Molecular clips based on propanediurea: exceptionally high binding affinities for resorcinol guests

Synthesis, Structures, and Complexation with Phenolic Guests of Acridone-Incorporated Arylene-Ethynylene Macrocyclic Compounds

Acridone units were incorporated into the arylene-ethynylene structure as polar arene units. Cyclic trimers consisting of three acridone-2,7-diyl units and three 1,3-phenylene units were synthesized by Sonogashira couplings via stepwise or direct route. X-ray analysis revealed that the trimer had a nearly planar macrocyclic framework with a cavity surrounded by three carbonyl groups. In contrast, the corresponding tetramer had a nonplanar macrocyclic framework. ¹ H NMR measurements showed that the trimer formed a 1 : 1 complex as a macrocyclic host with dihydric phenol guests, and the association constants were determined to be ca. 1.0×10³  L mol^-1 for hydroquinone or resorcinol guests in CDCl₃ at 298 K. The calculated structures of these complexes by the DFT method supported the presence of two sets of OH⋅⋅⋅O=C hydrogen bonds between the host and guest molecules. The spectroscopic data of the cyclic trimers and tetramers are compared with those of reference acridone compounds.

Synthesis of a monofunctional glycoluril molecular clip via cyclic imide formation on the convex site

We present a simple synthesis of a monohydroxylated glycoluril clip derivative prone to homodimerization from diester or diethanolamide clip derivatives.

Functionalisable acyclic cucurbiturils

Functionalised acyclic cucurbiturils can be prepared in a straightforward fashion and provide access to a wide variety of substituted derivatives.

Template-directed synthesis of cucurbituril analogues using propanediurea as a building block

Cucurbituril-like macrocycles were prepared in moderate yields by condensing propanediurea with formaldehyde, using, respectively, CaCl₂ and BaCl₂ as templates.

X-Ray structures and binding properties of molecular clips based on diethoxycarbonyl glycoluril

The crystal structures of two molecular clips derived from diethoxycarbonyl glycoluril were reported. Their unique binding behavior towards hydroquinone, which is different from Nolte's clips (high affinity for resorcinol), has been characterized through 1H NMR and IR. Job-plot analyses provide good evidence of a 1:1 stoichiometry for the complexes.Key words: crystal structure, molecular clips, binding properties

Isomeric 2,6-Pyridino-Cryptands Based on Dibenzo-24-crown-8

Cryptands 4 and 5 were synthesized from cis- and trans-bis(hydroxymethylbenzo)-24-crown-8 by reaction with pyridine-2,6-dicarboxylic acid chloride in 42 and 48% yields, respectively. The new cryptands form pseudorotaxanes with the paraquat derivative N,N'-bis(beta-hydroxyethyl)-4,4'-bipyridinium bis(hexafluorophosphate) ("paraquat diol", 6): Ka=1.0x10(4) and 1.4x10(4) M-1, respectively. The cryptands also form complexes with ammonium hexafluorophosphate. Formation of the paraquat/cryptand-based pseudorotaxanes can be switched off and on in a controllable manner on the basis of the cryptands' abilities to complex KPF6 strongly, providing a new mechanism for control of molecular shuttles. K+ displaces paraquat diol from the cryptands, converting yellow-orange solutions to colorless; however, addition of 18-crown-6 binds the KPF6 and allows the colored cryptand-paraquat complex to reform. Crystal structures are reported for both cryptands, both paraquat diol-based pseudorotaxanes, both NH4PF6 complexes, and both KPF6 complexes.

Divalent ligand for intramolecular complex formation to streptavidin

Monovalent ligand and divalent ligand have been synthesized, and their thermodynamic parameters of complexation to avidin and streptavidin have been analyzed in terms of multivalent binding.

Studies into the thermodynamic origin of negative cooperativity in ion-pairing molecular recognition

The association of synthetic receptors to target guests often proceeds through the cooperative action of multiple binding forces. An investigation into the thermodynamic origin of cooperativity in ion-pairing host-guest binding in water is described. The binding affinities of 1,2,3,4-butanetetracarboxylate, tricarballate, glutarate, and acetate to a C(3)(v) symmetric metallo-host (1) are characterized in terms of the binding constants (K(a)) and the thermodynamic parameters deltaG degrees, deltaH degrees, and deltaS degrees, as determined by isothermal titration calorimetry (ITC). These values are used to determine the individual contributions of the binding interaction to the overall binding. Several ways to view the combination of the individual binding events that make up the whole are analyzed, all of which lead to the conclusion of negative cooperativity. Combined, the data were used to evaluate the thermodynamic origin of negative cooperativity for this series of guests, revealing that entropy is the largest contributing factor. An interpretation of this result focuses upon differences in the number of water molecules displaced upon binding.

Complexation of phenolic guests by endo- and exo-hydrogen-bonded receptors

This article describes the complexation of phenol derivatives by hydrogen-bonded receptors. These phenol receptors are formed by self-assembly of calix[4]arene dimelamine or tetramelamine derivatives with 5,5-diethylbarbiturate (DEB) or cyanurate derivatives (CYA). The double rosette assemblies 3(3).(DEB)6/(CYA)6 have their phenol-binding functionalities (ureido groups) at the top and at the bottom of the double rosette (exo-receptors). The tetrarosette assemblies 4(3).(DEB)12/(CYA)12 form a cavity with binding sites between the two double rosettes for guest encapsulation (endo-receptors). An intrinsic binding constant Ka of 202 M-1 and 286 M-1 for the binding of 4-nitrophenol to the ureido functionalized exo- and endo-receptors, respectively, was observed. For the exo-receptor a 1:6 stoichiometry was observed while for the endo-receptor 1:4 binding stoichiometry was determined by Job plot and MALDI-TOF MS. The important role that the hydroxy group's acidity plays in the complexation of 4-nitrophenol is clarified by binding studies with different phenol derivatives. The hydrogen-bonded receptors showed a much smaller response towards less acidic phenol derivatives.

Host-[2]rotaxanes as cellular transport agents

Host-[2]rotaxanes, containing a diarginine-derivatized dibenzo-24-crown-8 (DB24C8) ether as the ring and a cyclophane pocket or an aromatic cleft as one blocking group, are cell transport agents. These hosts strongly associate with a variety of amino acids, dipeptides, and fluorophores in water (1 mM phosphate buffer, pH 7.0), DMSO, and a 75/25 (v/v) buffer to DMSO solution. All peptidic guests in all solvent systems have association constants (K(A)'s) in the range of 1 x 10(4) to 5 x 10(4) M(-)(1), whereas the K(A) range for the fluorophores is 1 x 10(4) to 9 x 10(5) M(-)(1). Association constants for the cyclophane itself, cyclophane 3, are smaller. These values are in the 1 x 10(3) to 5 x 10(3) M(-)(1) range, which shows that the rotaxane architecture is advantageous for guest binding. Cyclophane-[2]rotaxane 1 efficiently transports fluorescein and a fluorescein-protein kinase C (PKC) inhibitor into eukaryotic COS-7 cells, including the nucleus. Interestingly, cleft-[2]rotaxane 2 does not transport fluorescein as efficiently, even though the results from the fluorescence assays show that both [2]rotaxanes bind fluorescein with the same ability.

Self-association of facially amphiphilic methylene bridged glycoluril dimers

[structure: see text] Facially amphiphilic derivatives of methylene bridged glycoluril dimers are a versatile model system for systematic studies of self-assembly in water. Thorough physical organic characterization, including analytical ultracentrifugation, a technique rarely used in synthetic self-assembly studies, allows us to conclude that this class of molecules undergoes hydrophobically driven self-association to yield tightly associated discrete dimeric assemblies.