Lissoclibadins 1–3, three new polysulfur alkaloids, from the ascidian Lissoclinum cf. badium

The potential of marine natural Products: Recent Advances in the discovery of Anti-Tuberculosis agents

Tuberculosis (TB) is an infectious airborne disease caused by Mycobacterium tuberculosis. Since the 1990 s, many countries have made significant progress in reducing the incidence of TB and associated mortality by improving health services and strengthening surveillance systems. Nevertheless, due to the emergence of multidrug-resistant TB (MDR-TB), alongside extensively drug-resistant TB (XDR-TB) and TB-HIV co-infection, TB remains one of the lead causes of death arising from infectious disease worldwide, especially in developing countries and disadvantaged populations. Marine natural products (MNPs) have received a large amount of attention in recent years as a source of pharmaceutical constituents and lead compounds, and are expected to offer significant resources and potential in the fields of drug development and biotechnology in the years to come. This review summarizes 169 marine natural products and their synthetic derivatives displaying anti-TB activity from 2013 to the present, including their structures, sources and functions. Partial synthetic information and structure-activity relationships (SARs) are also included.

Copper catalyzed reaction of alcohols, alkyl halides and Na2S2O3: An odorless and ligand-free rout to unsymmetrical thioether synthesis

A CuI-catalyzed condensation reaction between alcohols, alkyl halides, and Na2S2O3 leading to structurally diverse thioethers is reported. A variety of alkyl halides and electron-rich benzyl alcohols were employed successfully in...

Exploration of marine natural resources in Indonesia and development of efficient strategies for the production of microbial halogenated metabolites

Nature is a prolific source of organic products with diverse scaffolds and biological activities. The process of natural product discovery has gradually become more challenging, and advances in novel strategic approaches are essential to evolve natural product chemistry. Our focus has been on surveying untouched marine resources and fermentation to enhance microbial productive performance. The first topic is the screening of marine natural products isolated from Indonesian marine organisms for new types of bioactive compounds, such as antineoplastics, antimycobacterium substances, and inhibitors of protein tyrosine phosphatase 1B, sterol O-acyl-transferase, and bone morphogenetic protein-induced osteoblastic differentiation. The unique biological properties of marine organohalides are discussed herein and attempts to efficiently produce fungal halogenated metabolites are documented. This review presents an overview of our recent work accomplishments based on the MONOTORI study.

Room temperature nickel-catalyzed cross-coupling of aryl-boronic acids with thiophenols: synthesis of diarylsulfides

A mild and easy to operate NiCl₂/2,2′-bipyridine-catalyzed cross-coupling of thiophenols with arylboronic acids has been developed for the synthesis of symmetric and unsymmetric diarylsulfides at room temperature and in air.

Synthesis and Identification of Pentathiepin-Based Inhibitors of Sporothrix brasiliensis

Sporothrix brasiliensis is the causative agent of zoonotic sporotrichosis in Brazil and is currently referred to as the most virulent species among those of clinical importance within the genus. Sporotrichosis is an emergent disease that has come to the forefront over two decades with a recent hot spot of sporotrichosis infection emerging in the state of Rio de Janeiro. The source of these infections is now at epidemic proportions with more than 4000 cases reported in Rio de Janeiro, Brazil, alone since 1998. We developed a focused library of a rare pentathiepin ring system and identified a potent substitution pattern that yielded compounds 21 and 22. These compounds were more potent than itraconazole which is the current standard of care for sporotrichosis.

Marine Natural Products from Indonesian Waters

Natural products are primal and have been a driver in the evolution of organic chemistry and ultimately in science. The chemical structures obtained from marine organisms are diverse, reflecting biodiversity of genes, species and ecosystems. Biodiversity is an extraordinary feature of life and provides benefits to humanity while promoting the importance of environment conservation. This review covers the literature on marine natural products (MNPs) discovered in Indonesian waters published from January 1970 to December 2017, and includes 732 original MNPs, 4 structures isolated for the first time but known to be synthetic entities, 34 structural revisions, 9 artifacts, and 4 proposed MNPs. Indonesian MNPs were found in 270 papers from 94 species, 106 genera, 64 families, 32 orders, 14 classes, 10 phyla, and 5 kingdoms. The emphasis is placed on the structures of organic molecules (original and revised), relevant biological activities, structure elucidation, chemical ecology aspects, biosynthesis, and bioorganic studies. Through the synthesis of past and future data, huge and partly undescribed biodiversity of marine tropical invertebrates and their importance for crucial societal benefits should greatly be appreciated.

Antimicrobial Activity of Substituted Benzopentathiepin-6-amines

A number of substituted benzopentathiepin-6-amines and their analogues without a polysulfur ring were synthesized and evaluated in vitro for antimicrobial activity against a panel of reference bacterial and fungal strains. Trifluoroacetamide 14 demonstrated high antibacterial activity against Staphylococcus aureus (MRSA strain) with a MIC of 4 μg/mL, which was four-fold higher than the activity of a reference drug amoxicillin. This compound was also most active against the Candida albicans fungus (MIC of 1 μg ml^-1), whereas amide 17 containing a morpholine substituent was most active against the Cryptococcus neoformans fungus (MIC of 2 μg ml^-1). These compounds have no hemolytic activity and are low cytotoxic. Replacement of the pentathiepine ring with 1,3-dithiolan-2-one or 1,3-dithiolane moieties leads to loss of antimicrobial activity. Based on the QSAR analysis and molecular docking data, bacterial DNA ligase might be one of the targets for the antibacterial activity of substituted benzopentathiepin-6-amines against S. aureus.

Natural Products with Heteroatom-Rich Ring Systems

This review focuses on all known natural products that contain a "heteroatom-rich" ring system, specifically a five-, six- or seven-membered ring that contains three or more heteroatoms. The isolation and biological activity of these natural products is discussed, along with the biosynthetic processes that Nature employs to assemble these rare heterocyclic frameworks.

Lissoclibadin 1, a Polysulfur Aromatic Alkaloid from the Indonesian Ascidian Lissoclinum cf. badium, Induces Caspase-Dependent Apoptosis in Human Colon Cancer Cells and Suppresses Tumor Growth in Nude Mice

Lissoclibadins, polysulfur aromatic alkaloids, were isolated from the Indonesian ascidian Lissoclinum cf. badium. Lissoclibadins 1 (1), 3 (2), 4 (3), 7 (4), 8 (5), and 14 (6) inhibited the growth of four human solid cancer cell lines: HCT-15 (colon adenocarcinoma), HeLa-S3 (cervix adenocarcinoma), MCF-7 (breast adenocarcinoma), and NCI-H28 (mesothelioma). Lissoclibadin 1 (1) exerted the most potent cytotoxic effects in vitro and mainly promoted apoptosis through an intrinsic pathway with the activation of a caspase-dependent pathway in HCT-15 cells. In vivo studies demonstrated that 1 suppressed tumor growth in nude mice carrying HCT-15 cells without significant secondary adverse effects. In conclusion, the results obtained in the present study demonstrate that 1 has potential as a chemotherapeutic candidate for preclinical investigations.

Natural Products Diversity of Marine Ascidians (Tunicates; Ascidiacea) and Successful Drugs in Clinical Development

This present study reviewed the chemical diversity of marine ascidians and their pharmacological applications, challenges and recent developments in marine drug discovery reported during 1994-2014, highlighting the structural activity of compounds produced by these specimens. Till date only 5% of living ascidian species were studied from <3000 species, this study represented from family didemnidae (32%), polyclinidae (22%), styelidae and polycitoridae (11-12%) exhibiting the highest number of promising MNPs. Close to 580 compound structures are here discussed in terms of their occurrence, structural type and reported biological activity. Anti-cancer drugs are the main area of interest in the screening of MNPs from ascidians (64%), followed by anti-malarial (6%) and remaining others. FDA approved ascidian compounds mechanism of action along with other compounds status of clinical trials (phase 1 to phase 3) are discussed here in. This review highlights recent developments in the area of natural products chemistry and biotechnological approaches are emphasized.

Approach for 2-(arylthio)imidazoles and imidazo[2,1-b]thiazoles from imidazo[2,1-b][1,3,4]thiadiazoles by ring-opening and -reconstruction

Useful heterocyclic synthons of imidazo[2,1-b][1,3,4]thiadiazoles were developed to synthesize imidazo[2,1-b]thiazoles and 2-(arylthio)-1H-imidazoles under mild reaction conditions.

Synthesis and antiproliferative properties of a new ceramide analog of varacin

A benzopentasulfane was synthesized in 8 steps with a ceramide attached through an amide bond to the 7-position of the heterocycle structure. The anticancer activity of this synthetic ceramide-benzopolysulfane drug conjugate was analyzed against five human cancer cell lines MDA-MB-231 (breast), DU145 (prostate), MIA PaCa-2 (pancreas), HeLa (cervix), and U251 (glioblastoma). The ceramide-benzopolysulfane conjugate had IC50 values ranging from 10 to >20 μM with complete cell killing at 12.5 μM for MDA-MB-231 and 20 μM for DU145 and HeLa cells. The ceramide-benzopolysulfane conjugate had IC50 values 1.8 and 4.0 times lower than a PEG benzopolysulfane, N-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)benzo[f][1,2,3,4,5]-pentathiepine-7-carboxamide, for MDA-MB-231 and DU145 cells, respectively. The parent "unsubstituted" benzopolysulfane, o-C6H4S5, had IC50 values 4.2 times lower and 2.7 times higher than the ceramide benzopolysulfane for MDA-MB-231 and DU145 cells, respectively. The results indicate that the polysulfur linkage is needed for activity since benzenedithiol, o-C6H4(SH)2, had IC50 values greater than 30 μM with little effect on MDA-MB-231 and DU145 cells. Thus, to account for the bioactivity, a bimolecular reaction of cellular thiol with the ceramide benzopolysulfane is a proposed followed by thiozone (S3) extrusion.

Synthesis, characterization, mechanism of decomposition, and antiproliferative activity of a class of PEGylated benzopolysulfanes structurally similar to the natural product varacin

Benzopolysulfanes, 4-CH(3)(OCH(2)CH(2))(3)NHC(O)-C(6)H(4)-1,2-S(x) (x = 3-7 and 9) were synthesized with a PEG group attached through an amide bond and examined for water solubility, antitumor activity, and propensity to equilibrate and desulfurate. LCMS and HPLC data show the PEG pentasulfane ring structure predominates, and the tri-, tetra-, hexa-, hepta-, and nonasulfanes were present at very low concentrations. The presence of the PEG group improved water solubility by 50-fold compared to the unsubstituted benzopolysulfanes, C(6)H(4)S(x) (x = 3, 5, and 7), based on intrinsic solubility measurements. Polysulfur linkages in the PEG compounds decomposed in the presence of ethanethiol and hydroxide ion. The PEG pentathiepin desulfurated rapidly, and an S(3) transfer reaction was observed in the presence of norbornene; no S(2) transfer reaction was observed with 2,3-dimethylbutadiene. The antitumor activities of the PEG-substituted benzopolysulfane mixtures were analyzed against four human tumor cell lines PC3 (prostate), DU145 (prostate), MDA-MB-231 (breast), and Jurkat (T-cell leukemia). The PEG-conjugated polysulfanes had IC(50) values 1.2-5.8 times lower than the parent "unsubstituted" benzopolysulfanes. Complete cell killing was observed for the PEG polysulfanes at 4 microM for PC3 and DU145 cells and at 12 muM for MDA-MB-231 cells. The results suggest that solubilization of the polysulfur linkage is a key parameter to the success of these compounds as drug leads.

Discovery of new pyridoacridine alkaloids from Lissoclinum cf. badium that inhibit the ubiquitin ligase activity of Hdm2 and stabilize p53

Compounds that stabilize p53 could suppress tumors providing a additional tool to fight cancer. Mdm2, and the human ortholog, Hdm2 serve as ubiquitin E3 ligases and target p53 for ubiquitylation and degradation. Inhibition of Hdm2 stabilizes p53, inhibits cell proliferation and induces apoptosis. Using HTS to discover inhibitors, we identified three new alkaloids, isolissoclinotoxin B, diplamine B, and lissoclinidine B from Lissoclinum cf. badium. Lissoclinidine B inhibited ubiquitylation and degradation of p53, and selectively killed transformed cells harboring wild-type p53, suggesting this compound could be used to develop new treatments.

Marine pharmacology in 2005-2006: antitumour and cytotoxic compounds

During 2005 and 2006, marine pharmacology research directed towards the discovery and development of novel antitumour agents was reported in 171 peer-reviewed articles. The purpose of this article is to present a structured review of the antitumour and cytotoxic properties of 136 marine natural products, many of which are novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids and peptides. The organisms yielding these bioactive marine compounds included invertebrate animals, algae, fungi and bacteria. Antitumour pharmacological studies were conducted with 42 structurally defined marine natural products in a number of experimental and clinical models which further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines were reported for 94 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy is the fact that marine anticancer research was sustained by a global collaborative effort, involving researchers from Australia, Belgium, Benin, Brazil, Canada, China, Egypt, France, Germany, India, Indonesia, Italy, Japan, Mexico, the Netherlands, New Zealand, Panama, the Philippines, Slovenia, South Korea, Spain, Sweden, Taiwan, Thailand, United Kingdom (UK) and the United States of America (USA). Finally, this 2005-2006 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine antitumour agents continued at the same active pace as during 1998-2004.

Marine natural products

This review covers the literature published in 2005 for marine natural products, with 704 citations (493 for the period January to December 2005) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (812 for 2005), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Characterization and online detection of aromatic alkaloids in the ascidian Lissoclinum cf. badium by liquid chromatography/UV detection mass spectrometry

A detection method based on high-performance liquid chromatography coupled with ultraviolet diode-array detection and electrospray ionization ion trap tandem mass spectrometry (HPLC-UV-ESI-MS/MS) was developed to investigate the total alkaloids prepared from the ascidian Lissoclinum cf. badium. The aromatic alkaloids possessing polysulfide structures are the major bioactive constituents isolated from ascidians of the genera Lissoclinum, Eudistoma, and Polycitor. These compounds presented various important biological activities. The ESI-MS fragmentation behavior of this kind of alkaloids was studied, and the fragmentation was characterized by elimination of the NH(CH(3))(2) moiety. The use of reversed-phase HPLC/UV-ESI-MS allowed the online separation and detection of 25 aromatic alkaloids. This approach provided data that can be used for detection of biologically active aromatic alkaloids from marine organisms.

Cytotoxicity of Lissoclibadins and Lissoclinotoxins, Isolated from a Tropical Ascidian Lissoclinum cf. badium, against Human Solid-Tumor-Derived Cell Lines

The in vitro growth inhibitory activity of lissoclibadins and lissoclinotoxins isolated from the tropical ascidian Lissoclinum cf. badium against nine human cancer cell lines was examined to evaluate their potential anticancer efficacy. Lissoclibadins 1 (1) and 2 (2), and lissoclinotoxin F (4) showed the strongest activity of the six compounds tested, which were more potent than the anticancer drug cisplatin. Compound 1 has a trimeric structure, and compounds 2 and 4 are structural isomers possessing dimeric structures connected by disulfide and sulfide bonds of trans- and cis-orientations, respectively. Lissoclibadin 3 (3), a dimeric compound connected by two sulfide bonds, and two monomeric compounds (5, 6) were less active than 1, 2, and 4. Lissoclibadin 2 (2) was the most interesting compound possessing potent inhibitory activity against colon (DLD-1 and HCT116), breast (MDA-MB-231), renal (ACHN), and non-small-cell lung (NCI-H460) cancer cell lines and showing no toxicity following a 50 mg/kg single treatment to mice, and preferable stability in rat plasma.