The use of carbohydrates as starting materials for organic synthesis is illustrated by the synthesis of several polyhydroxylated piperidine, pyrrolidine, indolizine and pyrrolizidine alkaloids. Nucleophilic displacement by azide ion at C-2 in a D-glucose derivative, with subsequent intramolecular cyclisation through nitrogen onto the C-6 or C-5 position and functional group manipulation, led to the synthesis of: 1,5-dideoxy-1,5-imino-D-mannitol; 1,2,5-trideoxy-1,5-imino-D-arabinohexitol; 1,5-dideoxy-1,5-imino-D-glucitol; 2-Acetamido-1,5-imino-1,2,5- trideoxy-D-glucitol; 2-Acetamido-1,5-imino-1,2,5-trideoxy-D-mannitol; (2S, 3R, 4R, 5S)-3,4,5-trihydroxypipecolic acid; (2S, 3R, 4R, 5R)-3,4,5- trihydroxypipecolic acid and 2,5-dideoxy-2,5-imino-D-mannitol. Nucleophilic displacement by azide ion at C-3 in a D-glucose derivative, with subsequent intramolecular cyclisation through nitrogen onto the C-6 position, produced the tosylate salt of 3,6-dideoxy-3,6-imino-1,2-0-isopropylidene- ⫏-D-glucofuranose, a highly divergent intermediate, from which the pyrrolidines: 1,4-dideoxy-1,4-imino-L-gulitol, 1,4-dideoxy-1,4-imino-D-lyxitol and (2S, 3S, 4R) - 3,4-dihydroxyproline were prepared directly. Periodate cleavage of the C1-2 bond and a 2-C chain extension from C-2 with subsequent intramolecular cyclisation, produced the pyrrolizidine (IS, 2R, 8R) - 1,2-dihydroxypyrrolizidine. An intramolecular Wadsworth Emmans cyclisation between a lactol at C-1 and a phosphonate, produced by a DCC coupling of the amine with dimethoxyphosphinylacetic acid, led to the formation of the indolizine (1S, 2R, 8S, 8aR) - 1,2,8-trihydroxyoctahydroindolizine. The synthesis of 1,4-dideoxy-1,4-imino-D-lyxitol, was achieved by connection of C1 and C4 of a D-mannose derivative through nitrogen. Methyl 3,5-0-isopropylidene- ⫏-D-xylofuranoside was elaborated to both enantiomers of 1,4-dideoxy-1,4-imino-arabinitol. The _D-enantiomer was produced by introduction of a nitrogen between C-2 and C-5, the L- enantiomer by introduction of a nitrogen between C-1 and C-4. (2R, 3S, 4R) - 3,4-dihydroxyproline was prepared from _D-ribonolactone. The key step of the synthesis was a nucleophilic displacement by azide ion at C-2 in which the stereochemistry was unexpectedly retained.

In recent years, two mechanisms have been proposed for the enzymatic formation of acetoacetate by liver extracts. One of these, the "HMG-CoA cycle", involves the condensation of acetyl-CoA and acetoacetyl-CoA to form β-hydroxy- β-methylglutaryl-CoA (HMG-CoA) via the action of the HMG-CoA condensing enzyme, with the release of free coenzyme A (CoASH) (reaction 1). Acetyl-CoA + acetoacetyI-CoA + H₂O⇆ HMG-CoA + CoASH (1) followed by cleavage of the HMG-CoA to acetyl-CoA and free acetoacetate, via the action of the HMG-CoA cleavage enzyme (reaction 2). HMG-CoA⇆ acetoacetate + acetyl-CoA (2) The second mechanism which has been proposed involves a direct deacylation of acetoacetyl CoA through the action of a specific acetoacetyl-CoA thioesterase (reaction). Acetoacetyl-CoA + H₂O→ acetoacetate + CoASH (3) Evidence is presented which indicates acetoacetate formation by a soluble enzyme system from bicarbonate extracts of whole beef liver proceeds largely, if not exclusively, via HMG-CoA (reactions 1 and 2). Both the HMG-CoA condensing and cleavage enzymes have been partially purified from beef liver bicarbonate extracts, each free of contamination by the other, in good yields. The level of activity of these two enzymes is sufficiently high to account for all the acetoacetate formed by liver tissue. The possibility that the specific acetoacetyl-CoA thioesterase may play a minor role in the enzymatic synthesis of acetoacetate is also discussed. The intracellular and tissue localization of the enzymes of acetoacetate formation is also discussed. In liver homogenates, most, if not all, of the acetoacetate-synthesizing activity appears to be associated with the mitochondrion. Evidence is also presented that the primary reason for the inability of extrahepatic tissue preparations to catalyze the accumulation of acetoacetate may be the lack of one of the enzymes involved, i.e., the HMG-CoA condensing enzyme, and not merely further metabolic degradation of acetoacetate, as has generally been assumed. An enzyme fraction in chicken liver extracts which inhibits the in vitro formation of acetoacetate by chicken liver homogenates has also been studied. Evidence is presented that this enzyme fraction exerts its effect through the inactivation of coenzyme A. Preliminary observations indicate that this enzyme may be a 3’-nucleotidase, removing the 3’- phosphate of coenzyme A, forming dephosphocoenzyme A. The occurrence of a highly active β-hydroxybutyryl dehydrogenase in extracts of dry culture of C. kluyveri has been noted. This enzyme differs from the similar enzyme reported in mammalian tissues, in that it is very specific for triphosphopyridine nucleotide, and is virtually inactive with diphosphopyridine nucleotide (DPN) (reaction). Acetoacetyl-CoA + TPNH + H⁺⇆β - hydroxybutyryl-CoA (4) + TPN⁺ / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

The products arising from the liquid-phase pyrolyses of 3,5-dimethyl-3-carbomethoxy-1-pyrazoline and 4,5-dimethyl-3-carbomethoxy-2- pyrazoline have been isolated and identified. The pyrolysis of 3,5-dimethyl-3-carbomethoxy-1-pyrazoline has been found to yield a mixture of 5 isomers consisting of 15% methyl trans-2-methyl-2-pentenoate, 10% methyl cis-2-methyl-2-pentenoate, 3% methyl trans-2-methyl-3-pentenoate. 45% methyl cis-1,2-dimethylcyclopropane-1-carboxylate and 27% methyl trans-1,2-dimethylcyclopropane-1-carboxylate. The pyrolysis of 4,5-dimethyl-3-carbomethoxy-2-pyrazoline yielded a mixture of 7 isomers consisting of 25.5% methyl trans-3-methy1-2-pentenoate, 26% methyl cis-3-methyl-2-pentenoate, 3% methyl trans-3-methyl-3-pentenoate, 2% methyl cis-3-methyl-3-pentenoate, 26% methyl trans-1,2-dimethylcyclo-propane-3-carboxylate, 16% methyl cis-1,2-dimethylcyclopropane-3-trans-carboxylate and 0.8% methyl 3-ethyl-3-butenoate. Pyrolysis of both pyrazolines has also been obtained in the vapour-phase and under these conditions a higher proportion of cyclopropanecarboxylic esters was formed than that obtained in the liquid-phase pyrolysis: 3,5-dimethyl-3-carbo-methoxy-1-pyrazoline yielded a mixture containing 94.5% cyclopropane carboxylic esters and 4,5-dimethyl-3-carbomethoxy-2-pyrazoline yields a mixture containing 67% of cyclopropane carboxylic esters. The vapour-phase pyrolysis of the 1-pyrazoline occurred readily at 200° whereas the vapour-phase pyrolysis of the 2-pyrazoline was found to require a catalyst. This catalyst is believed to facilitate the transformation of the 2-pyrazoline to the readily pyrolisable 1-pyrazoline form. Studies have been made of the equilibration of the unsaturated, esters arising from the pyrolysis of the pyrazolines and have shown that the composition of the olefin portion of the pyrolysis mixture in general is not an equilibrium mixture. A mechanism for the pyrolysis is suggested. The unsaturated esters arising from the pyrolysis of 4,5-dimethyl-3-carbomethoxy-2-pyrazoline have been synthesised and identified and structural assignments have been made. / Science, Faculty of / Chemistry, Department of / Graduate

Three types of 2-alkenylthiazolines were designed and synthesized by a two-step method starting with 2-methylthiazoline and aromatic aldehydes, alkyl aldehydes and alkenyl aldehydes, respectively. Diels-Alder reactions of several 2-styryl-1,3-thiazolines with maleic anhydride in toluene were attempted. Expected Diels-Alder products were not observed or separated. Only starting materials were recovered. Several 2-alkenyl-1,3-thiazolines were successfully reacted with benzoyl chloride to form the N-benzoyl mono-substituted products. This is in sharp contrast with the di-benzoylation of 2-methylthiazoline reported previously by the Pittman group. 2-Methylbenzothiazole was reacted with different folds of aroyl chlorides. However, only di-aroylation products were observed even when a 1:1 2-methylbenzothiazole:aroyl chloride ratio was employed. Finally, N-methyl cyclic ketene N,O- and N,S-acetals were reacted with different alkylsulfonyl chlorides, respectively. Only di-substituted products were found in the N,O-acetal reacitons and only mono-substituted products were found in the N,S-acetal reactions even when different folds of sulfonyl chloride was employed.

Doctor of Philosophy / Department of Chemistry / Duy H. Hua / The first chapter in this thesis includes the design, synthesis, and evaluation of anti-Alzheimer and anti-norovirus activities of tricyclic pyrones (TPs). Alzheimer’s disease is a major cause of dementia and sixth leading cause of death; it is a growing problem all over the world. On the other hand, norovirus, a highly contagious agent is responsible for more than 90% of non-bacterial gastroenteritis causing severity mainly in the closed environments. No drugs exist to eradicate the symptoms developed by both of these disorders. Studies have shown that the development of Alzheimer’s disease and the infection of norovirus are dependent on cholesterol metabolism. More specifically, the inhibition of acyl-CoA: cholesterol acyltrasferase (ACAT) led to the reduction of plaques in Alzheimer’s disease as well as reduced the infection of norovirus. Mimicking the structure of CP2, a TP with promising anti-Alzheimer activities, a library of tricyclic pyrones containing phenyl, naphthyl, heterocyclic, and dipeptidyl moieties were synthesized and evaluated for their anti-Alzheimer and anti-norovirus efficacies. Several TPs containing phenyl and naphthyl groups showed sub-micromolar to nanomolar potencies for the protection of neuronal MC65 cells from Aβ-oligomers induced death. Similarly, the TPs containing pyrrolyl, imidazolyl, and quinolinyl moieties were effective to inhibit the norovirus replication in low micromolar range. The most effective TPs from MC65 cells protection assay were also effective in the inhibition ACAT and up-regulation ABCA1 gene. The second chapter in this thesis includes the design, synthesis, and anti-norovirus activity of thiouridine nucleosides. Many nucleosides have demonstrated effective inhibition of viral RNA polymerase, and some are progressing at different level of clinical trials for the treatment of hepatitis C virus. Some of the nucleosides, including 2’-C-methyl and 2’-amino substituted analogs, were found to effectively inhibit the norovirus replication. In the search of more potent anti-noroviral compounds, two thiouridine nucleosides were synthesized and evaluated as anti-norovirus agents. Both of these analogs were ineffective up to 50 μM for the inhibition of norovirus replication in cell based assay. Proposed work of converting these nucleosides to their phosphoramidate derivatives is also described.

Non covalent interactions are valuable tools for crystal engineering. Hydrogen bonding often plays a central role for molecular association among possible non covalent interactions. Together with hydrogen bonding, arene-arene interactions and van der Waals interactions can control crystal assembly. Understanding non covalent interactions permits the design of molecules whose functionalities can interact non covalently so that molecules will pack in a predicted fashion. For two decades Prof. Mash's group has been studying crystal packing based on a piperazinedione core scaffold which can have three orthogonal non covalent interactions and lead to controlled three dimensional crystal packing. Alkoxy-substituted piperazinediones were previously studied for crystal packing and liquid crystal properties. It was found that alkoxy piperazinediones pack in three dimesions as designed and exhibit interesting thermochemical properties. Given that small changes in structure can cause large changes in packing and liquid crystal properties, the replacement of alkoxy groups with alkyl groups in molecules provides an opportunity to investigate the role of oxygen in crystal packing and liquid crystal properties. A series of alkyl piperazinediones was synthesized in a convergent way where an intermediate tetrabromide was converted into a series of tetra alkyne piperazinediones, then into tetra alkyl piperazinediones. This approach overcame limitations in the synthesis of alkoxy piperazinediones, where every target molecule requires 10 to 11 steps starting from 2,3-dimethylbenzene-1,4-diol (Scheme 2.1). Crystal structure analyses were done for three different piperazinediones. It appears that crystal packing of alkyl piperazinediones mimics that of alkoxy piperazinediones.

A highly convergent strategy for the synthesis of the antitubulin polyketide disorazole C1 is proposed based around the alkyne precursor I, featuring a novel Evans-Tishchenko/ring closing alkyne metathesis approach. Due to the inherent symmetry of the molecule this retrosynthesis leads to two fragments: a β- hydroxyketone II and the oxazole C(1)-(9) fragment III. A review of previous syntheses of disorazole C1 and established structure activity relationships (SARs) highlights a gap in current knowledge relating to the role of the oxazole in tubulin binding. Therefore, the focus of this research has been towards developing new routes for the synthesis of the C(1)-C(9) fragment that can be adapted to the synthesis of heterocyclic analogues to further establish the SAR of disorazole C1. Chapter 2 focuses on a disconnection at the C(5)-C(6) bond and a novel synthesis of the racemic C(1)-C(9) fragment has been achieved via a lithiation of methyl 2- methyl-1,3-oxazole-4-carboxylate and coupling to aldehyde V. First generation asymmetric routes to the C(1)-C(9) fragment centred on i. a biomimetic amino acid condensation route via an oxazoline intermediate based on the precedent of Meyers et al. and ii. a C(4)-C(5) disconnection approach based around the epoxide VII; are discussed in chapter 3. A second generation C(4)-C(5) disconnection centred on the novel tosylate VIII is discussed in chapter 4. Attempts to synthesise the parent C(1)- C(9) oxazole fragment using the tosylate VIII via i. a palladium catalysed C-H activation of ethyl 4-oxazole carboxylate and ii. lithiation of oxazole are reported. Coupling of fragment VIII (X = OTs) with ethyl 1H-pyrazole-4-carboxylate and a CuAAC coupling of the azide derived from tosylate VIII with methyl propiolate has allowed the successful completion of the synthesis of pyrazole and triazole analogues of this fragment.

In this thesis, synthetic chemistry was used as a tool in the exploration of various aspects of natural products discovered by the natural products research group at the University of Canterbury. Work on the constituent amino acids and connectivity of the pteratides, a potently cytotoxic series of cyclodepsipeptides, had been completed before the beginning of this work (carried out by Miss C. Chen). The elucidation of the stereochemistry of the constituent amino acids was undertaken in this present work. The synthesis of all stereochemical entities of a number of unusual amino acids, which were either not available commercially or were expensive, was carried out, providing reference materials for comparison to the natural products. The synthesis of the diastereoisomers of one of these amino acids, 4-methylproline, was carried out by modification of literature procedures, which led to the development of an improved, concise and stereoselective synthesis. The hydrolysis of the natural products, derivatisation of the resultant hydrolysates, synthetic and commercial reference amino acids and HPLC analysis allowed the full stereochemical assignment of the pteratide series. The total synthesis of spiro-mamakone A, a cytotoxic polyketide isolated by Dr S. van der Sar, was undertaken. The synthesis was not successfully completed due to difficulties in the late-stage formation of a crucial enedione motif. However, very advanced intermediates were successfully synthesised. These synthetic analogues of the natural product were analysed for biological activity, allowing valuable insight into the structure-activity relationship, for example, demonstrating the importance of the enedione moiety to biological activity.

No description available.

No description available.