This thesis is divided into three separate parts with amino alcohols as the common feature. The first part describes the development of a novel three-component approach to the synthesis of α-hydroxy-β-amino esters. Utilizing a highly diastereoselective Rh(II)-catalyzed 1,3-dipolar cycloaddition of carbonyl ylides to various aldimines, syn-α-hydroxy-β-amino esters formed in high yields and excellent diastereoselectivities. This methodology was also applied in a short enantioselective synthesis of the C-13 side-chain of Taxol. The second part of the thesis describes a total synthesis of D-erythro- Sphingosine based on a cross-metathesis approach to assemble the polar head group and the aliphatic chain. The last part deals with the application of amino alcohols as scaffolds in a diversity-oriented protocol for the development of libraries of small polycyclic molecules. The design of the libraries is based on the iterative use of two powerful ring-forming reactions; a ring-closing metathesis and an intramolecular Diels-Alder reaction, to simultaneously introduce structural complexity and diversity. / QC 20101222

Particle dispersions provide a promising tool for the engineering of functional materials that exploit self-assembly of complex structures. Dispersion made from magnetic colloidal particles is a great choice; they are biocompatible and remotely controllable among many other advantages. However, their dominating dipolar interaction typically limits structural complexity to linear arrangements. This paper shows how a magnetostatic equilibrium state with noncollinear arrangement of the magnetic moments, as reported for ferromagnetic Janus particles, enables the controlled self-organization of diverse structures in two dimensions via constant and low-frequency external magnetic fields. Branched clusters of staggered chains, compact clusters, linear chains, and dispersed single particles can be formed and interconverted reversibly in a controlled way. The structural diversity is a consequence of both the inhomogeneity and the spatial extension of the magnetization distribution inside the particles. We draw this conclusion from calculations based on a model of spheres with multiple shifted dipoles. The results demonstrate that fundamentally new possibilities for responsive magnetic materials can arise from interactions between particles with a spatially extended, anisotropic magnetization distribution.

Notre équipe a récemment décrit la synthèse de nouveaux iminosucres de type indolizidines et quinolizidines, qui se sont avérés être de puissants inhibiteurs sélectifs d’α-glucosidases (IC50 nanomolaires). Ces molécules, de structure originale, ont la particularité de posséder un centre quaternaire en jonction de cycles et une configuration D-gluco. Dans le but de mieux comprendre le mode d’interaction de ces molécules avec les glycosidases, nous nous sommes intéressés à la synthèse de leurs analogues comportant un motif aziridine, inclus dans un squelette 1 azabicyclo[4.1.0]heptane.L’approche synthétique que nous avons choisie pour accéder aux aziridinyl iminosucres implique une cycloaddition 1,3-dipolaire régio- et stéréoselective de cétonitrones dérivées de sucres avec des alcynes pour former des isoxazolines et un réarrangement de Baldwin stéréosélectif en 2 acylaziridines. Pour les acylaziridines polybenzylées la conversion en aziridinyl iminosucres a été effectuée par réduction diastéréosélective de leur fonction cétone et déprotection dans des conditions réductrices de Birch. Pour les acylaziridines polyacétylées les iminosucres finaux ont été obtenus par réduction en présence d’hydrures métalliques.Grâce à cette stratégie de synthèse originale, efficace, et économique en atomes, nous avons préparés 7 aziridinyl iminosucres, et 5 isoxazolines polyhydroxylées. Tous ces nouveaux iminosucres ont été évalués comme inhibiteurs de glycosidases, et se sont avérées être des inhibiteurs moyens (IC50 micromolaires) mais sélectifs des α-glucosidases. L’obtention de complexes cristallins avec une α-glucosidase bactérienne a permis de montrer par cristallographie leur mode d’interaction avec cette enzyme, à l’échelle moléculaire. / Our team has recently described the synthesis of new indolizidine and quinolizidine iminosugars, which revealed to be potent and selective α-glucosidase inhibitors (nanomolar IC50). These original molecules exhibit a quaternary center at the ring junction and a D-gluco configuration. With the aim to define the mode of interaction of these molecules with glycosidases, we engaged in the synthesis of analogues containing an aziridine moiety included in a 1-azabicyclo[4.1.0]heptane scaffold.Our synthetic approach towards aziridinyl iminosugars involves a stereoselective 1,3-dipolar cycloaddition between carbohydrate-derived cyclic ketonitrones and alkynes, and a stereoselective Baldwin rearrangement into 2-acylaziridines. The latter (if polybenzylated) were converted into aziridinyl iminosugars through diastereoselective reduction of their ketone function and deprotection under Birch conditions. In the case of polyacetylated acylaziridines, the final iminosugars were obtained by reduction with hydrides.Using this strategy, we have prepared 7 aziridinyl iminosugars, and 5 polyhydroxylated isoxazolines. All these new iminosugars were evaluated as glycosidase inhibitors, and they revealed to be modest (micromolar IC50) but selective inhibitors of α-glucosidases. Their complexes with a crystalline bacterial α-glucosidase allowed crystallographic elucidation of their mode of interaction with this enzyme at the molecular level.

We have studied the effect of the dipolar magnetic coupling (also known as Néel coupling or "orange-peel" coupling) in tunneling magnetoresistive (TMR) elements. With an in situ scanning tunneling microscope we directly accessed the roughness of the films and found a close correspondence between the values for the coupling fields determined by the magneto-optical Kerr effect and the ones computed on the basis of the measured morphology parameters. We confirm an increase of the dipole coupling between magnetic layers with decreasing barrier thickness as predicted by the model. Deviations from the theoretical predictions are observed for the case of thinner soft magnetic layers, which can be explained by reduced magnetisation in very thin films. We demonstrate the importance of dipolar coupling for understanding the magnetic behaviour of TMR elements by comparing TMR curves for optimised and nonoptimised structures.

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Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Quantum information processing (QIP) has the potential to reduce the complexity of many classically ‘hard’ computational problems. To implement quantum information algorithms, a suitable physical quantum computer architecture must be identified. One approach is to store quantum information in the electron spins of an array of paramagnetic N@C₆₀ endohedral fullerene molecules, using the electron-electron dipolar interaction to permit the formation of the entangled quantum states needed to implement QIP. This thesis explores two different chemical methods to create two-spin centre arrays that contain N@C₆₀. The first method uses a double 2,3 dipolar cycloaddition reaction to a dibenzaldehyde-terminated oligo-p-phenylene polyethynylene (OPE) unit , to create an (S_3/2, S_3/2) N@C₆₀-N@C₆₀ dimer with a fixed spin centre separation of 2.7 nm. The second approach is via a self-assembly scheme in which a Lewis base functionalised N@C₆₀ molecule coordinates to an antiferromagnetic metallic ring magnet to form a (S_3/2, S_3/2) two-spin centre N@C₆₀-Cr₇Ni system with an inter-spin separation of 1.4 nm. In both systems, a significant perturbation of the electron spin transition energies is observed using CW ESR, this perturbation is shown to be well accounted for by the inclusion of an electron-electron dipolar coupling term in the electron spin Hamiltonians. To create entanglement in an ensemble of two-spin centre molecules, the dipolar coupling interaction must lie within a narrow distribution. To achieve this not only the separation but also the orientation of the inter-spin axis with respect to the applied magnetic field must be controlled for which a method of macroscopic alignment is required. The potential of using a uniaxially drawn liquid crystal elastomer to exert uniaxial order on fullerene dimers is tested, finding that the degree of alignment is insufficient, possibly a result of the propensity for the fullerene molecules to phase separate from the elastomer. This phase separation is shown to restrict N@C₆₀ phase coherence lifetime to 1.4 µs at 40 K due to instantaneous spin diffusion. The electron spin environment of both N@C₆₀ and an N@C₆₀-C₆₀ dimer in a polymer matrix is examined using polystyrene as the host matrix. By deuteration of the polystyrene matrix, a maximum phase coherence lifetimes of 48 µs and 21 µs are measured for the N@C₆₀ and N@C₆₀-C₆₀ dimer, respectively. The concept of reading out the electron spin state of N@C₆₀ molecules by coupling it to a spin system that can be probed using optically detected magnetic resonance (ODMR) such as an NV- centre has been previously suggested. To this end, the photostability of N@C₆₀ under 637 nm laser illumination has been examined in solution. The effect of the presence of an atmospheric concentration of oxygen is striking, affording a 57-fold retardation in the photodecomposition of N@C₆₀ compared to a degassed solution. When ambient oxygen is present, the average number of excitations that are required to cause decomposition is ≈60000. Finally, for future UV photophysics experiments involving N@C₆₀, the best solvent to use was found to be decalin, finding that it significantly slowed decomposition of N@C₆₀ in both ambient and degassed solutions. The conclusions of this work make a significant contribution to the field of QIP with N@C₆₀, showing that there is a bright future for N@C₆₀.