The reef sponge Erylus formosus (Demospongiae: Geodiidae) from the Bahamas and southern Florida contains a suite of triterpene glycosides that, at a natural volumetric concentration, deters predation by the fish Thalassoma bifasciatum in laboratory assays, and a natural assemblage of reef fishes in field assays. Antifeedant metabolites were isolated by bioassay-guided fractionation of extracts of E. formosus using standard chromatographic methods and identified by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. Included in the deterrent mixture from E. formosus collected in the Bahamas and Florida were at least 6 related triterpene glycosides possessing identical aglycones but with different sugar residues. Two additional compounds with a penasterol triterpene core (formoside, and an N-acetyl galactosamine derivative, formoside B) were found in specimens from the Bahamas but not Florida. Formoside, while being the major deterrent metabolite of E. formosus from the Bahamas, is less potent than the other triterpene glycosides on a weight per volume basis. As a mixture, the triterpene glycosides protect E. formosus from predatory reef fishes, but when these compounds were separated into fractions some failed to deter feeding at natural concentrations. As compounds of this type are beginning to be recognized as prevalent sponge metabolites, we suggest that terpene glycosides may have important ecological functions, just as a defensive role has been ascribed to similar compounds in sea stars, sea cucumbers, and terrestrial plants.
Studies of the Brazilian gorgonian octocoral Heterogorgia uatumani have resulted in the discovery of two metabolites that inhibit fish feeding under natural conditions. These are the previously reported eunicellane diterpenoid, (6E)-2alpha,9alpha-epoxyeunicella-6, 11(12)-dien-3beta-ol (1) and a new sesquiterpene lactone, heterogorgiolide (2). The structures of 1 and 2 were determined by spectroscopic methods and by comparison of spectral data with literature values. Field bioassays of the two compounds, at their natural concentrations, confirmed that they deter predation by a complex assemblage of reef fishes. This is an unusual observation showing that defenses are derived from both sesqui- and diterpenoid metabolites.
A novel concept in polymeric liquid crystalline (LC) materials, via electrostatic grafting or complexation of functionalized mesogens and appropriate polymers, is described. It is applied to three specific systems characterized by side‐chain LC architecture, two of which involve hydrogen‐bonding interactions, the third ionic interactions. In these systems, complexation tends to create greater order in the mesophases present. In the hydrogen‐bonded systems, the transition temperature from the isotropic state tends to decrease compared to that of the functionalized mesogen; in the ionically‐bonded system, the reverse is true. At low concentrations, the mesogens act as plasticizers.
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