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Second generation of calix[6]tren ligands with functionalized appending arms

par De Leener, Gaël ;Lascaux, Angélique ;Reinaud, Olivia;Jabin, Ivan
Référence Journée Scientifique Annuelle de la SRC
Publication Non publié, 2011-10-13

Poster de conférence

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Résumé :

Metallo-enzymes are ubiquitous. More than 30% of enzymes present a metal ion in their active sitethat is a key for catalysis. Interesting sub-families present a mononuclear active site where a single metal ion(Zn2+ or Cun+) is coordinated to a polyhistidine core. The elaboration of model compounds of such metalloenzymesis important for understanding the fundamental mechanisms involved in their bio-catalytic cycles. Inthis context, we have developed three generations of calix[6]arene based biomimetic complexes that combine ametal ion and a hydrophobic cavity.1 These metal complexes display a single coordination site accessible for anexogenous ligand that is fully controlled by the hydrophobic funnel. One of the ligand belonging to the thirdgeneration of compounds combines a calix[6]arene pocket to a tren cap (tren = [tris(2-aminoethyl)amine]).Calix[6]tren shows remarkably versatile host-guest properties either toward ammonium ions, polar neutralmolecules and metal ions (Zn and Cu).2,3 Very interestingly, the protonation of the apical nitrogen atom allows acontrol of the environment on the host-guest properties. The development of efficient synthetic methodologiesfor the selective functionnalization of calix[6]tren is now required in order to obtain water-soluble or graftableanalogues.In this context, we have successfully obtained a new generation of calix[6]tren ligands decorated withappending arms (i.e. 3 and 4). The key step of their synthesis consists of a [1+1] macrocyclisation reactionbetween a trisamine calix[6]arene and a tris-acid cap. The host-guest properties of the intermediatecalix[6]trenamides4,5 (1 and 2) were studied by 1H NMR spectroscopy. It was shown that these tris-amidoreceptors are able to selectively recognize polar neutral guests displaying H-bond donor and acceptor groups,fluoride anion and contact ammonium fluoride salts. Finally, the efficient binding of Zn2+ by the two calix[6]trenligands 3 and 4 has been clearly observed by 1H NMR spectroscopy, paving the way to development of watersolubleand graftable calix[6]tren based complexes.