The extract of a sample of the sponge Theonella aff. swinhoei collected in Madagascar exhibited promising in vitro antiplasmodial activity. The antiplasmodial activity was ascribed in part to the known metabolite swinholide A. Further investigation of the extract afforded three unusual cyclic peptides, cyclotheonellazoles A-C (1-3), which contain six nonproteinogenic amino acids out of the eight acid units that compose these natural products. Among these acids the most novel were 4-propenoyl-2-tyrosylthiazole and 3-amino-4-methyl-2-oxohexanoic acid. The structure of the compounds was elucidated by interpretation of the 1D and 2D NMR data, HRESIMS, and advanced Merfay's techniques. The new compounds were found to be nanomolar inhibitors of chymotrypsin and sub-nanomolar inhibitors of elastase, but did not present antiplasmodial activity.

The extract of a sample of the tunicate Didemnum molle (MAY13-117) collected in Mayotte afforded eight new metabolites, mollecarbamates A-D (1-4) and molleureas B-E (5-8), along with the two known natural products, N,N'-diphenylethyl urea (10) and molleurea A (11). Another sample of D. molle (MAD11-BA065) collected in Baie des Assassins, Madagascar, afforded molledihydroisoquinolone (9). Mollecarbamates 1-4 are a family of compounds that possess repeating o-carboxyphenethylamide units and a carbamate moiety, while the molleureas 5-8 contain tetra- and penta-repeating carboxyphenethylamide units and a urea bridge in different positions. Molledihydroisoquinolone (9) is a cyclic form of o-carboxyphenethylamide. We propose that these unique natural products are most probably produced by an unprecedented biosynthetic pathway that contains a yet unknown chorismate mutase variant. The structures of the compounds were elucidated by interpretation of the data from 1D and 2D NMR, HRESIMS, and MS/MS analyses of the positive ESIMS experiments. Compounds 1-8 were tested against pathogenic bacteria and in a cytoprotective HIV cell based assay but did not show any significant effects in these assays.

AbstractNetamines O (I) and Q (III) are found to be moderately cytotoxic, whereas Netamines O, P (IIa) and Q exhibit antiplasmodial activities.

Marine invertebrates produce a large number of unique and structurally diversified natural products which represent a major source of bioactive molecules, particularly for pharmaceuticals leads. This great potential has elicited worldwide scientific and economic interests in searching novel drugs from marine invertebrates. These efforts have resulted in several thousands of novel marine natural products exhibiting a wide range of bioactivities such as anticancer, antiviral, antifungal, and antibacterial properties. To date, the pioneering countries in marine natural products discovery such as USA, Japan, Australia, and Spain are benefiting from the great commercial and social value of such research. Since the early 1990s, the Chemistry Laboratory of Natural Substances and Food Sciences (LCSNSA, University of La Réunion) has been trying to gain a foothold in this field of research. The laboratory which is located at Reunion Island is at a strategic location for the research of natural bioactive molecules. Indeed, with a series of islands scattered in the western Indian Ocean along the southeast coast of Africa (Madagascar, Seychelles, the Comoros, Mayotte, Mauritius, Eparses islands), Reunion Island belongs to a global biodiversity hotspot. This paper will therefore provide an outline of the contribution made by the LCSNSA to marine natural products research in the west of Indian Ocean. Over the last 15 years, our research programs were more precisely concentrated on marine invertebrates from Reunion Island, Mayotte, and Madagascar. Among the numerous marine invertebrates encountered in these areas, sponges, ascidians, and soft corals have predominated in all our collection expeditions and have therefore received special attention from our research group. More than 100 new compounds showing relevant bioactivity were isolated. Among these compounds, a series of guanidine alkaloids, designated netamines A-S were isolated from a Madagascan sponge, Biemna laboutei. Absolute configurations of netamines I and J determined via a joint experimental and theoretical circular dichroism study are also discussed in this paper.

A dichloromethane extract of the soft coral Rhytisma fulvum fulvum collected in Madagascar afforded a novel compound possessing an unprecedented pentacyclic skeleton, bisdioxycalamenene (1), as well as seven known sesquiterpenes. The structures of the compounds were elucidated using 1D and 2D NMR techniques, as well as high-resolution mass spectrometry. The absolute configuration of 1 was determined using X-ray diffraction analysis and anomalous dispersion effects. The structure elucidation and a possible biogenesis of the compound are discussed.

In our continuing program to isolate new compounds from the Madagascar sponge Biemna laboutei, five new tricyclic guanidine alkaloids, netamines O - S (1-5, resp.), have been identified together with the known compounds netamine E (6) and mirabilin J (7). The structures of all new netamines were assigned on the basis of spectroscopic analyses. Their relative configurations were established by analysis of ROESY data and comparison with literature data. Netamines O, P, and Q, which were isolated in sufficient quantities, were tested for their cytotoxic activities against KB cells and their activities against the malaria parasite Plasmodium falciparum. Netamines O and Q were found to bemoderately cytotoxic. Netamines O, P, and Q exhibited antiplasmodial activities with IC50 values of 16.99 +/- 4.12, 32.62 +/- 3.44, and 8.37 +/- 1.35 mu m, respectively.

Chemical examination of the CH2Cl2-MeOH (1:1) extract of the Madagascar sponge Biemna laboutei resulted in the isolation of seven new tricyclic alkaloids, netamines H-N (1-7), along with the known netamine G and mirabilins A, C, and F. Their structures were elucidated by interpretation of 1D and 2D NMR spectra and HRESIMS data. All compounds were evaluated for their cytotoxicity against KB cells and their antiplasmodial activity. Netamine M (6) was found to be cytotoxic, with an IC50 value in the micromolar range, and netamine K (4) exhibited activity against Plasmodium falciparum with an IC50 value of 2.4 μM.

Derivatives of salarin A, salarin C and tulearin A, three new cytotoxic sponge derived nitrogenous macrolides, were prepared and bio-evaluated as inhibitors of K562 leukemia cells. Interesting preliminary SAR (structure activity relationship) information was obtained from the products. The most sensitive functionalities were the 16,17-vinyl epoxide in both salarins, the triacylamino group in salarin A and the oxazole in salarin C (less sensitive). Regioselectivity of reactions was also found for tulearin A.

Marine sponges of the genus Theonella have been shown to be a rich source of unique bioactive secondary metabolites with diverse structures, such as; macrolides, alkaloids, sterols and peptides. In the course of our ongoing research to discover potential biomedicines from marine invertebrates, we examined a sample of Thonella sp. collected in Madagascar. The crude extract was separated on a Sephadex LH-20 column and the semi-pure compounds were separated on reversed phase HPLC column to afford three novel cyclic peptides, cyclotheonazoles A-C, which contain the unique; 4-propenoyl-2-tyrosylthiazole amino acid (PTT), 3-amino-2-keto-4-methyl hexanoic acid (AKMH) and diaminoproiponic acid (Dpr), moieties. These metabolites are related in structure to oriamide that was isolated a decade ago from a Theonella sp. collected in Sodwana Bay, South Africa. The structure elucidation, by 2D-NMR, HRMS and advances Marfey techniques, and the biological activity of the compounds will be presented.

Nitrogenous compounds isolated from the Madagascan sponge Fascaplysinopsis sp, namely, four groups of secondary metabolites, salarins, tulearins, taumycins and tausalarin are represented. As well as several salarin C derivatives synthesized for SAR. e.g. glycosidation of a desoctanoyl derivative.

Seven new nitrogenous macrolides, designated salarins D–J (4–10), closely related to salarins A–C (1–3), have been isolated from the Madagascar Fascaplysinopsis sp. sponge. The structure and relative stereochemistry of compounds 4–10 were elucidated by interpretation of MS, COSY, HSQC, HMBC, and NOESY spectra. Salarin B's structure (2), based on the structure of salarin J (10), is now amended to also incorporate the C-14 to -17 THF ring system. All compounds were evaluated for their cytotoxicity against K562 and UT-7 human leukemia cells. While salarins D, E, H, and J displayed dose and time dependent inhibition of proliferation, salarins F and I were not active in these assays.

A new steroidal alkaloid, plakinamine L (1) with an unprecedented acyclic side chain, was isolated from the marine sponge Corticium sp. collected near Salary (south-west of Madagascar). The structure was elucidated by combined spectroscopic methods.

Three new alkaloids, designated isohalitulin (4), haliclorensin B (5), and haliclorensin C (6), were isolated from two specimens of the Madagascan sponge Haliclona tulearensis, collected at two locations in Salary Bay, north of Tulear. Their structures were elucidated by extensive spectroscopic means. Alkaloids 4-6 exhibited mild toxicity in the brine shrimp test.

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.

Two novel alpha-oxoamides, salaramide A (1) and its homologue salaramide B (2), were isolated from the Madagascar marine sponge, Hippospongia sp., collected in Salary Bay, north of Tulear. The structures of 1 and 2 were elucidated by interpretation of mass spectra, 1D and 2D NMR spectra, and confirmed by chemical transformation.

The sponge Fascaplysinopsis sp. (order Dictyoceratida, Family Thorectidae) from the west coast of Madagascar (Indian Ocean) is a particularly rich source of bioactive nitrogenous macrolides. The previous studies on this organism led to the suggestion that the latter should originate from associated microsymbionts. In order to evaluate the influence of microsymbionts on lipid content, 10 samples of Fascaplysinopsis sp. were investigated for their sterol composition. Contrary to the secondary metabolites, the sterol patterns established were qualitatively and quantitatively stable: 14 sterols with different unsaturated nuclei, D5, D7 and D5,7, were identified; the last ones being the main sterols of the investigated sponges. The chemotaxonomic significance of these results for the order Dictyoceratida is also discussed in the context of the literature. The conjugated diene system in D5,7 sterols is known to be unstable and easily photo-oxidized during storage and/or experiments to produce 5a,8a-epidioxy sterols. However, in this study, no 5a,8a-epidioxysterols (or only trace amounts) were observed. Thus, it was supposed that photo-oxidation was avoided thanks to the natural antioxidants detected in Fascaplysinopsis sp. by both the DPPH and b-caroten bleaching assays.

L’eponge Fascaplysinopsis sp. de la famille des Thorectidae (ordre Dictyoceratida) est une espece commune de la zone Sud-Ouest de Madagascar (Salary). La determination de sa composition chimique a ete envisagee avec un double objectif : 1.La recherche de molecules bioactives pour la decouverte de nouveaux candidats medicaments. 2.La recherche de marqueurs chimiotaxonomiques pour une meilleure connaissance de la biodiversite insulaire. La recherche de molecules bioactives a conduit a l’isolement et a l’identification de 16 macrolides azotes de structures nouvelles presentant une cytotoxicite in vitro envers les lignees cellulaires leucemiques UT-7 et K562. Le squelette caracteristique de ces macrolides nous laisse supposer qu’il s’agirait en realite de metabolites biosynthetises par des micro-organismes symbiontes et non par l’eponge elle-meme. La recherche de marqueurs chimiotaxonomique a ete menee a partir de la composition sterolique. Il a ete demontre que cette derniere restait qualitativement et quantitativement stable quelque soit le lieu de collecte ; critere fondamental pour l’utilisation de ces constituants membranaires en tant que marqueurs chimiotaxonomiques. 14 sterols de noyaux insatures en Delta 5, Delta 7 et Delta 5,7 ont ete identifies. La presence majoritaire des sterols diinsatures Delta 5,7 (60,8%) semble confirmer l’appartenance de Fascaplysinopsis a l’ordre des Dictyoceratida. En outre, la detection de sterols Delta 5,7 en general difficilement deceles chez les invertebres marins en raison de leur grande instabilite et de leur photo-sensibilite, nous a suggere que Fascaplysinopsis sp. devait biosynthetiser des molecules anti-oxydantes capables de preserver les sterols Delta 5,7 et donc d’eviter leur oxydation en 5alpha,8alpha-epidioxysterols. Des tests anti-radicalaire et anti-oxydant appliques aux extraits bruts de l’eponge ont permis de confirmer cette hypothese.

A large variety of unique N-atom containing compounds (alkaloids) without terrestrial counterparts, have been isolated from marine invertebrates, mainly sponges and ascidians. Many of these compounds display interesting biological activities. In this report we present studies on nitrogenous compounds, isolated by our group during the last few years, from Indo-Pacific sponges, one ascidian and one gorgonian. The major part of the review deals with metabolites from the Madagascar sponge Fascaplysinopsis sp., namely, four groups of secondary metabolites, the salarins, tulearins, taumycins and tausalarins.