In this work, Raman spectroscopy and density functional theory (DFT) calculations have been used in order to understand the nature of the interaction between the carotenoid bixin and organic solvents with dielectric constant varying from ca. 2 (toluene) to ca. 47 (dimethyl sulfoxide). Raman shifts registered for the main carotenoid marker band, the C=C stretching mode (1525-1533 cm-1), were used as a probe to monitor spectral changes due to chemical interaction between bixin in the solid state with the analogous solvated species. Raman spectra of bixin in solution showed significant bathochromic shifts in the wavenumber position of ν(C=C) when compared with the solid state. Among the solutions, subtle differences were observed and the polarizability rather than dielectric constant of the solvents seems to be a more appropriate parameter to explain the differences in Raman shifts which could be correlated with the solvation degree of bixin. Correlation between DFT analysis and molecular dynamics simulations obtained for cis-bixin in DMSO and CHCl3 demonstrated that the interaction of the solute with the respective solvents occurs in specific portions of the molecule, however, this result was not confirmed by the experimental data since bixin is solvated by larger numbers of solvent molecules.

Abstract The gorgonian Phyllogorgia dilatata is endemic to the Brazilian coast which is listed as threatened with extinction. This species is known to produce sterols, mono- to tetra-terpenes, conjugated polyenals and peptides. The main objective of this study is to present an alternative method for identification of different classes of compounds based upon a Raman mapping technique using FT-Raman spectroscopy. The Raman analysis performed directly on the tissues (in situ) revealed the occurrence of peridinin, diadinoxanthin, conjugated polyenal and linoleic acid, that were also confirmed by Raman analysis of partitioned crude extracts. We have demonstrated that the technique has potential for use in guiding chromatographic separations and in providing information with respect to the early stages of a tissue necrosis through “purpling”. It may become a valuable non-destructive technique for monitoring the accumulation or production of metabolites during a biological interaction.

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-11beta,12beta-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. Bioassay-guided 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-11beta,12beta-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.

Este trabalho relata o primeiro estudo sobre a composição química da gorgônia Lophogorgia punicea, coletada no litoral sudeste do Brasil. A análise da mistura de esteróides monohidroxilados feita através de CGAR-EM revelou a presença de 9 derivados do esqueleto colestano contendo de 26 a 29 carbonos, bastante comuns em invertebrados marinhos. O estudo mais detalhado dos extratos brutos desta gorgônia, proporcionou o isolamento e a identificação por métodos espectroscópicos de hidroquinona e de um esteróide poliidroxilado denominado punicina (1). Punicina é um esteróide inédito com um padrão de oxigenação no carbono C-17 raro em organimos marinhos.

The natural products chemistry of the gorgonian Lophogorgia punicea, collected on the Southeast Brazilian coast, were investigated for the first time. Gas chromatography - mass spectral analysis of the monohydroxylated sterol mixture revealed the presence of nine common C26 to C29 cholestane derivatives. A detailed study of the crude extract of Lophogorgia punicea led to the isolation of hydroquinone and a new polyhydroxylated sterol named punicin (1). The structure of punicin was determined by interpretation of spectral data including 2D NMR and HRFABMS. Punicin is an unprecedented sterol possessing a C-17 hydroxyl group, a feature uncommon in marine organisms.