[Show abstract][Hide abstract] ABSTRACT: During an investigation of new actinomycete species from Caribbean sponges for novel bioactive natural products, frigocyclinone (1), dimethyldehydrorabelomycin (3) and six new angucyclinone derivatives were isolated from Streptomyces sp. strain M7_15 associated with the sponge Scopalina ruetzleri. Of these, monacyclinones A–B (4–5) contain the core ring structure of dehydrorabelomycin (2) with the aminodeoxysugar found in frigocyclinone (1). Monacyclinone C (6) is a hydroxylated variant of frigocyclinone (1) and monacyclinone D (7) is a Baeyer Villiger derivative of (6) which also exists as the open chain hydrolysis product monacyclinone E (8). Monacyclinone F (9) contains two unique epoxide rings attached to the angucyclinone moiety and an additional aminodeoxysugar attached through an angular oxygen bond. All structures were confirmed through spectral analyses. Activity against rhabdomycosarcoma cancer cells (SJCRH30) after 48 h of treatment was observed with frigocyclinone (1; EC50 = 5.2 µM), monacyclinone C (6; 160 µM), monacyclinone E (8; 270 µM), and monacyclinone F (9; 0.73 µM). The strongest bioactivity against rhabdomycosarcoma cancer cells and gram-positive bacteria was exhibited by compound 9, suggesting that the extra aminodeoxysugar subunit is important for biological activity.
[Show abstract][Hide abstract] ABSTRACT: Covering: up to 2013Dinoflagellates produce unique polyketides characterized by their size and complexity. The biosynthesis of a limited number of such metabolites has been reported, with studies largely hampered by the low yield of compounds and the severe scrambling of label in the isotopically-labeled precursors. Nonetheless, of the successful biosynthetic experiments that have been reported, many surprising and unique processes have been discovered. This knowledge has been accessed through a series of biochemical labeling studies, and while limited molecular genetic data has been amassed, it is still in the early stages of development. In an attempt to meet this challenge, this review has compared some of the biosynthetic processes with similar ones identified in other microbes such as bacteria and myxobacteria, with the idea that similar genes and enzymes are employed by dinoflagellates.
[Show abstract][Hide abstract] ABSTRACT: An antimalarial screen for plants collected from Papua New Guinea identified an extract of Horsfieldia spicata as having activity. Isolation of the active constituents led to the identification of two new compounds: myristicyclins A (1) and B (2). Both compounds are procyanidin-like congeners of myristinins lacking a pendant aromatic ring. Myristicyclin A was found to inhibit the ring, trophozoite, and schizont stages of Plasmodium falciparum at similar concentrations in the mid-μM range.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
Proceedings of the National Academy of Sciences 11/2013; 110(47). DOI:10.1073/pnas.1314132110 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A major hurdle in using complex systems for drug screening is the difficulty of defining the mechanistic targets of small molecules. The zebrafish provides an excellent model system for juxtaposing developmental phenotypes with mechanism discovery using organism genetics. We carried out a phenotype-based screen of uncharacterized small molecules in zebrafish that produced a variety of chemically induced phenotypes with potential genetic parallels. Specifically, kalihinol F caused an undulated notochord, defects in pigment formation, hematopoiesis, and neural development. These phenotypes were strikingly similar to the zebrafish mutant, calamity, an established model of copper deficiency. Further studies into the mechanism of action of kalihinol F revealed a copper-chelating activity. Our data support this mechanism of action for kalihinol F and the utility of zebrafish as an effective system for identifying therapeutic and target pathways.
[Show abstract][Hide abstract] ABSTRACT: Defined experimental regimes were used to determine the effects of nutrient limitation on the toxicity of Alexandrium peruvianum in batch culture. Subsamples for cell counts and spiroimine analysis at six day intervals were used to investigate the concentrations and composition of these compounds throughout growth. An erythrocyte lysis assay for hemolytic activity was performed on cell pellets and supernatants also collected every six days over the entire growth period from all treatments. From the data, growth rates, cellular spiroimine quotas and effective concentration-fifty (EC50s) for cellular and supernatant associated hemolytic activity were calculated. Phosphate limitation was identified as a key regulator of toxicity in this species, yielding maximum values of 54.1 pg cell−1 for 13-desmethyl spirolide C, 96.4 pg cell−1 for 12-methylgymnodimine and a potent hemolytic EC50 value of 7.1 × 103 cells. The concentrations of spiroimines detected in A. peruvianum among various treatments, in addition to a unique profile of paralytic shellfish poisoning toxins, is unique in the body of microalgal literature. Because of the multiple toxin arsenal produced by this organism, the evaluation of a single toxin clearly would have underestimated the potential virulence and significance of this clone. This study provides the first evidence that growth and toxin production of A. peruvianum are influenced by altered nutrient ratios.
[Show abstract][Hide abstract] ABSTRACT: As part of our screening for anti-HIV agents from marine invertebrates, the MeOH extract of Didemnum molle was tested and showed moderate in vitro anti-HIV activity. Bioassay-guided fractionation of a large-scale extract allowed the identification of two new cyclopeptides, mollamides E and F (1 and 2), and one new tris-phenethyl urea, molleurea A (3). The absolute configurations were established using the advanced Marfey's method. The three compounds were evaluated for anti-HIV activity in both an HIV integrase inhibition assay and a cytoprotective cell-based assay. Compound 2 was active in both assays with IC(50) values of 39 and 78 μM, respectively. Compound 3 was active only in the cytoprotective cell-based assay, with an IC(50) value of 60 μM.
[Show abstract][Hide abstract] ABSTRACT: Routine sampling of the water quality stations in the New River Estuary (Jacksonville, North Carolina, USA) during November 2004 revealed the presence of a previously unidentified dinoflagellate. Preliminary observations of its morphology suggested it to be consistent with that of Alexandrium peruvianum (Balech et Mendiola) Balech et Tangen. Observations using brightfield, epifluorescence and scanning electron microscopy confirmed the diagnostic thecal plates to be those of A. peruvanium. Clonal cultures established from cells isolated from the New River Estuary samples were also used for further studies of morphology and for the presence of toxins. Thecal morphology was consistent with that described by Balech clearly separating it from the sister species Alexandrium ostenfeldii. Three classes of toxins were detected from these cultures. An erythrocyte lysis assay (ELA) was used to confirm the presence of hemolytic toxins in A. peruvianum cultures. A cellular EC50 for lysis was 1.418 × 104 cells, well within the range the maximal cells densities found in the New River and more potent when compared on a cellular basis with Prymnesium parvum. Another toxin class detected in A. peruvianum cultures was the fast acting 13-desmethy C and D spirolides also produced by the sister species A. ostenfeldii. The last toxin type detected in the A. peruvianum cultures was the paralytic shellfish toxins, GTX 2, 3, B1, STX and C1,2. These findings expand the geographic range of occurrence for A. peruvianum in the U.S. to be much greater than previously considered. The morphological characters agreed with previously reported molecular data in separating A. peruvianum from A. ostenfeldii. It is also the first confirmed report that this species produces PSP toxins, spirolides and naturally occurring hemolytic substances. In light of these findings additional attention is needed for the detection of Alexandrium species in all coastal waters of the U.S. This added effort will enhance the evaluation of the relative impacts of the species to shellfish safety and bloom surveillance.
[Show abstract][Hide abstract] ABSTRACT: Green plant-origin electrophilic compounds are a newly-recognized class of neuroprotective compounds that provide neuroprotection through activation of the Nrf2/ARE pathway. Electrophilic hydroquinones are of particular interest due to their ability to become electrophilic quinones upon auto-oxidation. Although marine organisms frequently produce a variety of electrophilic compounds, the detailed mechanisms of action of these compounds remain unknown. Here, we focused on the neuroprotective effects of strongylophorine-8 (STR8), a para-hydroquinone-type pro-electrophilic compound from the sponge Petrosia (Strongylophora) corticata. STR8 activated the Nrf2/ARE pathway, induced phase 2 enzymes, and increased glutathione, thus protecting neuronal cells from oxidative stress. Microarray analysis indicated that STR8 induced a large number of phase 2 genes, the regulation of which is controlled by the Nrf2/ARE pathway. STR8 is the first example of a neuroprotective pro-electrophilic compound from marine organisms.
Biochemical and Biophysical Research Communications 11/2011; 415(1):6-10. DOI:10.1016/j.bbrc.2011.09.114 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two known papuamides C (1) and D (2) together with two new depsipeptides, papuamides E (3) and F (4), were isolated from an undescribed sponge of the genus Melophlus collected in the Solomon Islands. The planar structures of the compounds were elucidated on the basis of spectroscopic studies. Papuamides C-F (1-4) showed cytotoxicity against brine shrimp with LD(50) values between 92 and 106 μg/mL.
[Show abstract][Hide abstract] ABSTRACT: The novel gymnodimine congener 12-methylgymnodimine was isolated from the dinoflagellate Alexandrium peruvianum from the New River in North Carolina. In addition, the presence of 13-desmethylspirolide C was confirmed by NMR characterization. This marks the first time these two classes of cyclic imines have been found in the same organism, providing further evidence for a direct genetic relationship between the biosynthetic pathways for gymnodimines and spirolides suggested by comparison of their structures.
[Show abstract][Hide abstract] ABSTRACT: A new fascaplysin analogue, 3-bromohomofascaplysin A (1), along with two known analogues, homofascaplysin A (2) and fascaplysin (3), were isolated from a Fijian Didemnum sp. ascidian. The absolute configurations of 3-bromohomofascaplysin A (1) and homofascaplysin A (2) were determined via experimental and theoretically calculated ECD spectra. The differential activities of 1-3 against different blood-borne life stages of the malaria pathogen Plasmodium falciparum were assessed. Homofascaplysin A (2) displayed an IC(50) of 0.55±0.11 nM against ring stage parasites and 105±38 nM against all live parasites. Given the stronger resistance of ring stage parasites against most current antimalarials relative to the other blood stages, homofascaplysin A (2) represents a promising agent for treatment of drug resistant malaria.
[Show abstract][Hide abstract] ABSTRACT: 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 β,26,27-triol. Both compounds exhibited moderate antimycobacterial activities with an MIC of 45 µg/mL.
[Show abstract][Hide abstract] ABSTRACT: Four new tris-bromoindole cyclic guanidine alkaloids, araiosamines A-D, were isolated from the methanol extract of a marine sponge, Clathria (Thalysias) araiosa, collected from Vanuatu. Their carbon skeletons delineate a new class of indole alkaloids apparently derived from a linear polymerization process involving a carbon-carbon bond formation. Comparison of the structures including the relative configurations suggests a common intermediate containing a dihydroaminopyrimidine moiety capable of undergoing various modalities of conjugate addition to yield unprecedented ring systems.
The Journal of Organic Chemistry 04/2011; 76(14):5515-23. DOI:10.1021/jo200327d · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Four new depsipeptides, mirabamides E-H (1-4), and the known depsipeptide mirabamide C (5) have been isolated from the sponge Stelletta clavosa, collected from the Torres Strait. The planar structures were determined on the basis of extensive 1D and 2D NMR and HRESIMS. The absolute configurations were established by the advanced Marfey's method, NMR, and GC-MS. The four new compounds all showed strong inhibition of HIV-1 in a neutralization assay with IC(50) values of 121, 62, 68, and 41 nM, respectively.
[Show abstract][Hide abstract] ABSTRACT: Two ring-A-aromatized bile acids, 1 and 2, were isolated from the sponge Sollasella moretonensis, collected from the seabed of northern Queensland. Structures were assigned on the basis of extensive 1D and 2D NMR studies, as well as analysis by HRESIMS. Compound 2 has previously been produced synthetically, though this marks its first isolation from a natural source.
[Show abstract][Hide abstract] ABSTRACT: The karlotoxins are a family of amphidinol-like compounds that play roles in avoiding predation and in prey capture for the toxic dinoflagellate Karlodinium veneficum. The first member of the toxin group to be reported was KmTx 1 (1), and here we report an additional five new members of this family (3-7) from the same strain. Of these additional compounds, KmTx 3 (3) differs from KmTx 1 (1) in having one less methylene group in the saturated portion of its lipophilic arm. In addition, 64-E-chloro-KmTx 3 (4) and 10-O-sulfo-KmTx 3 (5) were identified. Likewise, 65-E-chloro-KmTx 1 (6) and 10-O-sulfo-KmTx 1 (7) were also isolated. Comparison of the hemolytic activities of the newly isolated compounds to that of KmTx 1 shows that potency correlates positively with the length of the lipophilic arm and is disrupted by sulfonation of the polyol arm.