Chemical defenses of the endemic Brazilian gorgonian Lophogorgia violacea Pallas (Octocorallia, Gorgonacea)

Abstract

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.

Chemical mediation of interactions among marine organisms

“…265 A similar study of the endemic Brazilian gorgonian Lophogorgia violacea using field feeding assays for bioassay-guided fractionation yielded a mixture of 5 furanocembranoid diterpenes that appear to deter fish predation in an additive manner. 267 Crude extracts from common species of gorgonians collected in the Caribbean, 281 " 282 Singapore, 283 and the Pacific, 270 ' 284 have been surveyed for predator deterrent activity in laboratory assays against a generalist predator or in field assays against natural assemblages of reef fishes. The earliest survey demonstrated that approximately 60% of the extracts tested deterred feeding by Thalassoma bifasciatum at natural concentrations determined as the percentage of dry mass.…”

Chemical Mediation of Interactions Among Marine Organisms

“…265 A similar study of the endemic Brazilian gorgonian Lophogorgia violacea using field feeding assays for bioassay-guided fractionation yielded a mixture of 5 furanocembranoid diterpenes that appear to deter fish predation in an additive manner. 267 This mixture included two new furanocembranoids, 7-acetoxy-hydroxylophotoxin 76 and 3-methoxy-8-hydroxylophotoxin 77 and the known compounds, lophotoxin 78, deoxylophotoxin 79 and 13-acetoxy-11P, 12P-epoxypukalide 80. Crude extracts from common species of gorgonians collected in the Caribbean, 281 " 282 Singapore, 283 and the Pacific, 270 ' 284 have been surveyed for predator deterrent activity in laboratory assays against a generalist predator or in field assays against natural assemblages of reef fishes.…”

Cembrane Diterpenes Chemistry and Biological Properties

“…52, 58-63, 627-631, 640-644 [24,29,179,184] Eunicea pinta 333-340 [104] Eunicea knighti 163-165 [63] Eunicea mammosa 161, 162, 203, 321-332 [62,[100][101][102][103] Eunicea succinea 158-160, 202, 311-320, 620 [61,98,99] Eunicea tourniforti 36-39 [19] Leptogorgia sp. 482-487, 519 [147,148] Leptogorgia alba 473, 474 [138] Leptogorgia laxa 155, 156 [59] Leptogorgia setacea 475, 476 [142] Lophogorgia peruana 157, 462-471, 526 [60,[137][138][139][140]143] Pseudopterogorgia sp. 532 [159] Pseudopterogorgia bipinnata 531, 619 [158] Pseudopterogorgia kallos 527-530 [134] Gorgonacea Plexaura flexuvsa 557 [163] Sea pen Gyrophyllum sibogae 66, 67 [31] Pseudopterogorgia acerosa 477 [143] Tetralophuzia setifomis 106 […”

“…Coralloidolide A (460) and B (461)was isolated from the Mediterranean alcyonacean Alcyonium coralloides [136]. The chemical study of the gorgonian Lophogorgia peruana collected at the Gulf of California has led to the isolation of the five new diterpenes, lophodiol A, lophodiol B, 17-acetoxylophotoxin, 15,16-epoxylophotoxin, and 17-acetoxy-15, 16-epoxylophotoxin (462-466) [60], along with the known com-pounds, lophotoxin (467) [137,138], lopholide (468) [138,139], deoxylophotoxin (469) [140], and the lophotoxin analogs 470 and 471 [140]. Pukalide (472), isolated from the soft coral Sinularia abrupt, is a diterpenoid with a cembrane skeleton, bearing butenolide, epoxide, isopropenyl, and an unprecedented , -disubstituted furan--carboxylate function [141].…”