Terpenoids from Octocorals of the Genus Pachyclavularia

The Tetrahydrofuran Motif in Marine Lipids and Terpenes

Heterocycles are particularly common moieties within marine natural products. Specifically, tetrahydrofuranyl rings are present in a variety of compounds which present complex structures and interesting biological activities. Focusing on terpenoids, a high number of tetrahydrofuran-containing metabolites have been isolated during the last decades. They show promising biological activities, making them potential leads for novel antibiotics, antikinetoplastid drugs, amoebicidal substances, or anticancer drugs. Thus, they have attracted the attention of the synthetics community and numerous approaches to their total syntheses have appeared. Here, we offer the reader an overview of marine-derived terpenoids and related compounds, their isolation, structure determination, and a special focus on their total syntheses and biological profiles.

Organocatalytic activity of granaticin and its involvement in bactericidal function

We previously discovered that actinorhodin, a benzoisochromanequinone antibiotic produced by Streptomyces coelicolor A3(2), serves as a catalyst facilitating the oxidation of ascorbic acid and cysteine (PNAS 48:17,152, 2014). In the present study, we screened for similar ascorbic acid-oxidizing activity in the culture broth of various Streptomyces spp., and discovered marked activity in the culture broth of Streptomyces vietnamensis. The principle active compound was granaticin, a pigmented antibiotic that is structurally related to actinorhodin. The absence of any metals in the purified granaticin fraction indicated that granaticin was an organocatalyst. Granaticin catalyzed the oxidation of L-ascorbic acid, generating L-dehydroascorbic acid and hydrogen peroxide (H₂O₂) at a 1:1 stoichiometric ratio, with 15 times higher reactivity than that of actinorhodin at an optimum pH of 7.0. Granaticin also oxidizes sulfhydryl compounds, including L-cysteine and glutathione. Growth inhibitory assays demonstrated that knockout mutants of the catalase gene exhibit high sensitivity to granaticin. The results suggest that the bactericidal activity of granaticin is exerted by the oxidation of sulfhydryl groups of cellular components and the toxicity of H₂O₂ generated during the oxidation reaction.

Antiamoebic effects of sesquiterpene lactones isolated from the zoanthid Palythoa aff. clavata

Opportunistic parasitic protozoa of genus Acanthamoeba are responsible to cause severe infections in humans such as Acanthamoeba Keratitis or Amoebic Granulomatous Encephalitis. Current treatments are usually toxic and inefficient and there is a need to access new therapeutic agents. The antiamoebic effects of nephthediol (1) and fourteen germacranolide and eudesmanolide sesquiterpene lactones (2-5, 7-12) isolated from the indigenous zoanthid Palythoa aff. clavata collected at the coast of Lanzarote, Canary Islands were studied against Acanthamoeba castellanii Neff, and the clinical strains A. polyphaga and A. griffini. 4-epi-arbusculin A (11) presented the lowest IC₅₀ value (26,47 ± 1,69 µM) against A. castellanii Neff and low cytotoxicity against murine macrophages, followed by isobadgerin (2), which also showed to be active against A. castellanii Neff cysts. The studies on the mode of action of compounds 2 and 11 revealed these sesquiterpene lactones induce mechanisms of PDC on A. castellanii Neff.

Marine Pharmacology in 2016-2017: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis and Antiviral Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The review of the 2016-2017 marine pharmacology literature was prepared in a manner similar as the 10 prior reviews of this series. Preclinical marine pharmacology research during 2016-2017 assessed 313 marine compounds with novel pharmacology reported by a growing number of investigators from 54 countries. The peer-reviewed literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral activities for 123 marine natural products, 111 marine compounds with antidiabetic and anti-inflammatory activities as well as affecting the immune and nervous system, while in contrast 79 marine compounds displayed miscellaneous mechanisms of action which upon further investigation may contribute to several pharmacological classes. Therefore, in 2016-2017, the preclinical marine natural product pharmacology pipeline generated both novel pharmacology as well as potentially new lead compounds for the growing clinical marine pharmaceutical pipeline, and thus sustained with its contributions the global research for novel and effective therapeutic strategies for multiple disease categories.

Streptomyces albogriseolus SY67903 Produces Eunicellin Diterpenoids Structurally Similar to Terpenes of the Gorgonian Muricella sibogae, the Bacterial Source

Microeunicellols A (1) and B (2), two undescribed eunicellin diterpenoids, were isolated from the culture of a bacterial symbiont, Streptomyces albogriseolus SY67903. Their structures, including absolute configurations revealed by spectroscopic data and single-crystal X-ray diffraction analysis, are closely related with the diterpenoids from its host, a South China Sea gorgonian, Muricella sibogae. This is the first report of eunicellin diterpenoids, commonly coral-derived, from a bacterial symbiont of coral. The chemical metabolic relationship between the bacterium and its host is discussed. Biological evaluation revealed that compound 1 possessed cytotoxicities against several human cancer cell lines.

New Eunicellin-Type Diterpenes from the Panamanian Octocoral Briareum Asbestinum

Gorgonian octocorals are considered a prolific source of secondary metabolites with a wide range of biological activities, including anti-inflammatory activity. In particular, the genus Briareum is known for producing a wealth of diterpenes with complex chemical structures. The chemical study of the methanolic extract of Briareum asbestinum collected in Bocas del Toro, on the Caribbean side of Panama, led to the isolation of three new eunicellin-type diterpenes: briarellin T (1), asbestinin 27 (2), asbestinin 28 (3) and the previously described asbestinin 17 (4). The structures of the new compounds were determined by extensive NMR analyses and HRMS. Anti-inflammatory activity assays showed a significant reduction of the pro-inflammatory cytokines TNF-α, IL-6, IL-1β and IL-8 as well as a downregulation of COX-2 expression in LPS-stimulated THP-1 macrophages. These findings support the potential use of these marine compounds as therapeutic agents in the treatment of inflammatory diseases.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

Populeuphrines A and B, two new cembrane diterpenoids from the resins of Populus euphratica

Two new cembrane diterpenoids, named populeuphrines A and B (1 and 2), together with three known analogues (3-5) were isolated from the resins of Populus euphratica. The planar structures and relative configurations of 1 and 2 were elucidated by detailed 1 D and 2 D NMR spectroscopic analyses. The absolute configurations of 1 and 2 were determined by X-ray diffraction analysis and quantum chemical computation. Biological activities of all the isolates against proliferation of human cancer cells and umbilical cord mesenchymal stem cells were evaluated.

New Furanocembranoids from Briareum violaceum

Three new furanocembranoids—briaviodiol F (1) and briaviotriols A (2) and B (3)—along with a known analogue, briaviodiol A (4), were obtained from a cultured-type octocoral Briareum violaceum. The structures of cembranoids 1–3 were elucidated by using spectroscopic methods. In vitro study demonstrated that compounds 2 and 4 exerted inhibition effects on inducible nitric oxide synthase (iNOS) release from RAW 264.7, a macrophage cell line that originated from a mouse monocyte macrophage, stimulated with lipopolysaccharides.

Briaviolides K-N, New Briarane-Type Diterpenoids from Cultured Octocoral Briareum violaceum

Four new briarane diterpenoids, briaviolides K-N (1-4), have been obtained from the cultured-type octocoral Briareum violaceum. Using a spectroscopic approach, the structures of briaranes 1-4 were identified. This study employed an in vitro model of lipopolysaccharide (LPS)-induced inflammation in the murine macrophage RAW 264.7 cell line, and found that among the four briaranes, briarane 2 possessed anti-inflammatory activity against inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein expressions in cells. In addition, principal component analysis using the chemical global positioning system (ChemGPS) for natural products (ChemGPS-NP) was employed in order to analyze the structure-activity relationship (SAR), and the results indicated that the ring conformation of the compound has a leading role in suppressing the expressions of pro-inflammatory iNOS and COX-2 proteins in macrophages.