Iminosugars are known to behave as carbohydrate mimics in biological systems by virtue of their similar structures. However as the ring nitrogen prevents metabolism it means that iminosugars have the potential to become inhibitors of these systems. It is known, for example, that iminosugars can behave as mimics in the hydrolysis mechanism. This leads to possible medicinal applications of iminosugars. One such case is lysosomal storage disorders which arise as a result of a genetic defect which causes missense mutations coding for the N-acetylhexosaminidase enzymatic protein. N-Acetylhexosaminidases are a sub-member of the class of glycosidase enzymes. They are responsible for the cleavage of N-acetylhexosamine residues from glycoconjugates in the lysosome. Mutations in the gene coding for this protein lead to a deficiency in the enzymatic activity resulting in accumulation of unhydrolysed substrate in the lysosome. Lysosomal storage disorders have a phenotype of poor motor development and neurological problems. The infantile form usually leads to death before the age of five. An iminosugar mimic could give rise to a possible treatment for lysosomal storage disorders by acting as a molecular chaperone during protein folding, promoting correct folding by its intrinsic affinity for the native fold of the enzyme. Likewise in the treatment of cancer, the inhibitory ability of iminosugars has potential applications. In cancer, extracellular hydrolysis occurs which favours cancer cell survival. Macrophages, which attack and eliminate cancer cells, can be activated by macrophage activating factor (MAF) which displays an α-N-acetylgalactosamine residue that appears essential for the activation cascade. Cancer cells secrete an α-N-acetylgalactosaminidase enzyme that acts to decrease the potency of MAF, thus promoting cancer cell survival. Inhibition of cancer cell α-N-acetylgalactosaminidase may restore macrophage activation and generate potential therapeutics. Chapter 1 of this thesis contains extended discussion of the aforementioned, and related, diseases and the therapeutic applications of iminosugars. Some historically and biologically important iminosugars are described along with some current iminosugar drugs. Chapter 2 describes the synthetic strategies explored in an attempt to synthesise all the members of the 2-acetamido pyrrolidine iminosugars. An overview of the compounds synthesised towards this end by a past group member is given along with the work performed as part of this thesis to complete this goal. Both enantiomers with arabino- and ribo- stereochemistry and D-lyxo- were previously synthesised. The syntheses of both enantiomers with xylo- stereochemistry along with the L-lyxo- compound were completed as part of this thesis, from either D- or L-glucuronolactone and D-ribose, respectively. Chapter 3 details the synthetic strategy adopted to synthesise the enantiomer of D-DNJNAc, the first potent α-N-acetylgalactosaminidase inhibitor to be found. The synthesis towards another piperidine iminosugar, 6-deoxy DGJNAc, is presented in the second half of this chapter, along with two related compounds.

No description available.

Glycosaminoglycans (GAGs) are complex biopolymers that play important roles in inflammation, coagulation, angiogenesis, cell adhesion and viral invasion by interacting with several different proteins.1,2 Structurally, GAGs are built up of several different sulfated disaccharide units.3 Specific GAG sequences that uniquely recognize their cognate proteins exist. Such specificity typically arises from the binding of unique sulfation patterns on the linear GAG chain to highly electropositive protein domains. Thus, these highly charged, sulfated biopolymers potentially represent a new class of therapeutics. Yet, the major stumbling block to the development to these agents is their extremely complicated and tedious chemical synthesis. We hypothesized that replacing the saccharide skeleton with an equivalent non-saccharide and readily synthesized organic skeleton would usher in an era of new, GAG-based therapeutics. This challenge has been addressed on two fronts, computational design and chemical synthesis, by focusing on the heparin pentasaccharide-antithrombin system that represents an exhaustively studied model GAG-protein system. With respect to chemical synthesis, a microwave-based synthetic procedure that can rapidly introduce multiple sulfate groups on a poly-hydroxyl substrate within minutes was developed.4 Using this method, the synthesis of a previously designed activator (IAS5), which otherwise proved to be problematic, was successfully completed. Biochemical screening of IAS5 and its analogs revealed that these molecules could activate antithrombin up to 30-fold in comparison to the 300-fold activation by the heparin pentasaccharide. In an effort to develop more potent antithrombin activators, a new method to predict high affinity GAG sequences for a given GAG-binding protein based on combinatorial virtual-library screening was developed.5 This combinatorial virtual-library screening method was applied to a library of 24,576 non-saccharide, sulfated molecules that were created using the structure of IAS5 as a template. Thirty seven‘hits’ that had common structural features were identified from this study. Interestingly, all these ‘hits’ bind to antithrombin similarly and orient the 4 negative charges identical to the corresponding groups in the heparin pentasaccharide. The synthesis of selected targets is currently in progress and several synthetic steps have already been optimized.

Iminosugars are polyhydroxylated alkaloids, and can be viewed as sugar analogues in which the endocyclic oxygen atom has been replaced with nitrogen. These compounds are highly medically relevant and their biological activity is largely due to their inhibition of glycosidases. Several examples of the iminosugar class are currently marketed as drugs, and many more are in earlier stages of development for a variety of diseases and disorders. The most fruitful approaches to the chemical synthesis of iminosugars have utilised carbohydrate starting materials as optically pure chiral building blocks, or chirons. Most of the monosaccharides are not readily available, but the relatively few naturally abundant cheap sugars have been exploited as chirons for over a century. The availability of the rare sugars is growing with the development of a new biotechnological approach to their synthesis, known as Izumoring. This thesis is primarily concerned with the chemical synthesis of iminosugars from carbohydrate starting materials. The synthesis of unnaturally functionalised sugar polyols and their suitability as substrates for the Izumoring process is also discussed. Chapter 1 provides a brief general overview of the history, natural occurrence and therapeutic application of iminosugars. General strategies for their synthesis from carbohydrate chirons are discussed. Chapter 2 concerns divergent syntheses of several iminosugar targets from both enantiomers of glucuronolactone and their biological evaluation. A new scaleable synthesis of the natural product 1-deoxynojirimycin is presented that has since been adopted for commercial purposes, as well as an efficient strategy for the synthesis of both enantiomers of 2,5-dideoxy-2,5-imino- mannitol and their novel amino acid analogues. Access to hexosaminidase inhibiting acetamido- substituted piperidines is presented, including 2-acetamido-1,5-imino-1,2,5-trideoxy-D- galactitol, which has been found to be one of the few known potent and specific inhibitors of α- N-acetyl-galactosaminidase. This inhibitory profile may allow the compound’s use for further investigation of a strategy for cancer treatment. Chapter 3 concerns the synthesis of carbon branched pyrrolidines and their biological evaluation. A novel and highly potent α-glycosidase inhibitor has been discovered, synthesised by a strategy that utilises the benzhydryl ether as key protecting group. A mild method for the introduction of this protecting group has been shown to be general to a range of sterically congested and/or acid/base sensitive carbohydrate lactones. Chapter 4 concerns the synthesis of deoxygenated and fluorinated sugar alcohols and their successful biotechnological transformation into ketoses by the Izumoring process. Publications arising from this work are included in the Appendix.

This thesis firstly describes a synthesis of the natural product taurospongin A, a potent DNA polymerase beta inhibitor. Sharpless asymmetric dihydroxylation on olefin <b>E-1.60</b> followed by selective deoxygenation at C(2) via Barton‒McCombie reaction delivers the desired C(1)–C(10) carboxylic acid core. Subsequent esterification of the C(1)–C(10) fragment with C(1′)–C(25′) fatty acid furnishes the natural product in 13.5% yield. The structure of an unnamed natural product <b>2.14</b> isolated in 1974 is proven to be misassigned by previous studies within the Robertson group. As described in this thesis, two proposed structures A and B are obtained via total synthesis in order to reveal the identity of the natural product. A synthesis of key intermediate spirocycles <b>2.148</b> and <b>2.158</b> with desired trans- diol moiety is described by a dihydroxylation reaction on an electron deficient gamma-keto unsaturated acid with subsequent spirocyclisation reaction. Finally, methodology for generating high-value synthetic intermediates by an asymmetric, one-pot enzymatic di/polycarbonyl reduction is described. The concept of such methodology is first proven by the synthesis of (3R)-hydroxybutyl (3R)-hydroxybutanoate <b>3.20</b>. This thesis then describes substrate scope studies and corresponding stereochemical proof to provide more information about this methodology.

A síntese em fase sólida é o método mais utilizado na obtenção de peptídeos em laboratório. Em geral, as diferentes etapas do processo são realizadas em temperatura ambiente. De fato, até o início desta década, temperaturas elevadas (>40ºC) eram empregadas apenas esporadicamente nas etapas de acoplamento. Em 1993, entretanto, Rabinovich e Rivier propuseram a realização de todas as etapas do processo a 75ºC. Em 1996, Saneei e colaboradores tentaram automatizar o processo a 40-50ºC, apesar de não ter sido feita nenhuma avaliação sistemática prévia. Em 1997, Varanda & Miranda descreveram o primeiro estudo sistemático feito com o objetivo de investigar aspectos, vantagens, desvantagens e limitações da SPFS em altas temperaturas. O presente trabalho teve como objetivo ampliar os conhecimentos sobre o método através da avaliação de três importantes aspectos considerados problemáticos na SPFS convencional: racemização, agregação e síntese de peptídeos longos. Para tanto, vários peptídeos foram escolhidos como modelos de estudo. Todos eles foram sintetizados por SPFS convencional (usando protocolos de rotina de nosso laboratório) e por SPFS em alta temperatura (empregando as condições experimentais descritas por Varanda & Miranda em 1997). Os materiais brutos foram comparados em: 1- suas recuperações a partir de suas peptidil-resinas correspondentes; 2- suas qualidades. RP-HPLC, determinação do conteúdo de aminoácidos e CE foram os métodos de análise empregados. Os produtos e subprodutos majoritários foram isolados para caracterização química por análise de aminoácidos de seus hidrolisados totais e por espectrometria de massas. Os resultados obtidos demonstraram que no aspecto racemização a SPFS em alta temperatura, nas condições experimentais empregadas, mostrou-se equivalente à SPFS convencional: a incidência de estereoisômeros contaminantes nos peptídeos brutos foi inferior a 1%. O estudo do aspecto agregação evidenciou que se por um lado as condições experimentais empregadas para a SPFS em alta temperatura levaram a uma suposta minimização, por outro os peptídeos brutos obtidos foram de qualidade muito inferior a daqueles provenientes da síntese convencional: interrupções do crescimento das cadeias em resíduos de glutamina levaram à formação significativa de peptídeos contaminantes delatados. Se a agregação está ou não relacionada ao favorecimento destas reações secundárias é questão ainda não respondida. A síntese da CCK-22 humana não sulfatada sugeriu que o método de SPFS em alta temperatura é adequado à sua obtenção com bom rendimento e em tempo reduzido. Entretanto, a síntese da CCK-33 correspondente, um protótipo de peptídeo longo de seqüência complexa, evidenciou que, para a obtenção deste tipo de composto, a mistura 25%DMSO/tolueno pode não ser o solvente ideal comum para as etapas de desproteção, neutralização e acoplamento. Nestas condições, a mistura DIC/HOBt pode também não ser a melhor opção. / Stepwise solid-phase synthesis (SPPS) is the method of choice to prepare peptides. Although deprotection, neutralization and acetylation have been generally carried out at room temperature, the couplings have not. Indeed, elevated temperatures have been used to enhance coupling efficiency in conventional SPPS. The idea of performing all the synthetic steps at high temperatures, shortening the peptide chain build-up process, has not been explored until the 90s. In 1993, Rabinovich & Rivier proposed some modifications to the conventional SPPS protocols and achieved some peptide syntheses by performing deprotection, neutralization, coupling and acetylation at 75 ºC. In 1996, Saneei and co-workers tried to automate the entire synthetic process at 40-50 ºC. In 1997, Varanda & Miranda reported the first systematic study on SPPS at elevated temperatures. These authors determined optimized synthesis conditions of unsulfated cholecystokinin-12 by investigating aspects of the methodology such as temperature, solvent systems, resins compatibility, type of resins, peptide-resins swelling properties and, also, coupling agents efficiencies. The main goal of the present work was to evaluate SPPS at elevated temperature in three different aspects: racemization, aggregation and applicability to the synthesis of long and complex. peptides. For that, we chose some model peptides and synthesized them manually using conventional SPPS (our laboratory\'s routine protocols) and SPPS at elevated temperature (Varanda & Miranda\'s protocols). The crude peptides were compared in their recoveries from the corresponding peptidyl-resins after final cleavage and full deprotection and in their qualities. RP-HPLC, CE and amino acid analyses were the techniques employed in the comparisons. The major products and by-products were isolated and characterized using amino acid analysis and mass spectrometry. The results can be summarized as follows: 1- no significant contamination resulting from racemization has been detected in the crude peptides. The amounts of stereoisomers present on the crude peptides were always lower than 1% independently of the SPPS method employed or the analytical technique used for comparison; 2- no final conclusion could be taken regarding to the aggregation phenomenon. Under the experimental conditions employed for SPPS at elevated temperature, some couplings were definitely favoured. Despite that, the crude materials obtained showed low purities. Isolation and characterization of the major contaminants led us to conclude that the occurrence of undesired chain termination have also been favoured. Whether aggregation is related to that or not is to be investigated. 3- the SPPS at elevated temperature protocol employed showed to be suitable for the synthesis of unsulfated human CCK-22. The same can not be said for the unsulfated human CCK-33, a large and complex peptide. Thus, we concluded that for the preparation of this type of compound 25%DMSO/toluene and/or its combination with DIC/HOBt may not be a good choice.

Les techniques de fluorescence sont des outils de choix pour l’étude et la compréhension fine des processus biologiques. Ceci requiert toutefois l’utilisation de sondes fluorescentes parfaitement adaptées au but visé et répondant aux différentes exigences requises pour l’application visée. Dans ce cadre, nous nous sommes plus particulièrement intéressés à l’élaboration de sondes biphotoniques de pH adaptées à une mesure très sensible de faibles variations de pH autour du pH neutre. Les variations et gradients de pH sont en effet impliqués dans un certain nombre de processus biologiques importants et peuvent être associées à des dysfonctionnements liés à certaines maladies. Dans ce cadre, nous avons développé de nouvelles sondes fluorescentes de pH fluorescentes présentant à la fois un comportement ratiométrique, une forte sensibilité autour du pH neutre et facilement excitables dans le proche IR par absorption à deux photons. Ces sondes de structure quadrupolaire et bolamamphiphile permettent ainsi la détection ratiométrique du pH dans des environnements biologiques au moyen d'une excitation biphotonique dans le proche IR. En parallèle, nous nous sommes intéressés à l’élaboration de nanoparticules hyperbrillantes dédiées à l’imagerie biologique par microscopie de fluorescence induite par excitation à deux photons. Nous nous sommes plus particulièrement attachées au design de nanoparticules organiques fluorescentes constituées de molécules organiques de bas poids moléculaire (FONs). Cette approche offre en effet une grande flexibilité et la possibilité d’accéder à des nanosondes ayant des brillances comparables aux très populaires quantum dots mais moins toxiques et plus facilement dégradables. L’ingénierie moléculaire des fluorophores utilisés pour la préparation des FON est cruciale puisqu’elle influence fortement à la fois les propriétés photophysiques (brillance, couleur…) et leur propriétés physico-chimiques (stabilité chimique et structurale, stabilité colloïdale). Dans ce contexte, une librairie de nouveaux chromophores dipolaires a été synthétisée et utilisées pour la préparation de FON par la méthode de nano-précipitation. Leurs propriétés ont été étudiées afin de déterminer la relation entre la structure du chromophore et les propriétés globales des nanoparticules constituées de ces colorants. Ce travail a permis d’identifier les paramètres structuraux permettant d’accéder à des nanoparticules présentant à la fois une brillance exceptionnelle, une émission modulable du vert au rouge et proche IR et une remarquable stabilité colloïdale. Ces nanoparticules présentent des potentialités majeures pour l’imagerie in vivo par excitation et détection dans le proche IR. / Fluorescence-based techniques are popular tools for the study and understanding of biological processes. This has prompted continuous research aimed at the development of a wide range of fluorescent probes specifically designed for specific applications. Among them, fluorescent pH probes are of much interest as pH variations or gradients are involved in many biological events and anomalous alterations are often related to the onset of dysfunctions and diseases. In this framework we have developed a series of promising two-photon pH fluorescent molecular probes. These quadrupolar bolaamphiphilic probes are of great interest, as they combine a steep pH dependence of their optical properties close to neutral pH, ratiometric behavior and large response to two-photon (2P) excitation in the NIR region. As such they offer much promise for ratiometric detection of the pH in biological environments and in situ monitoring of acidification. In parallel, we have been interest in the design of ultrabright nanoparticles for bioimaging purpose (in particular highly sensitive optical imaging). We chose to focus on Fluorescent Organic Nanoparticles made of organic molecules with low molecular weight (FONs) as they offer a flexible route and promising alternatives to toxic quantum dots. In this case the design of the dye used as building blocks of the FONs is of crucial importance and strongly influence the chemical and physical properties of the nanoparticles generated, such as their one and two-photon brightness and both their structural and colloidal stability. In that context a library of novel dipolar chromophores have been synthesized and used to prepare FONs using the nanoprecipitation method. Their properties were thoroughly investigated in order to determine the relationship between the molecular design of the isolated dye and the overall properties of the nanoparticles made of these dyes. As a result, Hyperbright FONs emitting in the green to NIR region and combining giant brightness and remarkable stability have been achieved. They offer major promise for bioimaging based on both excitation and detection in the NIR region.

Les 2,2´-bipyridines et leurs homologues, les N,N´-dioxydes, appartiennent à une classe de composés hétéroaromatiques très importante ayant montré de nombreuses applications dans le domaine de la chimie et principalement en synthèse asymétrique. Une des méthodes les plus performantes pour leurs synthèses s´est révélée être une réaction de cocyclotrimérisation d´alcynes en présence de dérivés nitriles.Une nouvelle variante de la réaction de cyclotrimérisation – cocyclotrimérisation de diynes halogénés avec des dérivés nitriles – permettant la formation de composés 2- et3-halogéno-pyridines a ainsi été développée. La réaction a été étudiée sur une large gamme de substrats permettant l´accès à une librairie de pyridines avec de bons rendements. La formation d´un sous-produit, issu d´un échange d´halogène, a été approfondie au cours de l´étude et son origine a été élucidée grâce à différentes expériences.Les 2-halogéno-pyridines ont été utilisées comme réactifs de départ pour la synthèse de ligands chiraux de type 2,2´-bipyridines. L´étape problématique s´est avérée être la réaction de dimérisation réductrice des 2-halogéno-pyridines donnant accès aux2,2-bipyridines correspondantes. L´efficacité de ces ligands chiraux de type 2,2´-bipyridinea été évaluée dans différentes réactions asymétriques catalysées par des métaux de transition telles que l´aldolisation de Mukaiyama, l´hydroxyméthylation, l´addition conjuguée, l´activation C–H d´indoles mais aussi la désymmétrisation d´époxydes meso, dans laquelle un des ligands bipyridines a montré une extraordinaire activité et robustesse. Ensuite, basées sur des analyses RMN, des calculs DFT et des analyses par diffraction des rayons X, les propriétés structurales de ce ligand ont été étudiées.De plus, une nouvelle famille de catalyseurs à chiralité axiale de type 2,2´-bipyridines N,N´-dioxydes a pu être synthétisée via 2 différentes approches, où seule l´étape clé de dimérisation diffère. La première approche, basée sur la réaction de dimérisation réductrice des 2-halogéno-pyridines, permet l´obtention d´un seul atropoisomère du N,N´-dioxydes cible après une séquence réactionnelle de 8 étapes tandis que la seconde approche, basée sur la réaction de dimérisation oxydante de pyridines N-oxydes, donne l´accès aux 2 atropoisomères en seulement 5 étapes. Le champs d´application de ces nouveaux catalyseurs de typeN,N´-dioxydes, en tant que base de Lewis, a été examiné dans l´allylation énantiosélective du benzaldéhyde ainsi que dans l´aldolisation de l´acétal de cétène trichlorosilylé en présence de l´acétophénone. / 2,2'-Bipyridines and their appropriate N,N'-dioxides form a significant class of heteroaromatic compounds, which has found application in various fields of chemistry and predominantly in asymmetric catalysis. One of the most powerful methods for their synthesis is cocyclotrimerization of alkynes with nitriles.A new variant of cyclotrimerization reaction – cocyclotrimerization of halodiynes with nitriles, which results in the formation of 2- and 3-halopyridines, has been developed. The reaction was studied on a wide range of substrates providing the pyridine products in good isolated yields. Formation of an unexpected product of halogen exchange reaction was observed during the course of the study and its origin was elucidated by experimental studies.The prepared 2-halopyridines were used as starting materials for syntheses of new chiral 2,2'-bipyridine ligands. The crucial step of their synthesis turned out to be the reductive dimerization of 2-halopyridines to the corresponding 2,2'-bipyridines. Application of the formed bipyridine ligands was then tested in various metal-catalyzed asymmetric reactions, namely Mukaiyama aldol reaction, hydroxymethylation, conjugate addition, C–H activation of indole and desymmetrization of meso-epoxides, in which one of the bipyridine ligands showed extraordinary activity and robustness. The structural properties of this ligand were then studied based on the NMR analyses, DFT calculations and single crystal X-ray analyses.New axially chiral 2,2'-bipyridine N,N'-dioxides were synthesized via two approaches, which differed in the type of the key dimerization step. While the first approach, based on the reductive dimerization of 2-halopyridines, furnished only one atropoisomer of the target N,N'-dioxide by an eight-step reaction sequence, the second approach, based on oxidative dimerization of pyridine-N-oxides, provided both atropoisomers in only five steps. The applicability of these novel N,N'-dioxides as Lewis base catalysts were then examined in the enantioselective allylation of benzaldehyde and aldol reaction of trichlorosilyl ketene acetal with acetophenone.

La variante « glyoxylique » de la réaction de Perkin permet de lier entre eux deux fragments aromatiques par un pont maléique. La rigidification de cet intermédiaire flexible mène à des systèmes aromatiques polycycliques étendus par création des liaisons carbone-carbone manquantes. Cette stratégie requiert l'utilisation d'acides arylacétiques et arylglyoxyliques, et l’utilisation d'unités bifonctionnelles a auparavant permis la synthèse de cibles variées allant des phénacènes plans aux (poly)hélicènes très distordus, mais aussi des macrocycles conjugués. Afin d'étendre la taille et la variété des molécules obtenues à l'aide de cette stratégie, des méthodes générales de protection/déprotection sont développées. Une dissymétrisation efficace des unités bifonctionnelles mène à des nouveaux précurseurs monoprotégés qui sont ensuite assemblés par la réaction de Perkin en oligomères de taille contrôlée possédant encore des fonctions chimiques réactives aux extrémités après déprotection. L'utilisation de ces derniers lors d'une deuxième réaction de Perkin donne alors accès à de longs précurseurs flexibles, d’au moins cinq unités, qui donneront ensuite de très longs phénacènes, de grands macrocycles mais aussi des cyclo-tris[5]hélicènes qui présentent une géométrie de Möbius persistante et une aromaticité de Möbius. / The “glyoxylic” variant of the Perkin reaction allows to link two aromatic fragments by a maleic bridge. The stiffening of the obtained flexible intermediate by the creation of the missing carbon-carbon bonds leads to extended polycyclic aromatic systems. This strategy relies on the use of arylacetic and arylglyoxylic acids, and the use of bifunctional units has previously allowed the synthesis of a variety of targets spanning from flat phenacenes to strongly distorted (poly)helicenes, as well as of conjugated macrocycles. This approach is generalized here by developing protection/deprotection techniques in order to enhance the size and the variety of the molecules that can be obtained by this strategy. These techniques enable an efficient dissymetrization of bifunctional units and the recycling of symmetrical side products. The new monoprotected building blocks are connected by Perkin reactions to yield oligomeric intermediates with reactive functions at their extremities after deprotection. Several of these intermediates are assembled in a second Perkin reaction to obtain long phenacenes, large macrocycles and also cyclo-tris[5]helicenes with persistent Möbius geometry and Möbius aromaticity.

Du fait de leurs exceptionnelles propriétés, un très vaste champ d'applications s'ouvre aux nanotubes de carbone. La connaissance de leur toxicité est un enjeu primordial afin de connaître les risques et les dangers que ces objets représentent.Le travail présenté dans cette thèse vise à la synthèse de dérivés ayant pour but de favoriser les interactions entre les nanotubes et le milieu vivant.La synthèse d'une série de dérivés du cholestérol utilisables pour la fonctionnalisation des nanotubes de carbone a été mise au point. L'utilisation de tels dérivés a pour but de favoriser les interactions entre les objets greffés et les membranes cellulaires.Par ailleurs, de nombreux intermédiaires de synthèse présentent des propriétés mésomorphes. Celles-ci ont été étudiées au moyen de différentes méthodes telles que la microscopie optique, la calorimétrie différentielle à balayage et la diffusion des rayons X.Des nanotubes HiPco ont pu être purifiés et fonctionnalisés. L'analyse de leur cytotoxicité a été abordée, celle-ci a permis de mettre en avant une diminution de la toxicité des nanotubes greffés comparée à celles de nanotubes purifiés. / Synthesis and study of mesomorphic properties of grafts for carbon nanotubes functionalizationIn order to study the toxicity of carbon nanotubes, cholesterol based derivatives were synthesized. Due to their exceptional properties, a wide field of applications is opened for carbon nanotubes. Regarding this field, knowing their toxicity becomes a key issue.The work presented here aims towards the synthesis of chemical derivatives designed to increase interactions between carbon nanotubes and a biological environment. The synthesis of a series of cholesterol derivatives aimed for the functionalization of carbon nanotubes has been developed. Such derivatives are intended to interact with cell membranes.Moreover, many synthetic intermediates have mesomorphic properties. These properties have been studied using different methods such as polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray scattering (MWAXS).HiPco nanotubes have been purified, functionalized and characterized with techniques such as Raman spectroscopy and X-ray diffraction (XRD).Finally, a study of carbon nanotubes toxicity is presented.