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

The chemical defenses of the Brazilian gorgonian octocoral Lophogorgia viol acea Pallas have been investigated using feeding preference experiments per formed in situ with an ecologically relevant, natural assemblage of predato ry fishes. Feeding experiments incorporating the crude extract of the anima l into palatable foods showed that the organic constituents of L. violacea provide a powerful chemical deterrence toward consumption by generalist fis h carnivores. Bioassay-guided fractionation of the extract and evaluation o f the fractions and purified compounds obtained in the same in situ assay r evealed that a complex mixture of furanocembranolides was responsible for t he overall feeding deterrence observed. The most potent feeding deterrent i dentified was lophotoxin (1), followed by two previously reported and struc turally related compounds, deoxylophotoxin (2), and 13-acetoxy-11 beta ,12 beta -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 isolate d. However, the four other related furanocembranolides (2-5) appear to cont ribute, in an additive manner, to the overall deterrent effects observed. T hese results add to earlier studies providing further evidence that compoun ds of this structural class provide effective chemical defenses against fis h predators in both temperate and tropical environments.