Stereoselective 9-step conversions of the ketone 17 into the tricyclic ketone 31 via two similar synthetic pathways are described. The highly stereoselective steps involved in the preparation of 31 were: a) the Lewis acid-catalyzed reaction of the silyl enol ethers 50 and 60 with the ethylene ketal of 3-buten-2-one to produce the diketones 37 and 39, respectively, b) the hydrogenation of the enone 32 to give the ketone 56, and c) the Birch reduction of the enone 61 to give 31. Compound 31 contains the correct relative configuration at each of the corresponding chiral centers present in the target molecule 16 and, therefore, appears to be an ideal intermediate for a projected total synthesis of (±)-16 (initially believed to be the sesterterpenoid suvanine). A 15-step total synthesis of the antimicrobial diterpene (±)-8-isocyano-10(14)-amphlilectadiene (23) from the intermediate 24 is described. The key steps in the synthesis of (±)-23 involved the stereoselective Birch reduction of 24, the epimerization of the aldehyde 91 to the corresponding a-formyl isomer, and the degradation of the carboxylic acid function of 95 to an isonitrile group. The last part of the synthetic work described in this thesis resulted in a 15-step conversion of the ketone 17 into the tricyclic ketone 164. Of particular note in this sequence of reactions are: a) the palladium(0)-catalyzed coupling reaction of the enol triflate 143 with lithium cyanide to produce the nitrile 144, b) the stereoselective alkylation of 144 to give compound 148, and c) the stereoselective Birch reduction of the enone 163 to produce 164. The methodology employed in the construction of the tricyclic intermediate 164 contributes to the development of a general route towards the synthesis of the spongiane diterpenes 18-22. [formula omitted] / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph.D.) OGI School of Science & Engineering at OHSU, March 2008. / Includes bibliographical references (leaves 163 - 169).

Submitted in fulfillment of the academic requirements for the Masters in Applied Sciences (Chemistry), Durban University of Technology, Durban, South Africa, 2016. / The main aim of this work was to produce levulinic acid (LA) from sugarcane bagasse (SB) and since there is approximately 3 000 000 tons of bagasse produced per annum by 16 factories that are located on the north coast of Kwa-Zulu Natal, after the extraction of sugar. For this project fructose was firstly used for the production of LA, thereafter SB was used to produce LA. Cellulose was extracted from sugarcane bagasse using two types of pre-treatments namely (i) acid-alkali pre-treatment and (ii) liquid hot water (LHW). In the latter method acid hydrolysis and enzymatic hydrolysis was used to hydrolyse cellulose to glucose. For the acid-alkali pre-treatment work, two types of bagasse was used namely (i) mill-run bagasse and (ii) depithed bagasse and for the LHW a mill-run bagasse (pellets form) was used. In both pre-treatment methods the glucose solution was then acid catalysed by two different acids (i) an environment friendly acid, methanesulfonic acid (MSA) and (ii) sulphuric acid, producing levulinic acid. The results showed that MSA and sulphuric acid produced almost the same yield of LA but, MSA is preferred for the production of LA since it is less toxic and less corrosive than sulphuric acid. / M

No description available.

Many bacteria accumulate carbon stores as poly-3-hydroxybutyrate (PHB) when growth is limited but carbon availability is not. This stored carbon can then be utilized during conditions of limited carbon availability. The net PHB accumulation in the cell is dependent on the balance between PHB synthesis and degradation. Sinorhizobium meliloti accumulates PHB in the free-living stage but not in the symbiotic stage. The physiological role of the PHB cycle in S. meliloti is unknown. As a first step to understand the genetics of PHB degradation, transposon-generated mutants that were not able to use PHB degradation intermediates, such as 3-hydroxybutyrate and acetoacetate, as a sole carbon source, were isolated. Genetic mapping revealed that there were at least three chromosomal loci involved in acetoacetate metabolism. Identification of these three loci determined that in S. meliloti: (1) acetoacetyl-CoA synthetase (AcsA), encoded by acsA2 gene, rather than the enzyme acetoacetate:succinyl-CoA transferase, is the enzyme that catalyzes activation of acetoacetate to acetoacetyl-CoA; (2) PHB synthase, encoded by phbC, is required for acetoacetate utilization; (3) a putative transporter protein encoding gene, aau-3, may also be involved in acetoacetate metabolism. acsA2 and aau-3 were 78% linked in co-transduction, while phbC was mapped to somewhere else on the chromosome. Biochemical analysis revealed that acsA2::Tn5 mutants lacked AcsA activity but not acetoacetate:succinyl-CoA transferase activity, while phbC::Tn5 maintained similar level of AcsA activity as wild type in vitro. PHB was absent in the phbC mutant. / One transposon-generated mutant, age-1, showed enhanced growth rate on acetoacetate medium. Genetic mapping and transductional analysis indicated that the location of the mutation in age-1 is tightly linked to acsA2. Fine mapping with PCR and DNA sequence techniques showed that Tn5 in age-1 was located at 132 by upstream of the putative translation start site of acsA2. Gene expression analysis indicated that age-1 insertion results in elevated transcription of acsA2. Thus enhanced growth rate on acetoacetate was due to the increased gene expression. acsA2 transcription was induced by acetoacetate and 3-hydroxybutyrate, and repressed by glucose and acetate. / All mutants formed root nodules that fixed nitrogen with varying decrease of impairment. Acetoacetate metabolism and the PHB degradation are not essential for symbiosis.