La spectroscopie RMN alliée à l’utilisation de solvants cristal-liquide fortement et faiblement orientants est une stratégie efficace pour élucider les structures et distributions conformationnelles de petites molécules organiques rigides et flexibles en solution, et déterminer les ordres orientationnel et positionnel des solutés comme des solvants orientés. Dans une première partie, afin d’explorer les différentes contributions aux couplages dipolaires d’un soluté donné, la très faible amplitude de l’ordre orientationnel d’une molécule quasi-sphérique, le tetramethylallène, dissoute dans un nématique thermotrope est exploitée. Dans cette situation limite, le caractère prédominant des mécanismes de réorientation et de vibration moléculaire est mis en évidence, et estimé. Dans une seconde partie, les données RMN obtenues à partir de solutés de petites tailles dissous dans des solvants smectiques sont combinées aux résultats de calculs reposant sur des concepts de thermodynamique statistique et de la théorie de la fonctionnelle de densité. L’efficacité de cette méthode dans la détermination des paramètres d’ordres positionnel du solvant et orientationnel des molécules-sondes est démontrée aussi bien dans le cas de phases conventionnelles smectiques A que celui plus délicat de smectiques interdigitées Ad. La stratégie d’analyse proposée est ensuite étendue à l’investigation des structures tridimensionnelles et équilibres conformationnels de molécules flexibles bioactives ou biomimétiques. Dans une perspective méthodologique, à l’aide d’études expérimentale et théorique portant sur le biphényle, molécule symétrique constituée d’un unique rotor, il est tout d’abord démontré l’intérêt des méthodes de simulations par dynamique moléculaire pour évaluer l’ensemble des couplages dipolaires d’un soluté donné dans une phase thermotrope, ultérieurement utilisés comme paramètres initiaux dans une analyse spectrale itérative, et in fine déterminées précisément. L’analyse spectrale chronophage et dont l’aboutissement est incertain si les paramètres initiaux sont difficiles à estimer, en est ainsi facilitée. Puis, les distributions conformationnelles d’anti-inflammatoires non stéroïdiens de dérivés salicylés et profènes, fluorés ou non, constitués d’un ou deux rotors indépendants sont présentées. Via l’utilisation inédite du modèle AP-DPD dans les solvants nématiques (chiraux) lyotropes faiblement orientants, et à partir des couplages dipolaires homo- et hétéronucléaires notamment obtenus grâce à l’expérience RMN GET-SERF, créée à propos pour permettre l’extraction simple et rapide des couplages 1H-19F, les surfaces d’énergie potentielle de ces biomolécules sont décrites de façon satisfaisante. Enfin, les équilibres conformationnels de deux stilbénoïdes constitués de deux rotors coopératifs sont déterminés dans deux solvants cristal-liquide, l’un fortement, l’autre faiblement orientant. Ces études comparatives permettent de discuter la fiabilité, la précision et l’accessibilité des observables RMN extraites dans les phases, et d’établir la complémentarité des analyses RMN réalisées dans ces solvants. / NMR spectroscopy in weakly and highly orienting media is used as a route for dealing with orientational, positional, structural and conformational problems of a variety of small rigid and flexible organic molecules in solution. First, the very weak orientational order of a quasi-spherical molecule dissolved in a nematic phase is exploited for exploring the role of the different contributions to the observed dipolar coupling. In such a limit condition, a predominant effect of the non-rigid reorientation-vibration coupling term emerges. Then, NMR data obtained from small rigid probes dissolved in smectic solvents are combined with a statistical thermodynamic density functional theory, in order to measure the positional order parameters of both solutes and solvent. The methodology gives good results when applied to a conventional smectic A liquid crystal and to the more delicate case of an interdigitated smectic Ad phase. The strategy is subsequently extended to the investigation of structure, order and conformational equilibrium of flexible bioactive or biomimetic molecules dissolved in various partially ordered NMR solvents. A first experimental and theoretical study is presented on the symmetric single-rotor molecule of biphenyl dissolved in a thermotropic liquid crystal. This test-case indicates molecular dynamics simulations are a promising tool for estimating a set of dipolar couplings of a solute in a thermotropic solvent, to be used as starting set of parameters in a standard operator-mediated NMR spectral analysis. Then, we report the conformational study of some single- and two-rotor nonsteroidal anti-inflammatory drugs, belonging to the families of salicylates and profens, dissolved in weakly orienting chiral nematic PBLG phases. A new pulse sequence, the Gradient Encoded heTeronuclear 1H-19F SElective ReFocusing NMR experiment (GET-SERF), is proposed here for the trivial edition of all 1H-19F couplings in one single NMR experiment, for a given fluorine atom. Starting from homo- and heteronuclear dipolar couplings, difficult to extract in thermotropic solvents because of a too complex spectral analysis, the torsional distributions of such molecules can be satisfactory described by the Additive Potential model combined with the Direct Probability Description of the torsional distribution in terms of Gaussian functions (AP-DPD approach). Finally, the conformational and orientational study of two stilbenoids displaying cooperative torsions is discussed in both a highly and weakly ordering liquid crystal phase. This comparative study allows to draw some conclusions on reliability, accuracy and accessibility of desired data in the two phases. Overall, this work proves NMR in liquid crystals is a flexible and meaningful tool for studying order, structure and conformation and it can greatly benefit from the availability of several aligning media inducing a different degree of order.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / As macroalgas sÃo fontes de molÃculas bioativas com propriedades antioxidantes, muitas das quais apresentam variaÃÃes ao longo do ano. Cinco algas verdes do gÃnero Caulerpa (C. cupressoides, C. mexicana, C. prolifera, C. racemosa e C. sertularioides) foram coletadas mensalmente na Praia do Pacheco, de janeiro a dezembro de 2006. ApÃs as coletas, elas foram transportadas para o laboratÃrio, lavadas com Ãgua corrente para retirada de impurezas e epÃfitas e liofilizadas. Os extratos algÃceos foram preparados em metanol (MeOH) na proporÃÃo 1:20 (p:v) sob agitaÃÃo por 1 h a 20ÂC em um agitador orbital, em seguida, filtrados, e os resÃduos submetidos a mais duas extraÃÃes sucessivas. O material das trÃs extraÃÃes metanÃlicas foi reunido e concentrado em um evaporador rotativo. PorÃÃes de 10 mg do extrato concentrado foram suspensas em 10 mL de MeOH (50%). Esse extrato (1 mg/mL) foi utilizado para a determinaÃÃo do conteÃdo fenÃlico total (CFT). A atividade antioxidante in vitro foi medida atravÃs da capacidade de sequestrar o radical DPPH, do poder de reduÃÃo de Ãons fÃrricos (FRAP), do branqueamento do β-caroteno (BCB) e da habilidade de quelaÃÃo de Ãons ferrosos (FIC), nas concentraÃÃes 5, 50, 500 e 1.000 Âg/mL, preparadas a partir do extrato. O quelante de metais EDTA foi utilizado como controle positivo no FIC, e o antioxidante sintÃtico BHA, nas demais determinaÃÃes. Os valores de CFT foram maiores no segundo semestre do ano e variaram de 4 a 32 mg AGE/g extrato. Os resultados do sequestro do radical DPPH, do BCB e do FIC nÃo exibiram padrÃo de variaÃÃo e apresentaram atividades superiores a 25%, 70% e 10%, respectivamente. O FRAP nos extratos de C. cupressoides, C. racemosa e C. serlularioides foi maior no segundo semestre do ano, no de C. mexicana o maior valor ocorreu no primeiro semestre e no de C. prolifera, as variaÃÃes ao longo do ano nÃo obedeceram a um padrÃo como nos demais. Em todas as metodologias as atividades dos extratos algÃceos foram inferiores Ãquelas dos controles positivos. As cinco espÃcies de Caulerpa podem ser consideradas fonte de potenciais antioxidantes, com possÃveis usos, como na indÃstria alimentÃcia, nÃo requisitando de um perÃodo do ano especÃfico para a extraÃÃo desses compostos antioxidantes, jà que embora haja variaÃÃo ao longo do ano, ela nÃo à muito pronunciada. / Macroalgae are sources of bioactive molecules with antioxidant properties, many of which present seasonal variation. Five green algae of the genus Caulerpa (C. cupressoides, C. mexicana, C. prolifera, C. racemosa and C. sertularioides) were collected monthly at Pacheco Beach, from January to December 2006. After collection, they were transported to the laboratory, washed under running water to remove impurities and epiphytes, and freeze-dried. The algae extracts were prepared in methanol (MeOH) in the proportion 1:20 (w:v) under stirring for 1 h at 20ÂC in an orbital shaker followed by filtration, and the residues were submitted to two further successive extractions. The filtrate from the three methanolic extractions was gathered and concentrated in a rotary evaporator. Portions of the concentrated extract (10 mg) were suspended in 10 mL MeOH (50%). This extract (1 mg/mL) was used in the determination of the total phenolic content (TPC). In vitro antioxidant activity was measured by DPPH radical scavenging, ferric-reducing antioxidant power (FRAP), β-carotene bleaching (BCB), and ferrous ion chelating (FIC), at the concentrations 5, 50, 500 and 1000 Âg/mL, prepared from the extract. The metal chelator EDTA was used as a positive control in FIC, while the remaining essays used the synthetic antioxidant BHA. The TPC values were higher in the second semester of the year and varied from 4 to 32 mg GAE/g extract. The DPPH radical scavenging, BCB and FIC results did not exhibit variation patterns and presented activities greater than 25%, 70% and 10%, respectively. FRAP in the extracts of C. cupressoides, C. racemosa and C. sertularioides was higher in the second half of the year, while for C. mexicana the largest value was found in the first half of the year, and for C. prolifera variations during the year did not obey a pattern similar to the others. In all methodologies the activities of the alga extracts were inferior to the positive controls. The five species of Caulerpa can be considered potential sources of antioxidants with possible uses, such as in the food industry, not requiring a specific annual period for the extraction of these antioxidant compounds, as though there is variation across the year, it is not highly pronounced.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-22T13:02:35Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Flávia Thuane Duarte do Monte (PDF).pdf: 1029138 bytes, checksum: ded4d1bd5809aa8f26493c20c0169546 (MD5) / Made available in DSpace on 2016-07-22T13:02:35Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Flávia Thuane Duarte do Monte (PDF).pdf: 1029138 bytes, checksum: ded4d1bd5809aa8f26493c20c0169546 (MD5) Previous issue date: 2016-02-22 / FACEPE / O colágeno é a proteína fibrosa de origem animal mais abundante, que representa 30% de proteína total e 6% em peso no corpo humano. A pele e os ossos de bovinos e suínos geralmente são as principais fontes de colágeno e gelatina. No entanto, devido ao risco de transferência de zoonoses, existe uma necessidade de obtenção desta proteína por meio de outras fontes. A pescada amarela (Cynoscion acoupa) é um importante representante da pesca nacional e possui grande valor comercial. O objetivo deste estudo foi utilizar resíduos do processamento de pescada amarela para obter colágeno e sugerir sua utilização como fonte alternativa para o colágeno mamífero. Colágeno pepsino solúvel (PSC) foi isolado a partir de escamas de pescada amarela e caracterizado com sucesso. O rendimento da extração de PSC foi de 8,3% (baseado no peso seco). A SDS-PAGE (7,5%) mostrou que o padrão de bandas do PSC consistiu de uma cadeia α1 e α2 na proporção de 2:1, bem como cadeias β e γ, sendo caracterizado como colágeno do tipo I. O espectro de absorção ultravioleta (UV) mostrou uma máxima absorção em 222 nm. PSC foi solúvel na faixa de pH de 1 à 4, com a máxima solubilidade em pH 1. O colágeno também demonstrou maior solubilidade na faixa de concentração de 0 à 2% (w/v) de NaCl. A temperatura máxima de transição (Tmax) para PSC foi de 30,4°C, tal como determinado por calorimetria exploratória diferencial (DSC). Os resultados obtidos neste estudo indicam a possibilidade do uso de escamas de pescada amarela como uma fonte de colágeno do tipo I, com grande potencial para aplicações biotecnológicas. / Collagen is the most abundant fibrous protein of animal origin, representing 30% of the total protein and 6% in weight of the human body. The skin and bones of bovines and pigs usually are the main sources of collagen. However, due to the risk of transfer of diseases, there is a need for obtaining this protein form other sources. The acoupa weakfish (Cynoscion acoupa) is an important representative of the national fishing and has great commercial value. The aim of this study was to use acoupa weakfish waste processing for obtain collagen and suggest its use as an alternative source mammal collagen. Pepsin soluble collagen (PSC) from scales of acoupa weakfish was isolated and characterized. The yield of PSC was 8.3% (based on dry weight). SDS-PAGE (7.5%) pattern showed that both PSC consisted of one α1 and one α2 chains in proportion 2:1, as well as β and  chains, and were characterized to be type I collagen. The PSC ultraviolet (UV) absorption spectrum showed a maximum absorption at 222 nm. The PSC was soluble at pH between 1 and 4, with maximum solubility at pH 1. He have also shown solubility majority at NaCl concentration from 0 to 2% (w/v). The maximum transition temperature (Tmax) for PSC was 30.4°C, as determined by differential scanning calorimetry (DSC). The results obtained in this study indicate the possibility of using acoupa weakfish scales as a source of type I collagen with great potential for biotechnological application.

A obtenção de moléculas enantiomericamente puras ou enriquecidas tem se demonstrado um desafio em química orgânica sintética. Nesse âmbito, a biocatálise aparece como uma importante ferramenta sintética. Neste trabalho, desenvolveu-se uma metodologia para a obtenção de 6-hidróxioct-7-inoato de metila, 5-hidróxihept-6-inoato de metila, e 4-hidróxihex-5-inoato de metila enantiomericamente enriquecidos via resolução cinética enzimática. Primeiramente foram investigadas variáveis como temperatura, tempo, quantidade de doador de acila, solvente e enzima adequada para a reação. Em uma segunda etapa do trabalho, foram desenvolvidas seqüências reacionais onde os hidroxiésteres originariam moléculas bioativas Utilizando o 5-hidróxihept-6-inoato de metila, após três etapas reacionais, foi possível sintetizar intermediários sintéticos avançados das moléculas bioativas goniotalamina e argentilactona. De maneira análoga, após algumas etapas reacionais, o 4-hidróxihex-5-inoato de metila originou os feromônios buibuilactona, japonilura e 4-hexanolida / The synthesis of enantiomerically pure or enriched molecules has been an important challenge in synthetic organic chemistry. Among a variety of disciplines dedicated to achive this goal, biocatalysis appears as an important synthetic tool. Herein, we developed a methodology to obtain methyl 6-hydroxyoct-7-ynoate, methyl 5-hydroxyhept-6-ynoate and methyl 4-hydroxyhex-5-ynoate enantiomerically enriched by an enzymatic kinetic resolution. Reaction conditions such as temperature, reaction time, amount of acyl donor, solvent and enzyme were screened, in order to obtain high yields and enantioselectivities. In the second part of our work, synthetic pathways were developed where the hydroxyesters lead to bioactive molecules. Using methyl 5-hydroxyhept-6-ynoate, after three steps, advanced synthetic intermediates for the synthesis of the bioactive molecules, such as goniothalamine and argentilactone, were prepared. In the same way, methyl 4-hydroxyhex-5-ynoate was submitted to a reaction sequence leading the pheromones buibuilactone, japonilure and 4-hexanolide.

The thesis entitled “Intermolecular Interactions in Molecular Crystals: Quantitative Estimates from Experimental and Theoretical Charge Densities” consists of four chapters and an Appendix. Chapter 1 highlights the principles of crystal engineering from charge density point of view. Chapter 2 (Section I - III) deals with the evaluation of weak intermolecular interactions and in particular related to the features of concomitant polymorphism. Chapter 3 describes the co-operative role of weak interactions in the presence of strong hydrogen bonds in small bioactive molecules in terms of topological properties. Chapter 4 unravels the inter-ion interactions in terms of charge density features in an ionic salt. The general conclusions of the works presented in this thesis are provided at the end of the chapters. Appendix A explores the varieties of hydrogen bonds in a simple molecule. Identification of intermolecular interactions based purely on distance-angle criteria is inadequate and in the context of ‘quantitative crystal engineering’, recognition of critical points in terms of charge density distribution becomes extremely relevant to justify the occurrence of any interaction in the intermolecular space. The results from single crystal X-ray diffraction data at 90K (compound in chapter 4 at 113K) have been compared with those from periodic theoretical calculations via DFT method at high-level basis set (B3LYP/6-31G**) in order to establish a common platform between theory and experiment. Chapter 1 gives a brief review on crystal engineering to analyze intermolecular interactions along with the description of both experimental and theoretical approaches used in the analysis of charge densities in molecular crystals. The eight of Koch and Popelier’s criteria, defined using the theory of “Atoms in Molecules”, to characterize hydrogen bonds have also been discussed in detail. Chapter 2 (I) presents the charge density analysis in coumarin, 1-thiocoumarin, and 3-acetylcoumarin. Coumarin has been extensively studied as it finds applications in several areas of synthetic chemistry, medicinal chemistry, and photochemistry. The packing of molecules in the crystal lattice is governed by weak C−HLO and C−HLπ interactions only. The variations in charge density properties and derived local energy densities have been investigated in these regions of intermolecular interactions. The lacuna of the identification of a lower limit for the hydrogen bond formation has been addressed in terms of all eight of Koch and Popelier’s criteria, to bring out the distinguishing features between a hydrogen bond (C−HLO) and a van der Waals interaction (C−HLπ) for the first time. Chapter 2 (II) highlights the nature of intermolecular interactions involving sulfur in 1-thiocoumarin, 2-thiocoumarin, and dithiocoumarin. These compounds pack in the crystal lattice mainly via weak C−HLS and SLS interactions. The analysis of experimental and theoretical charge densities clearly categorizes these interactions as pure van der Waals in nature. The distribution of charge densities in the vicinity of the S atom has been analyzed to get better insights into the nature of sulfur in different environments. Chapter 2 (III) provides a detailed investigation of the charge density distribution in concomitant polymorphs of 3-acetylcoumarin. The electron density maps in the two forms demonstrate the differences in the nature of the charge density distribution particularly in the features associated with C−HLO and C−HLπ interactions. The net charges derived based on the population analysis via multipole refinement and also the charges evaluated via integration over the atomic basins and the molecular dipole moments show significant differences. The lattice energies calculated from experimental charge density approach clearly suggest that form A is thermodynamically stable compared to form B. Mapping of electrostatic potential over the molecular surfaces also bring out the differences between the two forms. Chapter 3 describes the analysis of charge density distribution in three small bioactive molecules, 2-thiouracil, cytosine monohydrate, and salicylic acid. These molecules pack in the crystal lattice via strong hydrogen bonds, such as N−HLO, N−HLS, and O−HLO. In spite of the presence of such strong hydrogen bonds, the weak interactions like C−HLO and C−HLS also contribute in tandem to the packing features. The distribution of charge densities in intermolecular space provides a quantitative comparison on the strength of both strong and weak interactions. The variations in electronegativity associated with the S, O, and N atoms are clearly seen in the electrostatic potential maps over the molecular surfaces. Chapter 4 deals with study of intermolecular interactions in N,N,N´N´-tetramethylethlenediammonium dithiocyanate, analyzed based on experimental charge densities from X-ray diffraction data at 113 K and compared with theoretical charge densities. The packing in the crystal lattice is governed mainly by a strong N+−H…N− hydrogen bond along with several weak interactions such as C−HLS, C−HLN, and C−HLπ. The charge density distribution in the region of inter-ionic interaction is also highlighted and the electrostatic potential map clearly provides the insights in to its interacting feature. Appendix A describes the experimental and theoretical charge density studies in 1-formyl-3-thiosemicarbazide and the assessment of five varieties of hydrogen bonds.

[pt] As doenças negligenciadas são causadas por agentes infecciosos ou parasitas, gerando altas taxas de morbidade e mortalidade em todo o mundo. Os investimentos dos países desenvolvidos em pesquisa, produção de medicamentos e controle dessas enfermidades são muito reduzidos, pois elas afetam, majoritariamente, as populações com baixo Índice de Desenvolvimento Humano. Uma dessas enfermidades é a Doença de Chagas, causada pelo Trypanosoma cruzi. Apresenta-se na forma de uma infecção parasitária crônica e altamente debilitante, acometendo mais de 6 milhões de pessoas na América Latina e este número pode ter um incremento, de aproximadamente 25 por cento nos próximos anos. O fármaco referência para o tratamento da Doença de Chagas disponível no Brasil é o benznidazol, extremamente eficaz na fase aguda da doença, mas sua eficácia na fase crônica é limitada, o que torna essencial a busca por novos compostos que atuem também nesta fase. No presente trabalho, foram descritas rotas sintéticas para uma série de 12 derivados de tiazol, destes 8 são inéditos. Posteriormente, 10 deles foram avaliados quanto a sua atividade tripanocida e toxicidade em modelos in vitro. Os compostos possuindo o anel tiazólico foram estruturalmente planejados, a partir do levantamento bibliográfico, onde verificou-se que certos compostos com um centro tiazólico apresentam propriedade tripanocida. Nas sínteses, a 4-bromoacetofenona (55) foi utilizada como material de partida para a obtenção dos intermediários tiazólicos 4-(4-bromofenil)-2- metiltiazol (56) e 4-(4-bromofenil)-2-aminotiazol (57). A partir desses, diversas modificações foram feitas para se chegar às moléculas alvo. A elucidação estrutural dos compostos foi realizada por RMN de 1H e RMN de 13C. A avaliação preliminar da atividade tripanocida foi realizada na forma amastigota intracelular da Cepa Tulahuen e a toxicidade aguda (LC50) foi feita in vitro em células hospedeiras de mamíferos (linhagem celular L929). Dentre os compostos sintetizados, a maioria apresentou baixa toxicidade, com valores de LC50 maiores que 400 (micro)mol.L-1. O composto tiazólico piridil-substituído 59c apresentou os melhores resultados em termos de atividade tripanocida, tendo reduzido 76 por cento da infecção. em células hospedeiras em concentração de 20 (micro)mol.L-1 Esse composto servirá como base para otimizações estruturais visando a melhoria da atividade tripanocida. / [en] Neglected diseases are mainly caused by infectious agents or parasites, generating high morbidity and mortality rates worldwide. The investments from developed countries in research, production of drugs/medicines and control of these diseases are small, since they mainly affect populations with low Human Development Index. One of these illnesses is Chagas disease, caused by Trypanosoma cruzi. It presents as a chronic and highly debilitating parasitic infection, affecting more than 6 million people only in Latin America with a perspective of increasing approximately 25 percent in few years. The reference drug for the treatment of Chagas disease in Brazil is benznidazole, which is extremely effective in the acute phase of the disease, but its efficacy in the chronic phase is limited, which makes essential the search for new compounds that also act in this phase. In the present work, synthetic routes were developed for a series of 12 thiazole derivatives, from which eight have been described for the first time. These molecules had their preliminary trypanocidal activity and toxicity evaluated in in vitro models. The compounds with the thiazole ring were structurally planned, based on the bibliographic review, where it was found that certain compounds with this heterocycle display trypanocidal properties. In the synthesis, 1-(4- bromophenyl)ethenone (54) was used as a starting material to obtain the thiazole intermediates 4-(4-bromophenyl)-2-methylthiazole (56) and 4-(4-bromophenyl)thiazol-2- amine (57). Several modifications were performed on these intermediates to produce the target molecules. The structural elucidation of the compounds was performed by 1H NMR and 13C NMR. Preliminary evaluation of trypanocidal activity was performed in the amastigotes intracellular form of the Tulahuen strain and the acute toxicity (LC50) was tested in vitro in mammalian host cells (cell line L929). Among the synthesized compounds, most of them presented low toxicity, with LC50 values greater than 400 (micro)mol/mol.L-1. The thiazole compound pyridil-substituted 59c showed the best results in terms of trypanocidal activity, reducing 76 percent of the infection in host cells in a concentration of 20 (micro)mol/mol.L-1. This thia\ole derivative will be used as a lead compound for structural optimizations aiming at improving trypanocidal activity.

La nature contient un grand nombre de molécules naturelles à visée thérapeutique. Depuis plusieurs années, la chimie médicinale ne cesse de s’en inspirer afin de développer de nouvelles thérapies pour améliorer le quotidien des personnes atteintes de certaines pathologies. Cette thèse traitera de la conception de molécules hétérocycliques comme inhibiteurs d’enzymes et médiateurs d’interactions protéine-protéine. Les molécules bioactives sont la pierre angulaire de la chimie thérapeutique. Depuis la découverte de l’Aspirine en 1899, elles n’ont cessé d’impacter la société à plusieurs niveaux et ont contribué à l’amélioration de la qualité de vie des patients. Il y a cependant, plusieurs pathologies pour lesquelles il n’existe à ce jour aucun remède, ce qui met en exergue les limitations de la chimie médicinale et implique le développement de nouvelles stratégies thérapeutiques. La stéato-hépatite non-alcoolique ou NASH (Non-Alcoholic Steatohepatitis) est une maladie caractérisée par une accumulation de graisses dans le foie, menant à la formation de tissus cicatriciels sur le foie. Ces derniers altèrent les fonctions hépatiques du foie et peuvent mener à la cirrhose si aucun traitement n’est administré. A ce jour, il existe aucun médicament pour guérir de NASH. La serine-thréonine kinase 25 (STK25) est une sérine-thréonine kinase, qui serait impliquée dans le développement de la maladie de NASH. Ainsi, le premier chapitre de cette thèse rapporte la synthèse de triazolo-oxazines comme inhibiteurs potentiels de STK25. Il s’agit de la première approche inhibitrice rapportée dans la littérature. Des tests biologiques ont été effectués et la modélisation moléculaire des triazolo-oxazines a été réalisée. Face au problème de pharmacorésistance et l’absence de remèdes pour certaines maladies, il y a un besoin urgent pour de nouvelles stratégies thérapeutiques est présent. Depuis quelques années, les dégradeurs ciblés de protéines suscitent un engouement. En effet, ces derniers induisent la dégradation de protéines défectueuses en recrutant les complexes de ligase E3. Cette stratégie vient pallier l’absence de sites de liaison, caractéristique de plusieurs protéines impliquées dans le développement de cancers. Parmi les dégradeurs de protéines, il y a les agrafes moléculaires et les PROTACs. Dans le second chapitre de cette thèse, la synthèse de molécules hétérocycliques comme ligand de la ligase E3 DCAF15 pour le développement éventuel de nouveaux PROTACS sera rapportée. L’outil de modélisation moléculaire a permis la sélection de molécules indoliques comportant le motif -lactame et pyrrolidine . Bien qu’ils aient été synthétisés comme un mélange racémique, des tests pour la synthèse asymétrique de ces derniers seront également discuter. Les maladies infectieuses ravagent les pays de l’Amérique latine et l’Afrique subsaharienne. Les ressources insuffisantes, les conditions sanitaires et l’instabilité des régimes politiques rendent difficile l’administration et l’acheminement de traitements. Parmi ces maladies infectieuses, il y a la leishmaniose, la trypanosomiase humaine africaine et la trypanosomiase humaine américaine lesquelles sont toutes causés par des protozoaires. Dans le troisième chapitre, des molécules hétérocycliques, comportant le motif imidazolo-oxazine seront synthétisés comme candidats potentiels pour le traitement de ces maladies infectieuses. / Nature has provided an infinite number of bioactive small molecules for therapeutic benefits. For many years, it has inspired medicinal chemistry to develop new therapies to improve the well-being of humankind. This thesis will be about the conception of heterocyclic small molecules as enzyme inhibitors and protein-protein interaction mediators. Small molecules are the cornerstone of therapeutic chemistry. Since the discovery of Aspirin in 1899, small molecules have had a significant impact on several levels and have contributed to the improvement of quality of life. Nonetheless, many diseases still have no remedy; hence there exists a need for new therapeutic strategies. Non-alcoholic steatohepatitis, (NASH) is a disease characterized by a buildup of fat in the liver, leading to the formation of scars on the liver. These scars will affect the different functions of the liver and can even lead to cirrhosis if not treated. Up until now, there is no drug for NASH. STK25 is a serine-threonine kinase, suspected to be involved in the mechanism of action of NASH. The first chapter in this thesis involves the synthesis of triazolo-oxazines as potential STK25 inhibitors for NASH treatment. It is the first example of an enzymatic approach for NASH treatment. The synthesis of potential inhibitors was designed based of molecular modeling of other inhibitors targeting CDK. In a second chapter, a new approach of small molecules degraders that recruits E3 ligases complexes for the degradation of protein is described. Among the small molecule degraders, there are molecular glues and PROTACs. This chapter will describe the design and the synthesis of heterocyclic molecules as DCAF15 ligands for the eventual development of new PROTACs. Molecular docking has been useful for the selection of the - lactams et pyrrolidines small molecules. Infectious diseases have tremendous consequences in Latin America and Africa. The lack of means, health hazards and the political instability of governments make difficult the supply and administration of treatments. Among the infectious diseases, there are Leishmaniasis, human African trypanosomiasis, human American trypanosomiasis, which are caused by bacteria. In the third chapter, imidazolo-oxazine small molecules will be synthesized as potential candidates for the treatment of these parasitic infections.