Mollecarbamates, Molleureas, and Molledihydroisoquinolone, o-Carboxyphenethylamide Metabolites of the Ascidian Didemnum molle Collected in Madagascar.

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.

Cyclotheonellazoles A-C, Potent Protease Inhibitors from the Marine Sponge Theonella aff. swinhoei.

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.

Bisdioxycalamenene: A Bis-Sesquiterpene from the Soft Coral Rhytisma fulvum fulvum.

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.

Netamines O-S, Five New Tricyclic Guanidine Alkaloids from the Madagascar Sponge Biemna laboutei, and Their Antimalarial Activities.

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 be moderately 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 µM, respectively.

Netamines H-N, tricyclic alkaloids from the marine sponge Biemna laboutei and their antimalarial activity.

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--Fascaplysinopsis sp. metabolites.

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.

Recent N-atom containing compounds from indo-pacific invertebrates.

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.

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.

Salaramides A and B; two alpha-oxoamides isolated from the marine sponge Hippospongia sp. (Porifera, Dictyoceratida).

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.

Plakinamine L: a new steroidal alkaloid from the marine sponge Corticium sp.

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.

Sterols from the Madagascar sponge Fascaplysinopsis sp.

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, Δ(5), Δ(7) and Δ(5,7), 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 Δ(5,7) sterols is known to be unstable and easily photo-oxidized during storage and/or experiments to produce 5α,8α-epidioxy sterols. However, in this study, no 5α,8α-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 ß-caroten bleaching assays.

Isohalitulin and haliclorensins B and C, three marine alkaloids from Haliclona tulearensis.

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.

Tausalarin C: a new bioactive marine sponge-derived nitrogenous bismacrolide.

A novel nitrogenous bismacrolide, designated tausalarin C (1), was isolated from the Madagascar sponge Fascaplysinopsis sp. The structure of the compound was elucidated by interpretation of MS and 1D and 2D NMR spectra. It is suggested that tausalarin C is assembled from salarin A (2) and pretaumycin A. The relative configuration of the chiral centers of salarin A was determined by X-ray diffraction. Tausalarin C was found to inhibit proliferation of K562 leukemia cells. A possible biogenesis is discussed.

Saldedines A and B, dibromo proaporphine alkaloids from a Madagascan tunicate.

Two new dibromo proaporphine alkaloids, designated saldedines A (1) and B (2), were isolated from an unidentified tunicate collected at Salary Bay, Madagascar. Saldedines A and B are the first marine proaporphine alkaloids. Their structures were elucidated by extensive spectroscopic means, and the structure of 1 was confirmed by single-crystal X-ray diffraction analysis. Both saldedines A and B were tested for toxicity to brine shrimp and showed moderate activity.

24-O-ethylmanoalide, a manoalide-related sesterterpene from the marine sponge Luffariella cf. variabilis.

A new manoalide-related sesterterpene, 24-O-ethylmanoalide (3), was isolated from the Indian Ocean sponge Luffariella cf. variabilis, together with the known compounds manoalide (1), seco-manoalide, manoalide monoacetate and 24-O-methylmanoalide (2). The structure of compound 3 was elucidated by interpretation of its spectroscopic data.

Taumycins A and B, two bioactive lipodepsipeptides from the Madagascar sponge Fascaplysinopsis sp.

Two closely related lipodepsipeptides, taumycins A and B (1 and 2) have been isolated from the Madagascar sponge Fascaplysinopsis sp. The two compounds have the same 12-membered oxodepsipeptide ring system in common. Both were toxic to brine shrimp larvae, and taumycin A (1 microM), but not taumycin B, inhibited growth of the human UT-7 leukemic cell line. The structure of the two compounds, likely to be derived from microorganisms, was established by MS and 1D and 2D NMR data.

Marine bifunctional sphingolipids from the sponge Oceanapia ramsayi.

During the course of our continuing studies on marine natural lipid products,two known sphingolipids have been isolated for the first time from a specimen of the marine sponge Oceanapia ramsayi collected at Itampolo on the west coast of Madagascar in the Indian Ocean. The structures were elucidated using NMR data and by comparison with literature data. The occurrence of these sphingolipids within other Oceanapia spp. is discussed.

Flexusines A and B and epimukulol from the soft coral Sarcophyton flexuosum.

Three new cembranes, flexusines A (1) and B (2) and an epimukulol (3), were isolated from the soft coral Sarcophyton flexuosum collected near Reunion Island, Indian Ocean. Their structures were elucidated using 1D and 2D NMR spectral analyses.

Salarins a and B and tulearin a: new cytotoxic sponge-derived macrolides.

Three novel nitrogenous macrolides designated salarin A and B (1 and 2) and tulearin A (3) were isolated from the Madagascar Fascaplysinopsis sp. sponge. The structures of the compounds were elucidated by interpretation of MS and 1D and 2D NMR spectra. Both salarins carry an acetylcarbamate moiety, and in addition, 1 contains a triacylamine group and 2 a methoxymethylketone lactam. Tulearin A carries the naturally rare carbamate ester. The compounds were found to be toxic to brine shrimp larvae, and salarin A and tulearin A were also cytotoxic to leukemia cells.

Ptilomycalin D, a polycyclic guanidine alkaloid from the marine sponge Monanchora dianchora.

A new polycyclic guanidine alkaloid, ptilomycalin D, and the known crambescidic acid were isolated from the marine sponge Monanchora dianchora collected in Nosy-Be, northwest of Madagascar, in the Indian Ocean. The structures were elucidated using 1- and 2-D NMR and MS data, and their biogenetic implications are discussed.