Développement de diverses méthodologies RMN en milieu cristal liquide chiral

Le travail de cette thèse porte sur des développements de la RMN en milieu cristal liquide chiral. Dans un premier temps, de nouvelles méthodologies RMN 2D en milieu cristal liquide chiral ont été développées afin de simplifier l analyse spectrale des spectres proton et carbone-13 permettant de mesurer simplement des couplages dipolaires et de visualiser la différenciation énantiomérique. Ensuite, nous avons étudié l effet de la température, du champ magnétique, du degré de polymérisation et de la concentration en polymère sur la différenciation énantiomérique. Nous avons montré que ces paramètres modulent différemment celle-ci et qu ils sont importants dans le cadre d une optimisation de la méthode. Puis, nous avons décrit une méthode empirique de détermination de la configuration absolue par RMN du deutérium en abondance naturelle. Nous avons montré, dans le cas de dérivés d époxydes chiraux, qu à partir de l étude d une série de composés homologues de référence, nous avons une très bonne corrélation entre la forme tridimensionnelle du composé et son orientation dans la phase chirale anisotrope. Ceci nous a permis de déterminer la configuration absolue inconnue d un composé chiral. Enfin, cette même série de dérivés d époxydes a été étudiée par RMN du proton et du carbone-13. En calculant l orientation des composés, nous étions en mesure de déterminer la configuration absolue d un composé chiral inconnu nous amenant à la même conclusion que l étude par RMN du deutérium. De plus, en généralisant ce calcul à l ensemble de la molécule, nous avons montré qu il est possible de déterminer la configuration relative des protons diastéréotopes du méthylène.The aim of this thesis is the development of the NMR by using a chiral liquid crystal as solvent. In a first part, new 2D NMR experiments are described to simplify the proton and carbon-13 spectra. Thus we can easily measure the dipolar couplings and visualize the enantiomeric differentiation. In a second part, we have studied the effect of temperature, magnetic field, polymerisation degree and polymer concentration on the enantiomeric differentiation. We have demonstrated that these various experimental parameters affect differently the enantiomeric differentiation and are important in optimising experimental conditions. Next, we have described an empirical method to determine the absolute configuration using deuterium NMR in natural abundance. Using reference analogous compounds, we have shown that quadrupolar splittings and tridimensionnal geometry of the compounds can be correlated. Then we are able to determine the unknown absolute configuration of a chiral epoxide by studying a series of analogous compounds of known absolute configuration. Finally, the same series of compounds were studied by proton and carbon-13 NMR. By calculating the Saupe order parameters of the rigid part, we have shown that we are able too to determine the absolute configuration giving the same conclusion as previously. We have extended this calculus of order parameters to the entire molecule, and we have shown that the determination of the relative stereochemistry of methylen diastereotopic protons can be done.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Empirical determination of the absolute configuration of small chiral molecules using natural abundance 2H NMR in chiral liquid crystals

International audienceNatural abundance deuterium 2D NMR spectroscopy in polypeptide liquid crystals is used for empirically determining the absolute configuration of small chiral molecules

Phosphorylation Controls the Interaction of the Connexin43 C-Terminal Domain with Tubulin and Microtubules

International audienceConnexins are structurally related transmembrane proteins that assemble to form gap junction channels involved in the mediation of intercellular communication. It has been shown that the intracellular tail of connexin43 (Cx43) interacts with tubulin and microtubules with putative impacts on its own intracellular trafficking, its activity in channel communication, and its interference with specific growth factor signal transduction cascades. We demonstrate here that the microtubule binding of Cx43 is mainly driven by a short region of 26 amino acid residues located within the intracellular tail of Cx43. The nuclear magnetic resonance structural analysis of a peptide (K26D) corresponding to this region shows that this peptide is unstructured when free in solution and adopts a helix conformation upon binding with tubulin. In addition, the resulting K26D–tubulin molecular complex defines a new structural organization that could be shared by other microtubule partners. Interestingly, the K26D–tubulin interaction is prevented by the phosphorylation of K26D at a src kinase specific site. Altogether, the results elucidate the mechanism of the interaction of Cx43 with the microtubule cytoskeleton and propose a pathway for understanding the microtubule-dependent regulation of Cx43 gap junctional communications and the involvement of Cx43 in TGF-β signal transduction