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

Bioprospecting of Marine Organisms: Exploring Antibacterial Activities in Aqueous and Organic Extracts

This study evaluated the antibacterial activity of aqueous and organic extracts from 78 marine organisms, including seaweeds and sponges, collected along the coast of Ceará, Brazil. Extracts were obtained by maceration using distilled water and 50% acetonitrile and tested against Staphylococcus aureus, Staphylococcus epidermidis (Gram-positive), and Escherichia coli (Gram-negative) using the disk diffusion method, and inhibition zone diameters were measured. Antibacterial activity was observed in 30.7% of the extracts, with organic extracts showing higher efficacy. Several sponge species, particularly those from the genus Aplysina, as well as Amphimedon compressa, Amphimedon viridis, Mycale sp., and Pseudosuberites sp., demonstrated notable inhibitory effects. While seaweed aqueous extracts showed no activity, some organic extracts-especially from Amansia multifida-were effective against Gram-positive strains. In general, Gram-positive bacteria were more susceptible than Gram-negative bacteria. These findings underscore the biotechnological potential of marine organisms from the Brazilian coast as promising sources of antibacterial compounds and support future efforts focused on the isolation, characterization, and toxicological evaluation of active metabolites for pharmaceutical and industrial applications.

Antibacterial Methyl Ester Cembranoids from the Soft Coral Sarcophyton ehrenbergi and Their Structural Elucidation

Six previously undescribed methyl ester cembranoids, namely sarcoehrenolides L-Q (1-6), along with three known related ones (7-9), were isolated from the soft coral Sarcophyton ehrenbergi collected off Weizhou Island in the South China Sea. Their structures and absolute configurations were unambiguously established in the light of extensive spectroscopic data analysis, X-ray diffraction analysis, chemical conversion, and TDDFT-ECD calculations. All isolated compounds were evaluated via in vitro bioassays to investigate their antibacterial activity against eighteen human and fish pathogens. Compounds 2, 8, and 9 exhibited moderate antibacterial activity against Streptococcus parauberis with MIC values of 38.8, 37.4 and 31.6 μg/mL, respectively.

Cytotoxic and anti-bacterial evaluation of two new aromatic A-ring steroids isolated from the Red Sea soft coral Dendronephthya spp

A successful column chromatography of a CHCl3/MeOH crude extract of Dendronephthya spp. soft coral led to the isolation of two new aromatic A-ring steroids (1-2), together with three known compounds (3-5). Both 1 and 2 are 19-norsteroids. The chemical structures were elucidated based on extensive 1D, 2D NMR, and EIMS analyses. In cytotoxic bioassays, compounds 1-5 were tested against three cancer cell lines: MCF-7, NCI-1299, and HepG2, with IC50 in the ranges of 22.1-85.4, 26.9-88.7, and 25.9-93.7 μM, respectively. Compounds 1, 2, and 5 showed moderate degrees of inhibition against Escherichia coli and Pseudomonas sp. at 100 and 150 µg/mL, while exhibiting weak inhibition against Bacillus cereus and Staphylococcus aureus at 150 µg/mL.

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.

Two New Diterpenoids Formed by Transannular Diels-Alder Cycloaddition from the Soft Coral Sarcophyton tortuosum, and Their Antibacterial and PPAR-β Agonist Activities

Two new cembrane-derived tricyclic diterpenes belonging to the sarcophytin family, namely 4a-hydroxy-chatancin (1) and sarcotoroid (2), together with two known related ones (3 and 4), were isolated from the soft coral Sarcophyton tortuosum collected off Ximao Island in the South China Sea. The structures of the new compounds were elucidated by extensive spectroscopic analysis, a quantum mechanical nuclear magnetic resonance (QM-NMR) method, a time-dependent density functional theory electronic circular dichroism (TDDFT-ECD) calculation, X-ray diffraction analysis, and comparison with the reported data in the literature. A plausible biosynthetic pathway of compounds 1-4 was proposed, involving undergoing a transannular Diels-Alder cycloaddition. In the bioassay, the new compound 1 displayed significant inhibitory activities against the fish pathogens Streptococcus parauberis KSP28, oxytetracycline-resistant Streptococcus parauberis SPOF3K, and Photobacterium damselae FP2244, with MIC values of 9.1, 9.1, and 18.2 μg/mL, respectively. Furthermore, by conducting a luciferase reporter assay on rat liver Ac2F cells, compounds 1, 3, and 4 were evaluated for peroxisome proliferator-activated receptor (PPAR) transcriptional activity, and compound 3 showed selective PPAR-β agonist activity at a concentration of 10 μΜ.

Cembranoid Diterpenes from South China Sea Soft Coral Sarcophyton crassocaule

Cembranoid diterpenes are characteristic compounds of soft corals with diverse structures and significant activities, making them an important source of drug lead compounds. In this paper, five new cembranoid diterpenes, meijicrassolins A-E (1-5), were isolated from the soft coral Sarcophyton crassocaule, along with five previously reported compounds (6-10). The structures and absolute configuration for new compounds 1-5 were assigned by extensive spectroscopic analysis, single-crystal X-ray crystallography, quantum mechanical nuclear magnetic resonance (QM-NMR), and time-dependent density functional theory/electronic circular dichroism (TDDFT/ECD) calculations. Compounds 3, 4, and 9 showed moderate inhibition of nitric oxide generation in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Overall, our research results have enriched the library of secondary metabolites from soft corals, providing more molecular entities for subsequent research and development of related compounds.

Immunomodulatory Compounds from the Sea: From the Origins to a Modern Marine Pharmacopoeia

From sea shores to the abysses of the deep ocean, marine ecosystems have provided humanity with valuable medicinal resources. The use of marine organisms is discussed in ancient pharmacopoeias of different times and geographic regions and is still deeply rooted in traditional medicine. Thanks to present-day, large-scale bioprospecting and rigorous screening for bioactive metabolites, the ocean is coming back as an untapped resource of natural compounds with therapeutic potential. This renewed interest in marine drugs is propelled by a burgeoning research field investigating the molecular mechanisms by which newly identified compounds intervene in the pathophysiology of human diseases. Of great clinical relevance are molecules endowed with anti-inflammatory and immunomodulatory properties with emerging applications in the management of chronic inflammatory disorders, autoimmune diseases, and cancer. Here, we review the historical development of marine pharmacology in the Eastern and Western worlds and describe the status of marine drug discovery. Finally, we discuss the importance of conducting sustainable exploitation of marine resources through biotechnology.

In Vitro Insights into the Role of 7,8-Epoxy-11-Sinulariolide Acetate Isolated from Soft Coral Sinularia siaesensis in the Potential Attenuation of Inflammation and Osteoclastogenesis

The balance between bone-resorbing osteoclasts and bone-forming osteoblasts is essential for the process of bone remodeling. Excessive osteoclast differentiation plays a pivotal role in the pathogenesis of bone diseases such as rheumatoid arthritis and osteoporosis. In the present study, we examined whether 7,8-epoxy-11-sinulariolide acetate (Esa), a marine natural product present in soft coral Sinularia siaesensis, attenuates inflammation and osteoclastogenesis in vitro. The results indicated that Esa significantly inhibited lipopolysaccharide (LPS)-induced inflammation model of RAW264.7 cells and suppressed receptor activator for nuclear factor-κB ligand (RANKL)-triggered osteoclastogenesis. Esa significantly down-regulated the protein expression of iNOS, COX-2, and TNF-α by inhibiting the NF-κB/MAPK/PI3K pathways and reducing the release of reactive oxygen species (ROS) in RAW264.7 macrophages. Besides, Esa treatment significantly inhibited osteoclast differentiation and suppressed the expression of osteoclast-specific markers such as NFATC1, MMP-9, and CTSK proteins. These findings suggest that Esa may be a potential agent for the maintenance of bone homeostasis associated with inflammation.

Nine New Antibacterial Diterpenes and Steroids from the South China Sea Soft Coral Lobophytum catalai Tixier-Durivault

Five new cembrane-type diterpenes, lobocalines A-E (1-5), and four new steroids, lobocaloids A-D (9-12), along with six known related compounds (6-8 and 13-15) were isolated from the Yalong Bay soft coral Lobophytum catalai Tixier-Durivault. The structures of the new compounds were elucidated by extensive spectroscopic analysis, NMR calculation with DP4+ analysis, time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) calculations, X-ray diffraction analyses and comparison with the reported spectroscopic data of known compounds. Further, with the aid of X-ray diffraction analysis, the structure of lobocrasol B (15) was firmly revised as 15a. In in vitro bioassays, compound 2 showed moderate antibacterial activities against fish pathogenic bacteria Streptococcus parauberis KSP28 and Phoyobacterium damselae FP2244 with minimum inhibitory concentration (MIC) values of 8.7 and 17.3 µg/mL, respectively. All the steroids exhibited antibacterial activities against the S. parauberis KSP28 with MIC values ranging from 12.3 to 53.6 µg/mL. Compounds 2, 7 and 14 have remarkable inhibitory effects on the hemolysin production of Staphylococcus aureus, while compounds 8-12 have medium inhibitory effects on the pyocyanin production in Pseudomonas aeruginosa.

Two new compounds from the Hainan Soft Corals Sinularia tumulosa and Sinularia depressa with their anti-inflammatory or cytotoxic activities

The detailed chemical investigations of the South China Sea soft corals Sinularia tumulosa and Sinularia depressa, yielded two new compounds, namely tumulosterol A (1) and 11'-hydroxy-α-tocopherylquinone (3), along with four related known ones (2, 5-7). Their structures were determined by extensive spectroscopic analysis and comparison with the spectral data previously reported in the literature. In bioassays, compound 1 displayed significant cytotoxic effects against H1975 and MDA-MB-231 cells with IC50 values of 6.0 and 6.3 µM, respectively. In addition, compound 3 exhibited interesting inhibitory effect on lipopolysaccharide (LPS)-induced inflammatory responses in RAW264.7 cells with IC50 value of 9.5 µM.

Lobosteroids A-F: Six New Highly Oxidized Steroids from the Chinese Soft Coral Lobophytum sp

To explore the steroidal constituents of the soft coral Lobophytum sp. at the coast of Xuwen County, Guangdong Province, China, a chemical investigation of the above-mentioned soft coral was carried out. After repeated column chromatography over silica gel, Sephadex LH-20, and reversed-phase HPLC, six new steroids, namely lobosteroids A-F (1-6), along with four known compounds 7-10, were obtained. Their structures were determined by extensive spectroscopic analysis and comparison with the spectral data reported in the literature. Among them, the absolute configuration of 1 was determined by X-ray diffraction analysis using Cu Kα radiation. These steroids were characterized by either the presence of an α,β-α',β'-unsaturated carbonyl, or an α,β-unsaturated carbonyl moiety in ring A, or the existence of a 5α,8α-epidioxy system in ring B, as well as diverse oxidation of side chains. The antibacterial bioassays showed that all isolated steroids exhibited significant inhibitory activities against the fish pathogenic bacteria Streptococcus parauberis FP KSP28, Phoyobacterium damselae FP2244, and Streptococcus parauberis SPOF3K, with IC90 values ranging from 0.1 to 11.0 µM. Meanwhile, compounds 2 and 6-10 displayed potent inhibitory effects against the vancomycin-resistant Enterococcus faecium bacterium G7 with IC90 values ranging from 4.4 to 18.3 µM. Therefore, ten highly oxidized steroids with strong antibacterial activities were isolated from the Chinese soft coral Lobophytum sp., which could be developed as new chemotypes of antibacterial drug leads.

Structurally Diverse Diterpenes from the South China Sea Soft Coral Sarcophyton trocheliophorum

The present investigation of the South China Sea soft coral Sarcophyton trocheliophorum resulted in the discovery of six new polyoxygenated diterpenes, namely sartrocheliols A-E (1, 3, 5-8) along with four known ones, 2, 4, 9, and 10. Based on extensive spectroscopic data analysis, sartrocheliol A (1) was identified as an uncommon capnosane diterpene, while sartrocheliols B-E (3, 5-8) were established as cembrane diterpenes. They displayed diverse structural features not only at the distinctly different carbon frameworks but also at the various types of heterocycles, including the epoxide, γ-lactone, furan, and pyran rings. Moreover, their absolute configurations were determined by a combination of quantum mechanical-nuclear magnetic resonance (QM-NMR) approach, modified Mosher's method, and X-ray diffraction analysis. In the anti-tumor bioassay, compound 4 exhibited moderate cytotoxic activities against A549, H1975, MDA-MB-231, and H1299 cells with the IC₅₀ values ranging from 26.3 to 47.9 μM.

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.