Marine Metabolites: The Sterols of Soft Coral

A comprehensive review of marine sponge metabolites, with emphasis on Neopetrosia sp

The secondary metabolites that marine sponges create are essential to the advancement of contemporary medicine and are often employed in clinical settings. Over the past five years, microbes associated with sponges have yielded the identification of 140 novel chemicals. Statistics show that most are derived from actinomycetes (bacteria) and ascomycotes (fungi). The aim of this study was to investigate the biological activity of metabolites from marine sponges. Chlocarbazomycins A-D, which are a group of novel chlorinated carbazole alkaloids isolated from the sponge Neopetrosia fennelliae KUFA 0811, exhibit antimicrobial, cytotoxic, and enzyme inhibitory activities. Recently, marine sponges of the genus Neopetrosia have attracted attention due to the unique chemical composition of the compounds they produce, including alkaloids of potential importance in drug discovery. Fridamycin H and fridamycin I are two novel type II polyketides synthesized by sponge-associated bacteria exhibit antitrypanosomal activity. Fintiamin, composed of amino acids and terpenoid moieties, shows affinity for the cannabinoid receptor CB 1. It was found that out of 27 species of Neopetrosia sponges, the chemical composition of only 9 species has been studied. These species mainly produce bioactive substances such as alkaloids, quinones, sterols, and terpenoids. The presence of motuporamines is a marker of the species Neopetrosia exigua. Terpenoids are specific markers of Neopetrosia vanilla species. Although recently discovered, secondary metabolites from marine sponges have been shown to have diverse biological activities, antimicrobial, antiviral, antibacterial, antimicrobial, antioxidant, antimalarial, and anticancer properties, providing many lead compounds for drug development. The data presented in this review on known and future natural products derived from sponges will further clarify the role and importance of microbes in marine sponges and trace the prospects of their applications, especially in medicine, cosmeceuticals, environmental protection, and manufacturing industries.

An Overview of Secondary Metabolites from Soft Corals of the Genus Capnella over the Five Decades: Chemical Structures, Pharmacological Activities, NMR Data, and Chemical Synthesis

There has been no specific review on the secondary metabolites from soft corals of the genus Capnella till now. In this work, all secondary metabolites from different species of the title genus were described. It covered the first work from 1974 to May 2024, spanning five decades. In the viewpoint of the general structural features, these chemical constituents were classified into four groups: sesquiterpenes, diterpenes, steroids, and lipids. Additionally, the 1H and 13C NMR data of these metabolites were provided when available in the literature. Among them, sesquiterpenes were the most abundant chemical compositions from soft corals of the genus Capnella. A variety of pharmacological activities of these compounds were evaluated, such as cytotoxic, antibacterial, antifungal, and anti-inflammatory activities. In addition, the chemical synthesis works of several representative sesquiterpenes were provided. This review aims to provide an up-to-date knowledge of the chemical structures, pharmacological activities, and chemical synthesis of the chemical constituents from soft corals of the genus Capnella.

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.

Cytotoxic evaluation of new polyhydroxylated steroids from the Red Sea soft coral Litophyton mollis (Macfadyen, 1936)

An efficient column chromatography of the CH2Cl2/MeOH crude extract from the soft coral Litophyton mollis (Macfadyen, 1936) yielded seven steroids, including five 4α-methylated steroids (1-5) and two 19-oxygenated steroids (6-7). Notably, both compounds 3 and 7 are new, identified as (22E)-4α,24-dimethyl-5α-cholesta-22,24(28)-dien-3β,8β-diol (3) and (22E,24R)-7β-acetoxy-24-methyl-cholesta-5,22-dien-3β,19-diol (7). The chemical structures and relative configurations were elucidated through comprehensive spectroscopic analyses, including 1D and 2D NMR, as well as HRESIMS analysis. The cytotoxicity of metabolites 1-7 was evaluated against three cancer cell lines: MCF-7, HepG2, and NCI-1299. Remarkably, metabolites 6 and 7 exhibited strong cytotoxic activity against MCF-7, with IC50 values of 8.6 and 8.4 μM, respectively, while also showing moderate effects against NCI-1299, with IC50 values of 15.7 and 15.1 μM, respectively. Additionally, steroids 4 and 5 displayed weak cytotoxicity against all three cell lines, with IC50 values in the ranges of 34.7-37.5 and 30.8-46.3 μM, 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.

Unlocking the Potential of Octocoral-Derived Secondary Metabolites against Neutrophilic Inflammatory Response

Inflammation is a critical defense mechanism that is utilized by the body to protect itself against pathogens and other noxious invaders. However, if the inflammatory response becomes exaggerated or uncontrollable, its original protective role is not only demolished but it also becomes detrimental to the affected tissues or even to the entire body. Thus, regulating the inflammatory process is crucial to ensure that it is resolved promptly to prevent any subsequent damage. The role of neutrophils in inflammation has been highlighted in recent decades by a plethora of studies focusing on neutrophilic inflammatory diseases as well as the mechanisms to regulate the activity of neutrophils during the overwhelmed inflammatory process. As natural products have demonstrated promising effects in a wide range of pharmacological activities, they have been investigated for the discovery of new anti-inflammatory therapeutics to overcome the drawbacks of current synthetic agents. Octocorals have attracted scientists as a plentiful source of novel and intriguing marine scaffolds that exhibit many pharmacological activities, including anti-inflammatory effects. In this review, we aim to provide a summary of the neutrophilic anti-inflammatory properties of these marine organisms that were demonstrated in 46 studies from 1995 to the present (April 2023). We hope the present work offers a comprehensive overview of the anti-inflammatory potential of octocorals and encourages researchers to identify promising leads among numerous compounds isolated from octocorals over the past few decades to be further developed into anti-inflammatory therapeutic agents.

Pectin Nanoparticle-Loaded Soft Coral Nephthea sp. Extract as In Situ Gel Enhances Chronic Wound Healing: In Vitro, In Vivo, and In Silico Studies

This study shed light for the first time on the in vivo diabetic wound healing potential activity of natural marine soft coral polymeric nanoparticle in situ gel using an excision wound model. A Nephthea sp. methanol-methylene chloride extract loaded with pectin nanoparticles (LPNs) was created. For the preparation of in situ gel, ion-gelation techniques, the entrapment efficiency, the particle size, the polydispersity index, the zeta potential, the in-vitro drug release, and a transmission electron microscope were used and the best formula was selected. Using (UPLC-Q/TOF-MS), 27 secondary metabolites responsible for extract biological activity were identified. Isolation and identification of arachidic acid, oleic acid, nervonic acid, and bis-(2-ethylhexyl)-phthalate (DEHP) of Nephthea sp. was firstly reported here using NMR and mass spectral analyses. Moreover, LPN in situ gel has the best effects on regulating the proinflammatory cytokines (NF-κB, TNF-α, IL-6, and IL-1β) that were detected on days 7 and 15. The results were confirmed with an in vitro enzymatic inhibitory effect of the extract against glycogen synthase kinase (GSK-3) and matrix metalloproteinase-1 (MMP-1), with IC₅₀ values of 0.178 ± 0.009 and 0.258 ± 0.011 µg/mL, respectively. The molecular docking study showed a free binding energy of -9.6 kcal/mol for chabrolosteroid E, with the highest binding affinity for the enzyme (GSK-3), while isogosterone B had -7.8 kcal/mol for the enzyme (MMP-1). A pharmacokinetics study for chabrolohydroxybenzoquinone F and isogosterone B was performed, and it predicted the mode of action of wound healing activity.

Asymmetric Total Synthesis of Twin Bufogargarizins A and B

The first and asymmetric total synthesis of bufogargarizins A and B, two unusual and highly oxygenated twin steroids with rearranged A/B rings, was achieved. The synthetically challenging [7-5-6-5] tetracyclic ring system of bufogargarizin A was efficiently constructed by the first intramolecular Ru-catalyzed [5 + 2] cycloaddition reaction of a vinyl ether cyclopropane-yne. Notably, the interesting [5-7-6-5] tetracyclic skeleton of bufogargarizin B was diastereoselectively reassembled by unique retro-aldol/transannular aldol cascade reactions from the [7-5-6-5] tetracyclic framework.

Cembranoids from the Red Sea soft coral Sarcophyton glaucum protect against indomethacin-induced gastric injury

Soft corals and their secondary metabolites represent an exceptional source of potential drugs. In this regard, Sarcophyton glaucum-derived secondary metabolites were examined for their preventive activities against indomethacin-induced gastric ulcer. Extraction and chromatographic processing of a specimen of S. glaucum collected from the Red Sea waters of Jeddah city resulted in the isolation of eight metabolites including two furanone-based cembranoids (1 and 2), two known pyran-based cembranoids (3 and 4), a known aromadendrene derivative (5), a δ-lactone fatty acid derivative (6), and two known gorgostane-type sterols (7 and 8). Compounds 1 and 6 are new chemical structures, named Δ¹²⁽²⁰⁾-sarcophine and sarcoglaucanoate, respectively. In an initial pilot experiment, compounds 1 and 2 showed significant protective activities against indomethacin-induced peptic ulcer in rats. These data were evidenced by their ability to ameliorate the elevated ulcer indices and prevent histopathological alterations observed in the untreated animals. Their effects were mediated by enhanced mucin as shown by Alcian blue and periodic acid-Schiff (PAS) staining of stomach sections. Compounds 1 and 2 exerted significant antioxidant properties as they prevent reduced glutathione (GSH) depletion, malondialdehyde (MDA) accumulation, and superoxide dismutase (SOD) exhaustion. Furthermore, immunohistochemical analyses indicated that both compounds inhibited the expression of interleukin-6 (IL-6) and tumor necrosis-α (TNF-α) as compared to indomethacin alone-treated animals. These actions were accompanied by significant enhancement of tumor growth factor-β (TGF-β) expression. In conclusion, two cembranoids exhibited protective activities against indomethacin-induced peptic ulcer. This is, at least partly, mediated by their pro-mucin, antioxidant, anti-inflammatory, and TGF-β stimulating properties.

Molecular Network Guided Cataloging of the Secondary Metabolome of Selected Egyptian Red Sea Soft Corals

Soft corals are recognized as an abundant source of diverse secondary metabolites with unique chemical features and physiologic capabilities. However, the discovery of these metabolites is usually hindered by the traditional protocol which requires a large quantity of living tissue for isolation and spectroscopic investigations. In order to overcome this problem, untargeted metabolomics protocols have been developed. The latter have been applied here to study the chemodiversity of common Egyptian soft coral species, using only minute amounts of coral biomass. Spectral similarity networks, based on high-resolution tandem mass spectrometry data, were employed to explore and highlight the metabolic biodiversity of nine Egyptian soft coral species. Species-specific metabolites were highlighted for future prioritization of soft coral species for MS-guided chemical investigation. Overall, 79 metabolites were tentatively assigned, encompassing diterpenes, sesquiterpenes, and sterols. Simultaneously, the methodology assisted in shedding light on newly-overlooked chemical diversity with potential undescribed scaffolds. For instance, glycosylated fatty acids, nitrogenated aromatic compounds, and polyketides were proposed in Sinularia leptoclados, while alkaloidal terpenes and N-acyl amino acids were proposed in both Sarcophyton roseum and Sarcophyton acutum.

Chemical Review of Gorgostane-Type Steroids Isolated from Marine Organisms and Their 13C-NMR Spectroscopic Data Characteristics

Gorgostane steroids are isolated from marine organisms and consist of 30 carbon atoms with a characteristic cyclopropane moiety. From the pioneering results to the end of 2021, isolation, biosynthesis, and structural elucidation using ¹³C-NMR will be used. Overall, 75 compounds are categorized into five major groups: gorgost-5-ene, 5,6-epoxygorgostane, 5,6-dihydroxygorgostane, 9,11-secogorgostane, and 23-demethylgorgostane, in addition to miscellaneous gorgostane. The structural diversity, selectivity for marine organisms, and biological effects of gorgostane steroids have generated considerable interest in the field of drug discovery research.

Polyhydroxylated steroids from the Vietnamese soft coral Sarcophyton ehrenbergi

Fourteen polyhydroxylated steroids including six new compounds, ehrensteroids A - F (1-6), were isolated from the Vietnamese soft coral Sarcophyton ehrenbergi after applying various chromatographic separations. The structure elucidation was done by detailed analysis of 1D, 2D NMR and HR QTOF mass spectra. In addition, significant cytotoxicity (IC₅₀ values ranging from 8.45 ± 0.56 to 38.27 ± 2.39 μM) against all five tested cancer cell lines as LU-1 (lung cancer), HepG2 (hepatoma cancer), MCF-7 (breast cancer), HL-60 (acute leukemia), and SW480 (colon adenocarcinoma) was observed for compounds 1, 2, 6-10, and 12-14, whereas this activity on LU-1 (IC₅₀ = 21.91 ± 2.72 μM) and HepG2 (IC₅₀ = 20.32 ± 0.03 μM) cell lines was also observed for 4.

Marine dissolved organic matter: a vast and unexplored molecular space

Abstract

Marine dissolved organic matter (DOM) comprises a vast and unexplored molecular space. Most of it resided in the oceans for thousands of years. It is among the most diverse molecular mixtures known, consisting of millions of individual compounds. More than 1 Eg of this material exists on the planet. As such, it comprises a formidable source of natural products promising significant potential for new biotechnological purposes. Great emphasis has been placed on understanding the role of DOM in biogeochemical cycles and climate attenuation, its lifespan, interaction with microorganisms, as well as its molecular composition. Yet, probing DOM bioactivities is in its infancy, largely because it is technically challenging due to the chemical complexity of the material. It is of considerable interest to develop technologies capable to better discern DOM bioactivities. Modern screening technologies are opening new avenues allowing accelerated identification of bioactivities for small molecules from natural products. These methods diminish a priori the need for laborious chemical fractionation. We examine here the application of untargeted metabolomics and multiplexed high-throughput molecular-phenotypic screening techniques that are providing first insights on previously undetectable DOM bioactivities.

Key points

• Marine DOM is a vast, unexplored biotechnological resource.

• Untargeted bioscreening approaches are emerging for natural product screening.

• Perspectives for developing bioscreening platforms for marine DOM are discussed.

Prospects of Marine Sterols against Pathobiology of Alzheimer's Disease: Pharmacological Insights and Technological Advances

Alzheimer's disease (AD) is a degenerative brain disorder characterized by a progressive decline in memory and cognition, mostly affecting the elderly. Numerous functional bioactives have been reported in marine organisms, and anti-Alzheimer's agents derived from marine resources have gained attention as a promising approach to treat AD pathogenesis. Marine sterols have been investigated for several health benefits, including anti-cancer, anti-obesity, anti-diabetes, anti-aging, and anti-Alzheimer's activities, owing to their anti-inflammatory and antioxidant properties. Marine sterols interact with various proteins and enzymes participating via diverse cellular systems such as apoptosis, the antioxidant defense system, immune response, and cholesterol homeostasis. Here, we briefly overview the potential of marine sterols against the pathology of AD and provide an insight into their pharmacological mechanisms. We also highlight technological advances that may lead to the potential application of marine sterols in the prevention and therapy of AD.

A Water-Soluble 5/14-Carbobicyclic Steroid with a trans-9,11-Epoxy Ring from the Marine Dinoflagellate Amphidinium gibbosum: Insights into Late-Stage Diversification of Steroids

Gibbosterol A (1), a water-soluble 14-membered carbocyclic steroid with a twisted trans-9,11-epoxy ring, was discovered from the South China Sea dinoflagellate, Amphidinium gibbosum, together with its acid-induced cyclization product 2. It exhibits marked agonistic effects against human pregnane-X-receptor in a dose-dependent manner within the concentration range of 100 nM to 10 μM. Its 5/14-carbobicyclic nucleus is proposed to be originated from late-stage oxidative cleavage of the C5-C10 and C8-C9 bonds of β-sitosterol.

Cytotoxic polyhydroxy sterols from the Egyptian Red Sea soft coral Sarcophyton acutum

The methanolic extract and its sub-extracts (viz, n-hexane, DCM, EtOAc and MeOH) of the soft coral Sarcophyton acutum were evaluated as anti-Leishmania major and as anticancer (against the HepG2, MCF-7, and A549 cell lines) using the MTT assay. Six polyhydroxy sterols (1-6) were isolated from the most active cytotoxic and anti-leishmanial EtOAc-soluble fraction. Their structures were established as two new polyhydroxy sterols, acutumosterols A (1) and B (2), and four known structural analogues (3-6) by intensive spectroscopic analyses, and by comparison with data of related compounds. Compound 4 exerted noticeable cytotoxicity against HepG2 cell line (IC₅₀ 17.2 ± 1.5 μg/mL), while the other pure isolates showed weak to moderate cytotoxicity (24.8 ± 2.8-57.2 ± 5.2). The results were discussed in relation to the structural features of these closely related sterols.

Clade-Specific Sterol Metabolites in Dinoflagellate Endosymbionts Are Associated with Coral Bleaching in Response to Environmental Cues

Cnidarians cannot synthesize sterols (which play essential roles in growth and development) de novo but often use sterols acquired from endosymbiotic dinoflagellates. While sterol availability can impact the mutualistic interaction between coral host and algal symbiont, the biosynthetic pathways (in the dinoflagellate endosymbionts) and functional roles of sterols in these symbioses are poorly understood. In this study, we found that itraconazole, which perturbs sterol metabolism by inhibiting the sterol 14-demethylase CYP51 in dinoflagellates, induces bleaching of the anemone Heteractis crispa and that bleaching perturbs sterol metabolism of the dinoflagellate. While Symbiodiniaceae have clade-specific sterol metabolites, they share features of the common sterol biosynthetic pathway but with distinct architecture and substrate specificity features of participating enzymes. Tracking sterol profiles and transcripts of enzymes involved in sterol biosynthesis across time in response to different environmental cues revealed similarities and idiosyncratic features of sterol synthesis in the endosymbiont Breviolum minutum Exposure of algal cultures to high levels of light, heat, and acidification led to alterations in sterol synthesis, including blocks through downregulation of squalene synthase transcript levels accompanied by marked growth reductions.IMPORTANCE These results indicate that sterol metabolites in Symbiodiniaceae are clade specific, that their biosynthetic pathways share architectural and substrate specificity features with those of animals and plants, and that environmental stress-specific perturbation of sterol biosynthesis in dinoflagellates can impair a key mutualistic partnership for healthy reefs.

Sea Cucumber Sterol Alleviates the Lipid Accumulation in High-Fat-Fructose Diet Fed Mice

The effect of marine-derived sea cucumber sterol (SS) with a special sulfate group on lipid accumulation remains unknown, although phytosterol has been proved to have many biological activities, including lowering blood cholesterol. The purpose of the present study is to investigate the alleviation of SS on lipid accumulation and the possible underlying mechanism using high-fat-fructose diet fed mice. Dietary administration with SS for 8 weeks reduced significantly the body weight gain and lipid levels in serum and liver. Especially, SS was superior to phytosterol in lowering lipid accumulation due to the great promotion of fatty acid β-oxidation, the inhibition of cholesterol synthesis, and the acceleration of cholesterol efflux. The findings found that sea cucumber sterol exhibited a more significant effect than phytosterol on alleviating HFF-diet-induced lipid accumulation through regulating lipid and cholesterol metabolism, which might be attributed to the difference in the branch chain and sulfate group.

Erectsterates A and B, a pair of novel highly degraded steroid derivatives from the South China Sea soft coral Sinularia erecta

Two novel steroidal derivatives, erectsterates A (1) and B (2), a pair of epimers at C-10, were isolated from the South China Sea soft coral Sinularia erecta. Their structures were established by extensive spectroscopic analysis and deduction from biosynthesis route. Compounds 1 and 2 are rare steroids with a highly degradation in ring B and an ester linkage between A and C/D rings, similar with the known compounds chaxines B (3) and D from an edible mushroom Agrocybe chaxingu. To the best of our knowledge, this is the first report of such kind of steroid from soft coral. And a different biosynthetic route from the reported approach of chaxines was proposed in this paper. Interestingly, the ring C of 1 and 2 was formally oxidized by Baeyer-Villiger reaction to provide an unprecedented seven-membered lactone moiety in ring C of steroid. The in vitro anti-proliferative activities of 2 were evaluated against A549, HT-29, SNU-398 and Capan-1 cell lines. The results indicated that it showed weak cytotoxicity against the tested four cell lines.

Asymmetric Total Synthesis of Bufospirostenin A

The first and asymmetric total synthesis of bioactive bufospirostenin A, an unusual spirostanol with rearranged A/B rings, was accomplished. The synthetically challenging [5-7-6-5] tetracyclic ring system, found in bufospirostenin A and some other natural products, was efficiently constructed by the unique intramolecular rhodium-catalyzed Pauson-Khand reaction of an alkoxyallene-yne. The 11 stereocenters in the final product, including the 10 contiguous stereocenters, were installed diastereoselectively.

1H NMR-Based Isolation of Anti-Inflammatory 9,11-Secosteroids from the Octocoral Sinularia leptoclados

Octocoral Sinularia leptoclados has been identified as a source of bioactive 9,11-secosteroids. This study adopted a targeted isolation approach to the discovery and analysis of five 9,11-secosteroids, including two novel compounds named sinleptosterols A (1) and B (2) as well as five known analogues (8αH-3β,11-dihydroxy-24-methylene-9,11-secocholest-5-en-9-one (3), 8βH-3β,11-dihydroxy-24-methylene-9,11-secocholest-5-en-9-one (4), leptosterol A (5), (24S)-3β,11-dihydroxy-24-methyl-9,11-secocholest-5-en-9-one (6), and 3β,11-dihydroxy-9,11-secogorgost-5-en-9-one (7)) in terms of ¹H-NMR patterns and potency against neutrophilic inflammation. The structure of secosteroids 1 and 2 was deduced from general spectroscopic analysis and an examination of NMR spectra. Among the above-mentioned isolates, compound 4 had the most pronounced effect in inhibiting elastase release and superoxide anion generation, with the IC₅₀ values of 2.96 and 1.63 μM, respectively.

Sinulasterols A-C, three new bioactive oxygenated steroids from the South China Sea soft coral Sinularia depressa

Three new oxygenated steroids, sinulasterols A-C (1-3), along with seven known related steroids 4-10, were isolated from the Chinese soft coral Sinularia depressa. The structures of the new compounds were established from extensive spectroscopic data analyses and by comparison of their spectral data with those reported in the literature. Among the new compounds, metabolites 1 and 2 featured on unusual C-18 oxygenated pattern. In the TNF-α bioassay, compound 4 exhibited a potent inhibitory activity (IC₅₀ = 12.1 μM), which was analogous to the positive control dexamethasone (IC₅₀ = 8.7 μM), metabolites 1 and 2 displayed a moderate inhibitory activity (IC₅₀ 51.1 μM and 22.7 μM respectively).

First report of a lactonic disecosteroid from the buccinid gastropod Babylonia spirata

A lactonic steroid with an unprecedented 1, 10: 8, 9-disecoergostane framework was identified from the ethyl acetate-methanol extract of buccinid gastropod mollusk, Babylonia spirata collected from the southwestern coast of Indian peninsular region. The compound was characterized as 1, 10: 8, 9-disecoergosta-8-en-A-homo-6a-oxa-1-one by exhaustive spectroscopic methods including two-dimensional nuclear magnetic resonance and mass spectroscopic investigations. The disecosteroid displayed moderate carbolytic enzyme inhibition activity as distinguished by its inhibitive effects against α-amylase and α-glucosidase (IC₅₀ 0.40 and 0.54 mg/mL, respectively). The anti-inflammatory (5-lipoxidase inhibitory) activity of the titled secondary metabolite was found to be superior (IC₅₀ < 0.85 mg/mL) than the commercial anti-inflammatory drug (ibuprofen IC₅₀ > 0.85 mg/mL). However, significantly greater antioxidant property was recorded for the studied disecosteroid as evaluated by in vitro 2, 2-diphenyl-1-picrylhydrazyl radical inhibition potential (IC₅₀ 0.30 mg/mL) than that of standard, α-tocopherol (IC₅₀ > 0.50 mg/mL). The in silico molecular docking studies were conducted to explain the anti-5-lipoxidase and anti-α-amylase properties of the isolated compound. The molecular binding interactions of the ligands with the pro-inflammatory 5-lipoxidase and the carbolytic enzyme α-amylase, demonstrated that their binding energies/docking scores were positively associated with their in vitro bioactivities. A plausible pathway for the biosynthetic origin of lactonic disecosteroid in B. spirata was proposed from an ergosterol precursor. Structure-activity correlation study demonstrated that the biological activities of the disecosteroid were directly proportional to their electronic properties allied with lesser steric restrictions.

A new 5α,8α-epidioxysterol with immunosuppressive activity from the South China Sea soft coral Sinularia sp

A new 5α,8α-epidioxysterol, namely yalongsterol A (1), along with two known related steroids 5α,8α-epidioxy-24-methyl-cholesta-6,24(28)-dien-3β-ol (2) and (22E,24S)-5α,8α-epidioxy-24-methyl-cholesta-6,22-dien-3β-ol (3), were isolated from the South China Sea soft coral Sinularia sp. Their structures were established by extensive spectroscopic analyses and comparisons of the spectral data with those reported in the literature. In bioassay, compounds 1-3 showed moderate immunosuppressive activities against T and/or B lymphocyte cells with IC₅₀ values ranging from 19.30 to 59.49 μM, and low cytotoxicity on murine splenocytes with CC₅₀ values ranging from 40.88 to 62.29 μM.[Formula: see text].

Asymmetric synthesis of the tetracyclic core of bufogargarizin C by an intramolecular [5 + 2] cycloaddition

A concise asymmetric synthesis of the synthetically challenging 7/5/6/5-tetracyclic core of bufogargarizin C by a unique intramolecular [5 + 2] cycloaddition was reported.

Cytotoxic polyhydroxylated steroids from the South China Sea soft coral Lobophytum sp

Four new polyhydroxylated steroids lobophysterols A-D (1-4), together with two known related compounds sarcophytosterol (5) and klyflaccisteroid B (6), were isolated from the South China Sea soft coral Lobophytum sp. Their structures were elucidated on the basis of spectroscopic analysis and by comparison with those reported in the literature. In bioassay, compound 4 showed weak cytotoxicities against HT-29, SNU-398, and Capan-1 cells.

NR3E receptors in cnidarians: A new family of steroid receptor relatives extends the possible mechanisms for ligand binding

Steroid hormone receptors are important regulators of development and physiology in bilaterian animals, but the role of steroid signaling in cnidarians has been contentious. Cnidarians produce steroids, including A-ring aromatic steroids with a side-chain, but these are probably made through pathways different than the one used by vertebrates to make their A-ring aromatic steroids. Here we present comparative genomic analyses indicating the presence of a previously undescribed nuclear receptor family within medusozoan cnidarians, that we propose to call NR3E. This family predates the diversification of ERR/ER/SR in bilaterians, indicating that the first NR3 evolved in the common ancestor of the placozoan and cnidarian-bilaterian with lineage-specific loss in the anthozoans, even though multiple species in this lineage have been shown to produce aromatic steroids, whose function remain unclear. We discovered serendipitously that a cytoplasmic factor within epidermal cells of transgenic Hydra vulgaris can trigger the nuclear translocation of heterologously expressed human ERα. This led us to hypothesize that aromatic steroids may also be present in the medusozoan cnidarian lineage, which includes Hydra, and may explain the translocation of human ERα. Docking experiments with paraestrol A, a cnidarian A-ring aromatic steroid, into the ligand-binding pocket of Hydra NR3E indicates that, if an aromatic steroid is indeed the true ligand, which remains to be demonstrated, it would bind to the pocket through a partially distinct mechanism from the manner in which estradiol binds to vertebrate ER.

Cytotoxic steroids from the Vietnamese gorgonian Verrucella corona

Using various chromatographic separations, seventeen steroids including seven new compounds, verrucorosteroids A-F (1-6) and verrucorosterone (7), were isolated from the Vietnamese gorgonian Verrucella corona. Their structures were elucidated by spectroscopic analysis, including HR QTOF MS, 1D and 2D NMR. Among isolates, verrucorosterone (7), 5,6α-epoxy-3β-hydroxy-(22E)-ergosta-8,22-dien-7-one (14), and 5,6α-epoxy-3β-hydroxy-(22E)-ergosta-8(14),22-dien-7-one (15) showed significant cytotoxicity (IC₅₀ values ranging from 12.32 ± 1.47 to 33.77 ± 1.28 μM) against eight human cancer cell lines as LNCaP (prostate cancer), HepG2 (hepatoma cancer), KB (epidermoid carcinoma), MCF-7 (breast cancer), SK-Mel2 (melanoma), HL-60 (acute leukemia), LU-1 (lung cancer), and SW480 (colon adenocarcinoma).

Two new cytotoxic steroids from the Chinese soft coral Sinularia sp

Two new steroids, ximaosteroid E (1) and ximaosteroid F (2), along with two known related compounds (3 and 4), were isolated from the Chinese soft coral Sinularia sp. Notably, 1 possesses an uncommon dihydrofuran group. Their structures were established from extensive spectroscopic analyses and comparisons of their spectral data with those reported in the literature. The absolute configuration of 2 was determined by applying the modified Mosher's method. In bioassay, compounds 1, 2, and 4 showed significant cytotoxicity against the HL-60 tumor cell line with IC₅₀ values of 1.79, 4.03 and 0.69 μM, respectively.

Apoptotic and antiproliferative effects of Stigmast-5-en-3-ol from Dendronephthya gigantea on human leukemia HL-60 and human breast cancer MCF-7 cells

The genus Dendronephthya encompasses marine soft corals that produce a wide spectrum of biofunctional terpenoids. Anticancer properties of these metabolites are widely exploited as potential chemotherapeutic agents. The present study reports the purification and isolation of a potential antiproliferative constituent, stigmast-5-en-3-ol from the 70% ethanol extract of the soft coral Dendronephthya gigantea. Among several other 3β-hydroxy-Δ5-steroidal congeners, stigmast-5-en-3-ol indicated prominent antiproliferative effects on HL-60 (leukemia) and MCF-7 (breast cancer) cell lines with IC₅₀ values of 37.82 and 45.17 μg/ml respectively. Stigmast-5-en-3-ol increased apoptotic body formation, accumulation of sub G1 apoptotic cells, and DNA damage in HL-60 and MCF-7 cells. It increased the expression of Bax, caspases, and PARP cleavage while decreasing Bcl-xL levels in both cancer cell lines indicating that the effects are arbitrated via the mitochondria-mediated apoptotic pathway. Steroidal derivatives were identified by GC MS/MS and the identity of stigmast-5-en-3-ol was confirmed by NMR spectra. The present study suggests that stigmast-5-en-3-ol could be a promising candidate for anticancer drug research.

Asymmetric Total Synthesis of Cyclocitrinol

The first and asymmetric total synthesis of cyclocitrinol, an unusual C25 steroid, has been accomplished in a linear sequence of 18 steps from commercially available compound 11. The synthetically challenging bicyclo[4.4.1] A/B ring system with a strained bridgehead (anti-Bredt) double bond of cyclocitrinol was constructed efficiently and diastereoselectively via a type II intramolecular [5 + 2] cycloaddition.

Metagenomes Reveal Global Distribution of Bacterial Steroid Catabolism in Natural, Engineered, and Host Environments

Steroids are abundant growth substrates for bacteria in natural, engineered, and host-associated environments. This study analyzed the distribution of the aerobic 9,10-seco steroid degradation pathway in 346 publically available metagenomes from diverse environments. Our results show that steroid-degrading bacteria are globally distributed and prevalent in particular environments, such as wastewater treatment plants, soil, plant rhizospheres, and the marine environment, including marine sponges. Genomic signature-based sequence binning recovered 45 metagenome-assembled genomes containing a majority of 9,10-seco pathway genes. Only Actinobacteria and Proteobacteria were identified as steroid degraders, but we identified several alpha- and gammaproteobacterial lineages not previously known to degrade steroids. Actino- and proteobacterial steroid degraders coexisted in wastewater, while soil and rhizosphere samples contained mostly actinobacterial ones. Actinobacterial steroid degraders were found in deep ocean samples, while mostly alpha- and gammaproteobacterial ones were found in other marine samples, including sponges. Isolation of steroid-degrading bacteria from sponges confirmed their presence. Phylogenetic analysis of key steroid degradation proteins suggested their biochemical novelty in genomes from sponges and other environments. This study shows that the ecological significance as well as taxonomic and biochemical diversity of bacterial steroid degradation has so far been largely underestimated, especially in the marine environment.

Microbial steroid degradation is a critical process for biomass decomposition in natural environments, for removal of important pollutants during wastewater treatment, and for pathogenesis of bacteria associated with tuberculosis and other bacteria. To date, microbial steroid degradation was mainly studied in a few model organisms, while the ecological significance of steroid degradation remained largely unexplored. This study provides the first analysis of aerobic steroid degradation in diverse natural, engineered, and host-associated environments via bioinformatic analysis of an extensive metagenome data set. We found that steroid-degrading bacteria are globally distributed and prevalent in wastewater treatment plants, soil, plant rhizospheres, and the marine environment, especially in marine sponges. We show that the ecological significance as well as the taxonomic and biochemical diversity of bacterial steroid degradation has been largely underestimated. This study greatly expands our ecological and evolutionary understanding of microbial steroid degradation.

3β-Hydroxy-Δ5-steroidal congeners from a column fraction of Dendronephthya puetteri attenuate LPS-induced inflammatory responses in RAW 264.7 macrophages and zebrafish embryo model

Bioactive compounds from marine organisms and their action mechanisms have provided new insights into medicinal and natural product research. Here, we report the identification of 3β-hydroxy-Δ5-steroidal congeners from a purified column fraction (DPCMH24) of the soft coral Dendronephthya puetteri harvested from Jeju, South Korea. DPCMH24 exerted strong anti-inflammatory effects through a dose-dependent decrease in the levels of nitric oxide (NO) in LPS-induced RAW 264.7 macrophages (IC₅₀ value = 6.54 ± 0.38 μg mL⁻¹). Further, DPCMH24 attenuated the levels of PGE₂ and the pro-inflammatory cytokines, TNF-α, IL-1β, and IL-6. The above effects were mediated via the inhibition of nuclear factor κB activation and mitogen-activated protein kinase pathways. In vivo evaluation indicated that DPCMH24 reduced NO, iNOS, COX-2, ROS production and cell death in LPS-induced zebrafish embryos, confirming its anti-inflammatory potential. The constituent compounds were identified by GC-MS/MS analysis. These findings suggest that the steroidal congeners from D. puetteri may offer ample therapeutic potential against LPS-induced inflammation.

Bioactive compounds from marine organisms and their action mechanisms have provided new insights into medicinal and natural product research.

Cytotoxic steroid derivatives from the Vietnamese soft coral Sinularia brassica

Using various chromatographic separations, six ergostane-type steroids, including one new compound sinubrassione (1), and two pregnene-type steroid glycosides, including one new compound sinubrassioside (7), were isolated from methanol extract of the Vietnamese soft coral Sinularia brassica. The structure elucidation was confirmed by spectroscopic methods including 1D, 2D NMR and HR-ESI-MS. The cytotoxic activities of all the isolated compounds against three human cancer cell lines were also evaluated using MTT-based colorimetric assays.

Cytotoxic Serrulatane-Type Diterpenoids from the Gorgonian Euplexaura sp. and Their Absolute Configurations by Vibrational Circular Dichroism

Vibrational circular dichroism (VCD) method has become robust and reliable alternative for the stereochemical characterization of natural products. In this paper, three new serrulatane-type diterpenoids, euplexaurenes A-C (1-3), and a known metabolite, anthogorgiene P (4), were obtained from the South China Sea gorgonian Euplexaura sp. GXWZ-05. The absolute configuration of C-11 in 1-4, which was difficult to be determined by common means due to the high conformational flexibility of the eight-carbon aliphatic chain attached at C-4, was determined by VCD method, suggesting a new horizon to define the absolute configurations of natural products possessing chains. Compounds 1-4 were found to show selective cytotoxic activities against human laryngeal carcinoma (Hep-2) cell line with the IC50 values of 1.95, 7.80, 13.6 and 5.85 μM, respectively.

24-Methyl-Cholesta-5,24(28)-Diene-3β,19-diol-7β-Monoacetate Inhibits Human Small Cell Lung Cancer Growth In Vitro and In Vivo via Apoptosis Induction

24-methyl-cholesta-5,24(28)-diene-3β,19-diol-7β-monoacetate (MeCDDA) is a natural steroid compound isolated from a wild-type soft coral (Nephthea erecta). The present study aimed to investigate the anti-small cell lung cancer (SCLC) effects of MeCDDA in vitro and in vivo, as well as to elucidate its underlying mechanism. Our results indicated that H1688 and H146 cells show relevant sensitivity to MeCDDA, and the exposure to MeCDDA in SCLC cells caused dose-dependent growth inhibitory responses. In addition, MeCDDA treatment promoted cell apoptosis and increased the activities of caspases in H1688 cells, reducing the mitochondrial membrane potential and stimulating the release of cytochrome c into the cytosol. Along with the increase in Bax expression and reduction in Bcl-2, the MeCDDA treatment also significantly decreased Akt and mTOR phosphorylation. Finally, MeCDDA treatment in the mouse xenograft model of H1688 cells exhibited significant inhibition of tumor growth, corroborating MeCDDA as a potential pre-clinical candidate for the treatment of SCLC. Overall, our results demonstrate that the cytotoxic effects of MeCDDA towards H1688 and H146 cells, possibly through the activation of the mitochondrial apoptotic pathway and inhibition of the PI3K/Akt/mTOR pathway, merit further studies for its possible clinical application in chemotherapy.

Cytotoxic Steroids from the Vietnamese Soft Coral Sinularia leptoclados

Fifteen steroids, including two new compounds, leptosteroid (1) and 5,6β-epoxygorgosterol (2), were isolated and structurally elucidated from the Vietnamese soft coral Sinularia leptoclados. Their cytotoxic effect against a panel of eight human cancer cell lines was evaluated using sulforhodamine B (SRB) method. Significant cytotoxicity against hepatoma cancer (HepG2, IC₅₀=21.13±0.70 µM) and colon adenocarcinoma (SW480, IC₅₀=28.65±1.53 µM) cell lines were observed for 1 and against acute leukemia (HL-60, IC₅₀=20.53±2.26 µM) and SW480 (IC₅₀=26.61±1.59 µM) for ergost-5-en-3β,7β-diol (8). In addition, 3β,7β-dihydroxyergosta-5,24(28)-diene (13) showed significant cytotoxic activity on all tested cell lines with IC₅₀ values ranging from 13.45±1.81 to 29.01±3.21 µM.

Polyhydroxy Sterols Isolated from the Red Sea Soft Coral Lobophytum crassum and their Cytotoxic Activity

One new (1) together with four known sterols (2 - 5) and a sesquiterpene (6) were isolated from a polar extract of the Red Sea soft coral Lobophytum crassum. The compounds were identified as 24-methylenecholest-5-ene-1α,3 1α,11α-triol 1-acetate (1), 24-methylenecholest-5-ene-1α,3β,11α-triol (2), 24-methylenecholest-5-ene-3β-ol (3), 24-methylenecholestane-1α,3β,5a,6P,1-pentol (4), 24-methylenecholestane-3β,5α,6β-triol (5) and alismoxide (6) based on extensive NMR analysis. The cytotoxicity of compounds 1 - 6 was evaluated in vitro using three human cancer cell lines viz., HepG2, Hep-2 and HCT-116. Compound 1 showed selective cytotoxic activity against HepG2, while 3 exhibited cytotoxicity against all tested cell lines.

Klyflaccisteroids K-M, bioactive steroidal derivatives from a soft coral Klyxum flaccidum

New steroids, klyflaccisteroids K-M (1-3), were isolated from a soft coral Klyxum flaccidum. Their structures were elucidated on the basis of extensive spectroscopic analysis. Klyflaccisteroid K (1) is the unique 9,11-secosteroid with a 5,8-epidioxy-9-ene functional group. Klyflaccisteroid L (2) has an unusual 11-norsteroid skeleton and is the first example of 11-oxasteroid isolated from natural sources. Cytotoxicity assay showed that 1 and 3 possessed moderate to weak cytotoxicity against these cancer cells. Compound 1 was also found to display significant anti-inflammatory activity of suppressing superoxide anion generation (O₂^-) and elastase release, and compound 3 was found to show notable anti-inflammatory activity toward inhibition of elasstase release, too.

Cytotoxic Steroids from the Vietnamese Soft Coral Sinularia conferta

Twelve steroids, including five new compounds 1-5, were isolated and structurally elucidated from a methanol extract of the Vietnamese soft coral Sinularia conferta. Their cytotoxic effects against three human cancer cell lines, lung carcinoma (A-549), cervical adenocarcinoma (HeLa), and pancreatic epithelioid carcinoma (PANC-1), were evaluated using 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assays. Among isolated compounds, 10 exhibited potent cytotoxic effects on all three tested cell lines with IC₅₀ values of 3.64±0.18, 19.34±0.42, and 1.78±0.69 µM, respectively.

Anti-inflammatory activity of 3β-hydroxycholest-5-en-7-one isolated from Hippocampus trimaculatus leach via inhibiting iNOS, TNF-α, and 1L-1β of LPS induced RAW 264.7 macrophage cells

Hippocampus trimaculatus leach has been widely used in beverage and herbal medicine fabrication.

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.