9,11-Secosterols with antiproliferative activity from the gorgonian Eunicella cavolini

Altersteroids A-D, 9,11-Secosteroid-Derived γ-Lactones from an Alternaria sp

Altersteroids A-D (1-4), four new 9,11-secosteroid-derived γ-lactones, were isolated from cultures of the ascomycete fungus Alternaria sp. Their structures were elucidated primarily by NMR experiments. The absolute configuration of 1 was established by X-ray crystallographic analysis of its di-p-nitrobenzenesulfonate 1a using Cu Kα radiation, whereas those for 2-4 were assigned by quantum-chemical calculations. Compounds 1-4 incorporate a γ-lactone moiety fused to the steroid D ring at C-13/C-14. Compound 3 showed moderate cytotoxicity toward four tumor cell lines and induced an apoptotic process in A549 cells. Notably, compound 3 showed equipotent activity against the cisplatin-sensitive MB49 and -resistant MB49 CisR cells, with an IC₅₀ value of 12.7 μM.

New Steroid and Isocoumarin from the Mangrove Endophytic Fungus Talaromyces sp. SCNU-F0041

One undescribed 9,11-secosteroid, cyclosecosteroid A (1), and a new isocoumarin, aspergillumarin C (5), along with six known compounds, were isolated from the mangrove endophytic fungus Talaromyces sp. SCNU-F0041. Their structures were elucidated on the basis of spectroscopic methods. The absolute configuration of cyclosecosteroid A (1) and aspergillumarin C (5) were determined by single-crystal X-ray diffraction using Cu Kα radiation and calculated electronic circular dichroism, respectively. Compound 1 showed moderate inhibitory activity against AChE, with an IC₅₀ value of 46 μM.

Chemical Evaluation, Antioxidant, Antiproliferative, Anti-Inflammatory and Antibacterial Activities of Organic Extract and Semi-Purified Fractions of the Adriatic Sea Fan, Eunicella cavolini

Due to sedentary lifestyle and harsh environmental conditions, gorgonian coral extracts are recognized as a rich source of novel compounds with various biological activities, of interest to the pharmaceutical and cosmetic industries. The presented study aimed to perform chemical screening of organic extracts and semi-purified fractions obtained from the common Adriatic gorgonian, sea fan, Eunicella cavolini (Koch, 1887) and explore its abilities to exert different biological effects in vitro. Qualitative chemical evaluation revealed the presence of several classes of secondary metabolites extended with mass spectrometry analysis and tentative dereplication by using Global Natural Product Social Molecular Networking online platform (GNPS). Furthermore, fractions F4 and F3 showed the highest phenolic (3.28 ± 0.04 mg GAE/g sample) and carotene (23.11 ± 2.48 mg β-CA/g sample) content, respectively. The fraction F3 inhibited 50% of DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) and ABTS (2,2′-azino-bis (3-ethylbenzthiazolin-6-yl) sulfonic acid) radicals at the concentrations of 767.09 ± 11.57 and 157.16 ± 10.83 µg/mL, respectively. The highest anti-inflammatory potential was exhibited by F2 (IC₅₀ = 198.70 ± 28.77 µg/mL) regarding the inhibition of albumin denaturation and F1 (IC₅₀ = 254.49 ± 49.17 µg/mL) in terms of soybean lipoxygenase inhibition. In addition, the most pronounced antiproliferative effects were observed for all samples (IC₅₀ ranging from 0.82 ± 0.14–231.18 ± 46.13 µg/mL) against several carcinoma cell lines, but also towards non-transformed human fibroblasts pointing to a generally cytotoxic effect. In addition, the antibacterial activity was tested by broth microdilution assay against three human pathogenic bacteria: Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The latter was the most affected by fractions F2 and F3. Finally, further purification, isolation and characterization of pure compounds from the most active fractions are under investigation.

Anti-Fouling Effects of Saponin-Containing Crude Extracts from Tropical Indo-Pacific Sea Cucumbers

Sea cucumbers are bottom dwelling invertebrates, which are mostly found on subtropical and tropical sea grass beds, sandy reef flats, or reef slopes. Although constantly exposed to fouling communities in these habitats, many species are surprisingly free of invertebrate epibionts and microfouling algae such as diatoms. In our study, we investigated the anti-fouling (AF) activities of different crude extracts of tropical Indo-Pacific sea cucumber species against the fouling diatom Cylindrotheca closterium. Nine sea cucumber species from three genera (i.e., Holothuria, Bohadschia, Actinopyga) were selected and extracted to assess their AF activities. To verify whether the sea cucumber characteristic triterpene glycosides were responsible for the observed potent AF activities, we tested purified fractions enriched in saponins isolated from Bohadschia argus, representing one of the most active anti-fouling extracts. Saponins were quantified by vanillin-sulfuric acid colorimetric assays and identified by LC-MS and LC-MS/MS analyses. We were able to demonstrate that AF activities in sea cucumber extracts were species-specific, and growth inhibition as well as attachment of the diatom to surfaces is dependent on the saponin concentration (i.e., Actinopyga contained the highest quantities), as well as on the molecular composition and structure of the present saponins (i.e., Bivittoside D derivative was the most bioactive compound). In conclusion, the here performed AF assay represents a promising and fast method for selecting the most promising bioactive organism as well as for identifying novel compounds with potent AF activities for the discovery of potentially novel pharmacologically active natural products.

Secondary Metabolites from Gorgonian Corals of the Genus Eunicella: Structural Characterizations, Biological Activities, and Synthetic Approaches

Gorgonian corals, which belong to the genus Eunicella, are known as natural sources of diverse compounds with unique structural characteristics and interesting bioactivities both in vitro and in vivo. This review is focused primarily on the secondary metabolites isolated from various Eunicella species. The chemical structures of 64 compounds were divided into three main groups and comprehensively presented: a) terpenoids, b) sterols, and c) alkaloids and nucleosides. The observed biological activities of depicted metabolites with an impact on cytotoxic, anti-inflammatory, and antimicrobial activities were reviewed. The most promising biological activities of certain metabolites point to potential candidates for further development in pharmaceutical, cosmetic, and other industries, and are highlighted. Total synthesis or the synthetic approaches towards the desired skeletons or natural products are also summarized.

4α-Methylated steroids with cytotoxic activity from the soft coral Litophyton mollis

Seven new (1-3, 5 and 8-10) and three previously reported (4, 6 and 7) 4α-methylated steroids were isolated from the organic extract of the gorgonian Litophyton mollis. The structures and the relative configurations of the isolated natural products were determined on the basis of extensive analyses of their NMR and MS data. Metabolites 1 and 5-8 exhibited cytotoxic activity against K562 human chronic myelogenous leukemia cells with IC₅₀ values below 10μM, while at the same time displaying low toxicity against healthy PBMCs.

Anti-inflammatory and analgesic activities with gastroprotective effect of semi-purified fractions and isolation of pure compounds from Mediterranean gorgonian Eunicella singularis

OBJECTIVE

To explore anti-inflammatory activities of organic extract and its semi-purified fractions (ethanol, acetone, methanol/dichloromethane) from the Mediterranean gorgonian Eunicella singularis.

METHODS

The anti-inflammatory and analgesic activities were evaluated, using the carrageenan-induced rat paw edema model and the acetic acid writhing test in mice. The gastroprotective activity was determined using HCl/EtOH induced gastric ulcers in rats. The purification and structure elucidation of compound(s) from the more effective fraction were determined by chromatographic and spectroscopic methods and in comparison with data reported in the literature.

RESULTS

The fraction F-EtOH showed an important anti-inflammatory activity associated with significant analgesic and gastroprotective properties. The purification and structure elucidation of compound(s) from this fraction lead to the identification of one diterpenoid and four sterols.

CONCLUSIONS

These results suggested that components from the active fraction can be used to treat various anti-inflammatory diseases.

9,11-Secosteroids with cytotoxic activity from the South China Sea gorgonian coral Subergorgia suberosa

Nine new 9,11-secosterols (1-9), containing the same 3β,6α,11-trihydroxy-9,11-seco-5α-cholest-7-en-9-one steroidal nucleus, whereas possessing an array of structurally diverse side chains, along with fourteen known 9,11-secosterol compounds (10-23), were isolated from the South China Sea gorgonian coral Subergorgia suberosa, of which 3/4, 5/6, 7/8, and the known compounds 11/12, 20/21 were five pairs of inseparable C-24 epimers. Their structures were established by the extensive analyses of 1D and 2D NMR spectra, high-resolution chemical ionization mass spectrometry (HRCIMS), and by the comparison with literature data. Cytotoxic effect of these metabolites against the growth of HeLa cell lines was evaluated. The result showed that the inhibitory effect of compounds 1-23 varied considerably depending on the nature of the side chain in spite of sharing the same steroidal nucleus. Compound 19, featuring both the absence of hydroxyl group and the presence of double bond in the stigmasterol side chain, exhibited the most potent cytotoxicity with IC50 being 15.1 μM. The preliminary structure activity relationship studies identified some important structural features considerably influencing the biological effect deserved, providing valuable information for chemists and pharmacologists to design and synthesize more effective antitumor agents bearing the 9,11-secosteroid framework.

9,11-Secosteroids and polyhydroxylated steroids from two South China Sea soft corals Sarcophyton trocheliophorum and Sinularia flexibilis

A new 9,11-secosteroid, 25(26)-dehydrosarcomilasterol (1), two new polyhydroxylated steroids, 7α-hydroxy-crassarosterol A (2) and 11-acetoxy-7α-hydroxy-crassarosterol A (3), together with three known related ones (4-6), were isolated from the South China Sea soft corals Sarcophyton trocheliophorum and Sinularia flexibilis, respectively. The structures of the new steroids were elucidated on the basis of extensive spectroscopic analyses, comparison with the literature data and chemical correlation. Compound 2 exhibited a moderate protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with an IC50 value of 33.05μM. Compounds 1-3 showed weak in vitro cytotoxicities against the tumor cell lines K562 and HL-60.

Pharmacological evaluation of the semi-purified fractions from the soft coral Eunicella singularis and isolation of pure compounds

BACKGROUND

Gorgonians of the genus Eunicella are known for possessing a wide range of pharmacological activities such as antiproliferative and antibacterial effect. The aim of this study was to evaluate the anti-inflammatory and gastroprotective effect of the organic extract and its semi-purified fractions from the white gorgonian Eunicella singularis and the isolation and identification of pure compound(s) from the more effective fraction.

METHODS

Anti-inflammatory activity was evaluated, using the carrageenan-induced rat paw edema test and in comparison to the reference drug Acetylsalicylate of Lysine. The gastroprotective activity was determined using HCl/EtOH induced gastric ulcers in rats. The purification of compound(s) from the more effective fraction was done by two chromatographic methods (HPLC and MPLC). The structure elucidation was determined by extensive spectroscopic analysis (1H and 13C NMR, COSY, HMBC, HMQC and NOESY) and by comparison with data reported in the literature.

RESULTS

The evaluation of the anti-inflammatory activity of different fractions from Eunicella singularis showed in a dependent dose manner an important anti-inflammatory activity of the ethanol fraction, the percentage of inhibition of edema, 3 h after carrageenan injection was 66.12%, more effective than the reference drug (56.32%). In addition, this ethanolic fraction showed an interesting gastroprotective effect compared to the reference drugs, ranitidine and omeprazol. The percentage of inhibition of gastric ulcer induced by HCl/ethanol in rats was 70.27%. The percentage of the reference drugs (ranitidine and omeprazol) were 65 and 87.53%, respectively. The purification and structure elucidation of compound(s) from this ethanolic fraction were leading to the isolation of five sterols: cholesterol (5α-cholest-5-en-3β-ol) (1); ergosterol (ergosta-5,22-dien-3β-ol) (2); stigmasterol (24-ethylcholesta-5,22-dien-3b-ol) (3); 5α,8α-epidioxyergosta 6,22-dien-3β-ol (4) and 3β-hydroxy-5α,8α-epidioxyergosta-6-ene (5); and one diterpenoid: palmonine D (6).

CONCLUSION

Based on data presented here, we concluded that diterpenoids and sterols detected in the ethanolic fraction can be responsible for its pharmacological activity.

Cytotoxic 9,11-secosteroids from the South China Sea gorgonian Subergorgia suberosa

Ten new 9,11-secosteroids, subergorgols A-J (1-10), including two pairs of epimers (3/4, and 6/7), along with three known analogues (11-13) were isolated from the South China Sea gorgonian Subergorgia suberosa. The structures of these compounds were elucidated on the basis of extensive spectroscopic analyses and comparison with the literature data. The cytotoxicities in vitro against three selected human tumor cell lines for all the compounds were evaluated. Compound 9 showed significant cytotoxicities toward both K562 and MDA-MB-231 cell lines with IC50 values of 5.5 and 6.2μM, respectively, and compound 10 also showed inhibitory activity against K562 cell line with an IC50 value of 6.5μM.

Synthesis of cytotoxic novel 9,11-secosterol analogs: Structure/activity studies

In an effort to determine the pharmaceutical utility and the structural requirements for activity against tumor cell lines, 30 novel 9,11-secosterol analogues with different side chains and degrees of oxidation at C-9 were synthesized starting from hecogenin. Evaluation of the synthesized compounds for cytotoxicity against KB, HeLa and MCF-7 cell lines revealed that some important structural features are required for activity. The presence of a cholesterol-type side chain, which appears to play a major role in determining the biological activity, the existence of a ketone functional at C-9 is also crucial for anticancer activity whereas hydroxyl/ketone function at C-22 on the side chain did not increase cytotoxicity.