Alphonse Kelecom

Secondary metabolites from marine microorganisms

After 40 years of intensive research, chemistry of marine natural products has become a mature field. Since 1995, there are signals of decreased interest in the search of new metabolites from traditional sources such as macroalgae and octocorals, and the number of annual reports on marine sponges stabilized. On the contrary, metabolites from microorganisms is a rapidly growing field, due, at least in part, to the suspicion that a number of metabolites obtained from algae and invertebrates may be produced by associated microorganisms. Studies are concerned with bacteria and fungi, isolated from seawater, sediments, algae, fish and mainly from marine invertebrates such as sponges, mollusks, tunicates, coelenterates and crustaceans. Although it is still to early to define tendencies, it may be stated that the metabolites from microorganisms are in most cases quite different from those produced by the invertebrate hosts. Nitrogenated metabolites predominate over acetate derivatives, and terpenes are uncommon. Among the latter, sesquiterpenes, diterpenes and carotenes have been isolated; among nitrogenated metabolites, amides, cyclic peptides and indole alkaloids predominate.

Effects of the lignan, pinoresinol on the moulting cycle of the bloodsucking bug Rhodnius prolixus and of the milkweed bug Oncopeltus fasciatus

Abstract The furano-lignan pinoresinol was toxic to fourth-instar larvae of the milkweed bug Oncopeltus fasciatus and of the haematophagous insect Rhodnius prolixus , a vector of Chagas disease. At lower doses, it also exerted antifeedant activity and dose-dependent antimoulting activity on both insects.

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.

A chemotaxonomic study of diterpenes from marine brown algae of the genus Dictyota

Abstract Diterpenes from Dictyota species appear to be valuable taxonomic markers and showed, for various species, strong correlation with botanic data. Our results corroborate the Theory of Micromolecular Evolution that states that higher oxidation levels, in a given taxon, are characteristic of evolutionarily more advanced components.

Effects of the essential oil obtained from Pilocarpus spicatus Saint-Hilaire (Rutaceae) on the development of Rhodnius prolixus nymphae

Bioassays against fifth-instar nymphae of Rhodnius prolixus were conducted with essential oil of Pilocarpus spicatus extracted by hydrodistillation. The main results may be summarized as follows: (i) high levels of toxicity and paralysis together with discrete moulting inhibition were caused by topical application of either 0.5 µL or 1.0 µL per insect of the crude essential oil; (ii) partial fagoinhibition, high moulting inhibition, prolonged intermoulting period and high number of paralyzed insects, but no toxicity were observed after oral treatment using either 5 µL or 10 µL of Pilocarpus spilcatus essential oil per mL of ingested blood meal. The importance of these results in relation to the relevant biological events in R. prolixus is herein discussed.

Diterpenes of marine brown algae of the family dictyotaceae: Their possible role as defense compounds and their use in chemotaxonomy

Marine brown algae of the family Dictyotaceae are protected against predation. Their survival strategy is, at least in part, based on the production of chemical defenses. These compounds are diterpenes that seem to establish a specific predator-prey relationship, and which are found as food-chain markers. The use of Dictyotaceae diterpenes in chemotaxonomy is briefly discussed.

Lignanes from the Brazilian Melia azedarach, and their activity in Rhodnius prolixus (Hemiptera, Reduviidae)

A study of the phagoinhibitor and anti-moulting activities of the Brazilian Melia azedarach, collected in the State of Rio de Janeiro, Brazil, allowed the isolation of four lignanes identified as pinoresinol (1), bis-epi-pinoresinol (2), the hemicetal (3) and the diacid (4). These substances are devoid of anti-moulting activity.

Development of a Larvicidal Nanoemulsion with Pterodon emarginatus Vogel Oil.

Pterodon emarginatus Vogel is a Brazilian species that belongs to the family Fabaceae, popularly known as sucupira. Its oil has several biological activities, including potent larvicidal property against Aedes aegypti. This insect is the vector of dengue, a tropical disease that has been considered a critical health problem in developing countries, such as Brazil. Most of dengue control methods involve larvicidal agents suspended or diluted in water and making active lipophilic natural products available is therefore considered a technological challenge. In this context, nanoemulsions appear as viable alternatives to solve this major problem. The present study describes the development of a novel nanoemulsion with larvicidal activity against A. aegypti along with the required Hydrophile Lipophile Balance determination of this oil. It was suggested that the mechanism of action might involve reversible inhibition of acetylcholinesterase and our results also suggest that the P. emarginatus nanoemulsion is not toxic for mammals. Thus, it contributes significantly to alternative integrative practices of dengue control, as well as to develop sucupira based nanoproducts for application in aqueous media.

Cariocal, a new seco-abietane diterpene from the labiate coleus barbatus

Abstract cariocal is a new seco-diterpene isolated from a cardioactive fraction of the false boldo, Coleus barbatus . The structure was deduced from chemical and spectral data.