No description available.

Plusieurs analogues de nucléosides thérapeutiques (Ara-C, Clofarabine), utilisés pour le traitement de leucémies, présentent un arrangement 1’,2’-cis entre la nucléobase reliée au centre anomère et le substituant (électroattracteur) en C-2’. Récemment, notre laboratoire a développé une approche synthétique pour former sélectivement des analogues de nucléosides et de thionucléosides 1’,2’-trans et 1’,2’-cis à partir de précurseurs acycliques. Ce mémoire présente une nouvelle méthodologie pour accéder efficacement aux analogues de nucléosides 1’,2’-cis à partir de furanosides. Différents groupements en position anomérique ont été examinés, sous conditions cinétiques en utilisant le bromure de diméthylbore pour générer sélectivement des produits acycliques ou cycliques. Les intermédiaires cinétiques de différents furanosides de méthyle formés en présence de Me2BBr ont été piégés in situ par un thiol pour générer des thioacétals acycliques avec de bonnes voire d’excellentes diastéréosélectivités. Les produits générés sont en accord avec une rétention globale de l’information stéréochimique du centre acétal et deux déplacements SN2 consécutifs ont été suggérés pour rationaliser ces résultats. Toutefois, l’objectif de synthétiser des analogues de nucléosides à partir de furanosides de méthyle a échoué. Tel que démontré par le Dr Michel Prévost, l’activation par Me2BBr des lactols des quatres différents furanosides suivie d’une addition in situ d’une base silylée a permis de former diastéréosélectivement les analogues de nucléosides 1’,2’-cis correspondants avec d’excellents rendements. Nous avons démontré que d’autres substrats peuvent être employés et que l’induction stéréochimique est sous contrôle du substituant électroattracteur en C-2. D’autres acides de Lewis, tel que TMSBr, peuvent également être utilisés. Cette méthodologie a également été étendue à d’autres nucléophiles tels que des Grignards ou des éthers d’énols silylés, conduisant à de bonnes sélectivités. / Many therapeutically relevant nucleoside analogs (Ara-C, Clofarabine) for the treatment of leukemia have a 1’,2’-cis arrangement between the nucleobase attached at the anomeric center and the non-hydrogen substituent at C-2’. Recently, our laboratory has developed a versatile approach to the synthesis of 1’,2’-trans and 1’,2’-cis nucleoside and thionucleoside analogues from acyclic scaffolds. This work will present a new methodology to access efficiently 1’,2’-cis nucleoside analogues from cyclic furanoside. Activation of various anomeric groups by Me2BBr was investigated, and under kinetic control acyclic substrates or cyclic ones could be generated selectively. Trapping the kinetic product of methyl furanoside formed in presence of Me2BBr by thiol in the presence of base led to the formation of acyclic thioacetal in good to excellent diastereoselectivity. The results obtained are in accordance with total retention of the stereochemical information of the acetal moiety and thus suggested that the mechanism of these two reactions is two successive SN2 displacements. The objective of synthesizing nucleoside analogs from methyl furanoside was unsuccessful. As shown recently by Dr Michel Prévost, activation of all four furanoside lactol scaffolds by Me2BBr with an in situ addition of silylated nucleobase afforded 1’,2’-cis pyrimidine nucleoside analogues in very good yields and with diastereoselectivities greater or equal to 20:1. Expending this methodology to other scaffolds provided evidence of stereoelectronic control of the C-2 electron-withdrawing substituent. Other Lewis acids such as TMSBr can be used. This methodology was also applied to other nucleophiles such as allyl Grignard and silylated enols ethers, which were successfully alkylated in good yield and 1,2-cis diastereoselectivity.

Les virus sont au centre de problème de santé publique. En raison de l'apparition de nouveaux virus et pour certains de leur résistance aux traitements existants il est toujours d’actualité de développement de nouveaux agents antiviraux. En général, la stratégie de lutte contre les infections virales est basée sur la vaccination ou sur l'activité des petites molécules, interférant avec un ou plusieurs processus biologiques participant au cycle de vie du virus. Dans ce contexte, nous avons conçu et synthétisé des petites bibliothèques de molécules visant des propriétés anti-filovirus. Dans ce projet de recherche, nous avons mis l'accent sur le développement de composés ciblant la protéine Niemann-Pick C1, les protéases cathepsine et le processus de réplication. Lors du développement des inhibiteurs de Neimann-Pick C1 plus de 70 composés ont été synthétisés, portant le squelette pipérazine. Afin d'obtenir des inhibiteurs de cystéine cathepsines pouvant être impliqués dans la réplication du virus Ebola, nous avons synthétisé une petite bibliothèque de composés porteurs de groupement 1,3,5-triazine et possédant des activité de l’ordre du nanomolaire sur les cathepsines B, K, L et S. Enfin, pour inhiber la réplication du virus en ciblant SAH hydrolase, nous avons proposé une série de C-nucléosides carbocyclic ayant motif de 4-aza-7,9-dideazaadenosine. / The viruses cause the problem of public health. Due to the appearance of new viruses and their resistance to existing treatments there is still relevant to develop new antivirals. Generally, the strategy to combat viral infections is based on vaccination or on the activity of small molecules, interfering with one or more biological processes participating in virus life cycle. In this context, we took an effort to design and synthesize the library of small molecules possessing anti-filovirus properties. In this research project, we were focused on the developing of compounds targeting Niemann-Pick C1 protein, cathepsin proteases and replication process. In our effort into the development of the inhibitors of Neimann-Pick C1 we prepared the series of about 70 compounds, having in common the piperazine moiety. Diverse 1,4-N,N - substituents of piperazine, differencing in a size and shape were studied. In order to obtain efficient cysteine cathepsins inhibitors, we synthesized the small library of compounds bearing 1,3,5-triazine moiety. Finally, to inhibit the virus replication by targeting SAH hydrolase, we proposed the series of carbocyclic C-nucleosides having motif of 4-aza-7,9-dideazaadenosine.

No description available.

No description available.

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No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Alline Torquato Vasconcelos - 2014.pdf: 3499445 bytes, checksum: 93905607504e61e452d7ce82396c17a9 (MD5) Previous issue date: 2014-06-06 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Lamivudine (β-L-2',3'-dideoxy-3'-thiacytidine, 3TC) is a nucleoside-based anti-HIV/HBV drug that has provided insights into the nucleic acid double-stranded helix assembly. Two crystal structures thereof assembled with nucleobase pairing and helical stacking as mimicries of DNA, but without the phosphodiester linkages in the fiber periphery, have recently demonstrated that nucleosides bring themselves the chemical information to assemble DNA duplexes even if the covalent backbone is absent. Here, we report the third structural example in which nucleosides are base-paired and helically base-stacked. A DNA-like double stranded helix was prepared cocrystallizing lamivudine with fumaric acid. We have named it as lamivudine duplex III. When substituting maleic acid present in the first example of lamivudine duplex for its trans-stereoisomer, the formation of a DNA-mimicry is still observed but with changes in the crystal stoichiometry, nucleobase pairing pattern and duplex backbone. Lamivudine duplex III exhibits both base pairing motifs present in the antecedent duplexes. In this structure, there are four protonated lamivudine molecules paired in-plane with four neutral ones. These crystallographically independent base pairs are held together through three hydrogen bonds as occurs in lamivudine duplex I made up of cytosine-cytosine+ base pairing only. But, contrarily to the duplex I with pairing between neutral and cationic drug units only, the duplex III has one neutral 3TC=3TC pair in its asymmetric unit. These molecules are kept in contact through only two peripheral N―H•••O hydrogen bonds as in two of the three neutral lamivudine pairs of the second example of lamivudine duplex. In both structures, each neutral pair is face-to-face stacked on top of one another and face-to-tail stacked on bottom of another one. Even in agreement with its higher structural complexity, the duplex III is present with very puckering conformations besides the three different orientations of the OH moiety at C5’. Five-membered oxathiolane ring adopts three envelop puckering modes and two twist conformations. This is the first report of a twist pucker for lamivudine despite of the large number of reported crystal structures thereof. Another remarkable characteristic of the duplex III is in its fiber periphery. There are hydrogen bonds between the 5’-OH moieties of neighbor pairs pointing in the direction of the missing phosphodiester linkages that would covalently bond two adjacent monomers in the strand. Furthermore, the geometry of these interactions reveals the antiparallel orientation of each strand relative to one another into the nucleoside duplex backbone. Noteworthy similarities between the duplexes crystallizing together with either hydrogen maleate or hydrogen fumarate are their left handedness and the outline of surface grooves of similar depth. But, while all hydrogen maleate counterions are lodged on the grooves of the duplex I, some hydrogen fumarate units are also interacting with themselves into one-dimensional chain of counterions. The third example of unusual double-stranded helices of lamivudine strengthens the fact that nucleosides can self-aggregate into DNA-like duplexes even without the covalent phosphodiester linkages in fiber periphery. Besides that, the structure described here adds knowledge on lamivudine versatility to assemble DNA-mimicry in crystals. / A lamivudina (β-L-2',3'-dideoxy-3'-thiacytidine, 3TC) é um fármaco a base de nucleosídeos utilizado para o tratamento de SIDA e Hepatite B. A obtenção de estruturas do tipo dupla hélice de ácidos nucleicos com esse fármaco tem sido alvo de estudo. Recentemente foram reportadas duas estruturas cristalinas mimetizando DNA, formadas por pares de nucleosídeos empacotados em uma dupla hélice, mas sem ligações fosfodiéster na periferia da cadeia. Estas estruturas demonstraram que os nucleosídeos possuem informação química suficiente para a formação de estruturas dessa natureza mesmo com a ausência das ligações covalentes fosfodiéster. Neste trabalho um terceiro exemplo de uma estrutura contendo bases de nuclosídeos pareadas e sobrepostas helicoidalmente, mimetizando DNA, é reportado. Essa modificação cristalina foi preparada através da cocristalização da lamivudina com o ácido fumárico e a estrutura obtida foi denominada duplex III. Com a substituição do ácido maleico, presente no primeiro exemplo de dupla hélice de lamivudina, pelo seu estéreoisômero trans, o ácido fumárico, a formação de uma estrutura mimetizando o DNA também foi observada, porém, com diferenças na estequiometria do cristal, nos padrões de interação do pareamento das bases, assim como no esqueleto da dupla hélice. O pareamento das bases na duplex III de lamivudina possui padrões de interação semelhante a ambas estruturas precedentes. Na duplex III existem quatro pares parcialmente protonados, onde uma lamivudina protonada está pareada com outra neutra. Esse tipo de pareamento se dá através de três ligações de hidrogênio e é semelhante ao pareamento presente na estrutura da duplex I de lamivudina composto apenas por pares do tipo 3TC+≡3TC. Diferentemente da duplex I que possui exclusivamente pares parcialmente protonados, a duplex III possui também um par neutro do tipo 3TC=3TC na sua unidade assimétrica. O pareamento dessas bases é formado apenas por duas ligações de hidrogênio do tipo N―H•••O, semelhante a dois dos três pares neutros que constituem a duplex II de lamivudina. O empacotamento dos pares neutros na duplex III é semelhante ao da duplex II, cada par neutro empacota com uma padrão face a face com o par que o antecede e face a cauda com o par subsequente. Devido à grande complexidade estrutural da duplex III, temos uma maior variação nas conformações assumidas tanto pelo anel oxatiolano quanto pelo fragmento citosinico, assim como nas três orientações adotadas pelo grupo hidroxílico ligado ao carbono C5’. O anel oxatiolano de cinco membros, adota três diferentes conformações do tipo envelope e duas conformações do tipo cambaleante. Apesar de essas serem as primeiras estruturas reportadas com conformações do tipo cambaleante para a lamivudina, esse tipo de conformação é comum para várias outras estruturas cristalinas. Outra característica que merece destaque na estrutura obtida da duplex III está nos padrões de interação presentes na periferia da dupla hélice. Nota-se a presença de ligações de hidrogênio entre os grupos 5’-OH de pares vizinhos, que ocorrem na direção onde as ligações fosfodiéster deveriam existir entre dois monômeros adjacentes. Além disso, a geometria dessas ligações de hidrogênio revelam uma orientação antiparalela de uma fita em relação a outra no esqueleto da duplex. Existem algumas semelhanças notáveis entre as duplexes I e III, cristalizadas com hidrogenomaleato e hidrogenofumarato, como a espiralização a esquerda e o fato de ambas não possuírem diferença entre sulcos principais e secundários, uma vez que todos os sulcos ao longo da cadeia possuem dimensões semelhantes. Porém, todos os contraíons estão acomodados nos sulcos da duplex I, enquanto que na duplex III alguns contraíons interagem entre si formando uma cadeia unidimensional de contraíons. Esse terceiro exemplo de uma estrutura atípica de dupla hélice de lamivudina reforça o fato de que nucleosídeos podem se agregar em estruturas semelhantes a dupla hélice do DNA, mesmo com a ausência das ligações covalentes fosfodiéster. Além disso a estrutura da duplex III adiciona conhecimento quanto a versatilidade da lamivudina em formar estruturas mimetizando DNA em cristais.

De acordo com a Organização Mundial de Saúde (World Health Organization - WHO), aproximadamente 40 milhões de pessoas ao redor do mundo estão infectadas com HIV/AIDS. Atualmente, a epidemia tem sido controlada em grande parte do mundo ocidental, porém, projeções sugerem que, até o fim desta década, o número de incidência da doença poderá duplicar. Apesar das significantes melhoras na morbidade e mortalidade de pacientes infectados pelo HIV, o rápido surgimento de cepas resistentes aos agentes anti-HIV, além dos efeitos adversos e o alto custo de fármacos de última geração, torna-se necessário o continuo desenvolvimento de novas classes de agentes anti-HIV. A transcrição e multiplicação do RNA viral são dependentes das interações seqüência-específica entre duas proteínas reguladoras virais essenciais, Tat e Rev, com seus respectivos sítios no RNA, TAR e RRE. Durante a última década, os aminoglicosídeos foram introduzidos como ligantes universais do RNA, sendo capazes de se ligar ao TAR e ao RRE. A literatura apresenta diversos aminoglicosídeos que são capazes de se ligar ao TAR e inibir a interação Tat-TAR bem como, inibir competitivamente a ligação da proteína Rev ao RRE, como, por exemplo, a neomicina e tobramicina. Considerando a importância dos aminoglicosídeos e análogos nucleosídicos, conhecidamente eficazes na terapia antirretroviral, o trabalho foi direcionado para a síntese de conjugados de aminociclitol, 2- desoxi-estreptramina, e adenosina, bem como, dímeros de adenosina via estratégia de click chemistry por reação de cicloadição azido-alcino catalisada por Cu(I) (CuAAC). Para a síntese destes produtos, o precursor adenosina foi convertido no derivado 5\'-azido-5\'- desoxi-adenosina, o qual foi condensado com diversos diinos terminais comerciais, contendo diferentes grupos espaçantes, com a finalidade de explorar suas influências nas propriedades eletrônicas e estéricas nos conjugados de interesse frente à atividade anti-HIV. Os derivados alcinos presentes na posição C-5\' de adenosina, via grupo triazol, foram empregados para a síntese dos monômeros nucleosídeo-aminociclitóis, assim como, na síntese de dímeros nucleosíde0-aminociclitóis, via reação de cicloadição 1,3-dipolar, na presença de CuSO4, quantidade catalítica, e ascorbato de sódio, para geração in situ de Cu(I). Adicionalmente, alguns dos compostos, na concentração de 1mM, foram testados empregando o ensaio de ELISA para detecção da presença de proteína viral p24 em linhagem células H9 e avaliação de sua atividade antirretroviral. De acordo com o ensaio biológico, um dos compostos preparados apresentou, proporcionalmente ao crescimento da linhagem H9 (HIV) controle, atividade de inibição de formação da proteína viral p24 similar ao composto padrão zidovudina (AZT). Além disso, outros dois compostos também apresentaram um resultado relevante uma vez que suas atividades foram similares ao composto padrão lamivudina (3TC). Estes resultados sugerem que a presença de uma cadeia metilênica mais extensa, como cadeia lateral ou grupo espaçante, pode influenciar positivamente a atividade biológica por efeito hidrofóbico ou estérico. Por fim, os ensaios de viabilidade celular demonstraram que os compostos testados não foram citotóxicos nas condições testadas. / According to World Health Organization - WHO about 40 million of people are infected with HIV/AIDS. Currently, the epidemic has been controlled largely in the western world, since, projections suggest that, until this decade end, the disease incidence could increase. Despite significant improvements in morbidity and mortality of HIV-patients, quick emergence of resistant strains to anti-HIV agents, in addition to adverse effects and high cost of recent drugs, becomes necessary the ongoing development of new classes of HIV agents. Transcription and translation of the viral RNA are dependent of sequence-specific interactions among two essential viral regulatory proteins, Tat and Rev, and their corresponding TAR and RRE sites in HIV-1 RNA. Over the past decade, aminoglycosides were established as universal RNA linkers, being able to link to TAR and RRE. The literature reports several aminoglycosides that bind to TAR and inhibit Tat-TAR interaction, as well as, competitively inhibit the bind between Rev protein and RRE, such as: neomycin and tobramycin. Considering the importance of nucleosides analogs, effective in antiretroviral therapy, and aminoglycosides, the work was driven to the synthesis of aminocyclitol, 2- deoxy-streptamine, conjugated to the adenosine, as well as, conjugated dimers of adenosine by molecular duplication via click chemistry strategy involving copper-catalysed azide-alkyne cycloaddition reaction (CuAAC). For the synthesis of these products, the starting material adenosine was converted to 5\'-azide-5\'-deoxy-adenosine, which was conjugated with several commercials terminal dialkynes containing different intercalating groups in order to explore the influences of the steric and electronic properties of conjugates towards anti-HIV activity. Alkynes derivated at C-5\' position of adenosine, via triazole group, were used in the synthesis of nucleoside-linked aminocyclitols, as well as, nucleoside conjugated dimers by 1,3-dipolar cycloaddition reaction under microwave-assisted conditions (MW), using the catalytic system CuSO4/sodium ascorbate for the in situ generation of Cu(I). Additionally, several compounds, at concentration of 1mM, were tested in vitro by ELISA for detection of p24 protein in H9 cells to antiretroviral evaluation. According with the biologic assay, one of the compounds showed inhibition of p24 protein production similar to zidovudine (AZT), when compared to H9 cells line growth control, Furthermore, two compounds also showed important activities similar to lamivudine (3TC). These results suggest that the presence of a longer methylenic chain, as side chain or intercalating groups, could influence positively in the biologic activity due to hydrophobic or steric effects. Ultimately, the cell viability assays showed that compounds were not cytotoxic in the tested conditions.

Introduction : Le virus de l’hépatite C (VHC), est l’une des premières causes de pathologie hépatique dans le monde. Ce virus à ARN est responsable de l’hépatite C qui aboutit au développement de la cirrhose et du cancer du foie. Selon l’Organisation Mondiale de la Santé, le VHC infecte actuellement plus de 170 millions de personnes dans le monde, soit 3% de la population. L’hépatite C chronique connait toujours en Tunisie un taux de guérison faible pour le génotype 1 car le traitement standard actuellement disponible est la bithérapie interféron pégylé associé à la ribavirine. A l’heure actuelle, le développement de différentes molécules ciblant spécifiquement le VHC, appelées les antiviraux à action directe (AAD), apparait comme une potentielle révolution dans le traitement de l’infection par le VHC.Ces AAD comprennent les inhibiteurs de protéase (IP), les inhibiteurs nucléos(t)idiques (IN) et les inhibiteurs non-nucléosidiques (INN) de la polymérase NS5B ainsi que les inhibiteurs de la protéine NS5A. La quasi-espèce virale est formée d’un mélange complexe de variants viraux parmi lesquels se trouvent des variants associés à des degrés variables à la résistance aux AAD. Ces variants peuvent donc exister naturellement en absence de toute pression médicamenteuse et sont susceptibles d’avoir un impact sur la réponse aux différents traitements par AAD. Notre objectif était de déterminer la prévalence des variants associés à la résistance dans les souches tunisiennes circulantes en préambule à l’introduction deces molécules en Tunisie. Méthodes : L’amplification et le séquençage direct de la protéase NS3, de la polymérase NS5B ainsi que la région NS5A ont été effectuées chez 149 patients tunisiens naïfs de traitement et infectés par le VHC de génotype 1 (génotype 1b = 142 ; génotype 1a = 7). Résultats : Douze séquences NS3 (12/131 ; 9,2%) ont montré des mutations connes pour conférer une résistance aux IP. Une seule séquence (1/95 ; 1,1%) a montré la mutation V321I connue pour conférer une résistance aux IN-NS5B. Trente quatre séquences (34/95 ; 35,8%) ont montré des mutations connues pour diminuer la sensibilité des INN-NS5B. Une seule séquence de génotype 1a (1/7 ; 14,3%) et 17 séquences de génotype 1b (17/112 ; 16,2%) ont montré des mutations connues pour conférer une résistance au inhibiteurs de la protéine NS5A. Conclusions : Notre étude a permis de mettre en évidence la présence de substitutions conférant une diminution de la sensibilité aux AAD chez des patients tunisiens naïfs de tout traitement anti-VHC. Des études in situ seront nécessaires pour évaluer l’impact de ces mutations sur la réponse au traitement. / Introduction: Hepatitis C virus (HCV) is a major cause of liver disease worldwide. This RNA virus is responsible for hepatitis C, which leads to the development of cirrhosis and liver cancer. According to the World Health Organization, HCV infects more than 170 million people worldwide, about 3% of the population. Chronic hepatitis C still know in Tunisia low cure rates for genotype 1, because the currently standard treatment available is combination therapy of pegylated interferon plus ribavirin. At present, the development of different molecules that specifically target HCV, called direct-acting antivirals (DAA) appears as a potential revolution in the treatment of HCV infection. These DAA include protease inhibitors (PI), nucleos(t)ide (NI) and non-nucleoside inhibitors (NNI) for NS5B polymerase and NS5A inhibitors. The viral quasispecies is formed by a complex mixture of viral variants including variants associated with variable degrees of resistance to DAA. These variants may therefore exist naturally in absence of drug pressure and may affect response to different treatments by DAA. Our objective was to determine the prevalence of variants associated with resistance in circulating Tunisian strains preamble to the introduction of these molecules in Tunisia. Methods: Amplification and direct sequencing of NS3 protease, NS5B polymerase and NS5A region were performed in 149 Tunisian naïve patients infected with HCV genotype 1 (genotype 1b = 142; genotype 1a = 7) . Results: Twelve sequences NS3 (12/131; 9.2%) showed mutations known to confer resistance to PI. One sequence (1/95; 1.1%) showed the V321I mutation known to confer resistance to NS5B-IN. Thirty four sequences (34/95; 35.8%) showed mutations known to reduce the sensitivity of NS5B-INN. One genotype 1a sequence (1/7; 14.3%) and 17 genotype 1b sequences (17/112; 16.2%) showed mutations known to confer resistance to NS5A inhibitors.Conclusions: Our study highlighted the presence of substitutions conferring decreased susceptibility to DAA in naïve patients infected with HCV genotype 1. Field studies will be needed to evaluate the impact of these mutations on the treatment response.

Living organisms employ different kinds of mechanisms, to regulate the functions of genes or their products, which may help in maintaining homeostasis inside the cell or may help in fighting hostile environment in the case of pathogenic organisms. These mechanisms act at the transcriptional, post-transcriptional, translational, and post-translational levels. In order to understand the physiology of an organism, it is essential to obtain an in-depth knowledge of such mechanisms, in which several proteins participate in interlinked pathways. In this regard, the present study focuses on two such proteins: (i). the newly identified Fic (Filamentation induced by cAMP) protein; and (ii). NDK (Nucleoside Diphosphate Kinase), which had been studied for decades. Fic protein and NDK share several common features: (i). both use nucleoside triphosphate (NTPs) or nucleoside diphosphate (NDPs) or their derivatives as one of their substrates; (ii). they have been found to be involved in diverse cellular pathways, involving different types of substrates that form the second substrate of these proteins; (iii). both are ubiquitously present in all the living organisms - from bacteria to humans to plants. However, there is very little information on these proteins from mycobacterial systems, which include some major human pathogens, Mycobacterium tuberculosis and Mycobacterium leprae, which are the causative agents of Tuberculosis and Leprosy, respectively. In view of these reasons, in the present study, the structural and/or functional features of the Fic and NDK proteins from Mycobacterium tuberculosis, were analysed, as it might be of medical significance for effectively combating the pathogen. The Chapter 1 of the thesis contains the Introduction to the research work and Chapter 2 is on the overall Materials and Methods. The remaining chapters pertain to the data obtained on the structural and/or functional features of the Fic and NDK proteins from Mycobacterium tuberculosis. Chapter 3. Cloning, Expression and Purification of Mycobacterium tuberculosis Fic The role of FIC (Filamentation induced by cAMP) domain containing proteins in the regulation of many vital pathways, mostly through the transfer of NMPs from NTPs to specific target proteins (NMPylylation), in microorganisms, higher eukaryotes, and plants is emerging. In order to understand the biological role of FIC domain containing proteins in mycobacteria, the gene for the FIC domain containing protein of the human pathogen, Mycobacterium tuberculosis, MtuFic, was cloned, overexpressed, purified to homogeneity, and biochemically characterised. Neither the His-tagged nor the GST-tagged MtuFic protein, overexpressed in Escherichia coli, nor expression of Mtufic in Mycobacterium smegmatis, yielded the protein in the soluble fraction. However, the maltose binding protein (MBP) tagged MtuFic (MBP-MtuFic) could be obtained partly in the soluble fraction. Denatured-refolded protein was used for the antibody generation in mice and rabbit. The cellular localisation and secretion of MtuFic were characterised using the antibody. Chapter 4. Biochemical Characterisation of Mycobacterium tuberculosis Fic Sequence alignment with several FIC motif containing proteins, complemented with homology modeling on the FIC motif containing protein, VbhT of Bartonella schoenbuchensis as the template, showed conservation and interaction of residues constituting the FIC domain. MtuFic, possesses the critical His144 residue, in the characteristic FIC Motif, HPFREGNGRSTR (HPFxxGNGRxxR), spanning 144th to 155th residue. Site-specific mutagenesis of the His144, or Glu148, or Asn150 of the FIC motif, or of Arg87 residue that constitutes the FIC domain, or complete deletion of the FIC motif, abolished the NTP to NMP conversion activity. The activity of MtuFic was consistent with the biochemical activities hitherto reported for a variety of bacterial FIC domain containing proteins. Studies were also carried out on NMPylylation in the presence of eukaryotic proteins and eukaryotic and mycobacterial cell lysates. Although formation of NMPs from NTPs mediated by MBP-MtuFic could be detected, we could not identify any protein as the target substrate either in the human macrophage (THP1) cells or in the M. tuberculosis cells. VopSΔ30 (kind gift from Dr. Kim Orth), along with human G proteins as targets, were used as the positive controls. Various possibilities for the inability to detect a protein target substrate are discussed. Chapter 5. Transcriptional Analysis of Mycobacterium tuberculosis fic Gene (Mtufic) In parallel, in order to understand the transcriptional regulation of Mtufic, primer extension analysis was carried out. The Transcription Start Site (TSS; +1 site) of Mtufic were mapped under different growth/stress conditions, which tubercle bacilli encounter in human host. Mtufic got expressed mainly through two transcripts, T1 and T2, arising from two different transcription start sites (TSS). Putative promoter regions were cloned in a promoter probe vector, which expresses a GFP protein of very high intensity, in order to qualitatively detect the activity of the promoters. The half-life of the gfp mRNA was determined to be 4 min and therefore justifiably quantitated the Mtufic promoter activity by determining the gfp mRNA levels. The levels of Mtufic mRNA were two-fold higher under nutrient-depleted stationary phase of growth, as compared to the levels at mid-log phase. The activity of P1 and P2, as quantitated real-time using the short half-life gfpm2+ mRNA levels in Mycobacterium smegmatis transformants, showed that the activity of P2 was upregulated two-fold under nutrient-depleted stationary phase of growth, while that of P1 remained unaltered while of P1 and P2 were low under hypoxia. Co-transcription of Mtufic, with the immediate upstream gene, Rv3642c, of unknown function, was observed. Taken together, the data strongly indicated that the expression of Mtufic gets altered under nutrient-depleted and hypoxic conditions, which are the stress conditions experienced by tubercle bacilli in granuloma in tuberculosis patients. Chapter 6. Functional Characterisation of Mycobacterial FtsZ-NDK Interaction During the past few decades, our laboratory has been carrying out extensive molecular and functional studies on the cytokinetic protein, FtsZ, of different mycobacterial species, and of a variety of other mycobacterial proteins that are believed to be interacting with the cell division machinery. In this regard, in parallel to the work on MtuFic, we carried out work on the identification and characterisation of the proteins that interact with mycobacterial FtsZ. In this context, we found for the first time that the nucleoside diphosphate kinase (NDK), which can generate NTPs from ATP/GTP and NDPs, interacts with FtsZ and that the interaction was conserved across several mycobacterial species. Therefore, the FtsZ-NDK interaction was extensively characterised in vitro, using the recombinant, purified FtsZ and NDK proteins from different mycobacterial species. This novel finding on the interaction of NDK with FtsZ adds another role to NDK, namely in bacterial cell division.

Les analogues de nucléosides ont reçu une attention particulière en raison de leurs importantes applications anticancéreuses et antivirales. Dans cette thèse, de nouveaux analogues nucléosidiques de type 1′,2′-cis et 1′,2′-trans ribo portant un centre stéréogénique quaternaire fonctionnalisé en position C3′ ont été synthétisés par des réactions de N-glycosylation stéréosélectives, qui ont été contrôlées en installant différents types de groupes protecteurs sur le C2′ substituant hydroxyle. Le précurseur acyclique critique de 2,4-syn diol a été obtenu par réduction diastéréosélective d’une β-hydroxycétone en utilisant la délivrance d'hydrure intermoléculaire. Une approche pour une séparation facile des 2,4-syn et 2,4-anti diols par protection/déprotection acétonide a été établie, de sorte que le 2,4-syn diol pur puisse être rapidement accessible par oxydation allylique successive et protection acétonide. Une stratégie alternative a également été développée pour la préparation d'analogues nucléosidiques en C1′-β de type ribo portant un centre quaternaire C3′ avec un groupe hydroxyle C5′ libre. Dans cette stratégie, les diacétates de type ribo ont servi de donneur de glycosyle qui ont été synthétisés à partir d’une époxydation diastéréosélective d’un précurseur de glycal. La réaction énantiosélective consécutive de Mukaiyama aldol et le transfert d'allyle intramoléculaire de radicaux libres catalysé par photoredox ont été établis et développés dans notre laboratoire pour installer le centre stéréogénique quaternaire. Des nucléosides 5′-triphosphates portant soit une purine soit une pyrimidine ont ensuite été synthétisés et sont testés contre le cancer et les infections virales. De plus, l'analogue L-1′,2′-cis-4′-thionucléoside portant un centre quaternaire stéréogénique fonctionnalisé en position C3′ avec un substituant hydroxyle en C2′ a été synthétisé par une stratégie acyclique avec 1′,2′-syn thioaminal précurseur, qui a subi une cyclisation intramoléculaire de type SN2 de type S1′→C4′. Le 1′,2′-syn thioaminal a été synthétisé par une addition de nucléobase diastéréosélective sur un dithioacétal. / Nucleoside analogues have received extensive attention due to their important anticancer and antiviral applications. In this thesis, novel 1′,2′-cis and trans ribo-like nucleoside analogues bearing an all-carbon C3′ quaternary stereogenic center were synthesized using stereoselective N-glycosylation reactions, which were controlled by installing different types of protecting groups on the C2′ hydroxyl substituent. The critical acyclic 2,4-syn diol precursor was obtained by diastereoselective reduction of a β-hydroxy ketone using intermolecular hydride delivery. An approach for easy separation of the 2,4-syn and 2,4-anti diols through acetonide protection/deprotection was established to rapidly access the pure 2,4-syn diol through successive allylic oxidation and acetonide protection. An alternative strategy was also developed for the preparation of ribo-like C1′-β nucleoside analogues bearing an all-carbon C3′ quaternary center with a free C5′ hydroxyl group. In this strategy, ribo-like diacetates served as the glycosyl donors which were synthesized from a diastereoselective epoxidation of a glycal precursor. A consecutive enantioselective Mukaiyama aldol reaction followed by a photoredox catalyzed free radical intramolecular allyl transfer were established and developed in our lab to install the all-carbon quaternary stereogenic center. Nucleoside 5′-triphosphates bearing either a purine or a pyrimidine nucleobase were then synthesized and are currently being tested against cancer and viral infections. In addition, L-1′,2′-cis-4′-thionucleoside analogues bearing an all-carbon C3′ stereogenic quaternary center along with a C2′ hydroxyl substituent were synthesized using an acyclic strategy from a 1′,2′-syn thioaminal precursor followed by a S1′→C4′ intramolecular SN2-like cyclization. The 1′,2′-syn thioaminal was synthesized by a diastereoselective nucleobase addition onto a dithioacetal.