Attempts were made to synthesize cleanly and efficiently a 3,6-branchpoint mannose monomer via three synthetic routes. This monomer was then to be used in a solution-phase synthesis of a high mannose-type nonasaccharide using a PEG soluble polymer support developed in our laboratory. The monomer was to meet the requirements of (1) stable protecting groups on positions 2 and 4; (2) easily cleavable groups on positions 3 and 6; (3) a group which is stable and a good donor on position 1. The key step in the synthesis of the first monomer, containing allyl groups on positions 3 and 6, involved using Ogawa's stannylation methodology. The key step in the second route involved benzylating a monomer containing two ester groups on positions 3 and 6 using Bundel's methodology. The third route, based on well established literature procedures, gave the desired compound in acceptable yield but with more purification effort. / Using a similar approach to that taken independently by Stork and Hindsgaul, attempts were made to construct $ beta$-glycosides using antimony as a temporary connector. (Abstract shortened by UMI.)

Three activated modified dimers 9, 21 and 35, which contain a dialkyl sulfide backbone, have been synthesized. / These dimers, as well as dimer A, have been incorporated into DNA strands by solid-phase techniques. The number of these dimers being incorporated varied from 1-3.$ sp*$ / Thermal studies have shown that the oligomers containing modified dimers indeed bind to their complementary DNA or RNA, except for two oliglomers in which dimer 9 or 21 was incorporated three times. They only bind relatively poorly to complementary RNA, but not at all to DNA. The incorporation of 35 into DNA oligomers showed good binding to its complementary RNA, but not DNA. / All sulfide-containing oligomers have been oxidized to sulfone-containing oligomers using oxone. In thermal studies, hybrids of the sulfone-containing oligomers with their complementary DNA and RNA showed much poorer binding properties than the corresponding sulfide-containing oligomers. / The synthesis of nucleoside 28, the upper half of dimer 21, as well as an improved procedure for the preparation of 2$ sp prime$-O-methyluridine, are described. ftn$ sp*$Please refer to the dissertation for diagrams.

Chiral auxiliary 1,2-di-O-isopropylidene-3-C-cyanoethyl-5-deoxy-5-isopropylamino-D-xylofuranose 3-32 was synthesized. Cyclic phosphoramidite 3-34 derived from 3-32 is a useful precursor for the stereoselective synthesis of phosphorothioate. The chiral auxiliary can be easily removed at the end of the synthesis by treatment with concentrated ammonia. The major dithymidine phosphorothioate isomer with a SP configuration was obtained. / The allyl group was investigated as a protecting group for the internucleotide linkage. The removal of the allyl group in dimer 4-6S or 4-6O was achieved by treatment with nucleophiles. Solid phase study indicated this to be a general method for the routine solid phase synthesis of oligonucleotide phosphorothioates and phosphates.* / A new type of chiral auxiliary 5-20 which incorporates indole and imidazole moieties was synthesized. It led to the stereoselective synthesis of a novel indolophosphorothioate 5-37 with 90% de and the formation of an alkylphosphinate analog 5-41 as a single diastereomer. / Chiral indolo-oxazaphosphorine 6-22 was prepared from L-tryptophan. Dithymidine phosphorothioate with ≥95% de was obtained while using 6-22 as a precursor. The removal of the chiral auxiliary was achieved by heating in concentrated ammonia at 55ºC for 16 hours. The indolo-oxazaphosphorines derived from L- or D-tryptophans led to the formations of dithymidine phosphorothioates with RP or SP configurations, respectively. The methodology was applied successfully to the solid phase synthesis of phosphorothioate dimers.* / *Please refer to dissertation for diagrams.

A strategy for the total synthesis of palau'amine is disclosed. The bias of a bicyclic framework is used as a key feature for the enantioselective synthesis of the highly functionalized hexasubstituted cyclopentane core of the molecule. A synthetic approach centering on a tin-catalyzed aldol and a Pauson-Khand reaction is presented. This pathway yielded a penta-substituted cyclopentane ring with four stereocenters positioned and the requisite functionalities to allow for further progress. Installation of the last stereocenter was investigated on a model substrate.

Two annulation strategies have been examined as a potential route to highly functionalised, oxygenated decalins of the type embodied in natural product azadirachtin. Both approaches employ a Michael addition of a latently functionalised nucleophile to an $ alpha, beta$-unsaturated keto ester to assemble the annulation precursor. / One approach deploys the in-house developed 4C siloxy diene, 1-trimethylsiloxy-1-methoxy-3-phenylthio-1,3-butadiene as the nucleophilic component in a Lewis acid mediated 1,4 conjugate addition to triethyl 4-oxo-2-cyclohexen-1,1,3-tricarboxylate. The potential of the keto ester moiety in the E Michael adduct, to function as the nucleophilic component, in a Claisen condensation in the conventional sense was examined. Cyclisation onto the tethered electrophile was achieved with an acyl chloride as the electrophilic partner. The stereochemistry of this kinetically controlled, essentially irreversible closure was found to lead exclusively to cis product geometry. The method provides a concise route to highly functionalised cis decalins incorporating a latent angular hydroxymethylene equivalent. Access to the corresponding trans series was explored. / A second strategy designed to examine three modes of cyclisation to a functionalised decalin intermediate required the development of metallo-cuprate chemistry. A convenient, operationally simple route to the higher-order homo bis trimethylstannyl cyano cuprate was invented through the intermediacy of a novel bis amido cuprate. Bis trimethylstannyl cuprate was shown to add to acetylene to provide the desired cuprate trimethylstannylvinyl cyano cuprate in synthetically useful yields. The conjugate addition of this cuprate to enones and enone-esters alike was compared with similar addition of other mixed stannylvinyl cuprates. Two novel mixed trimetylstannyl and trimethylstannylvinyl amido cuprates, requiring only one equivalent of valuable tin reagent for their preparation are described and briefly evaluated as selective tin transfer reagents. Finally BSA was shown to efficiently promote conjugate addition of homo bis trimethylstannylyinyl cuprate to enone and enone esters alike without unwanted side-reactions. The method was successfully used to generate a key Michael adduct in 92% yield. The activating potential of this reagent (BSA) as a newly discovered $ pi$ Lewis donnor was assessed, relative to other conventional activating agents. / A second study designed to more easily access transfused decalins, employed a cis trimethylstannylvinyl cuprate as the Michael donnor in 1,4-conjugate addition to triethyl 4-oxo-7-cyclohexen-1.1.3-tricarboxyiate. The trimethylstannylvinyl residue in the resulting adduct was evaluated as a latent nuclcophile in the synthesis of several cyclisation precursors. None were found suitable in this capacity. The most expedient route to a promising annulation precursor retained the vinyl stannane moiety and employed a Claisen rearangement to install the C$ sb2$ electrophilic centre with complete control of relative stereochemistry of three contiguous stereogenic centres.

THE DEVELOPMENT OF METAL CATALYZED, ONE-STEP APPROACHES TO α-AMINO ACIDS, PYRROLES AND α-SUBSTITUTED AMIDES The purpose of this research was to develop new, one pot methods to assemble nitrogen-contained biologically relevant products, such as pyrroles, amido acid derivatives, and α-substituted amines/amides. These products are all generated from readily available building blocks, such as imines, acid chlorides, alkynes, and/or carbon monoxide, and often via metal catalysis. Chapter 2 of this thesis describes how α-phenoxyamides can be used in palladium catalyzed carbonylations to form α-amino acid derivatives, instead of the previously reported synthesis with imines/acid chlorides. Notably, these substrates are analogous of the in situ formed N-acyl iminium salts, but more stable, and in the presence of a palladium(0) complex (Pd2dba3) and Lewis acids can undergo carbon-oxygen bond activation to form palladacycles. Coupling this oxidative addition with carbonylation provides a mild, one step, catalytic route to prepare α-amino acid derivatives in high yield. In chapter 3, we show that α-(3-pyridyloxy)amides can directly undergo oxidative react with palladium catalysts, and be employed in the palladium catalyzed carbonylation to form α-amino acid derivatives. Notably, this reaction requires neither acidic nor basic co-catalysts, and is tolerant to various sensitive substituents. Moreover, this carbonylation reaction can be coupled with alkyne trapping and form pyrroles in one step from α-(3-pyridyloxy)amides and alkynes. Chapter 4 describes an alternative route to readily form pyrroles, via the phosphine mediated coupling of α, β-unsaturated imines and acid chlorides. This provides a novel approach to regioselectively assemble of polysubstituted pyrroles from simple starting materials. The application of this method for the synthesis of lukianol A is also described. In chapter 5, our studies f / Le Développement d'Approches en Un Pot, Catalysées par un Métal de Transition pour la Synthèse d'-Acides Aminés, Pyrroles et d'Amides -SubstituésL'objectif de cette recherche était de dévolopper une nouvelle méthode en un pot pour former des produits biologiquement importants contenant un azote, tels que les pyrroles, les dérivés d'acides aminés et les amines/amides α-substitués. Ces produits sont tous générés à partir de produits de départ facilement disponible, tels que les imines, les chlorures d'acides, les alcynes et/ou le monoxide de carbone, et souvent via la catalyse par un métal de transition.Le chapitre 2 de cette thèse décrit comment les α-phenoxyamides peuvent être utilisés dans les carbonylations catalysées par le palladium pour former des dérivés d'α-acides aminés, au lieu de la synthèse, précédemment reportée, avec des imines et des chlorures d'acides. Ces substrats sont similaires aux sels d'iminiums N-acylés formés in situ mais ils ont l'avantage d'être plus stable, et en présence d'un complexe de palladium(0) (Pd2dba3) et d'un acide de Lewis, ils peuvent subir une activation de liaison carbone-oxygène pour former des palladacyles. Le couplage de cette addition oxydante avec la carbonylation fournit un voie douce et en une étape pour préparer des dérivés d'α-acides aminés avec de hauts rendements.Dans le chapitre 3, nous montrons que, sans l'assistance d'acides de Lewis, les α-(3-pyridyloxy)amides peuvent directement subir une addition oxydante avec un catalyseur de palladium et peuvent être employés dans la carbonylation catalysée par le palladium pour former des dérivés d'α-acides aminés. Cette réaction exige aucuns co-catalyseurs acides ou basiques, et elle tolère de nombreux substituents sensibles. De plus, cette réaction de carbonylation peut se coupler à la cycloaddition avec un alcyne pour former des pyrroles en une é

The optimized synthesis of acyclic dialkoxy disulfides and aromatic polysulfides is described and their physical properties probed. A theoretical survey of dialkoxy disulfides and thionosulfites was undertaken in order to determine the most efficacious method for accurately modeling these compounds. In particular, the origin of the high barrier to rotation in the dialkoxy disulfides was determined to be due to a generalized anomeric effect resulting from two lone pair donations of each sulfur atom into each of their respective sulfur-oxygen antibonding orbitals. The origin of the high rotational barrier was also verified experimentally, in particular with respect to solvent and substituent effects. Complimentary to this thermal process, the decomposition of dialkoxy disulfides was also investigated. It was determined that these compounds decompose under first order kinetics via an initial asymmetric S-O homolytic cleavage. Activation parameters for both of these processes were determined. Theoretical modeling on the relative ground state energies of dialkoxy disulfides is also described. It has been ascertained that the equilibrium position between the two isomers can be influenced by the ring size of the molecule; larger rings promote the dialkoxy disulfide isomer. These modeling studies were successfully corroborated experimentally. Of note is the synthesis of a new 8-membered ring dialkoxy disulfides as well as novel 7- membered ring thionosulfites. These compounds were also confirmed by single X-ray crystallography. The kinetics of desulfurization of acyclic aromatic tri- and tetrasulfides is described. Tetrasulfides were found to transfer a suI fur atom to triphenylphosphine over ten times faster than their trisulfide analogues.

Several novel cellulose derivatives with triphenylmethyl or 1-methylnaphthalene substituents at the primary hydroxyl positions and n-alkyl or benzyl substituents at the secondary hydroxyl positions have been prepared and characterized. The 6-O-trityl-2,3-O-alkyl cellulose and 6-O-trityl-2,3-O-benzyl cellulose derivatives form lyotropic chiral nematic liquid crystalline phases that display reflection colours. Both left and right-handed chiral nematic phases have been observed; the twist sense depends on the nature of the side-group substitution and the solvent. The chiroptical activity of the phenyl chromophores attached to these polymers depends on several factors such as the presence or absence of a chiral nematic structure and in the case of mesophases it also depends on the chiral nematic twist sense. / The polymer 6-O-$ alpha$-(1-methylnaphthalene)-2,3-O-pentyl cellulose forms a right-handed thermotropic chiral nematic mesophase. This polymer shows dilute solution chiroptical activity from the naphthyl chromophores, indicative of a helical arrangement of chromophores along the chain.

Anomalous phosphorescence decays arising from the interaction of tryptophan side chain with proximal disulfide linkages are investigated with a number of proteins in rigid media at 77K. Changes in the lifetime of the fast, or anomalous, component provide evidence for subtle ligand-induced conformational changes with both an anti-galactan antibody and the enzyme lysozyme. The induced changes are seen to occur both directly at, and at a distance from, the combining sites. Recognition of the disulfide interaction is used to rationalize earlier fluorescence results with these systems. / The distance dependence of the tryptophan-disulfide interaction at the triplet level is established through a time-dependent phosphorescence study of a model system. The interaction is shown to fall off exponentially with separation, so that measured variations in the anomalous decays can detect geometrical changes of much less than one angstrom. / Temperature-dependent studies of the tryptophan-disulfide interaction with both proteins and the model system are described. The evidence obtained suggests that the disulfide perturbation of the triplet state of tryptophan occurs as a result of a photo-induced one-electron transfer. / The steep distance dependence of the interaction and the utility of these decays in revealing conformational heterogeneity is demonstrated from the non-exponential behavior of several single tryptophan-containing proteins and peptides.

The reaction of a series of 1,1-disubstituted-1-silacyclo-3-pentenes with butyllithium reagents was studied. This reaction depends critically on the substituent at silicon. 1,1-Dimethyl- or 1,1-diphenyl-1-silacyclo-3-pentene has the propensity to undergo anionic polymerization whereas 1,1-bis(4-tert-butylphenyl)-1-silacyclo-3-pentene was metalated cleanly to give the anion derived from proton abstraction on the cyclopentenyl ring. The regioselectivity of the reaction of the silacyclopentenyl anion with electrophiles was examined and found to be influenced by the steric size of the electrophile. Small electrophiles favor $ alpha$-selection while larger ones show slight $ gamma$-preference. / The regiochemistry of reactions of $ alpha$-silylallyl lithium with alkyl halides can be controlled with metal-ion complexing substituents on silicon to give selectively the $ alpha$-substituted allylsilane. The extent of $ alpha$-selection depends significantly on the nature of the ligand and solvent. Allyl (bis(2-ethoxyethyl)aminomethyl) dimethylsilane gives higher $ alpha$-selection than allylsilanes with fewer binding heteroatoms. When the ligand is chiral the alkylation reaction also proceeds stereoselectively. Changing the solvent from tetrahydrofuran to diethyl ether further increases the yield of the $ alpha$-isomer. The synthetic utility of these silyl-ligands was demonstrated by an application to the synthesis of $ alpha$-(E)-bisabolene.