Valéria Laneuville Teixeira

Ecological roles of natural products of the Brazilian red seaweed Laurencia obtusa

Laboratory and field experiments were performed to assess the ecological roles of natural products produced by the Brazilian red seaweed Laurencia obtusa. Laboratory assays revealed that the natural concentration of the crude organic extract of L. obtusa significantly inhibited feeding by two herbivores: the crab Pachygrapsus transversus and the sea urchin Lytechinus variegatus. It was verified that this chemically defensive action was due to halogenated sesquiterpenoid elatol, found to be the major natural product of this red seaweed. In addition, it was verified that the antifouling property of the chemicals produced by L. obtusa could make this red alga less attractive for fish grazing. Direct protection against two herbivore species and indirect protection against herbivory by fouling inibition constitute evidence that the major natural product from Brazilian L. obtusa plays multiple environmental roles, thereby increasing the adaptive value of these metabolites. On the other hand, the evidence reinforces the idea that marine natural products may have different functions in the sea.

Antifoulant diterpenes produced by the brown seaweed Canistrocarpus cervicornis

This paper reports the antifouling properties of the dichloromethane crude extract (DC) and 3 pure compounds isolated from the Brazilian brown seaweed Canistrocarpus cervicornis against establishment of the mussel Perna perna. DC extract showed a strong inhibition activity against byssal threads. Two natural dolastanes and one seco-dolastane diterpene, namely (4R, 9S, 14S)-4α-acetoxy-9β,14α-dihydroxydolast-1(15),7-diene (1), (4R,7R,14S)-4α,7α-diacetoxy-14-hydroxydolast-1(15),8-diene (2) and isolinearol (3), were isolated from DC extract. Dolastane (1) inhibited 60% of byssal fixation, while compound 2 and the seco-dolastane (3) strongly inhibited (82%) the establishment of P. perna. This is the first report of this type of chemical skeleton in three powerful compounds that could be further explored for the development of antifouling technology.

Produtos naturais de algas marinhas e seu potencial antioxidante

Free radicals and other reactive species of oxygen are co-produced in some biological reactions and they play important physiological role, and nevertheless they are reported as factors that take straight part in the pathophysiologic mechanism associated with continuity and complications of the several pathological process such as arteriosclerosis, diabetes mellitus, cancer, and arthritis, among others. In this way, the antioxidant therapy should prevent the development and progress of these complications. Seaweeds can be valuable source of natural antioxidant compounds since they have a well-developed antioxidant defense system. The present work is a compilation of the antioxidant activities of marine natural products and benthonic marine seaweeds crude extracts researches.

The Effects of the Diterpenes Isolated from the Brazilian Brown Algae Dictyota pfaffii and Dictyota menstrualis against the Herpes Simplex Type-1 Replicative Cycle

We describe in this paper that the diterpenes 8,10,18-trihydroxy-2,6-dolabelladiene ( 1) and (6 R)-6-hydroxydichotoma-4,14-diene-1,17-dial ( 2), isolated from the marine algae DICTYOTA PFAFFII and D. MENSTRUALIS, respectively, inhibited HSV-1 infection in Vero cells. We initially observed that compounds 1 and 2 inhibited HSV-1 replication in a dose-dependent manner, resulting in EC (50) values of 5.10 and 5.90 microM, respectively, for a multiplicity of infection (MOI) of 5. Moreover, the concentration required to inhibit HSV-1 replication was not cytotoxic, resulting in good selective index (SI) values. Next, we found that compound 1 sustained its anti-herpetic activity even when added to HSV-1-infected cells at 6 h after infection, while compound 2 sustained its activity for up to 3 h after infection, suggesting that these compounds inhibit initial events during HSV-1 replication. We also observed that both compounds were incapable of impairing HSV-1 adsorption and penetration. In addition, the tested molecules could decrease the contents of some HSV-1 early proteins, such as UL-8, RL-1, UL-12, UL-30 and UL-9. Our results suggest that the structures of compounds 1 and 2, Brazilian brown algae diterpenes, might be promising for future antiviral design.

A dolabellane diterpene from the brown alga Dictyota pfaffii as chemical defense against herbivores

Abstract Laboratory and field experiments assessed the defensive properties of the crude extract and major secondary metabolite found in the Brazilian brown alga Dictyota pfaffii. Natural concentrations of the crude organic extract of D. pfaffii significantly inhibited feeding by the sea urchin Lytechinus variegatus and generalist herbivore fishes in the field. In contrast, the crude extract did not inhibit feeding by the crab Pachygrapsus transversus. Chemical defensive action against the sea urchin and the generalist fishes was due to the diterpenoid 10,18-diacetoxy-8-hydroxy-2,6-dolabelladiene found as the major natural product in D. pfaffii. However, this compound did not inhibit feeding by P. transversus as readily as the crude extract. This is the first report showing that Dictyota species produce dolabellane diterpenes as chemical defense against herbivory. In addition, these results widen the action spectrum of secondary metabolites found in species of this brown algal genus. Since dolabellanes constitute the major skeleton type found in Dictyota, we suggest that these diterpenes may play an important ecological function as defenses to the Dictyota species worldwide.

Polyphenols, Terpenes and Sterols in Brazilian Dictyotales and Fucales (Phaeophyta)

In this work concentrations of polyphenols (phlorotannins), terpenes and sterols of brown algae were estimated in species of Fucales and Dictyotales and were tested as chemical defence against the amphipod Parhyale hawaiensis. While Fucales show high quantities of sterols, the Dictyotales are rich in terpenes. Both orders were found to be very poor in polyphenols, in contrast with general results reported from temperate regions. A dolastane diterpene from Dictyota cervicornis, Dictyol H from Dictyota mertensii and the steroidal fraction from Sargassum furcatum were not active against the amphipod. In fact these metabolites seemed to some extent to stimulate grazing by the herbivore.

Variation in chemical defenses against herbivory in southwestern Atlantic Stypopodium zonale (Phaeophyta)

Abstract Many seaweeds produce secondary metabolites that deter herbivory, but intraspecific variation in both the identity and the concentration of chemical defenses has been documented rarely. In order to evaluate the occurrence of chemical variation in the brown seaweed Stypopodium zonale along the Brazilian coast, we investigated the defensive properties of crude extracts and major secondary metabolites found in specimens from two distant locations (Forno inlet, Búzios, southeastern Brazil and Fernando de Noronha archipelago, northeastern Brazil) against herbivory by the crab Pachygrapsus transversus and the sea urchin Lytechinus variegatus. At natural concentrations, the extracts from S. zonale from Búzios and Fernando de Noronha significantly deterred feeding by P. transversus and L. variegatus, although the former was more effective as a defense than the latter. Corroborating these results, the major metabolites atomaric acid, found in individuals from Búzios, and stypoldione, from Fernando de Noronha specimens, also inhibited herbivory, but atomaric acid was more effective as a defense against L. variegatus and P. transversus than stypoldione. The variation between S. zonale from two distant and different geographic locations in Brazil suggests that defensivechemicals from this seaweed are not qualitatively or quantitatively absolute or invariant characteristics of the species, and may represent an ecological specialization to successfully prevent herbivory.

Chemosystematic and biogeographic studies of the diterpenes from the marine brown alga Dictyota dichotoma

Abstract Dictyota dichotoma is claimed to be the only cosmopolitan species of the genus Dictyota . It is also the species that has been the most extensively studied by phytochemists, yielding a plethora of diterpenes as major secondary metabolites. The question whether D. dichotoma is a true cosmopolitan species of defined limits is examined in this work. Diterpenes isolated from several populations, collected all over the world, are used as a criterion. The dissimilarity between diterpene compositions and mainly the important differences observed for the taxonomic indices suggested that D. dichotoma is actually a complex of species. The cosmopolitan character of its geographic distribution should be revised.

Dolastane diterpenes from the marine brown alga Dictyota cervicornis

Abstract One known and two new dolastane diterpenes have been isolated from Dictyota cervicornis . The structures and absolute configurations of the new metabolites were established from spectral data and chemical correlation to known compounds.

Chemotaxonomic study of the diterpenes from the brown alga Dictyota menstrualis

1. Subject and sourceIn order to continue our chemosystematic studies of the genus DictyotaLamouroux, Dictyotales, Phaeophyta (Cavalcanti et al., 1998a and referencesquoted therein) we examined D. menstrualis (Hoyt) Schnetter, Ho¨rnig & Weber-Peukert collected at Enseada do Forno, Bu´ zios, Rio de Janeiro State, Brazil (22845