Secondary Metabolites from Echinoderms as Chemotaxonomic Markers

Free Sterol Composition of Deep-Sea Holothurian Orphnurgus cf. glaber

The free sterol fraction from the deep-sea holothurian Orphnurgus cf glaber Walsh, 1891, has been isolated and studied by GC–MS. Sterols containing Δ7, Δ0, Δ5, polyunsaturated and 5,8-epidioxy modified cores were found. A high percentage of compounds with polyunsaturated cores distinguish this composition from those of previously studied holothurians. Almost all identified compounds had saturated side chains, which is also a specific feature of this fraction. Peculiarities of biosynthesis and metabolism of the found sterols are discussed.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

A new sulfated triterpene glycoside from the sea cucumber Colochirus quadrangularis, and evaluation of its antifungal, antitumor and immunomodulatory activities

Our continuing search for marine bioactive secondary metabolites led to the screening of crude extracts of sea cucumbers by the model of Pyricularia oryzae. A new sulfated triterpene glycoside, coloquadranoside A (1), together with four known triterpene glycosides, philinopside A, B, E and pentactaside B (2-5) were isolated from the sea cucumber Colochirus quadrangularis, and their structures were elucidated using extensive spectroscope analysis (ESI-MS, 1D and 2D NMR) and chemical methods. Coloquadranoside A possesses a 16-acetyloxy group in the holostane-type triterpene aglycone with a 7(8)-double bond, a double bond (25,26) at its side chain, and two β-d-xylose in the carbohydrate chain. Coloquadranoside A exhibits in vitro some antifungus, considerable cytotoxicity (IC₅₀ of 0.46-2.03 μM) against eight human tumor cell lines, in vivo antitumor, and immunomodulatory activity.

Asterosaponins: Structures, Taxonomic Distribution, Biogenesis and Biological Activities

Asterosaponins are a class of steroid oligoglycosides isolated from starfish with characteristic structures and diverse biological activities. In this review, we have attempted to combine the most important data concerning asterosaponins and give a list of these secondary metabolites with their structural peculiarities. The purpose of this review is to provide a brief but as complete as possible principal information about their chemical structures, taxonomic distribution in the marine environment, distribution in different geographical areas and depths, some properties, biological activities, and functions. Some other rare steroid metabolites from starfish, closely related in structures and probably biogenesis to asterosaponins, are also discussed.

Triterpenoids in Echinoderms: Fundamental Differences in Diversity and Biosynthetic Pathways

Echinoderms form a remarkable phylum of marine invertebrates that present specific chemical signatures unique in the animal kingdom. It is particularly the case for essential triterpenoids that evolved separately in each of the five echinoderm classes. Indeed, while most animals have Δ5-sterols, sea cucumbers (Holothuroidea) and sea stars (Asteroidea) also possess Δ7 and Δ9(11)-sterols, a characteristic not shared with brittle stars (Ophiuroidea), sea urchins (Echinoidea), and crinoids (Crinoidea). These particular Δ7 and Δ9(11) sterols emerged as a self-protection against membranolytic saponins that only sea cucumbers and sea stars produce as a defense mechanism. The diversity of saponins is large; several hundred molecules have been described in the two classes of these saponins (i.e., triterpenoid or steroid saponins). This review aims to highlight the diversity of triterpenoids in echinoderms by focusing on sterols and triterpenoid glycosides, but more importantly to provide an updated view of the biosynthesis of these molecules in echinoderms.

A Holothurian Triterpene Glycoside Holothurin A2 (= Echinoside A) Isolated From the Starfish Choriaster granulatus

A triterpene glycoside identified as holothurin A2 (= echinoside A) was isolated from the extract of the tropical starfish Choriaster granulatus and identified by extensive nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization (ESI) mass spectrometry techniques. The fact of obtaining this typical for tropical sea cucumbers metabolite in starfish may be explained by feeding of C. granulatus on sea cucumbers of the family Holothuriidae that allows to use triterpene glycosides as food source markers in predators of sea cucumbers.

Approaches for the isolation and identification of hydrophilic, light-sensitive, volatile and minor natural products

Water-soluble, volatile, minor and photosensitive natural products are yet poorly known, and this review discusses the literature reporting the isolation strategies for some of these metabolites.

The Roles of Spinochromes in Four Shallow Water Tropical Sea Urchins and Their Potential as Bioactive Pharmacological Agents

Spinochromes are principally known to be involved in sea urchin pigmentation as well as for their potentially interesting pharmacological properties. To assess their biological role in sea urchin physiology, experiments are undertaken on crude extracts from four species and on four isolated spinochromes in order to test their antibacterial, antioxidant, inflammatory and cytotoxic activities. First, the antibacterial assays show that the use of crude extracts as representatives of antibacterial effects of spinochromes are inaccurate. The assays on purified spinochromes showed a decrease in the growth of four strains with an intensity depending on the spinochromes/bacteria system, revealing the participation of spinochromes in the defense system against microorganisms. Secondly, in the 2,2-diphenyl-1-picrylhydrazyl antioxidant assays, spinochromes show an enhanced activity compared to the positive control. This latter observation suggests their involvement in ultraviolet radiation protection. Third, spinochromes present a pro-inflammatory effect on lipopolysaccharide-stimulated macrophages, highlighting their possible implication in the sea urchin immune system. Finally, cytotoxicity assays based on Trypan blue exclusion, performed in view of their possible future applications as drugs, show a weak cytotoxicity of these compounds against human cells. In conclusion, all results confirm the implication of spinochromes in sea urchin defense mechanisms against their external environment and reveal their potential for pharmacological and agronomical industries.

Structure elucidation of five novel isomeric saponins from the viscera of the sea cucumber Holothuria lessoni

Sea cucumbers are prolific producers of a wide range of bioactive compounds. This study aimed to purify and characterize one class of compound, the saponins, from the viscera of the Australian sea cucumber Holothuria lessoni. The saponins were obtained by ethanolic extraction of the viscera and enriched by a liquid-liquid partition process and adsorption column chromatography. A high performance centrifugal partition chromatography (HPCPC) was applied to the saponin-enriched mixture to obtain saponins with high purity. The resultant purified saponins were profiled using MALDI-MS/MS and ESI-MS/MS which revealed the structure of isomeric saponins to contain multiple aglycones and/or sugar residues. We have elucidated the structure of five novel saponins, Holothurins D/E and Holothurinosides X/Y/Z, along with seven reported triterpene glycosides, including sulfated and non-sulfated saponins containing a range of aglycones and sugar moieties, from the viscera of H. lessoni. The abundance of novel compounds from this species holds promise for biotechnological applications.

When a repellent becomes an attractant: harmful saponins are kairomones attracting the symbiotic Harlequin crab

Marine organisms have developed a high diversity of chemical defences in order to avoid predators and parasites. In sea cucumbers, saponins function as repellents and many species produce these cytotoxic secondary metabolites. Nonetheless, they are colonized by numerous symbiotic organisms amongst which the Harlequin crab, Lissocarcinus orbicularis, is one of the most familiar in the Indo-Pacific Ocean. We here identify for the first time the nature of the molecules secreted by sea cucumbers and attracting the symbionts: saponins are the kairomones recognized by the crabs and insuring the symbiosis. The success of this symbiosis would be due to the ability that crabs showed during evolution to bypass the sea cucumber chemical defences, their repellents becoming powerful attractants. This study therefore highlights the complexity of chemical communication in the marine environment.

Discovery of novel saponins from the viscera of the sea cucumber Holothuria lessoni

Sea cucumbers, sometimes referred to as marine ginseng, produce numerous compounds with diverse functions and are potential sources of active ingredients for agricultural, nutraceutical, pharmaceutical and cosmeceutical products. We examined the viscera of an Australian sea cucumber Holothuria lessoni Massin et al. 2009, for novel bioactive compounds, with an emphasis on the triterpene glycosides, saponins. The viscera were extracted with 70% ethanol, and this extract was purified by a liquid-liquid partition process and column chromatography, followed by isobutanol extraction. The isobutanol saponin-enriched mixture was further purified by high performance centrifugal partition chromatography (HPCPC) with high purity and recovery. The resultant purified polar samples were analyzed using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS)/MS and electrospray ionization mass spectrometry (ESI-MS)/MS to identify saponins and characterize their molecular structures. As a result, at least 39 new saponins were identified in the viscera of H. lessoni with a high structural diversity, and another 36 reported triterpene glycosides, containing different aglycones and sugar moieties. Viscera samples have provided a higher diversity and yield of compounds than observed from the body wall. The high structural diversity and novelty of saponins from H. lessoni with potential functional activities presents a great opportunity to exploit their applications for industrial, agricultural and pharmaceutical use.

Triterpene Saponins from the Sea Cucumber Stichopus chloronotus

Sea cucumbers have been used as a dietary delicacy and important ingredient in Asian traditional medicine and functional foods over many centuries. Using combined chromatographic methods, six triterpene saponins (1-6), including a new compound, stichloroside F (1), were isolated from a methanol extract of the sea cucumber Stichopus chloronotus Brandt. Their structures were determined on the basis of spectroscopic (1H and 13C NMR, HSQC, HMBC, 1H-1H COSY, ROESY) and FTICR-MS data and by comparison with literature values.

Variegatusides: new non-sulphated triterpene glycosides from the sea cucumber Stichopus variegates semper

Four new triterpene glycosides, variegatusides C–F (1–4), together with three structurally known triterpene glycosides, variegatusides A and B (5, 6), and holothurin B (7), were isolated from the sea cucumber Stichopus variegates Semper (Holothuriidae), collected from the South China Sea. Their structures were elucidated on the basis of extensive spectral analysis (nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESIMS)) and chemical evidence. Variegatusides C–F exhibit the same structural feature consisting of the presence of a 23-hydroxyl group at the holostane-type triterpene aglycone side chain. Variegatuside C (1) has a double bond (24, 25) in this same chain, while variegatuside D (2) exhibits a 8(9)-ene bond in the holostane-type triterpene aglycone, which has not been extracted from other sea cucumber species. Compound 4 is a native compound from the sea cucumber S. variegates Semper, which has been reported to be desacetylstichloroside B₁. Except for holothurin B, these glycosides have no sulfate group in their sugar chain and show potent antifungal activities in vitro biotests.

Structure elucidation, protein profile and the antitumor effect of the biological active substance extracted from sea cucumber Holothuria polii

Holothuria polii (Delle Chiaje, 1823) (Holothuriidae) is a sea cucumber inhabiting Mediterranean Sea coast of Egypt. The bioactive compound of its tegument has antifungal, antibacterial and antiparasitic effects. The present study aims to elucidate the structure of the bioactive material of H. polii for pharmacological and chemotaxonomic purposes. Furthermore, the study demonstrates its efficacy as a cytotoxic agents against two tumor cell lines HCT116 (colon adenocarcinoma cell line) and MCF7 (breast adenocarcinoma cell line). The biological active compound of the ethanol extract has been characterized by means of infrared (IR), proton-nuclear magnetic resonance ((1)H NMR), ultraviolet-visible (UV-Vis) and mass spectra. Protein profile was carried out using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Cytotoxic activity was carried out according to sulforhodamine-B assay. IR, (1)H NMR, UV-Vis and mass spectra showed that the extracted bioactive material is a nonsulfated hexaosides called bivittoside. This glycoside is composed of aglycone and a glycosidic chain (carbohydrate chain) enclosed with six sugar units, including xylose, glucose, 3-O-methylglucose and quinovose. There were no traces of dissolved proteins. The preliminary cytotoxic assay of bivittoside exhibited significant cytotoxic activity against two types of cultured tumor cell lines of HCT116 and MCF7. The half-maximal inhibitory concentration was 17.4 µg/ml and 18 µg/ml for MCF7 and HCT116, respectively. Although H. polii belongs to the genus Holothuria, the lacking of sulfate group and the fact that it contains up to six monosaccharides make it different from this genus. The present study suggests separation of H. polii from its genus to a new one. On the other hand, results support the hypothesis that H. polii bioactive compound has an antitumor effect.

Bioactivity as an options value of sea cucumbers in the Egyptian Red Sea

The utility of a species can be divided into its direct, indirect, and options values. In the marine environment, direct consumptive values predominate and often lead to overexploitation at the expense of significant options values derived through bioprospecting for natural products. We surveyed the waters of the Egyptian Red Sea coast (Gulf of Aqaba [north] and the Red Sea [south]) for species of sea cucumbers and analyzed extracts from species for a range of bioactivities with potential biomedical applications. All habitat types were surveyed within these regions. We found 22 species of sea cucumber of which two, Holothuria fuscogilva and Holothuria flavomaculata, were recorded in Egypt for the first time. Although none of the species identified were unique to the Gulf of Aqaba, 10 species were only found in the Red Sea sector. Bioassay results showed that although no species had antibacterial activity, most extracts exhibited activity against Candida and Leishmania but were most active against a LoVo mammalian carcinoma cell line. Our most significant finding was the intraspecific variation in bioactivity in individuals collected from different habitat types and sectors of the coast. This variation may reflect the effect of environment on secondary metabolite production or may indicate significant genetic diversity between populations within a species. Our results indicate a potentially significant options value to sea cucumbers through bioprospecting. Given the importance of economic development in countries such as Egypt and the perceived low conservation value of invertebrates such as sea cucumbers, the linking of these factors to conservation is vital for the maintenance and sustainable exploitation of these animals.

Qualitative and quantitative saponin contents in five sea cucumbers from the Indian ocean

To avoid predation, holothuroids produce feeding-deterrent molecules in their body wall and viscera, the so-called saponins. Five tropical sea cucumber species of the family Holothuriidae were investigated in order to study their saponin content in two different organs, the body wall and the Cuvierian tubules. Mass spectrometry techniques (MALDI- and ESI-MS) were used to detect and analyze saponins. The smallest number of saponins was observed in Holothuria atra, which contained a total of four congeners, followed by Holothuria leucospilota, Pearsonothuria graeffei and Actinopyga echinites with six, eight and ten congeners, respectively. Bohadschia subrubra revealed the highest saponin diversity (19 congeners). Saponin mixtures also varied between the two body compartments within a given animal. A semi-quantitative approach completed these results and showed that a high diversity of saponins is not particularly correlated to a high saponin concentration. Although the complexity of the saponin mixtures described makes the elucidation of their respective biological roles difficult, the comparisons between species and between body compartments give some clues about how these molecules may act as predator repellents.

Two new holostan-type triterpene glycosides from the sea cucumber Bohadschia marmorata JAEGER

Two new holostan-type triterpene glycosides, 17-hydroxy fuscocineroside B (1) and 25-hydroxy fuscocineroside B (2), together with a known triterpene glycoside, fuscocineroside B (3) were isolated from the sea cucumber Bohadschia marmorata JAEGER. The structures of the new triterpene glycosides were elucidated on the basis of spectroscopic analyses and chemical reactions. Compounds 1 and 3 showed considerable antifungal activities against six strains.

Hillasides A and B, two new cytotoxic triterpene glycosides from the sea cucumber Holothuria hilla Lesson

Two new triterpene glycosides, hillasides A (1) and B (2), were isolated from the sea cucumber H. hilla Lesson, together with one known glycoside holothuria B (3). Their structures were deduced by extensive spectral analysis and chemical evidences. The presence of conjugated double bonds [22E,24-diene] in the aglycone of 1 is a rare structural feature among sea cucumber glycosides. The two glycosides showed significant cytotoxicity against eight human tumour cell lines (A-549, MCF-7, IA9, CAKI-1, PC-3, KB, KB-VIN and HCT-8) with IC(50) in the range of 0.1-3.8 microg/ml.

Structural determination of kochiosides A-C, new steroidal glucosides from Kochia prostrata, by 1D and 2D NMR spectroscopy

Kochiosides A-C, three new steroidal glucosides, have been isolated from the ethyl acetate fraction of Kochia prostrata and their structures assigned from its (1)H and (13)C NMR spectra, DEPT and by 2D COSY, NOESY, HMQC and HMBC experiments.

Cytotoxic triterpene glycosides from the sea cucumber Pseudocolochirus violaceus

A new triterpene glycoside (1) along with the known intercedenside B (2) was isolated from the sea cucumber Pseudocolochirus violaceus. Glycoside 1 was elucidated as 3-O-{6-O-sodiumsulfate-3-O-methyl-beta-D-glucopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)-[beta-D-xylopyranosyl(1-->2)]-beta-D-quinovopyranosyl-(1-->2)-4-O-sodiumsulfate-beta-D-xylopyranosyl}-16beta-acetoxy-holosta-7, 24-diene-3beta-ol on the basis of extensive spectral studies and chemical evidence. Both the glycosides exhibited significant cytotoxicity against cancer cell lines MKN-45 and HCT-116.

Bioactive triterpene glycosides from the sea cucumber Holothuria fuscocinerea

Bioassay-guided fractionation of the active n-BuOH extract of the sea cucumber Holothuria fuscocinerea resulted in the isolation of three new triterpene glycosides, fuscocinerosides A (1), B (2), and C (3), along with two known glycosides, pervicoside C (4) and holothurin A (5), as active compounds causing morphological abnormality of Pyricularia oryzae mycelia. Compounds 1-5 possess the same tetrasaccharide moiety, 3-O-methyl-beta-D-glucopyranosyl-(1-->3)-beta-D- glucopyranosyl-(1-->4)-beta-D-quinovopyranosyl-(1-->2)-4-O-sodiumsulfato-beta-D-xylopyranosyl, linked to C-3 of holostane triterpene aglycones that differ in their side chains and 17-substituents. Their structures were elucidated by extensive spectral studies as well as chemical evidence. All the glycosides showed in vitro cytotoxicity against two human tumor cell lines.

Two New Sarasinosides from the Sponge Melophlus Sarasinorum

Two new 30-norlanostane-type oligoglycosides (6, 7) along with five known sarasinosides A1 (1), A2 (2), A3 (3), M (4), L (5) were isolated from the ethanol extract of the Australian sponge Melophlus sarasinorum. The skeleton of new sarasinoside A4 (6) possesses a rare 8α,9α-oxido-8,9-seco-moiety. Sarasinoside A5 (7) proved to be a 9-deoxy-congener of the previously described sarasinoside L (5). Compounds 1–7 have identical pentasaccharide chains and differ in the aglycone portions. The structures have been elucidated on the basis of NMR, MALDI-TOF MS and GC analyses.

Intercedensides D-I, cytotoxic triterpene glycosides from the sea cucumber Mensamaria intercedens Lampert

Six new triterpene glycosides, intercedensides D-I (1-6), were isolated from the whole bodies of the sea cucumber Mensamria intercedens Lampert, which is found in the South China Sea. Their structures were elucidated by extensive spectroscopic analysis (NMR and ESIMS) and chemical methods. lntercedensides D (1), E (2), G (4), and H (5) have a conjugated double bond system (22Z,24-diene) in the aglycon side chain, while intercedensides F (3) and I (6) have only a single double bond (24, 25) in this same chain. lntercedensides D-H (1-5) showed significant cytotoxicity (ED(50) 0.96-5.0 mug/mL) against 10 human tumor cell lines.

Intercedensides A-C, three new cytotoxic triterpene glycosides from the sea cucumber Mensamaria intercedens Lampert

Three new triterpene glycosides, intercedensides A (1), B (2), and C (3), were isolated from the sea cucumber Mensamria intercedens Lampert, which is found in the South China Sea, and their structures have been elucidated by spectroscopic analysis (NMR and ESIMS) and chemical transformations. Intercedensides A (1) and C (3) have a conjugated double bond (22E,24-diene) in the side chain of the aglycon. Intercedenside B (2) has two beta-D-xylose and two sulfate groups in the carbohydrate chain. All three glycosides showed significant cytotoxicity against 10 human tumor cell lines with ED(50) in the range 0.6-4.0 microg/mL. Intercedenside A (1) exhibited significant in vivo antineoplastic activity against mouse Lewis lung cancer and mouse S180 sarcoma. On the basis of these initially promising results, intercedensides A-C merit further study as potential anticancer agents.

Bioactive asterosaponins from the starfish Luidia quinaria and Psilaster cassiope. Isolation and structure characterization by two-dimensional NMR spectroscopy

An investigation of the polar extracts from two starfish, Luidia quinaria and Psilaster cassiope, led to the isolation of five sulfated "asterosaponins". Two of them, named luidiaquinoside (1) and psilasteroside (2), are new compounds. Luidiaquinoside (1) contains a novel pentasaccharide chain composed of d-glucose, d-quinovose, and d-fucose, with the d-glucose unit being the branching point. Psilasteroside (2) contains a hexasaccharide chain in which an arabinose residue is detectable in the furanose form. Both of these compounds possess a Delta(9(11)),3beta,6alpha-dihydroxysteroidal nucleus with a 20-hydroxy, 23-oxo functionality. The structures of the new asterosaponins were elucidated by a combination of NMR techniques including (1)H-(1)H (COSY, TOCSY, and ROESY) and (1)H-(13)C (HMQC and HMBC) spectroscopy, ESIMS and HRFABMS spectrometry, and GC analyses. The new asterosaponins show marginal in vitro cytotoxicity against RBL-2H3 (rat basophilic leukemia) cell lines.

Cytotoxic and antifungal triterpene glycosides from the Patagonian sea cucumber Hemoiedema spectabilis

Two new sulfated triterpene glycosides, hemoiedemosides A (1) and B (2), have been isolated from the Patagonian sea cucumber Hemoiedema spectabilis. Their structures have been established by a combination of spectroscopic analysis (NMR and FABMS) and chemical transformations. Both glycosides present the same aglycon and differ in the degree of sulfation of the tetrasaccharide chain. Hemoiedemoside B (2) is a new example of a small number of trisulfated triterpene glycosides from sea cucumbers belonging to the family Cucumariidae. Glycosides 1 and 2 exhibit considerable antifungal activity against the phytopathogenic fungus Cladosporium cucumerinum, while the semisynthetic desulfated derivative 1a is less active.

Two new cytotoxic and virucidal trisulfated triterpene glycosides from the Antarctic sea cucumber Staurocucumis liouvillei

Two new trisulfated triterpene glycosides, liouvillosides A (1) and B (2), have been isolated from the Antarctic sea cucumber Staurocucumis liouvillei. Their structures have been elucidated by spectroscopic analysis (NMR and FABMS) and chemical transformations. Liouvillosides A (1) and B (2) are two new examples of a small number of trisulfated triterpene glycosides from sea cucumbers belonging to the family Cucumariidae. Both glycosides were found to be virucidal against herpes simplex virus type 1 (HSV-1) at concentrations below 10 microg/mL.

Koreoside A, a new nonholostane triterpene glycoside from the sea cucumber Cucumaria koraiensis

The new triterpene glycoside koreoside A (1) has been isolated from the sea cucumber Cucumaria koraiensis. Koreoside A (1) is the first glycoside reported from holothurians that presents a delta(7) nonholostane aglycon without a lactone group and with a shortened side chain. Its structure has been elucidated by 13C and 1H NMR as well as FABMS studies.

Steroid and triterpenoid oligoglycosides of marine origin

Saponins have been considered for a long time typical metabolites of plant origin. It has been only in the last two decades that the world-wide investigation of marine organisms as sources of new bioactive metabolites disclosed the wide distribution of these molecules also among marine animals. Today saponins are recognized as the most common characteristic metabolites in two classes of the phylum Echinodermata (Holothuroidea and Asteroidea). Furthermore, several steroid and triterpenoid oligoglycosides have been isolated from different species of marine sponges, more rarely Anthozoans, and also from fishes of the genus Pardachirus, where they have been shown to act as shark repellents. This communication offers a general view of the distribution of steroid and triterpenoid oligoglycosides among marine organisms and focuses on a number of recent examples to discuss structural characteristics, biological activities, and methods of investigation.