Antioxidant Activity of Bolivian Plant Secondary Metabolites

University dissertation from Organic chemistry (S/LTH)

Abstract: Certain climatologically-adverse conditions in the basin of the Poopo Lake, located on the high plateau of the Bolivian Altiplano, have prevented the existence of a reliable agricultural system and the impact on the population of the area has been severe. These problems have been the main motivation in choosing this region for this particular study. However, many species of plants have somehow managed to survive and adapt to this environment and they have developed the capacity to synthesize secondary metabolites that have not only helped them to survive, but also to counteract the oxidative stress. 35 plant species and 5 lichen species were collected in the region, in order to evaluate their antioxidant activity. 28 compounds with anti-oxidant capacity have been identified from extracts of these species. All of the crude extracts, chromatographic fractions and pure compounds were studied using 4 assays (ABTS, DPPH, TBARS and ?-carotene). Two plant species that have presented the greatest activity have been selected for certain indepth studies. From Rheedia acumminata four compounds were isolated as potent antioxidant compounds, three of them(named acuminoxanthone, acuminophenone A and acuminophenone B) have not been reported previously. From Adesmia spinosisima, taxifolin, fustin and a phenyl derivate were isolated from the extract with high antioxidant activity, and it is possible that the compounds give a synergistic effect. Depsides and benzofurane compounds isolated from five lichen species were evaluated with the same antioxidant assays. All of the compounds showed high antioxidant capacity, compared with Trolox. Perlatolic acid is the best antioxidant compound among the lichen molecules. The TEAC antioxidant activity was correlated with various parameters in order to study QSARs. The analysis pointed out that the most important parameter involved in the antioxidant activity, as a free radical scavenger, is the energy of the highest occupied molecular orbital. A mathematic function was determined to predict the antioxidant activity for similar compounds. The great applicability of antioxidant products make these plants a potentially useful resource that could help to support the sustainable development of the region. The harvesting of these plants does not require the change of the current climatologic environment, mostly because these species have adapted so well to the region.

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