Antiparasitic metabolites from plants used in the Tacana Bolivian native tribe : Traditional medicine, an overview of natural products with medicinal interest

Abstract: The thesis aims to contribute to the preservation of traditional medicinal knowledge of the Tacana Bolivian native tribe, as well as to the isolation and characterization of antiparasitic metabolites from plants used for the treatment of endemic diseases. A selection of medicinal plants, made in collaboration with the Tacana communities who decided which plants have a specific medicinal propose, were collected and identified by the national herbarium of Bolivia, and confirmed by healers from the most representative communities. From the screened plants the most active species were selected, using as selection criteria the in vitro antiparasitic activity in Leishmania strains. These species were subjected to chemical analysis that includes the chromatographic isolation of their major metabolites and structural elucidation of these by spectroscopic techniques. The main metabolites identified were evaluated in a broad battery of parasite assays, besides the cytotoxicity, to determine the potency as well asselectivity to obtain a better understanding of the medicinal properties of the medicinal plants.In the first chapter, a general description about Tacana native tribe is given in order to understand the intimate connection that this people have with their environment. A cooperation project between the Tacana people, La Paz university and international organizations, facilitated the collection and taxonomical identification of 38 plants with medicinal uses to be added to the ethnobotany list of Tacana traditional medicine.In the second chapter, the laboratory work that was carried out to prepare ethanolic extracts of the plants collected is described, and the antiparasitic activity against leishmania promastigotes of each extract was evaluated in vitro besides the cytotoxicity in HeLa cells. This gave the selectivity index (SI),. Thus, three vegetable species were selected as the most active antiparasitic plants, identified as Hyptis mutabilis, Hyptis brevipes and Tessaria integrifolia. Additionally, two species were selected due to the extended use among Tacana people: Renealmia breviscapa and Trichilia adolfi. The last chapter is concentrated on the chemical exploration of selected plants. The ethanolic extracts of H. brevipes and H. mutabilis, both belonging to the same family, afforded the isolation of nine metabolites with diverse antiparasitic activity, some of them part of the brevipolide chemical family. The most active compound was found in H. mutabilis and identified as olguine. Super critical fluid extraction technique was applied to extract the chemical content of T. integrifolia, and eleven metabolites were isolated. Seven of them were identified as eremophilane-type sesquiterpenoids, the remaining were flavonoids and terpenoids. The relative chemical contents were compared in the crude extract and fractions using LC-MS techniques. The ethanolic extract of T. adolfi afforded nine new tetranortriterpenoids, and an extensive spectroscopic analysis was necessary to elucidate their complex structures. The trivial name trichilianone-type was proposed for compounds that possess a bicyclo-cyclopropane-hexanesystem as part of the terpenoic skeleton. The antiparasitic activity and cytotoxicity was reported together with a short analysis of the hypothetical biosynthetic pathway.