Controlling the Length of Cooperative Supramolecular Polymers with Chain Cappers.

The design and the characterization of supramolecular additives to control the chain length of benzene-1,3,5-tricarboxamide (BTA) cooperative supramolecular polymers under thermodynamic equilibrium is unraveled. These additives act as chain cappers of supramolecular polymers and feature one face as reactive as the BTA discotic to interact strongly with the polymer end, whereas the other face is nonreactive and therefore impedes further polymerization. Such a design requires fine tuning of the conformational preorganization of the amides and the steric hindrance of the motif. The chain cappers studied are monotopic derivatives of BTA, modified by partial N-methylation of the amides or by positioning of a bulky cyclotriveratrylene cage on one face of the BTA unit. This study not only clarifies the interplay between structural variations and supramolecular interactions, but it also highlights the necessity to combine orthogonal characterization methods, spectroscopy and light scattering, to elucidate the structures and compositions of supramolecular systems.

Hemicryptophanes with Improved Fluorescent Properties for the Selective Recognition of Acetylcholine over Choline.

The synthesis of two new fluorescent hemicryptophanes is reported. They were found to be efficient and selective receptors for acetylcholine over choline. When compared to other hemicryptophane hosts previously reported for the selective recognition of acetylcholine, they display improved fluorescent properties: their maximum emission wavelengths are red-shifted and the quantum yields are higher. NMR titration experiments and density functional theory (DFT) calculations support the results obtained from fluorescence spectroscopy and give insights into the interactions involved in the host/guest complexes and into the selectivity for acetylcholine over choline.

Selective recognition of acetylcholine over choline by a fluorescent cage.

A fluorescent hemicryptophane has been synthesized and can be used as a turn on receptor of acetylcholine. A binding constant of 2.4 × 104 M-1 was measured for this neurotransmitter, and its selective and sensitive detection over choline and choline phosphate was achieved. NMR and DFT calculations provide insight into the interactions involved in this selective recognition process.

Synthesis, resolution, and chiroptical properties of hemicryptophane cage controlling the chirality of propeller arrangement of a C3 triamide unit.

The five-steps synthesis of a hemicryptophane cage combining a benzene-1,3,5-tricarboxamide unit and a cyclotriveratrylene (CTV) moiety is described. Chiral high-performance liquid chromatography (HPLC) was used to resolve the racemic mixture. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental electronic circular dichroism (ECD) spectra with the calculated ones. X-ray molecular structures reveal that the capped benzene-1,3,5-tricarboxamide unit adopts a structurally chiral conformation in solid state: the chirality of CTV moiety controls the Λ or Δ orientation of the three amides.

Helical Chirality Induces a Substrate-Selectivity Switch in Carbohydrates Recognitions.

A new chiral hemicryptophane cage combining an electron-rich cyclotriveratrylene (CTV) unit and polar amine functions has been synthesized. The resolution of the racemic mixture has been performed by chiral HPLC, and the assignment of the absolute configuration of the two enantiomers has been achieved using ECD spectroscopy. In contrast with other hemicryptophane receptors, the two enantiomeric hosts display both remarkable enantioselectivities in the recognition of carbohydrates and good binding constants. Moreover, by switching the chirality of the CTV unit from M to P, a strong preference shift from glucose to mannose derivatives is observed.

A hemicryptophane with a triple-stranded helical structure.

A hemicryptophane cage bearing amine and amide functions in its three linkers was synthesized in five steps. The X-ray molecular structure of the cage shows a triple-stranded helical arrangement of the linkers stabilized by intramolecular hydrogen bonds between amide and amine groups. The chirality of the cyclotriveratrylene unit controls the propeller arrangement of the three aromatic rings in the opposite part of the cage. 1H NMR studies suggest that this structure is retained in solution.

High-Relaxivity Gd(III)-Hemicryptophane Complex.

The polytopic hemicryptophane cage HC1 combining a cyclotriveratrylene (CTV) unit and a tris(2-aminoethyl)amine (tren) moiety connected by three 2-hydroxyisophthalamide linkers was synthesized in 12 steps. The resulting highly functionalized covalent host is soluble in aqueous medium and has been used to complex Gd(III) ion. The Gd(III)@HC1 complex presents promising relaxivity properties when compared to the clinically used Dotarem MRI agent.

Enantiopure C1-Cyclotriveratrylene with a Reversed Spatial Arrangement of the Substituents.

Cyclotriveratrylene (CTV) is a macrocyclic cyclophane presenting a bowl-shaped conformation, used as building block to construct cryptophane and hemicryptophane capsules. A method to synthesize new enantiopure CTV derivatives with an unprecedented spatial arrangement of their substituents, exhibiting C1 symmetry, is described. The absolute configuration was assigned by ECD spectroscopy coupled with modeling. A statistical model has allowed for optimization of the proportion of C1 CTV, and the modularity of this approach is also highlighted.