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Analytical and biological studies of sesquiterpene lactones

University of British Columbia

Three related analytical and biological studies of sesquiterpene lactones mainly from Compositae were conducted. In the first one I examined various thin-layer chromatography (TLC) techniques for identification of sesquiterpene lactones and polyacetylenes. Vanillin and p-dimethylaminobenzaldehyde were found to be most useful of several benzaldehyde and benzoic acid derivatives for the detection of these compounds. Colors produced with these two reagents and with 78 sesquiterpene lactones and 25 polyacetylenes were of all shades of the spectrum and were specific for individual compounds. Therefore, these reagents can be used as an aid in the identification of these compounds by TLC. These spray reagents are the most sensitive of all reagents which have so far been used for the detection of sesquiterpene lactones or polyacetylenes using TLC. The vanillin spray reagent was used in the second study for the detection and preliminary identification of major sesquiterpene lactones in crude extracts of' 29 samples of Parthenium hysterophorus representing specimens from various areas of its world distribution. Some sesquiterpene lactones detected by this technique were subsequently isolated and also identified by NMR analyses. Three sesquiterpene lactones, coronopilin, hysterin, and dihydroisoparthenin, were shown for the first time to occur in this species. The chemical analyses of 10 selected compounds from 29 samples indicated the existence of 11 chemical types of P. hysterophorus. The most widespread is the North American type which is also present in Belize, Australia, and India. However, the South American samples differ greatly in their sesquiterpene lactone composition from the North American plants. In addition, the comparison of samples from various South American populations showed a high degree of diversity in chemistry. These results suggest the possibility of the existence of either several forms, or subspecies, or perhaps even several species of this plant. In the third study I examined the relationship between various biological activities of sesquiterpene lactones and their chemical structures. Antimicrobial screening tests were performed with. 57 sesquiterpene-lactones against 6 bacteria and 45 sesquiterpene lactones against 3 fungi. The presence of certain structural moieties in the compounds seems to be necessary for antimicrobial activities. However, different functional groups appear to be required for the different skeletal classes of sesquiterpene lactones and for different types of microorganisms. In addition, some other functional groups appear to enhance activity whereas others reduce activity of sesquiterpene lactones. Finally, the configuration of some functional groups alone may significantly influence the activity of certain sesquiterpene lactones. These results indicate that there is no simple general relationship between the antimicrobial activity of sesquiterpene lactones and their chemical structure. Four structurally similar sesquiterpene lactones were tested for their effects on survival of flour beetles. Three compounds containing the exocyclic methylene group on the lactone ring (coronopilin, helenalin, and parthenin) significantly reduced survival of beetles, whereas tenulin, lacking this moiety, had no effects. Therefore, the exocyclic methylene is most likely responsible for the detrimental properties of these sesquiterpene lactones on survival of the beetles. Many sesquiterpene lactones are potential allergens. In the last study cross-reactivity to 6 structurally similar sesquiterpene lactones of parthenin sensitized guinea pigs was examined. The presence of the exomethylene on the lactone ring was found to be necessary for cross-reactivity. However, compounds which were progressively structurally more different than parthenin, gave weaker allergenic responses.

Text

2010-03-29

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http://hdl.handle.net/2429/22972

Botany

University of British Columbia

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