Ligand (biologie)

300px|vignette|droite|Myoglobine en bleu lié à son ligand hème en orange. En biologie, un ligand (du latin ligandum, liant) est une molécule qui se lie de manière réversible à une macromolécule ciblée, protéine ou acide nucléique, jouant en général un rôle fonctionnel : stabilisation structurale, catalyse, modulation d'une activité enzymatique, transmission d'un signal. Ce terme, très utilisé pour l'étude de protéines, désigne les molécules qui interagissent avec la protéine de manière non-covalente et spécifique et qui jouent un rôle dans ses fonctions. Dans les systèmes vivants, une véritable liaison covalente irréversible entre un ligand et sa molécule-cible est rare. Contrairement à sa signification dans la chimie inorganique et l'étude des métaux, peu importe que le ligand se lie à un site de liaison métallique ou non. La liaison se réalise grâce aux forces entre molécules, telles que les liaisons ioniques, les liaisons d'hydrogène et les forces van der Waals. Généralement, l'in

Ligand synthesis for homogeneous catalysis

Michael Maurin

Organophosphorus compounds found applications in varied fields of the organic chemistry: they are particularly present in natural compounds such as the deoxyribonucleic acid (DNA) and in the field of catalysis in which their utility is also proven. Thus, this thesis work first focused on the preparation of various phosphorus ligands utilizable in transition metal catalysed reactions. Being given the importance of this type of reaction in organic synthesis, it appears essential to have many ligands at disposal in order to fine-tune and to optimize the reaction conditions as much as possible. Thus, the first objective of this work was to propose a simple and general method for the preparation of monodentate phosphorus ligands. Based on the use of phosphites in substitution for the usual phosphorus trihalides, this method was initially tested during the preparation of different simple triarylphosphines. Thereafter, this method was extended to the synthesis of new ligands having more complex structures. The yields obtained for the latter as well as the variety of the substrates authorized by this method confirmed its value and suggested its application to the synthesis of new heteroaromatic phosphines. The preparation of bidentate phosphorus ligands based on chiral biphenyl motifs was then addressed. For that purpose, the 2,2',6,6' -tetrabromobiphenyl was chosen as a pivot substrate for the development of a modular synthetic approach. Indeed, by means of successive halogen/metal permutational exchanges and after treatment with the suitable electrophile, it was possible to functionalize this substrate, isolate each atropisomer in enantiomerically pure form, and finally convert each one of those into chiral biphenylbisphosphines. In addition, it was also possible, during the synthesis of these ligands, to evaluate the rotational stability of some enantiomerically pure dilithiobiphenyls by means of dynamic nuclear magnetic resonance experiments.

EPFL2007

HER receptor dimerization controlled with bivalent ligands

Seymour de Picciotto

In this thesis, I show the ability of engineered bivalent ligands to control HER signaling by taking advantage of the dimerization-dependent mechanism of the four different receptors in the HER (EGFR) family. While monovalent wild-type ligands form HER homoe- and hetero-dimers according to the different members' relative expression levels, I hypothesize that bivalent ligands are able to drive dimerization of specific family members, independently of the cell's HER receptor composition. Using human telomerase reverse transcriptase (hTERT)-immortalized human mesenchymal stem cells (hTMSC), this study first confirms the bioactivity of the bivalent ligands: they exhibit an EC50 one order of magnitude lower than wild-type monomeric ligands and shown an avidity effect as shown from dose-response analysis of the pERK and pY-EGFR nodes. Then, I take advantage of known differences between EGFR hetero- and homodimer to investigate the bivalent ligands' ability to form selective dimers. I demonstrate that bivalent EGF is capable of inducing greater EGFR phosphorylation while preventing HER2 phosphorylation compared to wild-type EGF stimulation. Furthermore, the kinetics of EGFR activation by bivalent EGF differs from wild-type EGF with the appearance of a second activation peak at 20 minutes. Controlling the HER signaling network with these bivalent ligands has potential applications in tissue engineering, cancer therapy and in fundamental studies of the ErbB receptors activation mechanism

2009

Ligand synthesis for homogeneous catalysis

Michael Maurin

EPFL2007

Ligand synthesis for homogeneous catalysis

Single molecule analysis of neurokinin 1 receptor diffusion and ligand-induced changes

HER receptor dimerization controlled with bivalent ligands

Ligand synthesis for homogeneous catalysis

HER receptor dimerization controlled with bivalent ligands

Single molecule analysis of neurokinin 1 receptor diffusion and ligand-induced changes