Procesos biotecnológicos y fitoquímicos en la obtención de plaguicidas botánicos

Resumen

As part of our ongoing chemical and biotechnological research on the sustainable production of natural agrochemicals from Canary endemic species, we have selected two Pericallis (Asteraceae) species, an endemic genus from the Macaronesian region found in the Canary Islands, Madeira and Azores. This genus has been recently separated from Senecio, a well-known source of sesquiterpenes, diterpenes and pyrrolizidine alkaloids. In this work we have studied the chemical defenses of P. echinata, a species from Tenerife with a strict environmental conditions habitat and P. hadrosoma, an extremely endangered species from Gran Canaria. We have adapted P. echinata to aeroponic culture (aerial part and roots) and both species to in vitro culture of transformed roots, allowing for the sustainable production of benzofuranes and diterpenes. Extracts from biotechnological cultures and aerial extracts of the wild plants were investigated for comparative purposes. The extracts were fractionated by chromatographic techniques and the structures of isolated compounds were elucidated by mono and bidimensional NMR spectroscopic techniques, chemical correlation and comparison with bibliographic data. Fifty-nine compounds have been isolated from P. echinata and P. hadrosoma and ten are reported for the first time as new natural products. The phytochemical study of P. echinata resulted in the isolation of two new natural compounds, 10,11-dihydroxy-12-angeloxyeuparine (10) and 2,4-dihydroxy-5-formyl-acetophenone (30), thirteen benzofuranes, two aromatic compounds, six triterpenes, five sterols and four pyrrolizidine alkaloids. The study of P. hadrosoma gave four nor-sesquiterpenoids, twenty-two diterpenes, mostly with ent-kaurane skeleton, including the new compounds pericanoic acid (47), pericatriol (49), hadrosomic acid (50), perihadrosonol (51), pericalloic-A acid (53), pericalloic-B acid (53a), pericaldehide (57); two sterols and five pyrrolizidine alkaloids with (+)-neoplatyphilline (67) being described here for the first time. We have also investigated the biotransformation by Mucor plumbeus of 6-hydroxytremetone, a benzofurane from P. echinata, yielding new glycosylated derivatives. The ethanolic crude extracts, their fractions and isolated metabolites were bioassayed against different crop pests including insects (Spodoptera littoralis, Leptinotarsa decemlineata, Myzus persicae, Rhopalosiphum padi) and the nematode Meloidogyne javanica. Also their phytotoxic effects were tested on Lactuca sativa and Lolium perenne. Some benzofuranes from P. echinata were antifeedant against insects, mainly to the lepidopterous S. littoralis and the aphid M. persicae (5, 13, 1 and 12). Some showed phytotoxic effects (1, 6 and 11). P. hadrosoma, contained ent-kaurane diterpenes that promoted plant growth (43 and 51) and nor-sesquiterpenes with phytotoxic effects (40, 42, 46a and 50). Drosophila melanogaster was used as a ¿taste detection model¿, to test if natural products with deterrent activity on Spodoptera littoralis (benzofuranes 1, 6 and 12) could be related with a repulsive response due to their bitter taste. With this aim, behavior experiments (MultiCAFE, feeding color test, PER) and electrophysiological recordings were reported. Our initial results suggest that eupachinin (4) was the only molecule which had an aversive effect on Drosophila with an inhibitory effect on sugar detection (s-cell). We also tested the cytotoxic activity against different tumour cell lines of ent-kauranes from P. hadrosoma. Some of these compounds (40, 43, 44 and 50) showed promising activity against different tumour cell lines, especially on HCT116 colorectal carcinoma cells.