O mecanismo de defesa contra predadores no octocoral brasileiro Lophogorgia violacea foi investigado através de ensaios de preferência alimentar em campo frente a predadores. Os ensaios de palatabilidade com o extrato bruto da gorgônia demonstraram que seus metabólitos secundários possuem atividade deterrente significativa frente a peixes generalistas. O fracionamento do extrato bruto, guiado pelos ensaios em campo, revelou que uma mistura complexa de furanocembranolídeos é a responsável pela defesa química de L. violacea. O diterpeno lophotoxina (1) foi a principal substância isolada, seguida por outras duas similares, deoxilophotoxina (2) e 13-acetoxi-11β,12β-epoxipukalídeo (3), além de dois furanocembranolídeos inéditos na literatura, 7-acetoxi-8-hidroxilophotoxina (4) e 3-metoxi-8-hidroxilophotoxina (5). A lophotoxina (1), uma importante neurotoxina, originalmente isolada de L. rigida do Pacífico, demonstrou ser a mais potente dentre as substâncias fagoinibidoras presentes no extrato bruto. Por outro lado, os outros quatro furanocembranolídeos isolados também parecem contribuir, de maneira aditiva, para a atividade total observada. Estes resultados corroboram estudos prévios, confirmando que furanocembranolídeos são uma classe de substâncias de defesa frente ao consumo por peixes em ambientes tropicais e temperados.The chemical defenses of the Brazilian gorgonian octocoral Lophogorgia violacea Pallas have been investigated using feeding preference experiments performed in situ with an ecologically relevant, natural assemblage of predatory fishes. Feeding experiments incorporating the crude extract of the animal into palatable foods showed that the organic constituents of L. violacea provide a powerful chemical deterrence toward consumption by generalist fish carnivores. Bioassayguided fractionation of the extract and evaluation of the fractions and purified compounds obtained in the same in situ assay revealed that a complex mixture of furanocembranolides was responsible for the overall feeding deterrence observed. The most potent feeding deterrent identified was lophotoxin (1), followed by two previously reported and structurally related compounds, deoxylophotoxin (2), and 13-acetoxy-11β,12β-epoxypukalide (3), as well as two new furanocembranolides: 7-acetoxy-8-hydroxylophotoxin (4) and 3-methoxy-8-hydroxylophotoxin (5). Lophotoxin (1), a neurotoxin originally isolated from the Pacific gorgonian L. rigida, was the most potent feeding deterrent among the furanocembranolides isolated. However, the four other related furanocembranolides (2-5) appear to contribute, in an additive manner, to the overall deterrent effects observed. These results add to earlier studies providing further evidence that compounds of this structural class provide effective chemical defenses against fish predators in both temperate and tropical environments.
Visando a caracterização de substâncias de defesa contra predadores, a reinvestigação dos produtos naturais do octocoral Phyllogorgia dilatata Esper (Gorgonacea, Gorgoniidae) revelou a presença de novos metabólitos para esta espécie. Neste trabalho descreve-se o isolamento e a elucidação estrutural de três substâncias: o carotenóide peridinina (1), pigmento característico de dinoflagelados, caracterizando a presença de simbiontes nos tecidos dessa gorgônia; o diterpeno fagorrepelente 11β,12β-epoxipukalídeo (2), previamente descrito para uma outra espécie de octocoral; e um novo sesquiterpeno natural, (E) germacra-1(10),4(15),7(11)-trien-5-ol-8-ona (3).A bioassay-guided re-investigation of natural products from the Brazilian endemic octocoral Phyllogorgia dilatata Esper (Gorgonacea, Gorgoniidae), collected in Rio de Janeiro State, has revealed three further compounds from this species: the dinoflagellate pigment peridinin (1), the icthyodeterrent diterpene 11β,12β-epoxypukalide (2), both previously reported from other octocoral species, and the new natural sesquiterpene (E) germacra-1(10),4(15),7(11)-trien-5-ol-8-one (3). Spectroscopic analysis and comparison with literature data allowed the structure elucidation of 1-3.
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