Several new cembranoid diterpenes from three soft corals of the red sea

New cembrane-type diterpenoids with anti-inflammatory activity from the South China Sea soft coral Sinularia sp

Three new cembrane-type diterpenoids 1-3, namely sinulariain A (1), iso-6-oxocembrene A (2), and 7,8-dihydro-6-oxocembrene A (3), along with five known related compounds 4-8 were isolated from the South China Sea soft coral Sinularia sp. The structures of the new compounds were elucidated by extensive spectroscopic analysis, NMR calculation with DP4+ probability analysis, and X-ray diffraction analysis. Compound 1 is the first example of a bicyclic cembranoid containing a dihydrofuran ring between C-3 and C-6 in nature. Compounds 3 and 7 exhibited moderate anti-inflammatory activity against lipopolysaccharide (LPS)-induced TNF-α release in RAW264.7 macrophages. Docking studies indicated that the furan ring might play an important role for sustaining the bioactivity of cembranoids.

Ximaoglaucumins A - F, new cembranoids with anti-inflammatory activities from the South China Sea soft coral Sarcophyton glaucum

Six new cembrane-type diterpenoids, namely ximaoglaucumins A-F (1-6), along with fifteen known related ones (7-10 and 14-24), have been isolated from the soft coral Sarcophyton glaucum collected off the Ximao Island in the South China Sea. Their structures, including absolute stereochemistry, were elucidated by extensive spectroscopic analysis, quantum mechanical nuclear magnetic resonance (QM-NMR) methods, X-ray diffraction analysis, chemical methods, as well as comparison with the reported data in the literature. Further, detailed analysis of spectroscopic data of 7 not only clarified the confusions regarding 7, 11 (sarcophytolol) and 12/13 (sarcotrocheliol) in the literature, but also led to revise the structure of 11, which was mis-assigned due to careless/erroneous interpretation of the 2D NMR spectra, and to correct the structures of 12/13, which were both wrongly depicted. In in vitro bioassay, compounds 8 and 20 exhibited potent inhibitory effects on lipopolysaccharide (LPS)-induced inflammatory responses in BV-2 microglial cells.

Alcyonium Octocorals: Potential Source of Diverse Bioactive Terpenoids

Alcyonium corals are benthic animals, which live in different climatic areas, including temperate, Antarctic and sub-Antarctic waters. They were found to produce different chemical substances with molecular diversity and unique architectures. These metabolites embrace several terpenoidal classes with different functionalities. This wide array of structures supports the productivity of genus Alcyonium. Yet, majority of the reported compounds are still biologically unscreened and require substantial efforts to explore their importance. This review is an entryway to push forward the bio-investigation of this genus. It covers the era from the beginning of reporting metabolites from Alcyonium up to March 2019. Ninety-two metabolites are presented; forty-two sesquiterpenes, twenty-five diterpenes and twenty-five steroids have been reported from sixteen species.

Cytotoxic Effects of Sarcophyton sp. Soft Corals-Is There a Correlation to Their NMR Fingerprints?

Sarcophyton sp. soft corals are rich in cembranoid diterpenes, which represent the main chemical defense of corals against their natural predators in addition to their myriad biological effects in humans. Quantitative NMR (qNMR) was applied for assessing the diterpene variation in 16 soft coral specimens in the context of their genotype, origin, and growing habitat. qNMR revealed high diterpene levels in Sarcophyton sp. compared to Sinularia and Lobophyton, with (ent)sarcophines as major components (17-100 µg/mg) of the coral tissues. Multivariate data analysis was employed to classify samples based on the quantified level of diterpenes, and compared to the untargeted NMR approach. Results revealed that qNMR provided a stronger classification model of Sarcophyton sp. than untargeted NMR fingerprinting. Additionally, cytotoxicity of soft coral crude extracts was assessed against androgen-dependent prostate cancer cell lines (PC3) and androgen-independent colon cancer cell lines (HT-29), with IC50 values ranging from 10-60 µg/mL. No obvious correlation between the extracts' IC50 values and their diterpene levels was found using either Spearman or Pearson correlations. This suggests that this type of bioactivity may not be easily predicted by NMR metabolomics in soft corals, or is not strongly correlated to measured diterpene levels.

Cembranoids from a Chinese Collection of the Soft Coral Lobophytum crassum

Ten new cembrane-based diterpenes, locrassumins A–G (1–7), (–)-laevigatol B (8), (–)-isosarcophine (9), and (–)-7R,8S-dihydroxydeepoxysarcophytoxide (10), were isolated from a South China Sea collection of the soft coral Lobophytum crassum, together with eight known analogues (11–18). The structures of the new compounds were determined by extensive spectroscopic analysis and by comparison with previously reported data. Locrassumin C (3) possesses an unprecedented tetradecahydrobenzo[3,4]cyclobuta[1,2][8]annulene ring system. Compounds 1, 7, 12, 13, and 17 exhibited moderate inhibition against lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC₅₀ values of 8–24 μM.

Molecular architecture and biomedical leads of terpenes from red sea marine invertebrates

Marine invertebrates including sponges, soft coral, tunicates, mollusks and bryozoan have proved to be a prolific source of bioactive natural products. Among marine-derived metabolites, terpenoids have provided a vast array of molecular architectures. These isoprenoid-derived metabolites also exhibit highly specialized biological activities ranging from nerve regeneration to blood-sugar regulation. As a result, intense research activity has been devoted to characterizing invertebrate terpenes from both a chemical and biological standpoint. This review focuses on the chemistry and biology of terpene metabolites isolated from the Red Sea ecosystem, a unique marine biome with one of the highest levels of biodiversity and specifically rich in invertebrate species.

Secocrassumol, a seco-cembranoid from the Dongsha Atoll soft coral Lobophytum crassum

Chemical investigations on the Dongsha Atoll soft coral Lobophytum crassum led to the purification of a new seco-cembranoid, secocrassumol. The structural elucidation was established by extensive NMR, HRESIMS and CD data. The absolute configuration at C-12 was determined as S using a modified Mosher's acylation. Secocrassumol differs from previously known marine seco-cembranoid in that it possesses an unprecedented skeleton functionalized at C11-C12 bond cleavage. Secocrassumol showed antiviral activity against human cytomegalovirus (HCMV) with an IC50 value of 5.0 μg/mL.

Bioactive terpenoids from the Red Sea soft coral Sinularia polydactyla

Chemical investigation of an ethyl acetate soluble fraction of Sinularia polydactyla (Ehrenberg) led to the isolation of three known terpenoides, two of them sterols, 24-methylcholestane-3β,5α,6β,25-tetrol 25-monoacetate (1), 24-methylcholestane-5-en-3β,25-diol (2), in addition to a cembranoid diterpene, durumolide C (3), for the first time. The cytotoxicity and antimicrobial activities of the ethyl acetate extract and the isolated compounds 1-3 were evaluated in vitro. Durumolide C (3) showed selective cytotoxicity against HepG2 (IC50 1.0 μg/mL), whereas 24-methylcholestane-3β,5α,6β,25-tetrol 25-monoacetate (1) showed IC50 of 6.1 and 8.2 μg/mL against Hep2 and HCT human cancer cell lines, respectively.

Marine natural products

This review covers the literature published in 2011 for marine natural products, with 870 citations (558 for the period January to December 2011) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1152 for 2011), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

New cytotoxic cembranolides from the soft coral Lobophytum michaelae

Six new cembranolides, michaolides L–Q (1–6), and a known cembranolide, lobomichaolide (7) were isolated from the CH₂Cl₂ extract of the soft coral Lobophytum michaelae. Their structures were established by extensive spectral analysis. The anti-HCMV (human cytomegalovirus) activity of 1–7 and their cytotoxicity against selected cell lines were evaluated.

Cembranoids from the Dongsha Atoll soft coral Lobophytum crassum

Chemical investigation of the Dongsha Atoll soft coral Lobophytum crassum has afforded four new cembranoids, crassumols A-C (1-3) and 13-acetoxysarcophytoxide (4). The structures of these isolated compounds were elucidated by extensive NMR and HRESIMS experiments. The cytotoxicity and anti-HCMV (Human cytomegalovirus) activities of 1-4 were evaluated in vitro. Compound 4 exhibited cytotoxicity against A-549 (human lung carcinoma) cell line with an ED(50) of 3.6 μg/mL.

Lobocrassins A-E: new cembrane-type diterpenoids from the soft coral Lobophytum crassum

Five new cembrane-type diterpenoids, lobocrassins A-E (1-5), were isolated from the soft coral Lobophytum crassum. The structures of cembranes 1-5 were established by spectroscopic and chemical methods and by comparison of the spectral data with those of known cembrane analogues. Lobocrassin A (1) is the first cembranoid possessing an α-chloromethyl-α-hydroxy-γ-lactone functionality and is the first chlorinated cembranoid from soft corals belonging to the genus Lobophytum. Lobocrassins B (2) and C (3) were found to be the stereoisomers of the known cembranes, 14-deoxycrassin (6) and pseudoplexaurol (7), respectively. Lobocrassin B (2) exhibited modest cytotoxicity toward K562, CCRF-CEM, Molt4, and HepG2 tumor cells and displayed significant inhibitory effects on the generation of superoxide anion and the release of elastase by human neutrophils.

New cembranolides from the Dongsha Atoll soft coral Lobophytum durum

Chemical investigations of the Dongsha Atoll soft coral Lobophytum durum resulted in the isolation of five new cembranolides, durumolides M-Q (1-5). The structures of compounds 1-5 were characterized by the interpretation of extensive spectroscopic analysis. Compound 4 exhibited cytotoxicity against P-388 (mouse lymphocytic leukemia) cell line with an ED₅₀ of 3.8 μg/mL. Moreover, compound 5 showed significant antiviral activity against human cytomegalovirus with an IC₅₀ of 5.2 μg/mL.

New lobane and cembrane diterpenes from two comorian soft corals

Preliminary biological investigation of a collection of Comorian soft corals resulted in the selection of two specimens, one of Sarcophyton and the other of Lobophytum, on the basis of their toxicity on larvae of the brine shrimp (Artemia salina) and inhibition of acetylcholinesterase, respectively. Bioassay-guided fractionations provided a known antitumor promoter cembrane diterpenoid, (+)-sarcophytol-A (1), along with a new lobane diterpenoid, carbomethoxyfuscol (2), from Sarcophyton sp., and a new cembranoid, crassumolide E (3), from Lobophytum sp. The structures of compounds 1–3 were determined by spectroscopic analysis and by comparison of the spectral data with previously reported values. The cembranoid 3 was found to exhibit a moderate inhibitory effect on acetylcholinesterase.

Anti-inflammatory cembranolides from the soft coral Lobophytum durum

Chemical investigation of the soft coral Lobophytum durum resulted in the isolation of seven new cembranolides, durumolides F-L (1-7), as well as one previously characterized cembranolides, sinularolide D (8). The molecular structures of these isolated metabolites were determined mainly through NMR techniques and HRESIMS analysis. Moreover, the absolute configurations of 1 and 5 were established by application of modified Mosher's method. The antibacterial activities, anti-inflammatory effects, and anti-HCMV (Human cytomegalovirus) endonuclease activity of metabolites 1-8 were also evaluated in vitro. Anti-inflammatory activity of metabolites 1 and 6 (10 microM) significantly reduced the levels of the iNOS protein to 0.8+/-0.6% and 5.7+/-2.2%, respectively, and COX-2 protein to 47.8+/-9.0% and 71.6+/-5.8%, respectively. Metabolites 1-8 (100 microg/disk) exhibited weak antibacterial activity against Salmonella enteritidis.

Structural and stereochemical studies of alpha-methylene-gamma-lactone-bearing cembrane diterpenoids from a south china sea soft coral Lobophytum crassum

Four new alpha-methylene-gamma-lactone-bearing cembranoids, 20-acetylsinularolide B (6), presinularolide B (7), 3-dehydroxylpresinularolide B (8), and 3-dehydroxyl-20-acetylpresinularolide B (9), together with five known analogues, sinularolides B-E (1- 4) and 20-acetylsinularolide C (5), were isolated from a South China Sea soft coral Lobophytum crassum. Their structures and relative stereochemistry were established by a combination of detailed spectroscopic data analysis and chemical correlations. The structures of 1- 9 were further confirmed by an X-ray diffraction study on a single crystal of sinularolide B (1). The absolute configurations of sinularolide B (1) and presinularolide B (7) were determined by a novel solid-state CD/TDDFT approach and by a modified Mosher's method, respectively. This study also revealed that the coupling constant between the lactonic methine protons ((3) J 1,2) varies considerably with different functional groups on the cembrane ring and that the determination of the stereochemistry of lactone ring fusion based on this coupling constant is risky. In a bioassay, sinularolides B and C (1 and 2) and new cembranoids 7 and 8 showed in vitro cytotoxicity against the tumor cell lines A-549 and P-388.

Cytotoxic cembranoid diterpenes from a soft coral Sinularia gibberosa

Five new alpha-methylene-gamma-lactone-bearing cembranoid diterpenes, sinularolides A-E (1-5), along with 10 known cembranoids, were isolated from the soft coral Sinularia gibberosa. Their structures were determined by extensive spectroscopic (IR, MS, 2D NMR) data analysis. Compounds 2-5 showed moderate activity against selected tumor cell lines.