This thesis was aimed at the extraction, isolation and structure elucidation of insecticidally active secondary metabolites of Citrus aurantium plant parts for potential use either as commercial insecticides or as lead compounds. Fruits, leaves and shoots of C. aurantium were extracted in methanol and the chemicals recovered were fractionated by liquid-liquid partitioning using organic solvents of increasing polarity (petroleum ether, dichloromethane, ethyl acetate). Petri dish exposure bioassays revealed that only the petroleum ether fraction of the fruit methanol extract was toxic against Bactrocera oleae adults. The bioactive chemicals present in the fruits were produced and/or accumulated in the peels. Petri dish exposure and topical application bioassays revealed that a petroleum ether peel extract was toxic against B. oleae and Ceratitis capitata adults. In several cases, differences in susceptibility were revealed between the two species and between the two sexes of the same species. First gravity column fractionation of the peel extract revealed that only the F2 fraction was active, while fraction Ft has a synergistic effect. Further purification of the F2 fraction on the second gravity column, followed by HPLC, resulted in the isolation of three major compounds. The chemical structure of these components was elucidated by spectroscopic methods (UV, FTIR, GC-MS and *H NMR) and was assigned as osthol, bergapten and 6',7'- epoxybergamottin. Of the three isolated compounds, only the 6',7'-epoxybergamottin was active and its toxicity was the same to the synthesised 6',7'-epoxybergamottin. However, the synergism revealed between isolated bergapten and 6',7'- epoxybergamottin was not confirmed when isolated bergapten was replaced by synthetic bergapten, indicating that minor components present in the isolated bergapten were responsible for the synergistic effect. Crude or semi-purified peel extracts of C. aurantium may have potential for insect control. Moreover, 6',7'-epoxybergamottin has apparently never been reported to have deleterious effects on insects. At this early stage, the potential of 6',7'- epoxybergamottin as a lead compound for a new class of insecticides remains to be determined.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:583494 |
| Date | January 2004 |
| Creators | Siskos, Elias P. |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/55958/ |
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