Polyoxygenated cembranoids from the Hainan soft coral Lobophytum crassum

Polyoxygenated cembrane-type diterpenes from the Hainan soft coral Lobophytum crassum as a promising source of anticancer agents with ErbB3 and ROR1 inhibitory potential

A detailed chemical investigation of the Hainan soft coral Lobophytum crassum led to the identification of a class of polyoxygenated cembrane-type macrocyclic diterpenes (1-28), including three new flexible cembranoids, lobophycrasins E-G (2-4), and twenty-five known analogues. Their structures were elucidated by combining extensive spectroscopic data analysis, quantum mechanical-nuclear magnetic resonance (QM-NMR) methods, the modified Mosher's method, X-ray diffraction analysis, and comparison with data reported in the literature. Bioassays revealed that sixteen cembranoids inhibited the proliferation of H1975, MDA-MB231, A549, and H1299 cells. Among them, Compounds 10, 17, and 20 exhibited significant antiproliferative activities with IC50 values of 1.92-8.82 μM, which are very similar to that of the positive control doxorubicin. Molecular mechanistic studies showed that the antitumour activity of Compound 10 was closely related to regulation of the ROR1 and ErbB3 signalling pathways. This study may provide insight into the discovery and utilization of marine macrocyclic cembranoids as lead compounds for anticancer drugs.

A new capnosane-type diterpenoid from the South China sea soft coral Lobophytum pauciflorum

A new rare capnosane-type diterpenoid (1) along with two known compounds sarcophyolides D (2) and arbolide C (3), were isolated from the soft coral Lobophytum pauciflorum collected at Xisha Islands in the South China Sea. The structure of 1 was established based on comprehensive spectroscopic data, literature comparison, and quantum chemical calculations. Compound 1 exhibited moderate anti-inflammatory activities in the zebrafish model at a concentration of 20 μM.

Marine natural products

Covering: January to December 2021This review covers the literature published in 2021 for marine natural products (MNPs), with 736 citations (724 for the period January to December 2021) 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 (1425 in 416 papers for 2021), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of the number of authors, their affiliations, domestic and international collection locations, focus of MNP studies, citation metrics and journal choices is discussed.

Cembrane Diterpenes Possessing Nonaromatic Oxacycles from the Hainan Soft Coral Sarcophyton mililatensis

Documents on the chemical composition of the soft coral Sarcophyton mililatensis are sparse. The present investigation of the Hainan soft coral S. mililatensis resulted in the discovery of six new cembrane diterpenes, sarcoxacyclols A-F (1-6) and four known analogs (7-10). Their structures were elucidated by extensive spectroscopic analysis along with a comparison with the data in current literature. The nonaromatic oxacycles in their structures were the rarely found tetrahydrofuran ether across C-1 and C-12 and tetrahydropyran ether across C-1 and C-11, respectively. Moreover, the absolute configuration of compound 4 was established unambiguously by X-ray diffraction analysis using Ga Kα radiation (λ = 1.34139 Å). Based on the biogenetical consideration, the absolute configurations of other five new compounds were tentatively assumed. Assessment of the bioactivity for these secondary metabolites revealed that compound 1 exhibited significant tumor necrosis factor (TNF)-α inhibitory activity (IC50 = 9.5 μmol/L), similar to the positive control dexamethasone (IC50 = 8.7 μmol/L), but no obvious cytotoxicity towards RAW264.7 cells (CC50 > 50 μmol/L). The preliminary molecular docking suggested the crucial roles of the hydroxyl and acetoxyl groups in the computational prediction of the binding mode between the diterpene and the protein.

Isosarcophytoxide Derivatives with a 2,5-Dihydrofuran Moiety from the Soft Coral Sarcophyton cinereum

The present chemical investigation on the organic extract of the soft coral Sarcophyton cinereum has contributed to the isolation of four new cembranoids: 16β- and 16α-hydroperoxyisosarcophytoxides (1 and 2), 16β- and 16α-methoxyisosarcophytoxides (3 and 4), and a known cembranoid, lobocrasol (5). The structures of all isolates were elucidated by detailed spectroscopic analysis. Their structures were characterized by a 2,5-dihydrofuran moiety, of which the relative configuration was determined by DU8-based calculation for long-range coupling constants (⁴J_H,H). The cytotoxicity and immunosuppressive activities of all isolates were evaluated in this study.

Chemistry and bioactivity of secondary metabolites from South China Sea marine fauna and flora: recent research advances and perspective

Marine organisms often produce a variety of metabolites with unique structures and diverse biological activities that enable them to survive and struggle in the extremely challenging environment. During the last two decades, our group devoted great effort to the discovery of pharmaceutically interesting lead compounds from South China Sea marine plants and invertebrates. We discovered numerous marine secondary metabolites spanning a wide range of structural classes, various biosynthetic origins and various aspects of biological activities. In a series of reviews, we have summarized the bioactive natural products isolated from Chinese marine flora and fauna found during 2000-2012. The present review provides an updated summary covering our latest research progress and development in the last decade (2012-2022) highlighting the discovery of over 400 novel marine secondary metabolites with promising bioactivities from South China Sea marine organisms.

Uncommon Capnosane Diterpenes with Neuroprotective Potential from South China Sea Soft Coral Sarcophyton boettgeri

The first investigation of the South China Sea soft coral Sarcophyton boettgeri afforded five new capnosane diterpenes, sarboettgerins A-E (1-5), together with one known related compound, pavidolide D (6). Their structures, including absolute configurations, were elucidated by the extensive spectroscopic analysis, 13C NMR calculations, and X-ray diffraction. Among them, new compounds 1-5 were featured by the rarely encountered Z-geometry double bond Δ1 within the 5/11-fused bicyclic capnosane carbon framework. Plausible biogenetic relationships of all isolates were proposed, and they might give an insight into future biomimetic synthesis of these novel compounds. In an in vitro bioassay, compound 5 displayed potent anti-neuroinflammatory activity against LPS-induced NO release in BV-2 microglial cells, which might be developed as a new type of potential neuroprotective agent in future.

Cytotoxic and Antibacterial Isomalabaricane Terpenoids from the Sponge Rhabdastrella globostellata

Nine new isomalabaricane terpenoids (1-9) were isolated from the sponge Rhabdastrella globostellata of Ximao Island, together with 13 known ones (10-22). The structures were established by spectroscopic data interpretation and chemical calculations, as well as by comparison with spectroscopic data of known compounds. Notably, of the new isolates, hainanstelletin A (5) is the first representative of a nitrogenous isomalabaricane. The isolated compounds were evaluated against several cancer cell lines and two bacterial pathogens. In addition, moderate to strong antibacterial activities against Streptococcus pyogenes were also detected among geometric isomers 1, 2, and 10-12, with minimum inhibitory concentrations of 0.1-1.8 μg/mL.

Pitfalls in the structural elucidation of small molecules. A critical analysis of a decade of structural misassignments of marine natural products

Covering: July 2010 to August 2021This article summarizes more than 200 cases of misassigned marine natural products reported between July 2010 and August 2021, sorting out errors according to the structural elements. Based on a comparative analysis of the original and the revised structures, major pitfalls still plaguing the structural elucidation of small molecules were identified, emphasizing the role of total synthesis, crystallography, as well as chemical- and biosynthetic logic to complement spectroscopic data. Distinct "trends" in natural product misassignment are evident between compounds of marine and plant origin, with an overall much lower incidence of "impossible" structures within misassigned marine natural products.