Macrophilone A: Structure Elucidation, Total Synthesis, and Functional Evaluation of a Biologically Active Iminoquinone from the Marine Hydroid Macrorhynchia philippina

Marine Natural Products from Flora and Fauna of the Western Australian Coast: Taxonomy, Isolation and Biological Activity

Marine natural products occurring along the Western Australian coastline are the focus of this review. Western Australia covers one-third of the Australian coast, from tropical waters in the far north of the state to cooler temperate and Antarctic waters in the south. Over 40 years of research has resulted in the identification of a number of different types of secondary metabolites including terpenoids, alkaloids, polyketides, fatty acid derivatives, peptides and arsenic-containing natural products. Many of these compounds have been reported to display a variety of bioactivities. A description of the compound classes and their associated bioactivities from marine organisms found along the Western Australian coastline is presented.

Current Perspectives on Pyrroloiminoquinones: Distribution, Biosynthesis and Drug Discovery Potential

Pyrroloiminoquinones are a group of cytotoxic alkaloids most commonly isolated from marine sponges. Structurally, they are based on a tricyclic pyrrolo[4,3,2-de]quinoline core and encompass marine natural products such as makaluvamines, tsitsikammamines and discorhabdins. These diverse compounds are known to exhibit a broad spectrum of biological activities including anticancer, antiplasmodial, antimicrobial, antifungal and antiviral activities as well as the inhibition of several key cellular enzymes. The resurgence of interest in pyrroloiminoquinones and the convoluted understanding regarding their biological activities have prompted this review. Herein, we provided a concise summary of key findings and recent developments pertaining to their structural diversity, distribution, biogenesis, and their potential as chemical probes for drug development, including a discussion of promising synthetic analogs.

Biochemical and Toxinological Characterization of Venom from Macrorhynchia philippina (Cnidaria, Hydrozoa)

Macrorhynchia philippina is a colonial benthic hydroid from the Class Hydrozoa (Phylum Cnidaria) distributed in the tropical and subtropical marine waters from Atlantic Ocean, Indo-Pacific, and Mozambique. Its colonies somewhat resemble plants, causing confusion in the bathers who accidentally touch the animal. Acute burning/local pain, edema, erythema, and pruritus were symptoms already described, but its venom composition is unknown, as well as the participation of toxins for the symptom's development. Thus, herein, we show the biochemical composition and toxic effects of M. philippina venom. Colonies were collected and processed for histological analysis; alternatively, they were immersed into methanol containing 0.1% acetic acid for venom attainment, which was analyzed by mass spectrometry and submitted to edema and nociception evaluation in mice, hemolysis and antimicrobial assays in vitro. Before the molecule's extraction, it was possible to see the inoculation structures (hydrocladiums and hydrotheca) containing venom, which was released after the immersion of the animal in the solvents. The venom was composed mainly by low molecular mass compounds, able to cause significant reduction of the paw withdrawal latency from the hot plate test, 30 minutes after the injection. Moreover, significant edema was observed 10 and 30 minutes after the injection, indicating the activity of at least two inflammatory mediators. The venom caused no hemolytic activity but reduced the growth of A. baumannii and K. pneumoniae strains. This study is the first biochemical description of M. philippina venom, with molecules that cause fast inflammatory and painful effects, characteristic of the envenomation.

Marine Pyrrole Alkaloids

Nitrogen heterocycles are essential parts of the chemical machinery of life and often reveal intriguing structures. They are not only widespread in terrestrial habitats but can also frequently be found as natural products in the marine environment. This review highlights the important class of marine pyrrole alkaloids, well-known for their diverse biological activities. A broad overview of the marine pyrrole alkaloids with a focus on their isolation, biological activities, chemical synthesis, and derivatization covering the decade from 2010 to 2020 is provided. With relevant structural subclasses categorized, this review shall provide a clear and timely synopsis of this area.

Toxicological risks on the human health of populations living around the Mediterranean Sea linked to the invasion of non-indigenous marine species from the Red Sea: A review

The Mediterranean region is, by far, a prime travel destination, having hosted more than 330 million tourists in 2016, mostly for seaside holidays. A greatly increased influx of thermophilic Red Sea species, introduced through the Suez Canal in a process referred to as Lessepsian invasion (in honor of Ferdinand de Lesseps who instigated the building of the Suez Canal), have raised awareness among scientists, medical personnel, and the public, of health risks caused by some venomous and poisonous marine species. The main species of concern are the poisonous Lagocephalus sceleratus, and the venomous Plotosus lineatus, Siganus luridus, Siganus rivulatus, Pterois miles, Synancea verrucosa, Rhopilema nomadica, Macrorhynchia philippina and Diadema setosum. Recognizing that the main factors that drive the introduction and dispersal of Red Sea biota in the Mediterranean, i.e., Suez Canal enlargements and warming seawater, are set to increase, and international tourist arrivals are forecasted to increase as well, to 500 million in 2030, an increase in intoxications and envenomations by alien marine species is to be expected and prepared for.

Structural elucidation, total synthesis, and cytotoxic activity of effphenol A

A highly substituted phenol derivative, effphenol A (1), was isolated from the deep-sea-derived fungus Trichobotrys effuse FS524. Its complete structural assignment was established through a combination of spectroscopic analysis together with single-crystal X-ray diffraction experiments and further unequivocally confirmed by a biomimetic total synthesis. Structurally, effphenol A possesses a poly-substituted 6-5/6/6 tetracyclic ring system, which represents the first case of such a skeleton found in nature. Furthermore, the cytotoxic activity of effphenol A (1) toward four human cancer cell lines was assayed.

Discovery of Mitochondrial Transcription Inhibitors Active in Pancreatic Cancer Cells

Mitochondrial dysfunction is a hallmark of cancer cells and targeting cancer mitochondria has emerged as a promising anti-cancer therapy. Previously, we repurposed chlorambucil by conjugating it to a mitochondrial targeting triphenylphosphonium (TPP) group to design Mito-Chlor, a novel agent that acts on mitochondria DNA (mtDNA). Herein, we show that Mito-Chlor, but not chlorambucil, inhibits the nascent transcription of mtDNA. Clustering analysis of transcriptomic profile of our Bru-seq database led to the identification of another mitochondrial transcription inhibitor SQD1, which inhibits the proliferation of MIA PaCa-2 cells with an IC₅₀ of 1.3 μM. Interestingly, Mito-Chlor reduces expression of mitochondrial proteins, interferes with mitochondria membrane potential, and impairs oxidative phosphorylation while SQD1 does not. Both compounds increased cellular and mitochondrial reactive oxygen species and stimulated similar signaling pathways in response to oxidative stress. As mitochondrial transcription inhibitors and redox modulators, SQD1 and Mito-Chlor are promising for the treatment of pancreatic cancer by blocking mitochondrial function.

Creating and screening natural product libraries

Covering: up to 2020The National Cancer Institute of the United States (NCI) has initiated a Cancer Moonshot program entitled the NCI Program for Natural Product Discovery. As part of this effort, the NCI is producing a library of 1 000 000 partially purified natural product fractions which are being plated into 384-well plates and provided to the research community free of charge. As the first 326 000 of these fractions have now been made available, this review seeks to describe the general methods used to collect organisms, extract those organisms, and create a prefractionated library. Importantly, this review also details both cell-based and cell-free bioassay methods and the adaptations necessary to those methods to productively screen natural product libraries. Finally, this review briefly describes post-screen dereplication and compound purification and scale up procedures which can efficiently identify active compounds and produce sufficient quantities of natural products for further pre-clinical development.

Synthesis of a Diastereomer of the Marine Macrolide Lytophilippine A

The synthesis of a diastereomer of lytophilippine A required 22 longest linear steps using known building blocks. Cross-metathesis/asymmetric aldol addition and regioselective esterification/ring-closing metathesis served as efficient combi tools for scaffold construction. Detailed NMR investigations in different solvent (systems) provide evidence for a deep-seated configurational misassignment of the molecule named lytophilippine A.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Cesium carbonate-promoted synthesis of aryl methyl sulfides using S-methylisothiourea sulfate under transition-metal-free conditions

In the presence of cesium carbonate, an efficient synthesis of aryl methyl sulfides by the reactions of aryl halides with commercially available S-methylisothiourea sulfate is developed. This odourless and highly crystalline solid can be used as the substitute for malodorous methanethiol. The gram-scale reaction also proceeds smoothly without the use of column chromatography separation. Similarly, 2-(dimethylamino)ethylthio and cyclopropylmethylthio groups can be easily introduced into the aromatic rings from the corresponding S-[2-(dimethylamino)ethyl]isothiourea dihydrochloride and S-cyclopropylmethylisothiourea hydrobromide. The possible reaction mechanism is proposed. It is believed that this route to aryl alkyl sulfides is well competitive with currently known methods due to its wide substrate scope, excellent yields, easy operation and transition-metal-free conditions.

Macrophilones from the Marine Hydroid Macrorhynchia philippina Can Inhibit ERK Cascade Signaling

Six new macrophilone-type pyrroloiminoquines were isolated and identified from an extract of the marine hydroid Macrorhynchia philippina. The proton-deficient and heteroatom-rich structures of macrophilones B-G (2-7) were elucidated by spectroscopic analysis and comparison of their data with those of the previously reported metabolite macrophilone A (1). Compounds 1-7 are the first pyrroloiminoquines to be reported from a hydroid. The macrophilones were shown to inhibit the enzymatic conjugation of SUMO to peptide substrates, and macrophilones A (1) and C (3) exhibit potent and selective cytotoxic properties in the NCI-60 anticancer screen. Bioinformatic analysis revealed a close association of the cytotoxicity profiles of 1 and 3 with two known B-Raf kinase inhibitory drugs. While compounds 1 and 3 showed no kinase inhibitory activity, they resulted in a dramatic decrease in cellular protein levels of selected components of the ERK signal cascade. As such, the chemical scaffold of the macrophilones could provide small-molecule therapeutic leads that target the ERK signal transduction pathway.

Crystal structure of (E)-2-(tert-butyl-amino)-4-(tert-butyl-imino)-naphthalen-1(4H)-one

The title compound, C18H24N2O, is the first example of a naphtho-quinone imine derivative isolated in the 4-imine/2-amine tautomeric form having bulky alkyl substituents at the N atoms. The mol-ecular conformation is stabilized by an intra-molecular hydrogen bond between the amine and a carbonyl group and by London attraction between the two tert-butyl groups. Only van der Waals inter-actions were identified in the crystal packing.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as macrophilone A from Macrorhynchia philippina.