Axiriabilines A-D, uncommon nitrogenous eudesmane-type sesquiterpenes from the Hainan sponge Axinyssa variabilis

Eudesmane-type sesquiterpenoids: Structural diversity and biological activity

Sesquiterpenoids are integral constituents of terpenoid-bearing plants, comprising a diverse and abundant class of natural compounds, among which eudesmane-type sesquiterpenoids have bicyclic structures that feature the fusion of two six-membered carbon rings, thereby attracting considerable attention. They are widespread in nature, with multifaceted biological activities such as anti-inflammatory, anticancer, antimicrobial, antimalarial, and insecticidal activities, thus gaining focus in life science research. The discovery and identification of these active compounds have laid a foundation for unraveling their potential medicinal value. In this review, we comprehensively explore the natural eudesmane-type sesquiterpenoids isolated (totaling 391 compounds) between 2016 and 2022, elucidating their chemical structures, plant distribution patterns, and pertinent biological properties. Accordingly, the study serves not only as a framework for researchers to thoroughly comprehend these compounds but also as a robust reference for future endeavors aimed at exploring the pharmaceutical potential and prospective applications of these molecules.

Two new eudesmane-type sesquiterpene derivatives from Lecokia cretica (Lam.) DC

Two new sesquiterpene glucosides, 1α,6β,9β-trihydroxy-eudesm-4(15)-en-1,6-O-β-diglucopyranoside (1) and 1α,6β,9β-trihydroxy-eudesm-3-en-1,6-O-β-diglucopyranoside (2) were obtained along with the 1α,6β,9β-trihydroxy-5,10-bis-epi-eudesm-3-en-6-O-β-D-glucopyranoside (3), chlorogenic acid (4), luteolin 7-O-rutinoside (5) and luteolin 7-O- glucoside (6) from the whole plant parts of Lecokia cretica. Their structures were determined on the basis of 1 D, 2 D NMR and HRMS analyses. The in vitro cytotoxic activity of compounds 1-3 against human lung cancer cells (A549) and normal human lung cells (BEAS-2B) was determined using the MTT colorimetric assay. All the tested eudesmane derivatives were found to be inactive.

Bacterial Isothiocyanate Biosynthesis by Rhodanese-Catalyzed Sulfur Transfer onto Isonitriles

Natural products bearing isothiocyanate (ITC) groups are an important group of specialized metabolites that play various roles in health, nutrition, and ecology. Whereas ITC biosynthesis via glucosinolates in plants has been studied in detail, there is a gap in understanding the bacterial route to specialized metabolites with such reactive heterocumulene groups, as in the antifungal sinapigladioside from Burkholderia gladioli. Here we propose an alternative ITC pathway by enzymatic sulfur transfer onto isonitriles catalyzed by rhodanese-like enzymes (thiosulfate:cyanide sulfurtransferases). Mining the B. gladioli genome revealed six candidate genes (rhdA-F), which were individually expressed in E. coli. By means of a synthetic probe, the gene products were evaluated for their ability to produce the key ITC intermediate in the sinapigladioside pathway. In vitro biotransformation assays identified RhdE, a prototype single-domain rhodanese, as the most potent ITC synthase. Interestingly, while RhdE also efficiently transforms cyanide into thiocyanate, it shows high specificity for the natural pathway intermediate, indicating that the sinapigladioside pathway has recruited a ubiquitous detoxification enzyme for the formation of a bioactive specialized metabolite. These findings not only elucidate an elusive step in bacterial ITC biosynthesis but also reveal a new function of rhodanese-like enzymes in specialized metabolism.

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.

Biosynthesis of Sinapigladioside, an Antifungal Isothiocyanate from Burkholderia Symbionts

Sinapigladioside is a rare isothiocyanate-bearing natural product from beetle-associated bacteria (Burkholderia gladioli) that might protect beetle offspring against entomopathogenic fungi. The biosynthetic origin of sinapigladioside has been elusive, and little is known about bacterial isothiocyanate biosynthesis in general. On the basis of stable-isotope labeling, bioinformatics, and mutagenesis, we identified the sinapigladioside biosynthesis gene cluster in the symbiont and found that an isonitrile synthase plays a key role in the biosynthetic pathway. Genome mining and network analyses indicate that related gene clusters are distributed across various bacterial phyla including producers of both nitriles and isothiocyanates. Our findings support a model for bacterial isothiocyanate biosynthesis by sulfur transfer into isonitrile precursors.

New sterols from the South China Sea sponges Halichondria sp

A detailed chemical investigation of two specimen of South China Sea sponges Halichondria sp. (No. 19-XD-47 and No. 17-XD-87) have resulted in the isolation of three new sterols, namely, halichsterols A (1), B (2) and C (3), together with seven related known ones (4-10). Their structures were determined by extensive spectroscopic analysis and by comparison with the spectral data reported in the literature. In bioassay, compound 2 displayed significantly anti-inflammatory activity in lipopolysaccharide (LPS)-stimulated BV-2 microglial cells.

Natural Nitrogenous Sesquiterpenoids and Their Bioactivity: A Review

Nitrogenous sesquiterpenoids fromnatural sourcesare rare, so unsurprisingly neither the potentially valuable bioactivity nor thebroad structural diversity of nitrogenous sesquiterpenoids has been reviewed before. This report covers the progressduring the decade from 2010 to February 2020 on the isolation, identification, and bioactivity of 391 nitrogen-containing natural sesquiterpenes from terrestrial plant, marine organisms, and microorganisms. This complete and in-depth reviewshouldbe helpful for discovering and developing new drugs of medicinal valuerelated to natural nitrogenous sesquiterpenoids.

Cytotoxic Nitrogenous Terpenoids from Two South China Sea Nudibranchs Phyllidiella pustulosa, Phyllidia coelestis, and Their Sponge-Prey Acanthella cavernosa

A detailed chemical investigation of two South China Sea nudibranchs Phyllidiella pustulosa and Phyllidia coelestis, as well as their possible sponge-prey Acanthella cavernosa, led to the isolation of one new nitrogenous cadinane-type sesquiterpenoid xidaoisocyanate A (1), one new naturally occurring nitrogen-containing kalihinane-type diterpenoid bisformamidokalihinol A (16), along with 17 known nitrogenous terpenoids (2⁻15, 17⁻19). The structures of all the isolates were elucidated by detailed spectroscopic analysis and by the comparison of their spectroscopic data with those reported in the literature. In addition, the absolute stereochemistry of the previously reported axiriabiline A (5) was determined by X-ray diffraction (XRD) analysis. In a bioassay, the bisabolane-type sesquiterpenoids 8, 10, and 11 exhibited cytotoxicity against several human cancer cell lines.

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.

Cembrane-type diterpenoids from the South China Sea soft coral Sarcophyton mililatensis

Eight cembrane-type diterpenoids, namely, (+)-(6R)-6-hydroxyisosarcophytoxide (1), (+)-(6R)-6-acetoxyisosarcophytoxide (2), (+)-17-hydroxyisosarcophytoxide (3), sarcomililatins A-D (4-7), and sarcomililatol (8), were isolated from the soft coral Sarcophyton mililatensis collected from Weizhou Island, Guangxi Autonomous Region, together with 2 known related analogues, (+)-isosarcophytoxide (9) and (+)-isosarcophine (10). The structures of these compounds were elucidated by a combination of detailed spectroscopic analyses, chemical methods, and comparison with reported data. The absolute configuration of compound 1 was established by the modified Mosher׳s method, while the absolute configurations of compounds 4 and 5 were assigned by electronic circular dichroism (ECD) spectroscopy and that of compound 8 was established by time-dependent density functional theory electronic circular dichroism (TD-DFT ECD) calculation. In in vitro bioassays, compound 9 displayed significant cytotoxicity against the human cancer cell lines human promyelocytic leukemia cells (HL-60) and human lung adenocarcinoma cells (A-549) with IC50 values of 0.78±0.21 and 1.26±0.80 μmol/L, respectively. Compounds 4 and 9 also showed moderate inhibitory effects on the TNFα-induced Nuclear factor kappa B (NF-κB, a therapeutical target in cancer) activation, showing IC50 values of 35.23±12.42 and 22.52±4.44 μmol/L, respectively.

Racemic trinorsesquiterpenoids from the Beihai sponge Spongia officinalis: structure and biomimetic total synthesis

Two rare new furan butanolides, sponalisolides A (1) and B (2), were isolated from the Beihai sponge Spongia officinalis, and fully characterized by extensive spectroscopic analysis and biomimetic total synthesis.