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Development of hexahomotrioxacalix[3]arenes for the selective recognition, sensing and functionalization of ammonium ions

par Lambert, Simon
Président du jury Bruylants, Gilles
Promoteur Bartik, Kristin
Co-Promoteur Jabin, Ivan
Publication Non publié, 2023-05-16

Thèse de doctorat

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Résumé :

Synthetic molecular receptors can find applications in many areas among which the selective extraction, transport or detection of different species. In this thesis we focused our attention on the study of macrocyclic hexahomotrioxacalix[3]arenes. These receptors possess an 18-membered macrocycle resembling a crown ether (the 18 crown 6 ether) and when they are in their cone conformation, a cavity formed by three aromatic units.In the first part of this thesis, the binding properties of hexahomotrioxacalix[3]arene receptors towards ammonium ions were studied by 1H NMR spectroscopy and in silico methods. Our results showed that these receptors bind primary ammonium ions, including biomolecules, in their polyaromatic cavity even in a competitive environment (CDCl3/CD3OD (4:1)). A binding mode, similar for all guests, was reported with the ammonium head (NH3+) deeply inserted in the polyaromatic cavity of the receptor, enabling the formation of three H-bonds with the ethereal oxygens of the macrocycle. The high complementarity between primary ammonium ions and the receptors results in an unprecedented specificity for primary ammonium ions over secondary, tertiary and quaternary ones. The selective liquid-liquid extraction of primary ammonium salts from water and the selective recognition of lysine-containing peptides was achieved with these receptors. Our results have been reported in the paper “Specific Binding of Primary Ammonium Ions and Lysine-Containing Peptides in Protic Solvents by Hexahomotrioxacalix[3]arenes” Simon Lambert, Kristin Bartik and Ivan Jabin J. Org. Chem. 2020, 85, 10062-10071.In the second part of this thesis, a fluorescent hexahomotrioxacalix[3]arene was developed for the sensing of primary ammonium ions. A pyrene group was grafted on the large rim of an hexahomotrioxacalix[3]arene and its binding properties were studied by 1H NMR spectroscopy, in silico methods and fluorescence spectroscopy. Binding properties similar to those of the non-functionalized receptor were observed, with the same recognition mode. We showed that the fluorescent cavitand is able to sense, through quenching of its fluorescence, the biomolecules 3-iodothyronamine, serotonin and O-methylserotonin, while no quenching was observed with hexylammonium, dopamine and a C-12 diammonium ion. Quenching is attributed to charge and/or energy transfer between the excited pyrene and an aromatic unit of the guest enabling non-radiative deexcitation.In the last part of this thesis, an hexahomotrioxacalix[3]arene was used as a supramolecular protecting unit for the iteroselective functionalization of polyamines. The monofunctionalization of diamines of different length with three different reagents was studied and in all cases, a high iteroselectivity for the monofunctionalized product was observed. This supramolecular protection strategy was expanded with the recycling of the receptor and the in-situ accumulation of non-symmetric difunctionalized products. The complexation/decomplexation (protection/deprotection) of the diamines was achieved through acid/base additions and no loss in the iteroselectivity was observed in the additional cycles. This supramolecular protection method was also successfully used for the formation of asymmetric diurea compounds, not easily accessible through classical synthetic methods, through the reaction of two protected diamines of different sizes with a diisocyanate. This protection methodology was also applied to the iteroselective difunctionalization of a triamine and to the regio- and iteroselective monofunctionalization of a lysine on its less reactive amino group.