New cytotoxic sesterterpenes from the sponge Sarcotragus species

Structural analysis of previously unknown natural products using computational methods

Natural products exhibit structural diversity, and biologically active natural products with unprecedented molecular skeletons can potentially be isolated from natural resources in the future. Although it has often been difficult to determine the structures and configurations of new compounds that do not resemble known compounds, the determination of the chemical structures, including the absolute stereo configuration, is very important in drug discovery research. In our efforts to find new bioactive natural products, we have identified novel compounds such as the ubiquitin-proteasome system inhibitors and osteoclast differentiation inhibitors. Various natural products, mixtures of stereoisomers of natural products, and compounds with novel skeletal structures were studied. In cases where it was difficult to determine the structures by NMR spectroscopy, we could successfully determine the chemical structures by computational chemistry. This review presents the results of structural analysis obtained using computational methods for several natural products that we have recently isolated.

Antiprotozoal Linear Furanosesterterpenoids from the Marine Sponge Ircinia oros

Chemical investigation of the marine sponge Ircinia oros yielded four linear furanosesterterpenoids, including the known metabolites ircinin-1 (1) and ircinin-2 (2) and two new compounds, ircinialactam E (3) and ircinialactam F (4). Their chemical structures were elucidated by using a combination of [α]_D, NMR, HRMS, and FT-IR spectroscopy. The absolute configuration of C-18 in compounds 1-3 was identified as R by electronic circular dichroism (ECD) spectroscopy coupled with time-dependent density functional theory calculations. Compounds 1-4 showed moderate leishmanicidal, trypanocidal, and antiplasmodial activities (IC₅₀ values 28-130 μM). This is the second report of rare glycinyl lactam derivatives 3 and 4 from the genus Ircinia.

In Vitro Growth Inhibitory Activities of Natural Products from Irciniid Sponges against Cancer Cells: A Comparative Study

Marine sponges of the Irciniidae family contain both bioactive furanosesterterpene tetronic acids (FTAs) and prenylated hydroquinones (PHQs). Both classes of compounds are known for their anti-inflammatory, antioxidant, and antimicrobial properties and known to display growth inhibitory effects against various human tumor cell lines. However, the different experimental conditions of the reported in vitro bioassays, carried out on different cancer cell lines within separate studies, prevent realistic actual discrimination between the two classes of compounds from being carried out in terms of growth inhibitory effects. In the present work, a chemical investigation of irciniid sponges from Tunisian coasts led to the purification of three known FTAs and three known PHQs. The in vitro growth inhibitory properties of the six purified compounds have been evaluated in the same experiment in a panel of five human and one murine cancer cell lines displaying various levels of sensitivity to proapoptotic stimuli. Surprisingly, FTAs and PHQs elicited distinct profiles of growth inhibitory-responses, differing by one to two orders of magnitude in favor of the PHQs in all cell lines. The obtained comparative results are discussed in the light of a better selection of drug candidates from natural sources.

Sesterterpenoids with Anticancer Activity

Terpenes have received a great deal of attention in the scientific literature due to complex, synthetically challenging structures and diverse biological activities associated with this class of natural products. Based on the number of C5 isoprene units they are generated from, terpenes are classified as hemi- (C5), mono- (C10), sesqui- (C15), di- (C20), sester- (C25), tri (C30), and tetraterpenes (C40). Among these, sesterterpenes and their derivatives known as sesterterpenoids, are ubiquitous secondary metabolites in fungi, marine organisms, and plants. Their structural diversity encompasses carbotricyclic ophiobolanes, polycyclic anthracenones, polycyclic furan-2-ones, polycyclic hydroquinones, among many other carbon skeletons. Furthermore, many of them possess promising biological activities including cytotoxicity and the associated potential as anticancer agents. This review discusses the natural sources that produce sesterterpenoids, provides sesterterpenoid names and their chemical structures, biological properties with the focus on anticancer activities and literature references associated with these metabolites. A critical summary of the potential of various sesterterpenoids as anticancer agents concludes the review.

In Search of Alternative Antibiotic Drugs: Quorum-Quenching Activity in Sponges and their Bacterial Isolates

Owing to the extensive development of drug resistance in pathogens against the available antibiotic arsenal, antimicrobial resistance is now an emerging major threat to public healthcare. Anti-virulence drugs are a new type of therapeutic agent aiming at virulence factors rather than killing the pathogen, thus providing less selective pressure for evolution of resistance. One promising example of this therapeutic concept targets bacterial quorum sensing (QS), because QS controls many virulence factors responsible for bacterial infections. Marine sponges and their associated bacteria are considered a still untapped source for unique chemical leads with a wide range of biological activities. In the present study, we screened extracts of 14 sponge species collected from the Red and Mediterranean Sea for their quorum-quenching (QQ) potential. Half of the species showed QQ activity in at least 2 out of 3 replicates. Six out of the 14 species were selected for bacteria isolation, to test for QQ activity also in isolates, which, once cultured, represent an unlimited source of compounds. We show that ≈20% of the isolates showed QQ activity based on a Chromobacterium violaceum CV026 screen, and that the presence or absence of QQ activity in a sponge extract did not correlate with the abundance of isolates with the same activity from the same sponge species. This can be explained by the unknown source of QQ compounds in sponge-holobionts (host or symbionts), and further by the possible non-symbiotic nature of bacteria isolated from sponges. The potential symbiotic nature of the isolates showing QQ activity was tested according to the distribution and abundance of taxonomically close bacterial Operational Taxonomic Units (OTUs) in a dataset including 97 sponge species and 178 environmental samples (i.e., seawater, freshwater, and marine sediments). Most isolates were found not to be enriched in sponges and may simply have been trapped in the filtration channels of the sponge at the time of collection. Our results highlight potential for QQ-bioactive lead molecules for anti-virulence therapy both from sponges and the bacteria isolated thereof, independently on the symbiotic nature of the latter.

Minor enantiomer recycling – a strategy to improve enantioselectivity

In enantioselective reactions, the major, desired enantiomer is commonly obtained along with the minor, undesired enantiomer. By continuous recycling of this undesired enantiomer back to starting material, products with improved enantiomeric purity can be obtained. Such in situ minor enantiomer recycling can be accomplished by coupling the catalytic reaction to an exergonic transformation of a sacrificial reagent. The method has been applied to the synthesis of O-acylated cyanohydrins, which serve as starting materials for a variety of biologically active compounds.

New marine natural products from sponges (Porifera) of the order Dictyoceratida (2001 to 2012); a promising source for drug discovery, exploration and future prospects

The discovery of new drugs can no longer rely primarily on terrestrial resources, as they have been heavily exploited for over a century. During the last few decades marine sources, particularly sponges, have proven to be a most promising source of new natural products for drug discovery. This review considers the order Dictyoceratida in the Phylum Porifera from which the largest number of new marine natural products have been reported over the period 2001-2012. This paper examines all the sponges from the order Dictyoceratida that were reported as new compounds during the time period in a comprehensive manner. The distinctive physical characteristics and the geographical distribution of the different families are presented. The wide structural diversity of the compounds produced and the variety of biological activities they exhibited is highlighted. As a representative of sponges, insights into this order and avenues for future effective natural product discovery are presented. The research institutions associated with the various studies are also highlighted with the aim of facilitating collaborative relationships, as well as to acknowledge the major international contributors to the discovery of novel sponge metabolites. The order Dictyoceratida is a valuable source of novel chemical structures which will continue to contribute to a new era of drug discovery.

Targeting cancer with sesterterpenoids: the new potential antitumor drugs

Cancer remains a major cause of death in the world to date. A variety of anticancer drugs have been used in clinical chemotherapy, acting on the particular oncogenic abnormalities that are responsible for malignant transformation and progression. Interestingly, some of these anticancer drugs are developed from natural sources such as plants, marine organisms, and microorganisms. Over the past decades, a family of naturally occuring molecules, namely sesterterpenoids, has been isolated from different organisms and they exhibit significant potential in the inhibition of tumor cells in vitro, while the molecular targets of these compounds and their functional mechanisms are still obscure. In this review, we summarize and discuss the functions of these sesterterpenoids in the inhibition of cancer cells. Moreover, we also highlight and discuss chemical structure–activity relationships of some compounds, demonstrating their pervasiveness and importance in cancer therapy.

One-step preparation of O-(α-bromoacyl) cyanohydrins by minor enantiomer recycling: synthesis of 4-amino-2(5H)-furanones

O-(α-Bromoacyl) cyanohydrins were prepared in a single step from a range of different aldehydes in combination with α-bromoacyl cyanides. By the use of a cyclic procedure where the two minor diastereoisomers from a chiral Lewis acid-catalyzed reaction undergo Candida antarctica lipase B (CALB)-catalyzed hydrolysis followed by dehydrocyanation to regenerate the starting material, the products were obtained in good to high yields and in most cases with excellent diastereoselectivites. The synthetic importance of these compounds was demonstrated by the synthesis of 4-amino-2(5H)-furanones, a class of compounds that have shown both biological activity and utility as synthetic intermediates. This transformation was achieved by an intramolecular Blaise reaction, which gave the products in high to excellent yields and enantiomeric ratios.

Sustainable production of biologically active molecules of marine based origin

The marine environment offers both economic and scientific potential which are relatively untapped from a biotechnological point of view. These environments whilst harsh are ironically fragile and dependent on a harmonious life form balance. Exploitation of natural resources by exhaustive wild harvesting has obvious negative environmental consequences. From a European industry perspective marine organisms are a largely underutilised resource. This is not due to lack of interest but due to a lack of choice the industry faces for cost competitive, sustainable and environmentally conscientious product alternatives. Knowledge of the biotechnological potential of marine organisms together with the development of sustainable systems for their cultivation, processing and utilisation are essential. In 2010, the European Commission recognised this need and funded a collaborative RTD/SME project under the Framework 7-Knowledge Based Bio-Economy (KBBE) Theme 2 Programme 'Sustainable culture of marine microorganisms, algae and/or invertebrates for high value added products'. The scope of that project entitled 'Sustainable Production of Biologically Active Molecules of Marine Based Origin' (BAMMBO) is outlined. Although the Union is a global leader in many technologies, it faces increasing competition from traditional rivals and emerging economies alike and must therefore improve its innovation performance. For this reason innovation is placed at the heart of a European Horizon 2020 Strategy wherein the challenge is to connect economic performance to eco performance. This article provides a synopsis of the research activities of the BAMMBO project as they fit within the wider scope of sustainable environmentally conscientious marine resource exploitation for high-value biomolecules.

Screening of antileishmanial activity from marine sponge extracts collected off the Tunisian coast

The present study reports on the in vitro antileishmanial activity of two Ircinidae (Dictyoceratida, Demospongiae, Porifera) Ircinia spinosula and Sarcotragus sp. Sampled from the east coast of Tunisia. The ethyl acetate, dichloromethane, and aqueous extracts were tested against Leishmania major promastigotes. The anti-proliferative activity was checked using different extracts concentration during 72 h. We found that the IC50 (sub-inhibitory concentration) values ranged from 1.39 to 264.67 mug/ml. The most active extract was that from sarcotragus sp dichloromethane extract. Microscopic observations showed that the extracts promoted cellular alterations and induce enlargement of the nucleus and modification of the parasite shape. These promising results in relation with in vitro antileishmanial activity open the way for complementary investigation in order to purify and identify active molecules.

Hexa-, hepta- and nonaprenylhydroquinones isolated from marine sponges Sarcotragus muscarum and Ircinia fasciculata inhibit NF-k B signalling in H4IIE cells

Objectives

Marine organisms have proven to be a rich source of potent pharmacologically active compounds. Three polyprenyl-1,4-hydroquinone derivates (hexaprenyl-1,4-hydroquinone, heptaprenyl-1,4-hydroquinone and nonaprenyl-1,4-hydroquinone) were isolated from the Zoobenthos-inhabiting sponges Sarcotragus muscarum and Ircinia fasciculata from the Eastern Mediterranean Sea (phylum: Porifera; class: Demospongiae).

Methods

Hexa-, hepta- and nonaprenylhydroquinone were identified by 1H-NMR, H,H-COSY, heteronuclear multiple bond correlation, FAB-MS and UV spectroscopy. The effects of the compounds on cell viability was determined using the MTT assay; anti-oxidative potential was measured using the Trolox equivalent antioxidative capacity assay. Inhibition of nuclear factor-k B activity was detected by secreted alkaline phosphatase assay. Activity against an array of protein kinases was determined in 96-well FlashPlates.

Key findings

All compounds had prominent antioxidative activity, comparable to that of the synthetic vitamin E derivate Trolox. Hexaprenylhydroquinone showed the greatest cytotoxicity in H4IIE hepatoma cells (EC50 2.5 μM). All three compounds inhibited NF-k B signalling in this cell line, with heptaprenylhydroquinone being the most active. Screening of 23 kinases involved in signal transduction pathways (cell proliferation, survival, angiogenesis and metastasis) showed that hexaprenylhydroquinone and heptaprenylhydroquinone inhibited the activity of the epidermal growth factor receptor (IC50 1.6 and 1.4 μg/ml, respectively), and heptaprenylhydroquinone also inhibited the activity of other kinases (Src tyrosine kinase, vascular endothelial growth factor receptor 3 and insulin-like growth factor 1 receptor).

Conclusions

The prenylated hydroquinones isolated from the marine sponges S. muscarum and I. fasciculata showed cytotoxic and antioxidative activities and inhibited NF-k B signalling in H4IIE hepatoma cells and protein kinases. These findings may result in the generation of new lead substances in cancer therapy.

Antifouling Sesterterpenes from the New Zealand Marine Sponge Semitaspongia Bactriana

Three antifouling (AF) sesterterpenes have been isolated from the New Zealand marine sponge Semitaspongia bactriana with toxicity against the diatom Nitzschia closterium and bryozoan Bugula neritina. The three metabolites have been characterised by spectroscopic techniques as 7 E, 12 E, 20 Z-variabilin (1), cavernosolide (2) and lintenolide A (3) (also called spongianolide C) and have low micromolar activity against our two test species. The γ-hydroxybutenolide containing sesterterpenes (2 and 3) show the most promise, with relative stability and suitable lipophilicity for incorporation of either these metabolites, or synthetic analogues, as biocides to produce paints or plastics with AF properties.

Sesterterpenoids from the sponge Sarcotragus sp

Nineteen new sesterterpenoids and eight known compounds were isolated from the sponge Sarcotragus sp. collected from Soheuksan Island, Korea. The structures of these compounds were determined to be linear sesterterpenoids containing furan or related oxygenated functionalities on the basis of combined chemical and spectroscopic analyses. In addition, the configurations of several previously undetermined compounds were assigned. Several compounds exhibited moderate to major antibacterial activity (compounds 1- 3, 17, 18) and cytotoxicity ( 3, 11, 12) against the K562 cell line and inhibitory activity against isocitrate lyase ( 6, 13).

Glycerolipids from a Sarcotragus species sponge

One known and two new glycerolipids have been isolated from a Sarcotragus sp. marine sponge. The gross structures were established based on NMR and MS analysis.

Ircinin-1 induces cell cycle arrest and apoptosis in SK-MEL-2 human melanoma cells

We investigated the effects of ircinin-1, a lipid compound (a C25 sesterterpene tetronic acid) isolated from marine sponges (Sarcotragus sp.), on the modulation of cell cycle and induction of apoptosis in SK-MEL-2 human skin cancer cells (mutant p53). Ircinin-1 treatment on SK-MEL-2 cells resulted in a dose-dependent inhibition of cell growth and induced apoptotic cell death. Flow cytometric analysis revealed that ircinin-1 resulted in G1 arrest in cell cycle progression which was associated with a marked decrease in the protein expression of D-type cyclins and their activating partners Cdk 4 and 6 with concomitant inductions of p21WAF1/CIP1 and p27KIP1. The induction of p21WAF1/CIP1 appears to be transcriptionally upregulated and is p53-independent. In addition, ircinin-1 suppressed the phosphorylation of pRb protein and increased the co-association of pRb or proliferating cell nuclear antigen (PCNA) with p21WAF1/CIP1 in these cells. Ircinin-1 treatment also resulted in induction of apoptosis as determined by morphological changes, DNA fragmentation, alternated ratio of Bax/Bcl-2, cleavages of poly(ADP-ribose) polymerase and PLC-gamma1, and flow cytometric analysis. Ircinin-1 also induced cytochrome c release, cleavage activations of caspase-3 and -9, and upregulation of Fas and Fas-L. Even though the inhibitor of apoptosis protein (IAP) was expressed in ircinin-1-untreated or -treated SK-MEL-2 cells, only the level of cIAP-1, but not XIAP or cIAP-2, was decreased during ircinin-1-induced apoptosis at Western blot and RT-PCR studies. Taken together, these findings suggest that ircinin-1 has strong potential for development as an agent for prevention against skin cancer.