Triproamide and Pemukainalides, Cyclic Depsipeptides from the Marine Cyanobacterium Symploca hydnoides.

A new cyclic depsipeptide, triproamide (1), containing the rare 4-phenylvaline (dolaphenvaline, Dpv) and a ß-amino acid, dolamethylleucine (Dml), originally found in dolastatin 16, was isolated from the polar VLC-derived fraction of the extracts prepared from the marine cyanobacterium Symploca hydnoides. Triproamide (1) was isolated along with the known molecule kulokainalide-1 (2), as well as its two new analogues, pemukainalides A (3) and B (4). Their planar structures were elucidated based on extensive NMR and mass spectrometric data. The absolute and relative configurations of the compounds were determined utilizing a combination of Marfey's method, J-based configuration, and chiral-phase HPLC analyses. Kulokainalide-1 (2) and pemukainalide A (3) exhibited cytotoxicity against the MOLT-4 leukemia cell line with IC50 values of 5.9 and 5.6 µM, respectively.

Trikoramides B-D, Bioactive Cyanobactins from the Marine Cyanobacterium Symploca hydnoides.

Three new cyanobactins, trikoramides B (1)-D (3), have been isolated from the marine cyanobacterium, Symploca hydnoides, following a preliminary bioassay-guided isolation of the two most active polar fractions based on the brine shrimp toxicity assay. These new cyanobactins are new analogues of the previously reported cytotoxic trikoramide A (4) with differences mainly in the C-prenylated cyclotryptophan unit. Their planar structures were elucidated from their 1D and 2D NMR spectral data in combination with the HRMS/MS data. Marfey's method, 2D NOESY NMR spectroscopic and ECD spectra analyses were used to determine the absolute stereochemistry of trikoramides B (1)-D (3). Trikoramides B (1) and D (3) exhibited cytotoxicity against MOLT-4 acute lymphoblastic leukemia cell line with IC50 values of 5.2 µM and 4.7 µM, respectively. Compounds 1 and 3 were also evaluated for their quorum-sensing inhibitory assay based on the Pseudomonas aeruginosa PAO1 lasB-gfp and rhlA-gfp bioreporter strains. Although trikoramide B (1) exhibited weak quorum-sensing inhibitory activity, the Br-containing trikoramide D (3) exhibited moderate to significant dose-dependent quorum-sensing inhibitory activities against PAO1 lasB-gpf and rhlA-gfp bioreporter strains with IC50 values of 19.6 µM and 7.3 µM, respectively.

Trikoveramides A-C, cyclic depsipeptides from the marine cyanobacterium Symploca hydnoides.

Trikoveramides A - C, members of the kulolide superfamily of cyclic depsipeptides, were isolated from the marine cyanobacterium, Symploca hydnoides, collected from Bintan Island, Indonesia. Their planar structures were elucidated by a combination of NMR spectroscopy and HRMS spectral data. The absolute configurations of the amino acid and phenyllactic acid units were confirmed by Marfey's and chiral HPLC analyses, respectively, while the relative stereochemistry of the 3-hydroxy-2-methyl-7-octynoic acid (Hmoya) unit in trikoveramide A was elucidated by the application of the J-based configuration analysis and NOE correlations. The cytotoxic activity of the trikoveramides were evaluated against MOLT-4 human leukemia cells and gave IC50 values of 9.3 µM, 35.6 µM and 48.8 µM for trikoveramide B, trikoveramide C and trikoveramide A, respectively. In addition, trikoveramides A - C showed weak to moderate inhibition in the quorum sensing inhibitory assay based on the Pseudomonas aeruginosa lasB-gfp and rhlA-gfp bioreporter strains.

Marine Cyanobacteria: A Source of Lead Compounds and their Clinically-Relevant Molecular Targets.

The prokaryotic filamentous marine cyanobacteria are photosynthetic microbes that are found in diverse marine habitats, ranging from epiphytic to endolithic communities. Their successful colonization in nature is largely attributed to genetic diversity as well as the production of ecologically important natural products. These cyanobacterial natural products are also a source of potential drug leads for the development of therapeutic agents used in the treatment of diseases, such as cancer, parasitic infections and inflammation. Major sources of these biomedically important natural compounds are found predominately from marine cyanobacterial orders Oscillatoriales, Nostocales, Chroococcales and Synechococcales. Moreover, technological advances in genomic and metabolomics approaches, such as mass spectrometry and NMR spectroscopy, revealed that marine cyanobacteria are a treasure trove of structurally unique natural products. The high potency of a number of natural products are due to their specific interference with validated drug targets, such as proteasomes, proteases, histone deacetylases, microtubules, actin filaments and membrane receptors/channels. In this review, the chemistry and biology of selected potent cyanobacterial compounds as well as their synthetic analogues are presented based on their molecular targets. These molecules are discussed to reflect current research trends in drug discovery from marine cyanobacterial natural products.

Trikoramide A, a Prenylated Cyanobactin from the Marine Cyanobacterium Symploca hydnoides.

A new cyclic decapeptide, trikoramide A (1), has been isolated from samples of the marine cyanobacterium Symploca hydnoides, collected from Bintan Island, Indonesia. Trikoramide A (1) is a C-prenylated cyclotryptophan-containing cyanobactin. Its planar structure was deduced by 1D and 2D NMR spectroscopy as well as HR-MS/MS data. In addition, its absolute configuration was determined by Marfey's method and 2D NOESY NMR spectroscopic analysis. Compound 1 possessed cytotoxicity against the MOLT-4 and AML2 cancer cell lines with IC50 values of 4.8 and 8.2 µM, respectively.

Benderamide A, a Cyclic Depsipeptide from a Singapore Collection of Marine Cyanobacterium cf. Lyngbya sp.

Benderamide A (1), a (S)-2,2-dimethyl-3-hydroxy-7-octynoic acid (S-Dhoya)-containing cyclic depsipeptide that belongs to the kulolide superfamily, was isolated from a Singapore collection of cf. Lyngbya sp. marine cyanobacterium using a bioassay-guided approach. While the planar structure of 1 was elucidated using a combination of 1D and 2D NMR experiments and MS analysis, the absolute configuration was subsequently achieved using the results obtained from Marfey's analysis, comparative analysis of nuclear overhauser effect spectroscopy (NOESY) with the known compound 3, and one dimensional-nuclear overhauser effect (1D-NOE). Although 1 did not display antiproliferative activity against MCF7 breast cancer cells, the presence of an Ala instead of Gly suggests a possible mechanistic pathway to explain the consequential decrease in cytotoxicity compared to the closely related 2. In addition, results obtained from an LC⁻MS/MS-based molecular networking algorithm revealed two other closely related compounds encouraging further identification and isolation from the same marine cyanobacterium extract.

Anti-Chikungunya viral activities of aplysiatoxin-related compounds from the marine cyanobacterium Trichodesmium erythraeum.

Tropical filamentous marine cyanobacteria have emerged as a viable source of novel bioactive natural products for drug discovery and development. In the present study, aplysiatoxin (1), debromoaplysiatoxin (2) and anhydrodebromoaplysiatoxin (3), as well as two new analogues, 3-methoxyaplysiatoxin (4) and 3-methoxydebromoaplysiatoxin (5), are reported for the first time from the marine cyanobacterium Trichodesmium erythraeum. The identification of the bloom-forming cyanobacterial strain was confirmed based on phylogenetic analysis of its 16S rRNA sequences. Structural determination of the new analogues was achieved by extensive NMR spectroscopic analysis and comparison with NMR spectral data of known compounds. In addition, the antiviral activities of these marine toxins were assessed using Chikungunya virus (CHIKV)-infected cells. Post-treatment experiments using the debrominated analogues, namely compounds 2, 3 and 5, displayed dose-dependent inhibition of CHIKV when tested at concentrations ranging from 0.1 µM to 10.0 µM. Furthermore, debromoaplysiatoxin (2) and 3-methoxydebromoaplysiatoxin (5) exhibited significant anti-CHIKV activities with EC50 values of 1.3 µM and 2.7 µM, respectively, and selectivity indices of 10.9 and 9.2, respectively.

Bouillonamide: a mixed polyketide-peptide cytotoxin from the marine cyanobacterium Moorea bouillonii.

The tropical marine cyanobacterium, Moorea bouillonii, has gained recent attention as a rich source of bioactive natural products. Continued chemical investigation of this cyanobacterium, collected from New Britain, Papua New Guinea, yielded a novel cytotoxic cyclic depsipeptide, bouillonamide (1), along with previously reported molecules, ulongamide A and apratoxin A. Planar structure of bouillonamide was established by extensive 1D and 2D NMR experiments, including multi-edited HSQC, TOCSY, HBMC, and ROESY experiments. In addition to the presence of α-amino acid residues, compound 1 contained two unique polyketide-derived moieties, namely a 2-methyl-6-methylamino-hex-5-enoic acid (Mmaha) residue and a unit of 3-methyl-5-hydroxy-heptanoic acid (Mhha). Absolute stereochemistry of the α-amino acid units in bouillonamide was determined mainly by Marfey's analysis. Compound 1 exhibited mild toxicity with IC50's of 6.0 µM against the neuron 2a mouse neuroblastoma cells.

Pharmaceutical agents from filamentous marine cyanobacteria.

Filamentous marine cyanobacteria have emerged as an important source of novel lead compounds for drug discovery and development. The majority of these molecules are nitrogen-containing, belonging to the hybrid polyketide-polypeptide structural class. Owing to their specific interactions with cellular targets, several marine cyanobacterial compounds are currently being pursued for drug development in various disease areas, including cancer, neurodegenerative disorders and infectious disease. This review features more than 25 marine cyanobacterial metabolites and they are discussed based on their biological activities. Medically relevant molecular targets, such as microtubules, actin filaments, proteasome and histone deacetylase enzymes, of these compounds will be emphasized.

Biochemical studies of the lagunamides, potent cytotoxic cyclic depsipeptides from the marine cyanobacterium Lyngbya majuscula.

Lagunamides A (1) and B (2) are potent cytotoxic cyclic depsipeptides isolated from the filamentous marine cyanobacterium, Lyngbya majuscula, from Pulau Hantu, Singapore. These compounds are structurally related to the aurilide-class of molecules, which have been reported to possess exquisite antiproliferative activities against cancer cells. The present study presents preliminary findings on the selectivity of lagunamides against various cancer cell lines as well as their mechanism of action by studying their effects on programmed cell death or apoptosis. Lagunamide A exhibited a selective growth inhibitory activity against a panel of cancer cell lines, including P388, A549, PC3, HCT8, and SK-OV3 cells, with IC50 values ranging from 1.6 nM to 6.4 nM. Morphological studies showed blebbing at the surface of cancer cells as well as cell shrinkage accompanied by loss of contact with the substratum and neighboring cells. Biochemical studies using HCT8 and MCF7 cancer cells suggested that the cytotoxic effect of 1 and 2 might act via induction of mitochondrial mediated apoptosis. Data presented in this study warrants further investigation on the mode of action and underscores the importance of the lagunamides as potential anticancer agents.

Lagunamide C, a cytotoxic cyclodepsipeptide from the marine cyanobacterium Lyngbya majuscula.

Lagunamide C (1) is a cytotoxic cyclodepsipeptide isolated from the marine cyanobacterium, Lyngbya majuscula, from the western lagoon of Pulau Hantu Besar, Singapore. The complete structural characterization of the molecule was achieved by extensive NMR spectroscopic analysis as well as chemical manipulations. Several methods, including the advanced Marfey's method, a modified method based on derivatization with Mosher's reagents and analysis using LC-MS, and the use of (3)J(H-H) coupling constant values, were utilized for the determination of its absolute configuration. Compound 1 is related to the aurilide-class of molecules and it differs mainly in the macrocyclic structure by having a 27 membered ring system due to additional methylene carbon in the polyketide moiety. Lagunamide C displayed potent cytotoxic activity against a panel of cancer cell lines, such as P388, A549, PC3, HCT8, and SK-OV3 cell lines, with IC(50) values ranging from 2.1 nM to 24.4 nM. Compound 1 also displayed significant antimalarial activity with IC(50) value of 0.29 µM when tested against Plasmodium falciparum. In addition, lagunamide C exhibited weak anti-swarming activity when tested at 100 ppm against the Gram-negative bacterial strain, Pseudomonas aeruginosa PA01.

Lagunamides A and B: cytotoxic and antimalarial cyclodepsipeptides from the marine cyanobacterium Lyngbya majuscula.

Lagunamides A (1) and B (2) are new cyclic depsipeptides isolated from the marine cyanobacterium Lyngbya majuscula obtained from Pulau Hantu Besar, Singapore. The planar structural characterization of these molecules was achieved by extensive spectroscopic analysis, including 2D NMR experiments. In addition to Marfey's method and (3)J(H-H) coupling constant values, a modified method based on Mosher's reagents and analysis using LC-MS was deployed for the determination of the absolute configuration. Lagunamides A and B displayed significant antimalarial properties, with IC(50) values of 0.19 and 0.91 µM, respectively, when tested against Plasmodium falciparum. Lagunamides A and B also possessed potent cytotoxic activity against P388 murine leukemia cell lines, with IC(50) values of 6.4 and 20.5 nM, respectively. Furthermore, these cyanobacterial compounds exhibited moderate antiswarming activities when tested against Pseudomonas aeruginosa PA01.

Natural antifoulants from the marine cyanobacterium Lyngbya majuscula.

Filamentous benthic marine cyanobacteria are a prolific source of structurally unique bioactive secondary metabolites. A total of 12 secondary metabolites, belonging to the mixed polyketide-polypeptide structural class, were isolated from the marine cyanobacterium, Lyngbya majuscula, and were tested to determine if they showed activity against barnacle larval settlement. The assays revealed four compounds, dolastatin 16, hantupeptin C, majusculamide A, and isomalyngamide A, that showed moderate to potent anti-larval settlement activities, with EC(50) values ranging from 0.003 to 10.6 microg ml(-1). In addition, field testing conducted over a period of 28 days (using the modified Phytagel method) based on the cyanobacterial compound, dolastatin 16, showed significantly reduced barnacle settlement as compared to controls at all the concentrations tested. The results of this study highlight the importance of marine cyanobacteria as an underexplored source of potential environmentally friendly antifoulants.

Hantupeptins B and C, cytotoxic cyclodepsipeptides from the marine cyanobacterium Lyngbya majuscula.

Hantupeptins B (2) and C (3) were isolated, along with the previously reported hantupeptin A (1), from the marine cyanobacterium, Lyngbya majuscula, collected from Pulau Hantu Besar, Singapore. Their structures were elucidated by interpretation of extensive 1D and 2D NMR spectroscopic data. Compounds 2 and 3 are cyclic depsipeptides consisting of five alpha-amino/hydroxy acid residues, including phenyllactic acid, proline, N-methyl-valine, valine, N-methyl-isoleucine, and a beta-hydroxy acid unit with different degrees of unsaturation at the terminal end of each molecule. The absolute configurations of the common amino acids and phenyllactic acid were determined by the advanced Marfey's and chiral HPLC analyses, respectively. The complete stereochemistry of 3-hydroxy-2-methyl-7-octynoic acid moiety in hantupeptin A was elucidated by a combination of homonuclear J-resolved 2D NMR experiments and by Mosher's method. Hantupeptins B and C showed moderate in vitro cytotoxicity when tested against MOLT-4 (leukemic) and MCF-7 (breast cancer) cell lines.

Hantupeptin A, a cytotoxic cyclic depsipeptide from a Singapore collection of Lyngbya majuscula.

Chemical investigation of the marine cyanobacterium Lyngbya majuscula from Pulau Hantu Besar, Singapore, has led to the isolation of a cyclodepsipeptide, hantupeptin A (1). The planar structure of 1 was assigned on the basis of extensive 1D and 2D NMR spectroscopic experiments. The absolute configuration of the amino and hydroxyl acid residues in the molecule was determined by application of the advanced Marfey method, chiral HPLC analysis, and Mosher's method. Hantupeptin A showed cytotoxicity to MOLT-4 leukemia cells and MCF-7 breast cancer cells with IC(50) values of 32 and 4.0 microM, respectively.

Bioactive natural products from marine cyanobacteria for drug discovery.

The prokaryotic marine cyanobacteria continue to be an important source of structurally bioactive secondary metabolites. A majority of these molecules are nitrogen-containing compounds biosynthesized by large multimodular nonribosomal polypeptide (NRP) or mixed polyketide-NRP enzymatic systems. A total of 128 marine cyanobacterial alkaloids, published in the literature between January 2001 and December 2006, are presented in this review with emphasis on their biosynthesis and biological activities. In addition, a number of highly cytotoxic compounds such as hectochlorin, lyngbyabellins, apratoxins, and aurilides have been identified as potential lead compounds for the development of anticancer agents. A brief coverage on the distribution of natural product biosynthetic genes as well as the mechanisms of tailoring enzymes involved in the biosynthesis of cyanobacterial compounds will also be given.

Scytalidamides A and B, new cytotoxic cyclic heptapeptides from a marine fungus of the genus Scytalidium.

Two new cyclic heptapeptides have been isolated from the culture broth of a marine fungus, Scytalidium sp., collected from the Bahamas. The planar structures of scytalidamides A (1) and B (2) were assigned on the basis of 1D and 2D NMR spectroscopic techniques, while the absolute configuration of the amino acid residues in both molecules was determined by application of the advanced Marfey's method. The absolute stereochemistry of the uncommon 3-methylproline moiety in scytalidamide B (2) was confirmed by isolation and CD measurements, as well as application of the advanced Marfey's method. Scytalidamides A (1) and B (2) showed moderate in vitro cytotoxicity toward HCT-116 human colon adenocarcinoma with IC(50) values of 2.7 and 11.0 microM, respectively.

The guineamides, novel cyclic depsipeptides from a Papua New Guinea collection of the marine cyanobacterium Lyngbya majuscula.

The guineamides (1-6) are novel cyclic depsipeptides isolated and characterized from a Papua New Guinea collection of the marine cyanobacterium Lyngbya majuscula. The planar structures of these new natural products were established using an extensive array of 1D and 2D NMR experiments, including HSQC, TOCSY, and HMBC. Absolute stereochemistry was determined using a combination of chemical manipulations as well as Marfey's method. These metabolites all contain beta-amino or beta-hydroxy carboxylic acid residues, an increasingly common feature in marine cyanobacterial metabolites. The identification of 2,2-dimethyl-3-hydroxyhexanoic acid (Dmhha) in guineamides E (5) and F (6) represents the first report of such a residue in a natural product. In addition, characterization of the unique beta-amino acid 2-methyl-3-aminopentanoic acid (Mapa) in guineamide A (1), which has also been reported as a component of several marine molluscan metabolites, especially from those of Dolabella auricularia, further supports the diet-derived nature of such compounds as isolated from marine invertebrates. Guineamides B (2) and C (3) possess moderate cytotoxicity to a mouse neuroblastoma cell line with IC(50) values of 15 and 16 microM, respectively.

Lyngbouilloside, a novel glycosidic macrolide from the marine cyanobacterium Lyngbya bouillonii.

A glycosidic macrolide, lyngbouilloside (1), was characterized from the marine cyanobacterium Lyngbya bouillonii collected from Papua New Guinea. Its structure was elucidated by spectroscopic analysis and chemical derivatization. Relative stereochemistry was deduced from homonuclear and heteronuclear coupling constants as well as NOE information. Lyngbouilloside was modestly cytotoxic to neuroblastoma cells (IC(50) value of 17 microM).