floating or bead-bound adociasulfate aggregates. Single-molecule biophysical experiments also suggest that inhibition of kinesin activity does not involve adociasulfate aggregation. Furthermore, both mitotic and nonmitotic kinesins are inhibited by adociasulfates to a significantly different extent. We also report evidence that microtubule binding of nonkinesin microtubule binding domains may be affected by adociasulfates.

Actinoramide A Identified as a Potent Antimalarial from Titration-Based Screening of Marine Natural Product Extracts.

Methods to identify the bioactive diversity within natural product extracts (NPEs) continue to evolve. NPEs constitute complex mixtures of chemical substances varying in structure, composition, and abundance. NPEs can therefore be challenging to evaluate efficiently with high-throughput screening approaches designed to test pure substances. Here we facilitate the rapid identification and prioritization of antimalarial NPEs using a pharmacologically driven, quantitative high-throughput-screening (qHTS) paradigm. In qHTS each NPE is tested across a concentration range from which sigmoidal response, efficacy, and apparent EC50s can be used to rank order NPEs for subsequent organism reculture, extraction, and fractionation. Using an NPE library derived from diverse marine microorganisms we observed potent antimalarial activity from two Streptomyces sp. extracts identified from thousands tested using qHTS. Seven compounds were isolated from two phylogenetically related Streptomyces species: Streptomyces ballenaensis collected from Costa Rica and Streptomyces bangulaensis collected from Papua New Guinea. Among them we identified actinoramides A and B, belonging to the unusually elaborated nonproteinogenic amino-acid-containing tetrapeptide series of natural products. In addition, we characterized a series of new compounds, including an artifact, 25-epi-actinoramide A, and actinoramides D, E, and F, which are closely related biosynthetic congeners of the previously reported metabolites.

4-Quinolone alkaloids from Melochia odorata.

The methanol extract of Melochia odorata yielded three 4-quinolone alkaloids including waltherione A (1) and two new alkaloids, waltherione C (2) and waltherione D (3). Waltheriones A and C showed significant activities in an in vitro anti-HIV cytoprotection assay at concentrations of 56.2 and 0.84 µM and inhibition of HIV P24 formation of more than 50% at 1.7 and 0.95 µM, respectively. The structures of the alkaloids were established by spectroscopic data interpretation.

Isolation of pyrrolocins A-C: cis- and trans-decalin tetramic acid antibiotics from an endophytic fungal-derived pathway.

Three new decalin-type tetramic acid analogues, pyrrolocins A (1), B (2), and C (3), were defined as products of a metabolic pathway from a fern endophyte, NRRL 50135, from Papua New Guinea. NRRL 50135 initially produced 1 but ceased its production before chemical or biological evaluation could be completed. Upon transfer of the biosynthetic pathway to a model host, 1-3 were produced. All three compounds are structurally related to equisetin-type compounds, with 1 and 3 having a trans-decalin ring system, while 2 has a cis-fused decalin. All were active against Mycobacterium tuberculosis, with the trans-decalin analogues 1 and 3 exhibiting lower MICs than the cis-decalin analogue 2. Here we report the isolation, structure elucidation, and antimycobacterial activities of 1-3 from the recombinant expression as well as the isolation of 1 from the wild-type fungus NRRL 50135.

Characterization of the bafilomycin biosynthetic gene cluster from Streptomyces lohii.

New hope for old bones: The plecomacrolide bafilomycin has been explored for decades as an anti-osteoporotic. However, its structural complexity has limited the synthesis of analogues. The cloning of the bafilomycin biosynthetic gene cluster from the environmental isolate Streptomyces lohii opens the door to the production of new analogues through bioengineering.

Plakinamine M, a steroidal alkaloid from the marine sponge Corticium sp.

By means of bioassay-guided fractionation, a new steroidal alkaloid, plakinamine M (1), and the known compound, plakinamine L (2), with a unique acyclic side chain, were isolated from the marine sponge Corticium sp. collected from New Britain, Papua New Guinea. The structures were determined on the basis of extensive 1D and 2D NMR and HRESIMS. The two compounds showed inhibition of Mycobacterium tuberculosis with MIC values of 15.8 and 3.6 µg/mL, respectively.

Biosynthetically intriguing chlorinated lipophilic metabolites from geographically distant tropical marine cyanobacteria.

Five new vinylchlorine-containing metabolites, the lipoamides janthielamide A and kimbeamides A-C and the ketide-extended pyranone kimbelactone A, have been isolated from collections of marine cyanobacteria made in Curaçao and Papua New Guinea. Both janthielamide A and kimbeamide A exhibited moderate sodium channel blocking activity in murine Neuro-2a cells. Consistent with this activity, janthielamide A was also found to antagonize veratridine-induced sodium influx in murine cerebrocortical neurons. These lipoamides represent the newest additions to a relatively rare family of marine cyanobacterial-derived lipoamides and a new structural class of compounds exhibiting neuromodulatory activities from marine cyanobacteria.

Hoiamide D, a marine cyanobacteria-derived inhibitor of p53/MDM2 interaction.

Bioassay-guided fractionation of two cyanobacterial extracts from Papua New Guinea has yielded hoiamide D in both its carboxylic acid and conjugate base forms. Hoiamide D is a polyketide synthase (PKS)/non-ribosomal peptide synthetase (NRPS)-derived natural product that features two consecutive thiazolines and a thiazole, as well as a modified isoleucine residue. Hoiamide D displayed inhibitory activity against p53/MDM2 interaction (EC(50)=4.5 µM), an attractive target for anticancer drug development.

Credneramides A and B: neuromodulatory phenethylamine and isopentylamine derivatives of a vinyl chloride-containing fatty acid from cf. Trichodesmium sp. nov.

Credneramides A (1) and B (2), two vinyl chloride-containing metabolites, were isolated from a Papua New Guinea collection of cf. Trichodesmium sp. nov. and expand a recently described class of vinyl chloride-containing natural products. The precursor fatty acid, credneric acid (3), was isolated from both the aqueous and organic fractions of the parent fraction as well as from another geographically and phylogenetically distinct cyanobacterial collection (Panama). Credneramides A and B inhibited spontaneous calcium oscillations in murine cerebrocortical neurons at low micromolar concentrations (1, IC(50) 4.0 µM; 2, IC(50) 3.8 µM).

Malyngamide 2, an oxidized lipopeptide with nitric oxide inhibiting activity from a Papua New Guinea marine cyanobacterium.

A Papua New Guinea collection of the marine cyanobacterium cf. Lyngbya sordida yielded three known compounds as well as a new PKS-NRPS-derived malyngamide with anti-inflammatory and cytotoxic activity. Malyngamide 2 features an extensively oxidized cyclohexanone ring. Resolution of the ring core as a 6,8,9-triol rather then a 7,8,9-triol and relative configuration was based on chemical shift and bond geometry modeling in conjunction with homonuclear and heteronuclear coupling constants, NOE and ROE correlations, and other structural information. Malyngamide 2 exhibited anti-inflammatory activity in LPS-induced RAW macrophage cells (IC(50) = 8.0 µM) with only modest cytotoxicity to the mammalian cell line.

New antimycobacterial triterpenoids from Rhus taitensis.

Two new triterpenoids were isolated from the leaves and twigs of Rhus taitensis. Their structures were elucidated by 1D and 2D NMR spectroscopic studies as 1,10,24,25,30-pentahydroxysqualene and dammar-20(22),24-diene-3 ß,26,27-triol. Both compounds exhibited moderate antimycobacterial activities with an MIC of 45 µg/mL.

The hoiamides, structurally intriguing neurotoxic lipopeptides from Papua New Guinea marine cyanobacteria.

Two related peptide metabolites, one a cyclic depsipeptide, hoiamide B (2), and the other a linear lipopeptide, hoiamide C (3), were isolated from two different collections of marine cyanobacteria obtained in Papua New Guinea. Their structures were elucidated by combining various techniques in spectroscopy, chromatography, and synthetic chemistry. Both metabolites belong to the unique hoiamide structural class, characterized by possessing an acetate extended and S-adenosyl methionine modified isoleucine unit, a central triheterocyclic system comprised of two alpha-methylated thiazolines and one thiazole, and a highly oxygenated and methylated C-15 polyketide unit. In neocortical neurons, the cyclic depsipeptide 2 stimulated sodium influx and suppressed spontaneous Ca(2+) oscillations with EC(50) values of 3.9 microM and 79.8 nM, respectively, while 3 had no significant effects in these assays.

Apratoxin D, a potent cytotoxic cyclodepsipeptide from papua new guinea collections of the marine cyanobacteria Lyngbya majuscula and Lyngbya sordida.

Cancer cell toxicity-guided fractionation of extracts of the Papua New Guinea marine cyanobacteria Lyngbya majuscula and Lyngbya sordida led to the isolation of apratoxin D (1). Compound 1 contains the same macrocycle as apratoxins A and C but possesses the novel 3,7-dihydroxy-2,5,8,10,10-pentamethylundecanoic acid as the polyketide moiety. The planar structures and stereostructures of compound 1 were determined by extensive 1D and 2D NMR and MS data analyses and by comparison with the spectroscopic data of apratoxins A and C. Apratoxin D (1) showed potent in vitro cytotoxicity against H-460 human lung cancer cells with an IC 50 value of 2.6 nM.

Natural products chemistry and taxonomy of the marine cyanobacterium Blennothrix cantharidosmum.

A Papua New Guinea field collection of the marine cyanobacterium Blennothrix cantharidosmum was investigated for its cytotoxic constituents. Bioassay-guided isolation defined the cytotoxic components as the known compounds lyngbyastatins 1 and 3. However, six new acyl proline derivatives, tumonoic acids D-I, plus the known tumonoic acid A were also isolated. Their planar structures were defined from NMR and MS data, while their stereostructures followed from a series of chiral chromatographies, degradation sequences, and synthetic approaches. The new compounds were tested in an array of assays, but showed only modest antimalarial and inhibition of quorum sensing activities. Nevertheless, these are the first natural products to be reported from this genus, and this inspired a detailed morphologic and 16S rDNA-based phylogenetic analysis of the producing organism.

Tetrahdroxysqualene from Rhus taitensis shows antimycobacterial activity against Mycobacterium tuberculosis.

Tuberculosis has become a major health problem, in particular with the emergence of extremely drug resistant tuberculosis (XDRTB). In our search for new therapeutic leads against TB, we isolated a new triterpene (1) from the plant Rhus taitensis collected in Papua New Guinea. Tetrahydroxysqualene (1) was isolated using bioassay-guided fractionation of the methanolic extract of R. taitensis leaves and twigs. The structure of tetrahydroxysqualene (1) was elucidated on the basis of HRESIMS and 1D and 2D NMR spectra. Tetrahydroxysqualene (1) exhibited antituberculosis activity with an MIC of 10.0 microg/mL, while showing only modest cytotoxicity.

Development of a fluorescence-based assay to screen antiviral drugs against Kaposi's sarcoma associated herpesvirus.

Tumors associated with Kaposi's sarcoma-associated herpesvirus infection include Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. Virtually all of the tumor cells in these cancers are latently infected and dependent on the virus for survival. Latent viral proteins maintain the viral genome and are required for tumorigenesis. Current prevention and treatment strategies are limited because they fail to specifically target the latent form of the virus, which can persist for the lifetime of the host. Thus, targeting latent viral proteins may prove to be an important therapeutic modality for existing tumors as well as in tumor prevention by reducing latent virus load. Here, we describe a novel fluorescence-based screening assay to monitor the maintenance of the Kaposi's sarcoma-associated herpesvirus genome in B lymphocyte cell lines and to identify compounds that induce its loss, resulting in tumor cell death.