Structural & synthetic studies related to the chemical constituents of insect secretions

McDowell, Phillip Gerard (1978) Structural & synthetic studies related to the chemical constituents of insect secretions. University of Southampton, Doctoral Thesis.

Abstract

The soldier costs of the [duet African termite Amitermes evuncifer, a major peat in Nigeria, produces a selectively formioldal defence secretion in the frontal gland. This secretion is active against the predator ant Odontomachue troglydytes. The tricyclic ether 4,11--epoxy-cie-eudeemane has previously been suggested aa.a working hypothesis for the structure of the major component of the defence secretion. This thesis describes further evidence from the natural component, and from synthetic studies, in support of this structure.Further evidence has been derived from a new sample of the natural component. Infrared, carbon-13 NMR and lanthanide shift proton NMR data were entirely consistent with the proposed structure. Confirmation of the structure was obtained by unambiguous synthesis of the major component. Epi-B-eudesmol, epi-X-14-noreudesmol, and dihydrooccidentalal were synthesised and the cyclieotion of these intermediates with the mercury (II) ion is described. Furthermore, these chiral syntheses from starting materials of known absolute configuration has led to assignation of the absolute configuration of the natural compound.The defence secretion also contains a number of unidentified minor components, and the isolation and structural elucidation of five of these are described. Two monoterpenes, limonene and cis-p-ocimena were identified, together with three sesquiterpenes, 'fn-epieudeema-3,11-diene, caparrapi oxide and B-epicaparrapi oxide. The importance of microscale FT-NMR in this area is stressed, and some attempts to improve the existing technique for volatile insect samples are described. Finally, a section is presented describing the problems encountered in an investigation of phase chan_s pheromones in locusts. Current theories suggest the occurrence of a volatile pheromone, 5-ethyl-2-methoxyphenol, controlling phase change and aggregation in Locusts miqratoria, the Migratory locust. Evidence for the presence of this compound in the faeces of L. migratoris is described. The major problem encountered was the establishment of a viable bioassay of the phase change phenomenon.

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