title: Chemical investigations of natural products of potential biological interest
Creators: name: Subramanian, Ganapathy
Publisher: name: University of Glasgow
Year: 1967
Subjects: subject: Organic chemistry.

description: Section I gives an account of a chemical investigation of the aphid Megoura viciae Buckton. This study was made, in the light of reports of the toxicity of this insect to the predatory insect Adalia decempunctata. However the presence of a toxic principle could not be demonstrated. A brief survey of the different types of toxic principles found in insects is given to place the work in perspective. Section II deals with the isolation of the triterpene acid fractions from the native New Zealand plants Gaultheria antipoda and Gaultheria subcorymbosa. The investigation was undertaken in the light of what were considered to be reliable reports that the plant Gaultheria antipoda, contained a galactogenic principle. Arguments in support of the belief that this principle could possibly be a triterpene acid are advanced. It was found that ursolic acid was the sole triterpene acid present in both plants. Section III describes attempts at the isolation and characterisation of the constipatory principle present in several species of Hebe, one of which, Hebe stricta is well established as being effective in arresting loose bowel movements. Chemical examination revealed D-mannitol and condensed tannins to be major constituents of these plants and pharmacological studies indicated that the constipatory properties could be attributed to the condensed tannins in agreement with earlier assumptions. At the same time the opportunity was taken to perform gas-liquid chromatographic analyses of the alkanes and the components of the long chain esters present, as an extension of earlier work directed towards a possible chemotaxonomic differentiation within the genus Hebe. Section IV gives an account of an investigation of five species of Cortaderia for the presence of triterpene methyl ethers. This work was stimulated by the absence of arundoin in a sample of Cortaderia from Raglan, by a recent taxonomic revision of the grass family Arundinoideae and because of certain detailed botanical studies. Triterpene methyl ethers were found to be absent from Cortaderia atacamensis and Cortaderia selloana. Cortaderia fulvida and Cortaderia richardii were found to contain arundoin. Cortaderia toetoe was found to contain a mixture of three triterpene methyl ethers, which,after determination of the relative gas liquid chromatographic retention times of nine authentic triterpene methyl ethers on four different stationary phases and application of mass spectrometry, could be positively identified as arundoin, amyrin methyl ether and beta-amyrin methyl ether. In the case of amyrin methyl ether this would appear to be the first report of its natural occurrence. In addition,gas liquid chromatographic analyses were performed on the alkane fractions and on the components of the long chain esters present in the leaf surface wax of each species of Cortaderia. The results of these analyses in conjunction with the triterpene methyl ether analyses resulted in a partial chemotaxonomic differentation of the five species of Cortaderia. The two major triterpene methyl ethers present in the wax of Cuban sugar cane were identified as sawamilletin (taraxerol methyl ether) and arundoin. A third minor component had gas liquid chromatographic retention times corresponding to bauerenol methyl ether. A triterpene alcohol present in Artemisia vulgaris was shown to be O-desmethylarundoin (fernenol) through direct comparison of the derived methyl ether with arundoin. The mass spectra and nuclear magnetic resonance spectra of triterpene methyl ethers are discussed. An interesting facet of the mass spectra is the loss of neutral methanol as a major fragmentation process while the nuclear magnetic resonance spectra reveal the absorption of the 3 proton (ie the proton on the carbon atom bearing the methoxyl group) to occur at surprisingly high field. The preparation of synthetic triterpene methyl ethers is described. The co-occurrence of the three triterpene methyl ethers in Cortaderia toetoe and Cuban sugar cane has interesting biogenetic implications, so in order to set these in perspective, an account is given of the current postulates on the derivation of different triterpenes and steroids in terms of different conformational foldings of all trans squalene during cyclisation. Section V describes the chemistry of the pentacyclic triterpene arundoin and the preparation of the 9(11)-dienes from the methyl ethers of bauerenol and multiflorenol for the purposes of a direct comparison with the 9(11)-diene derived from arundoin.