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The aim of this project was to synthesize xanthoxal, a natural product which is a possible abscisic acid precursor. The xanthoxal will serve as a vital link: in a study on the biosynthesis of abscisic acid in plants. This study does not form part of this thesis. The synthetic pathway begins with mesityl oxide and ethyl acetoacetate as starting materials, and the target molecule was obtained via a I3-step route. The first step involved a Robinson annulation, which afforded the ketal of a ClO-ester ketone (ethyl2,6, 6-trimethyI4-oxo2-cyclohexene-I-carboxylate) which has a cyclohexene structure. The double bond in the 2,3 position of the ClO-ester ketone was isomerised to the 1,2 position followed by the simultaneous protection of the ketone, in the form of a ketal. The ester function of the ClO-ester acetal underwent reduction to afford an allylic alcohol . on which an asymmetric Sharpless epoxidation was carried out using (-) diethyl tartrate affording (+)-(1R, 2R)-I,2-Epoxy-4, 4-ethylenedioxy-2,6, 6-trimethylcyclohexane-lmethanol. The alcohol was oxidised by a Swem oxidation to the aldehyde in order to carry out a chain elongation. The side chain was prepared from 3,3-dimethylacrylic acid, which was first esterified then brominated to 4-bromosenecioate. The bromine was then replaced with triethyl phosphite, producing the Cs-phosphonate. Chain elongation by Homer-Emmons reaction was carried out on the aldehyde with the phosphonate, which resulted in a mixture ofE and Z CIs-esters. Since the yield of tht desired Z isomer, was very low, the E isomer was used to synthesize trans-xanthoxal, since this can be converted to the desired xanthoxal by uv radiation. The acetal was then removed followed by a simultaneous reduction of the ketone and ester groups to their corresponding alcohols using DffiAH. This reaction was only partially successful because only the keto group was reduced. The ester was then reduced with LiAIHt to form the primary alcohol, which was then selectively oxidised to the target molecule, the aldehyde (trans-xanthoxal). The synthesis of xanthoxal described here highlights the difficulties encountered when introducing the requisite functional groups on the cyclohexene ring skeleton to afford trans-xanthoxal. The pitfalls encountered during the reaction sequence are discussed and solutions are presented. Although the planned synthetic sequence did not produce the correct stereoisomer, procedures are available to convert it to the desired isomer. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.

It has been suggested that membrane characteristics associated with carcinomas could be related to an altered molecular structure of lipids in the plasma membrane. The microsomal fraction, mitochondria and soluble fractions of the cell are major sites of de novo synthesis and elongation of fatty acids. It was the purpose of this study to compare the utilization of AcSCoA in the biosynthetic pathway for saturated fatty acids in tumor and normal tissue, and discern if any deviations in the initial steps of the pathway were responsible forr the observed differences in the plasma membrane of tumors. Labeled 14C-AcSCoA was incorporated into saturated fatty acids in both adenocarcinomas and normal mammary tissue. The distribution and degree of incorporation of labeled 14C-AcSCoA was hoped to demonstrate any deviations in the pathway.Crude supernate, microsomal fraction, mitochondria and soluble fractions were isolated from mammary adenocarcinomas and from normal mammary tissue of Strain A female mice by differential centrifugation. The activity of fatty acid synthetase in the soluble fraction was determined. The crude supernate, the soluble fraction, the mitochondria + soluble fraction and the microsomal fraction + soluble fraction of both the adenocarcinoma and normal mammary tissue were incubated with labeled 14C-AcSCoA, Ma1SCoA and all necessary cofactors. The now labeled fatty acids were extracted from these incubation mixtures. The total percent of incorporated labeled 14C-AcSCoA in each fraction was determined. The percent of incorporation of label into individual saturated fatty acids in each fraction was determined by gas liquid chromatography and liquid scintillation counting. Carrier mixtures of known fatty acids were added to the samples used for GLC analysis to confirm the identity of the labeled fatty acids.Results of this study show that the percent of labeled i4C-AcSCoA incorporated into the various saturated fatty acids was similar in tumor and normal tissue. However, the total uptake of AcSCoA was nearly twice as great in normal tissue. The activity of fatty acid synthetase appearsto be characteristic of each individual mouse. In tumored mice fatty acid synthetase activity appears to be related to tumor weight, that is the larger the tumor the greater the activity. These results do not demonstrate support for a shift in the biosynthesis of saturated fatty acids in carcinomas. It may be that the altered lipid composition of the plasma membrane of tumor cells arises from the carcinoma's ability to utilize exogenous fatty acids.

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