Polyhydroxylated Steroids from the South China Sea Soft Coral Sarcophyton sp. and Their Cytotoxic and Antiviral Activities

Chemical investigation on the soft coral Sarcophyton sp. collected from the South China Sea yielded three new polyhydroxylated steroids, compounds (1–3), together with seven known ones (4–10). Their structures were established by extensive spectroscopic methods and comparison of their data with those of the related known compounds. All the isolates possessed the 3β,5α,6β-trihydroxylated steroidal nucleus. The cytotoxicities against selected HL-60, HeLa and K562 tumor cell lines and anti-H1N1 (Influenza A virus (IAV)) activities for the isolates were evaluated. Compounds 2, 3 and 5–8 exhibited potent activities against K562 cell lines with IC₅₀ values ranging from 6.4 to 10.3 μM. Compounds 1, 6–8 potently inhibited the growth of HL-60 tumor cell lines, and 6 also showed cytotoxicity towards HeLa cell lines. In addition, preliminary structure-activity relationships for the isolates are discussed. The OAc group at C-11 is proposed to be an important pharmacophore for their cytotoxicities in the 3β,5α,6β-triol steroids. Compounds 4 and 9 exhibited significant anti-H1N1 IAV activity with IC₅₀ values of 19.6 and 36.7 μg/mL, respectively.     

Topsensterols A–C,Cytotoxic Polyhydroxylated Sterol Derivatives from a Marine Sponge Topsentia sp.

Three new polyhydroxylated sterol derivatives topsensterols A–C (1–3) have been isolated from a marine sponge Topsentia sp. collected from the South China Sea. Their structures were elucidated by detailed analysis of the spectroscopic data, especially the NOESY spectra. Topsensterols A–C (l–3) possess novel 2β,3α,4β,6α-tetrahydroxy-14α-methyl Δ⁹⁽¹¹⁾ steroidal nuclei with unusual side chains. Compound 2 exhibited cytotoxicity against human gastric carcinoma cell line SGC-7901 with an IC₅₀ value of 8.0 μM. Compound 3 displayed cytotoxicity against human erythroleukemia cell line K562 with an IC₅₀ value of 6.0 μM.     

Isolation and Identification of Antitrypanosomal and Antimycobacterial Active Steroids from the Sponge Haliclona simulans

The marine sponge Haliclona simulans collected from the Irish Sea yielded two new steroids: 24-vinyl-cholest-9-ene-3β,24-diol and 20-methyl-pregn-6-en-3β-ol,5α,8α-epidioxy, along with the widely distributed 24-methylenecholesterol. One of the steroids possesses an unusually short hydrocarbon side chain. The structures were elucidated using nuclear magnetic resonance spectroscopy and confirmed using electron impact- and high resolution electrospray-mass spectrometry. All three steroids possess antitrypanosomal and anti-mycobacterial activity. All the steroids were found to possess low cytotoxicity against Hs27 which was above their detected antitrypanosomal potent concentrations.     

Secosteroids and Norcembranoids from the Soft Coral Sinularia nanolobata

Two new 9,11-secosteroids, 22α-acetoxy-24-methylene-3β,6α,11-trihydroxy-9,11-seco-cholest-7-en-9-one (1) and 11-acetoxy-24-methylene-1β,3β,6α-trihydroxy-9,11-seco-cholest-7-en-9-one (2), as well as two known norcembranoids, 5-epi-sinuleptolide (3) and sinuleptolide (4), were isolated from the soft coral Sinularia nanolobata. The structures of these metabolites were elucidated on the basis of extensive spectroscopic analysis. The anti-HCMV (human cytomegalovirus) activity of 1–4 and its cytotoxicity against selected cell lines were evaluated.     

Isolation of Araguspongine M,a New Stereoisomer of an Araguspongine/Xestospongin alkaloid,and Dopamine from the Marine Sponge Neopetrosia exigua Collected in Palau

A new stereoisomer of an araguspongine/xestospongin alkaloid, named araguspongine M (1), has been isolated together with 12 known compounds, araguspongines B (2) and D (3), dopamine, three galactosyl diacylglycerols, 24-methyl cholesterol, 5,6-dihydrocholesterol, β-sitosterol, and three 5α,8α-epidioxy sterols (11–13), from the marine sponge Neopetrosia exigua (formerly Xestospongia exigua) collected in Palau. The structure of 1 was assigned on the basis of its spectral data analysis. This is the first report on the isolation of dopamine from a marine sponge. This compound may be produced by an endosymbiotic Synechococcus-like cyanobacterium. Compounds 1–3 and 11–13 showed cytotoxicity against HL-60 at IC₅₀’s of 5.5, 5.5, 5.9, 22.4, 9.5, and 9.6 μM, respectively. The possible biosynthesis origin of the isolated metabolites is discussed.     

Two Novel Tyrosinase Inhibitory Sesquiterpenes Induced by CuCl2 from a Marine-Derived Fungus Pestalotiopsis sp. Z233

Two new sesquiterpenes, 1β,5α,6α,14-tetraacetoxy-9α-benzoyloxy-7βH-eudesman-2β,11-diol (1) and 4α,5α-diacetoxy-9α-benzoyloxy-7βH-eudesman-1β,2β,11,14-tetraol (2), were produced as stress metabolites in the cultured mycelia of Pestalotiopsis sp. Z233 isolated from the algae Sargassum horneri in response to abiotic stress elicitation by CuCl₂. Their structures were established by spectroscopic means. New compounds 1 and 2 showed tyrosinase inhibitory activities with IC₅₀ value of 14.8 µM and 22.3 µM.     

New Antioxidative Secondary Metabolites from the Fruits of a Beibu Gulf Mangrove,Avicennia marina

Further chemical investigation of the fruits of the mangrove, Avicennia marina, afforded three new phenylethyl glycosides, marinoids J–L (1–3), and a new cinnamoyl glycoside, marinoid M (4). The structures of isolates were elucidated on the basis of extensive spectroscopic analysis and by comparison of the data with those of related secondary metabolites. The antioxidant activity of the isolates was evaluated using the cellular antioxidant assay (CAA), and compounds 1–4 showed antioxidant activities, with EC₅₀ values ranging from 23.0 ± 0.71 μM to 247.8 ± 2.47 μM.     

Calcarides A–E,Antibacterial Macrocyclic and Linear Polyesters from a Calcarisporium Strain

Bioactive compounds were detected in crude extracts of the fungus, Calcarisporium sp. KF525, which was isolated from German Wadden Sea water samples. Purification of the metabolites from the extracts yielded the five known polyesters, 15G256α, α-2, β, β-2 and π (1–5), and five new derivatives thereof, named calcarides A–E (6–10). The chemical structures of the isolated compounds were elucidated on the basis of one- and two-dimensional NMR spectroscopy supported by UV and HRESIMS data. The compounds exhibited inhibitory activities against Staphylococcus epidermidis, Xanthomonas campestris and Propionibacterium acnes. As the antibacterial activities were highly specific with regard to compound and test strain, a tight structure-activity relationship is assumed.     

Territrem and Butyrolactone Derivatives from a Marine-Derived Fungus Aspergillus Terreus

Seventeen lactones including eight territrem derivatives (1–8) and nine butyrolactone derivatives (9–17) were isolated from a marine-derived fungus Aspergillus terreus SCSGAF0162 under solid-state fermentation of rice. Compounds 1–3 and 9–10 were new, and their structures were elucidated by spectroscopic analysis. The acetylcholinesterase inhibitory activity and antiviral activity of compounds 1–17 were evaluated. Among them, compounds 1 and 2 showed strong inhibitory activity against acetylcholinesterase with IC₅₀ values of 4.2 ± 0.6, 4.5 ± 0.6 nM, respectively. This is the first time it has been reported that 3, 6, 10, 12 had evident antiviral activity towards HSV-1 with IC₅₀ values of 16.4 ± 0.6, 6.34 ± 0.4, 21.8 ± 0.8 and 28.9 ± 0.8 μg·mL⁻¹, respectively. Antifouling bioassay tests showed that compounds 1, 11, 12, 15 had potent antifouling activity with EC₅₀ values of 12.9 ± 0.5, 22.1 ± 0.8, 7.4 ± 0.6, 16.1 ± 0.6 μg·mL⁻¹ toward barnacle Balanus amphitrite larvae, respectively.     

Gageostatins A–C,Antimicrobial Linear Lipopeptides from a Marine Bacillus subtilis

Concerning the requirements of effective drug candidates to combat against high rising multidrug resistant pathogens, we isolated three new linear lipopeptides, gageostatins A–C (1–3), consisting of hepta-peptides and new 3-β-hydroxy fatty acids from the fermentation broth of a marine-derived bacterium Bacillus subtilis. Their structures were elucidated by analyzing a combination of extensive 1D, 2D NMR spectroscopic data and high resolution ESIMS data. Fatty acids, namely 3-β-hydroxy-11-methyltridecanoic and 3-β-hydroxy-9,11-dimethyltridecanoic acids were characterized in lipopeptides 1 and 2, respectively, whereas an unsaturated fatty acid (E)-7,9-dimethylundec-2-enoic acid was assigned in 3. The 3R configuration of the stereocenter of 3-β-hydroxy fatty acids in 1 and 2 was established by Mosher’s MTPA method. The absolute stereochemistry of amino acid residues in 1–3 was ascertained by acid hydrolysis followed by Marfey’s derivatization studies. Gageostatins 1–3 exhibited good antifungal activities with MICs values of 4–32 µg/mL when tested against pathogenic fungi (R. solani, B. cinerea and C. acutatum) and moderate antibacterial activity against bacteria (B. subtilis, S. aeureus, S. typhi and P. aeruginosa) with MICs values of 8–64 µg/mL. Futhermore, gageostatins 1–3 displayed cytotoxicity against six human cancer cell lines with GI₅₀ values of 4.6–19.6 µg/mL. It is also noteworthy that mixed compounds 1+2 displayed better antifungal and cytotoxic activities than individuals.     

Neuritogenic and Neuroprotective Effects of Polar Steroids from the Far East Starfishes Patiria pectinifera and Distolasterias nipon

The neuritogenic and neuroprotective activities of six starfish polar steroids, asterosaponin Р₁, (25S)-5α-cholestane-3β,4β,6α,7α,8,15α,16β,26-octaol, and (25S)-5α-cholestane-3β,6α,7α,8,15α,16β,26-heptaol (1–3) from the starfish Patiria pectinifera and distolasterosides D₁–D₃ (4–6) from the starfish Distolasterias nipon were analyzed using the mouse neuroblastoma (NB) C-1300 cell line and an organotypic rat hippocampal slice culture (OHSC). All of these compounds enhanced neurite outgrowth in NB cells. Dose-dependent responses to compounds 1–3 were observed within the concentration range of 10–100 nM, and dose-dependent responses to glycosides 4–6 were observed at concentrations of 1–50 nM. All the tested substances exhibited notable synergistic effects with trace amounts of nerve growth factor (NGF, 1 ng/mL) or brain-derived neurotrophic factor (BDNF, 0.1 ng/mL). Using NB cells and OHSCs, it was shown for the first time that starfish steroids 1–6 act as neuroprotectors against oxygen-glucose deprivation (OGD) by increasing the number of surviving cells. Altogether, these results suggest that neurotrophin-like neuritogenic and neuroprotective activities are most likely common properties of starfish polyhydroxysteroids and the related glycosides, although the magnitude of the effect depended on the particular compound structure.     

New Furan and Cyclopentenone Derivatives from the Sponge-Associated Fungus Hypocrea Koningii PF04

Two new furan derivatives, hypofurans A and B (1 and 2), and three new cyclopentenone derivatives, hypocrenones A–C (3–5), along with seven known compounds (6–12), were isolated from a marine fungus Hypocrea koningii PF04 associated with the sponge Phakellia fusca. Among them, compounds 10 and 11 were obtained for the first time as natural products. The planar structures of compounds 1–5 were elucidated by analysis of their spectroscopic data. Meanwhile, the absolute configuration of 1 was determined as 2R,3R by the comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. All the isolates were evaluated for their antibacterial and antioxidant activity. Compounds 1, 10, and 12 all showed modest antibacterial activity against Staphylococcus aureus ATCC25923 (MIC, 32 μg/mL). In addition, compounds 1, 10 and 11 exhibited moderate DPPH radical scavenging capacity with IC₅₀ values of 27.4, 16.8, and 61.7 µg/mL, respectively.     

Aaptamine Derivatives with Antifungal and Anti-HIV-1 Activities from the South China Sea Sponge Aaptos aaptos

Five new alkaloids of aaptamine family, compounds (1–5) and three known derivatives (6–8), have been isolated from the South China Sea sponge Aaptos aaptos. The structures of all compounds were unambiguously elucidated by spectroscopic analyses, as well as by comparison with the literature data. Compounds 1–2 are characterized with triazapyrene lactam skeleton, whereas compounds 4–5 share an imidazole-fused aaptamine moiety. These compounds were evaluated in antifungal and anti-HIV-1 assays. Compounds 3, 7, and 8 showed antifungal activity against six fungi, with MIC values in the range of 4 to 64 μg/mL. Compounds 7–8 exhibited anti-HIV-1 activity, with inhibitory rates of 88.0% and 72.3%, respectively, at a concentration of 10 μM.     

Neritinaceramides A–E,New Ceramides from the Marine Bryozoan Bugula neritina Inhabiting South China Sea and Their Cytotoxicity

Five new ceramides, neritinaceramides A (1), B (2), C (3), D (4) and E (5), together with six known ceramides (6–11), two known alkyl glycerylethers (12 and 13) and a known nucleoside (14), were isolated from marine bryozoan Bugula neritina, which inhabits the South China Sea. The structures of the new compounds were elucidated as (2S,3R,3′S,4E,8E,10E)-2-(hexadecanoylamino)-4,8,10-octadecatriene-l,3,3′-triol (1), (2S,3R,2′R,4E,8E,10E)-2-(hexadecanoylamino)-4,8,10-octadecatriene-l,3,2′-triol (2), (2S,3R,2′R,4E,8E,10E)-2-(octadecanoylamino)-4,8,10-octadecatriene-l,3,2′-triol (3), (2S,3R,3′S,4E,8E)-2-(hexadecanoylamino)-4,8-octadecadiene-l,3,3′-triol (4) and (2S,3R,3′S,4E)-2-(hexadecanoylamino)-4-octadecene-l,3,3′-triol (5) on the basis of extensive spectral analysis and chemical evidences. The characteristic C-3′S hydroxyl group in the fatty acid moiety in compounds 1, 4 and 5, was a novel structural feature of ceramides. The rare 4E,8E,10E-triene structure in the sphingoid base of compounds 1–3, was found from marine bryozoans for the first time. The new ceramides 1–5 were evaluated for their cytotoxicity against HepG2, NCI-H460 and SGC7901 tumor cell lines, and all of them exhibited selective cytotoxicity against HepG2 and SGC7901 cells with a range of IC₅₀ values from 47.3 μM to 58.1 μM. These chemical and cytotoxic studies on the new neritinaceramides A–E (1–5) added to the chemical diversity of B. neritina and expanded our knowledge of the chemical modifications and biological activity of ceramides.     

Eunicellin-Based Diterpenoids,Hirsutalins S–V,from the Formosan Soft Coral Cladiella hirsuta

Four new eunicellin-type hirsutalins S–V (1–4), along with a known compound (–)-6α-hydroxy polyanthellin A (5), were isolated from the soft coral Cladiella hirsuta. The structures of the metabolites were determined by extensive spectroscopic analysis. Cytotoxity of compounds 1–5 against the proliferation of a limited panel of cancer cell lines was measured. Anti-inflammatory activity of compounds 1–5 was evaluated by measuring their ability in suppressing superoxide anion generation and elastase release in fMLP/CB-induced human neutrophils.     

New α-Glucosidase Inhibitory Triterpenic Acid from Marine Macro Green Alga Codium dwarkense Boergs

The marine ecosystem has been a key resource for secondary metabolites with promising biological roles. In the current study, bioassay-guided phytochemical investigations were carried out to assess the presence of enzyme inhibitory chemical constituents from the methanolic extract of marine green alga—Codium dwarkense. The bioactive fractions were further subjected to chromatographic separations, which resulted in the isolation of a new triterpenic acid; dwarkenoic acid (1) and the known sterols; androst-5-en-3β-ol (2), stigmasta-5,25-dien-3β,7α-diol (3), ergosta-5,25-dien-3β-ol (4), 7-hydroxystigmasta-4,25-dien-3-one-7-O-β-d-fucopyranoside (5), 7-hydroxystigmasta-4,25-dien-3-one (6), and stigmasta-5,25-dien-3β-ol (7). The structure elucidation of the new compound was carried out by combined mass spectrometry and 1D (¹H and ¹³C) and 2D (HSQC, HMBC, COSY, and NOESY) NMR spectroscopic data. The sub-fractions and pure constituents were assayed for enzymatic inhibition of alpha-glucosidase. Compound 1 showed significant inhibition at all concentrations. Compounds 2, 3, 5, and 7 exhibited a dose-dependent response, whereas compounds 4–6 showed moderate inhibition. Utilizing such marine-derived biological resources could lead to drug discoveries related to anti-diabetics.     

Cytotoxic and Antibacterial Cembranoids from a South China Sea Soft Coral,Lobophytum sp

Chemical examination of a South China Sea soft coral Lobophytum sp. led to the isolation of three new α-methylene-γ-lactone-containing cembranoids, (1R*,3R*,4R*,14R*,7E,11E)-3,4-epoxycembra-7,11,15(17)-trien-16,14-olide (1), (1R*,7S*,14S*,3E,11E)-7-hydroperoxycembra-3,8(19),11,15(17)-tetraen-16,14-olide (2), and (1R*,7S*,14S*,3E,11E)-18-acetoxy-7-hydroperoxycembra-3,8(19),11,15(17)-tetraen-16,14-olide (3), along with eleven known analogues 4–14. The structures of the new compounds were elucidated through extensive spectroscopic analysis, including 1D and 2D NMR data. Compounds 1–3 exhibited moderate cytotoxic activity against the selected tumor cell lines. Moreover, 2 and 3 were found to be moderate inhibitors against the bacteria S. aureus and S. pneumoniae.     

6-Bromohypaphorine from Marine Nudibranch Mollusk Hermissenda crassicornis is an Agonist of Human α7 Nicotinic Acetylcholine Receptor

6-Bromohypaphorine (6-BHP) has been isolated from the marine sponges Pachymatisma johnstoni, Aplysina sp., and the tunicate Aplidium conicum, but data on its biological activity were not available. For the nudibranch mollusk Hermissenda crassicornis no endogenous compounds were known, and here we describe the isolation of 6-BHP from this mollusk and its effects on different nicotinic acetylcholine receptors (nAChR). Two-electrode voltage-clamp experiments on the chimeric α7 nAChR (built of chicken α7 ligand-binding and glycine receptor transmembrane domains) or on rat α4β2 nAChR expressed in Xenopus oocytes revealed no action of 6-BHP. However, in radioligand analysis, 6-BHP competed with radioiodinated α-bungarotoxin for binding to human α7 nAChR expressed in GH₄C₁ cells (IC₅₀ 23 ± 1 μM), but showed no competition on muscle-type nAChR from Torpedo californica. In Ca²⁺-imaging experiments on the human α7 nAChR expressed in the Neuro2a cells, 6-BHP in the presence of PNU120596 behaved as an agonist (EC₅₀ ~80 μM). To the best of our knowledge, 6-BHP is the first low-molecular weight compound from marine source which is an agonist of the nAChR subtype. This may have physiological importance because H. crassicornis, with its simple and tractable nervous system, is a convenient model system for studying the learning and memory processes.     

Monacyclinones,New Angucyclinone Metabolites Isolated from Streptomyces sp. M7_15 Associated with the Puerto Rican Sponge Scopalina ruetzleri

During an investigation of new actinomycete species from Caribbean sponges for novel bioactive natural products, frigocyclinone (1), dimethyldehydrorabelomycin (3) and six new angucyclinone derivatives were isolated from Streptomyces sp. strain M7_15 associated with the sponge Scopalina ruetzleri. Of these, monacyclinones A–B (4–5) contain the core ring structure of dehydrorabelomycin (2) with the aminodeoxysugar found in frigocyclinone (1). Monacyclinone C (6) is a hydroxylated variant of frigocyclinone (1) and monacyclinone D (7) is a Baeyer Villiger derivative of (6) which also exists as the open chain hydrolysis product monacyclinone E (8). Monacyclinone F (9) contains two unique epoxide rings attached to the angucyclinone moiety and an additional aminodeoxysugar attached through an angular oxygen bond. All structures were confirmed through spectral analyses. Activity against rhabdomycosarcoma cancer cells (SJCRH30) after 48 h of treatment was observed with frigocyclinone (1; EC₅₀ = 5.2 µM), monacyclinone C (6; 160 µM), monacyclinone E (8; 270 µM), and monacyclinone F (9; 0.73 µM). The strongest bioactivity against rhabdomycosarcoma cancer cells and gram-positive bacteria was exhibited by compound 9, suggesting that the extra aminodeoxysugar subunit is important for biological activity.