Alcaloides pirrolizidinicos em borboletas Ithomiinal : alguns aspectos em ecologia quimica

AUTOR(ES)
DATA DE PUBLICAÇÃO

1993

RESUMO

Pyrrolizidine alkaloids (PAs) are esters derived from 1-methyl-hidroxyl-pyrrolizidines; the aminoalcohol is called a necine base and the esterified acid a necic acid. PAs occur as monoesters and open or cyclic diesters, the ring being saturated or unsaturated. There are more than 200 structures of PAs isolated from plants, mainly Senecio, Eupatorium (Asteraceae), Crotalaria (Fabaceae) and Heliotropium (Boraginaceae). PAs have shown pharmacological (hepatotoxic, cancerigen, anti-cancer activities) and biological activities (chemical mediators of plant-herbivore-predator interactions). Within this later category this study is concentrated on the acquisition of PAs by butterflies (Danainae and Ithomiinae) and moths (Arctiidae) from plant sources. These alkaloids are sequestered by insects from larval host plants or adult sources. Sequestering these PAs, insects became chemically protected against predators, and also utilized PAs as pheromone precursors. In this work, PA chemical patterns from 3 Ithomiinae butterflies, their larval host plants and adult sources have been studied by GC-MS. This study showed that: 1. Tithorea harmonia pseudethra sequesters PAs from its larval food plant Prestonia acutifolia (Apocynaceae: Echitoideae), and also acquires these alkaloids from adult plant sources. . 2. Aeria olena olena utilizes as larval host plant Prestonia coalita. No traces of PAs were verified in this but recently emerged adults some time contain PAs. Wild adults acquire PAs from adult vegetal sources. 3. Mechanitis polymnia polymnia utilizes several Solanum species as larval host plants (not PA plants). Wild caught males acquire PAs from adult plant sources. Males and females from these three species present mainly two 1,2-unsaturated monoester PAs esterified at C-9: lycopsamine and intermedine. These PAs are present from 100% to 7:1 of lycopsamine. Other distereoisomers are not found in these butterflies. GC-MS chemical analyses of larval host plants and adult vegetal sources showed a large array of PA structures, the more abundant and frequent PAs being lycopsamine, intermedine, equinatine, rinderine, indicine, supinine and amabiline. These PAs were isolated and characterized by physical methods. A new PA (laevigatine) was isolated from Eupatorium laevigatum. Callimorphine (a biosynthesized insect PA) was semisynthesized from retronecine esterified at C-9 with the rac- 1-acetyl-methyl-butanoic acid. Incorporation of PAs by PA deprived adult butterflies (with lycopsamine and its four known stereoisomers - indicine, intermedine, equinatine and rinderine) showed that: 1. Males isomerize PAs to mainly lycopsamine. 2. Females change only part of these PAs to lycopsamine. The stereochemistry inversion of 7-OH PAs may be closely related to the evolution of acquisition of PAs by butterflies and moths, reflecting in the biosynthesis of PA derived pheromones. Females may acquire transformed PAs from males by mating, because they rarely visit adult sources of PAs. Incoporation of labeled C PAs by Mechanitis polyimnia showed that: 1. When PAs are fed to the larvae, M. polymnia incorporates less PAs than when it fed to the adult, and 2. free monoesters are more efficiently N-oxidazed than free macrocyclics by larvae and adults. These results reflect the biology of M. polynmia, which does not feed as larvae on PA plants, and does not visit as adult macrocyclic PAs sources. Bioassays with wild caught and recently emerged adults showed that PAs have ecological activity of chemical protection against predation by the orb weaving spider Nephila clavipes.

ASSUNTO(S)

pirrolizidinas alcaloides

ACESSO AO ARTIGO

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