An array of bengamide E analogues modified at the terminal olefinic position: synthesis and antitumor properties

Total Synthesis of 4-epi-Bengamide E

Bengamide E is a bioactive natural product that was isolated from Jaspidae sponges by Crews and co-workers in 1989. It displays a wide range of biological activities, including antitumor, antibiotic, and anthelmintic properties. With the aim of investigating the structural feature essential for their activity, several total syntheses of Bengamide E and its analogues have been reported in the literature. Nevertheless, no synthesis of the stereoisomer with modification of its configuration at C-4 carbon has been reported so far. Here, we report the first total synthesis of the 4-epi-Bengamide E. Key reactions in the synthesis include a chemoenzimatic desymmetrization of biobased starting materials and a diastereoselective Passerini reaction using a chiral, enantiomerically pure aldehyde, and a lysine-derived novel isocyanide.

The Development of the Bengamides as New Antibiotics against Drug-Resistant Bacteria

The bengamides comprise an interesting family of natural products isolated from sponges belonging to the prolific Jaspidae family. Their outstanding antitumor properties, coupled with their unique mechanism of action and unprecedented molecular structures, have prompted an intense research activity directed towards their total syntheses, analogue design, and biological evaluations for their development as new anticancer agents. Together with these biological studies in cancer research, in recent years, the bengamides have been identified as potential antibiotics by their impressive biological activities against various drug-resistant bacteria such as Mycobacterium tuberculosis and Staphylococcus aureus. This review reports on the new advances in the chemistry and biology of the bengamides during the last years, paying special attention to their development as promising new antibiotics. Thus, the evolution of the bengamides from their initial exploration as antitumor agents up to their current status as antibiotics is described in detail, highlighting the manifold value of these marine natural products as valid hits in medicinal chemistry.

Toward E-selective Olefin Metathesis: Computational Design and Experimental Realization of Ruthenium Thio-Indolate Catalysts

The selective transformation of 1-alkenes into E-olefins is a long-standing challenge in olefin metathesis. Density functional theory (DFT) calculations predict high E-selectivity for catalysts incorporating a bidentate, dianionic thio-indolate ligand within a RuXX’(NHC)(py)(= CHR) platform (NHC = N-heterocyclic carbene; py = pyridine). Such complexes are predicted to yield E-olefins by favoring anti-disposed substituents in the transition state expected to be rate-determining: specifically, that for cycloreversion of the metallacyclobutane intermediate. Three pyridine-stabilized catalysts Ru21a-c were synthesized, in which the thio-indolate ligand bears a H, Me, or Ph substituent at the C2 position, and the NHC ligand is the unsaturated imidazoline-2-ylidene Me2IMes (which bears N-mesityl groups and methyl groups on the C4,5 backbone). Single-crystal X-ray diffraction analysis of Ru21c confirms the ligand orientation required for E-selective metathesis, with the thio-indolate sulfur atom binding cis to the NHC, and the indolate nitrogen atom trans to the NHC. However, whereas the new complexes mediated metathetic exchange of their 2-thienylmethylidene ligand in the presence of the common metathesis substrates styrene and allylbenzene, no corresponding self-metathesis products were obtained. Only small amounts of 2-butene (73% (Z)-2-butene) were obtained in self-metathesis of propene using Ru21a. Detailed DFT analysis of this process revealed that product release is surprisingly slow, limiting the reaction rate and explaining the low metathesis activity. With the barrier to dissociation of (Z)-2-butene being lower than that of (E)-2-butene, the calculations also account for the observed Z-selectivity of Ru21a. These findings provide guidelines for catalyst redesign in pursuit of the ambitious goal of E-selective 1-alkene metathesis.

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Bengamide Analogues Show A Potent Antitumor Activity against Colon Cancer Cells: A Preliminary Study

The limited success and side effects of the current chemotherapeutic strategies against colorectal cancer (CRC), the third most common cancer worldwide, demand an assay with new drugs. The prominent antitumor activities displayed by the bengamides (Ben), a family of natural products isolated from marine sponges of the Jaspidae family, were explored and investigated as a new option to improve CRC treatment. To this end, two potent bengamide analogues, Ben I (5) and Ben V (10), were selected for this study, for which they were synthesized according to a new synthetic strategy recently developed in our laboratories. Their antitumor effects were analyzed in human and mouse colon cell lines, using cell cycle analysis and antiproliferative assays. In addition, the toxicity of the selected analogues was tested in human blood cells. These biological studies revealed that Ben I and V produced a significant decrease in CRC cell proliferation and induced a significant cell cycle alteration with a greater antiproliferative effect on tumor cell lines than normal cells. Interestingly, no toxicity effects were detected in blood cells for both compounds. All these biological results render the bengamide analogues Ben I and Ben V as promising antitumoral agents for the treatment of CRC.

Common therapeutic target for both cancer and obesity

Obesity and cancer are two interrelated conditions of high epidemiological need, with studies showing that obesity is responsible for nearly 25% of the relative contribution to cancer incidence. Given the connection between these conditions, a drug that can operate on both obesity and cancer is highly desirable. Such a drug is accomplishable through the development of potent anti-angiogenesis agents due to the shared underlying role of angiogenesis in the development of both diseases. Prior research has demonstrated a key role of type-2 methionine aminopeptidase (MetAP2) for angiogenesis, which has led to the development of numerous of novel inhibitors. Several irreversible MetAP2 inhibitors have entered clinical trials without great success. Though this lack of success could be attributed to off-target adverse effects, the underlying causes remain unclear. More promising reversible inhibitors have been recently developed with excellent pre-clinical results. However, due to insufficient knowledge of the biological functions of N-terminal protein processing, it is hard to predict whether these novel inhibitors would successfully pass clinical trials and thereby benefit cancer and obesity patients. Significantly more efforts are needed to advance our understanding of the regulation of methionine aminopeptidases and the processes by which they govern the function of proteins.

An Olefin Cross-Metathesis Approach to Depudecin and Stereoisomeric Analogues

A new total synthesis of the natural product (-)-depudecin, a unique and unexplored histone deacetylase (HDAC) inhibitor, is reported. A key feature of the synthesis is the utilization of an olefin cross-metathesis strategy, which provides for an efficient and improved access to natural depudecin, compared with our previous linear synthesis. Featured by its brevity and convergency, our developed synthetic strategy was applied to the preparation of the 10-epi derivative and the enantiomer of depudecin, which represent interesting stereoisomeric analogues for structure-activity relationship studies.

The Bengamides: A Mini-Review of Natural Sources, Analogues, Biological Properties, Biosynthetic Origins, and Future Prospects

This review focuses entirely on the natural bengamides and selected synthetic analogues that have inspired decades of research. Bengamide A was first reported in 1986 from the sponge Jaspis cf. coriacea, and bengamide-containing sponges have been gathered from many biogeographic sites. In 2005, a terrestrial Gram-negative bacterium, Myxococcus virescens, was added as a source for bengamides. Biological activity data using varying bengamide-based scaffolds has enabled fine-tuning of structure-activity relationships. Molecular target finding contributed to the creation of a synthetic "lead" compound, LAF389, that was the subject of a phase I anticancer clinical trial. Despite clinical trial termination, the bengamide compound class is still attracting worldwide attention. Future breakthroughs based on the bengamide scaffold are possible and could build on their nanomolar in vitro and positive in vivo antiproliferative and antiangiogenic properties. Bengamide molecular targets include methionine aminopeptidases (MetAP1 and MetAP2) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). A mixed PKS/NRPS biosynthetic gene cluster appears to be responsible for creation of the bengamides. This review highlights that the bengamides have driven inspirational studies and that they will remain relevant for future research, even 30 years after the discovery of the first structures.

Design, synthesis and cytotoxicity of bengamide analogues and their epimers

Starting from d-glycero-d-gulo-heptonic acid γ-lactone and amino acids, a number of diastereoisomeric bengamide analogues were synthesized. Optimization of the reaction conditions revealed that microwave irradiation assistance is a powerful method for the preparation of aminolactams, as well as for the coupling reactions of the lactone 5 with aminolactams. Cytotoxic activity evaluation against six cancer cell lines (KB, HepG2, LU1, MCF7, HL60, and Hela) demonstrated that the configuration of C-2' seems to be critical for the cytotoxic activity of compounds 8b (2'R) and 8a (2'S). Additionally, comparison of cytotoxicity of the protected acetonide compounds with that of their corresponding deprotected bengamide analogues suggested that the flexibility of the ketide side chain should be required for their cytotoxic activity.

Marine Natural Products from New Caledonia--A Review

Marine micro- and macroorganisms are well known to produce metabolites with high biotechnological potential. Nearly 40 years of systematic prospecting all around the New Caledonia archipelago and several successive research programs have uncovered new chemical leads from benthic and planktonic organisms. After species identification, biological and/or pharmaceutical analyses are performed on marine organisms to assess their bioactivities. A total of 3582 genera, 1107 families and 9372 species have been surveyed and more than 350 novel molecular structures have been identified. Along with their bioactivities that hold promise for therapeutic applications, most of these molecules are also potentially useful for cosmetics and food biotechnology. This review highlights the tremendous marine diversity in New Caledonia, and offers an outline of the vast possibilities for natural products, especially in the interest of pursuing collaborative fundamental research programs and developing local biotechnology programs.

Chemistry and biology of bengamides and bengazoles, bioactive natural products from Jaspis sponges

Sponges corresponding to the Jaspidae family have proved to be a prolific source of bioactive natural products. Among these, the bengamides and the bengazoles stand out by virtue of their unprecedented molecular architectures and impressive biological profiles, including antitumor, antibiotic and anthelmintic properties. As a consequence, intense research activity has been devoted to these compounds from both chemical and biological standpoints. This review describes in detail the research into these classes of natural products and the benefits they offer in chemistry and biology.