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Acoustic and, to a lesser degree, visual signals are the predominant means of signaling in frogs. Nevertheless, certain lineages such as the mantelline frogs from Madagascar use the chemical communication channel as well. Males possess femoral glands on the hind legs, which recently have been shown to contain volatile compounds used in communication as pheromones. Many mantelline species occur in sympatry, and so far species recognition is regarded to occur mainly by acoustic signals. The analysis of the gland constituents of Mantidactylus femoralis by GC/MS revealed the presence of volatile macrolides and secondary alcohols. The new natural products mantidactolides A (4) and B (6), as well as several methyl carbinols, were identified, and their structures were confirmed by synthesis. The analysis of individuals from different locations of Madagascar revealed the presence of two groups characterized by specific patterns of compounds. While one group contained the alcohols and mantidactolide B, the other showed specific presence of the macrolides phoracantholide I (1) and mantidactolide A (4). Genetic analysis of some individuals showed no congruence between genetic relatedness and gland constituents. Several other individuals from related species had different gland compositions. This suggests that a basic set of biosynthetic machinery might be available to a broader group of related species.

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 β-caroten bleaching assays.

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.

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.