Conformationally Mobile Acyclic Cucurbit[n]uril-Type Receptors Derived from an S-shaped Methylene Bridged Glycoluril Pentamer.

We report the synthesis of the conformationally mobile S-shaped glycoluril pentamer building block 3a and two new acyclic CB[n]-type receptors P1 and P2. P1 (9 mM) and P2 (11 mM) have moderate aqueous solubility but their host•guest complexes are poorly soluble. Host P1 does not undergo intermolecular self-association whereas P2 does (Ks = 189±27 M-1). 1H NMR titrations show that P1 and P2 are poor hosts toward hydrophobic (di)cations 6 - 11 (P1: Ka = 375-1400 M-1; P2: Ka = 1950-19800 M-1) compared to Tet1 and Tet2 (Tet1: Ka = 3.09 × 106 to 4.69 × 108 M-1; Tet2: Ka = 4.59 × 108 to 1.30 × 1010 M-1). Molecular modelling shows that P1 and P2 exist as a mixture of three different conformers due to the two S-shaped methylene bridged glycoluril dimer subunits that each possess two different conformations. The lowest energy conformers of P1 and P2 do not feature a well-defined central cavity. In the presence of guests, P2 adapts its conformation to form 1:1 P2•guest complexes; the binding free energy pays the energetic price of conformer selection. This energetically unfavorable conformer selection results in significantly decreased Ka values of P1 and P2 compared to Tet1 and Tet2.

Unraveling the Structure-Affinity Relationship between Cucurbit[n]urils (n = 7, 8) and Cationic Diamondoids.

We report the measurement of the binding constants (Ka) for cucurbit[n]uril (n = 7, 8) toward four series of guests based on 2,6-disubstituted adamantanes, 4,9-disubstituted diamantanes, 1,6-disubstituted diamantanes, and 1-substituted adamantane ammonium ions by direct and competitive 1H NMR spectroscopy. Compared to the affinity of CB[7]·Diam(NMe3)2, the adamantane diammonium ion complexes (e.g., CB[7]·2,6-Ad(NH3)2 and CB[7]·2,6-Ad(NMe3)2) are less effective at realizing the potential 1000-fold enhancement in affinity due to ion-dipole interactions at the second ureidyl C═O portal. Comparative crystallographic investigation of CB[7]·Diam(NMe3)2, CB[7]·DiamNMe3, and CB[7]·1-AdNMe3 revealed that the preferred geometry positions the +NMe3 groups ≈0.32 Å above the C═O portal; the observed 0.80 Å spacing observed for CB[7]·Diam(NMe3)2 reflects the simultaneous geometrical constraints of CH2···O═C close contacts at both portals. Remarkably, the CB[8]·IsoDiam(NHMe2)2 complex displays femtomolar binding affinity, placing it firmly alongside the CB[7]·Diam(NMe3)2 complex. Primary or quaternary ammonium ion looping strategies lead to larger increases in binding affinity for CB[8] than for CB[7], which we attribute to the larger size of the carbonyl portals of CB[8]; this suggests routes to develop CB[8] as the tightest binding host in the CB[n] family. We report that alkyl group fluorination (e.g., CB[7]·1-AdNH2Et versus CB[7]·1-AdNH2CH2CF3) does not result in the expected increase in Ka value. Finally, we discuss the role of solvation in nonempirical quantum mechanical computational methodology, which is used to estimate the relative changes in Gibbs binding free energies.

A Nexus between Theory and Experiment: Non-Empirical Quantum Mechanical Computational Methodology Applied to Cucurbit[n]uril⋠Guest Binding Interactions.

A training set of eleven X-ray structures determined for biomimetic complexes between cucurbit[n]uril (CB[7 or 8]) hosts and adamantane-/diamantane ammonium/aminium guests were studied with DFT-D3 quantum mechanical computational methods to afford ΔGcalcd binding energies. A novel feature of this work is that the fidelity of the BLYP-D3/def2-TZVPP choice of DFT functional was proven by comparison with more accurate methods. For the first time, the CB[n]⋅guest complex binding energy subcomponents [for example, ΔEdispersion , ΔEelectrostatic , ΔGsolvation , binding entropy (-TΔS), and induced fit Edeformation(host) , Edeformation(guest) ] were calculated. Only a few weeks of computation time per complex were required by using this protocol. The deformation (stiffness) and solvation properties (with emphasis on cavity desolvation) of cucurbit[n]uril (n=5, 6, 7, 8) isolated host molecules were also explored by means of the DFT-D3 method. A high ρ2 =0.84 correlation coefficient between ΔGexptl and ΔGcalcd was achieved without any scaling of the calculated terms (at 298 K). This linear dependence was utilized for ΔGcalcd predictions of new complexes. The nature of binding, including the role of high energy water molecules, was also studied. The utility of introduction of tethered [-(CH2 )n NH3 ]+ amino loops attached to N,N-dimethyl-adamantane-1-amine and N,N,N',N'-tetramethyl diamantane-4,9-diamine skeletons (both from an experimental and a theoretical perspective) is presented here as a promising tool for the achievement of new ultra-high binding guests to CB[7] hosts. Predictions of not yet measured equilibrium constants are presented herein.

Cationic acyclic cucurbit[n]uril-type containers: synthesis and molecular recognition toward nucleotides.

We report the synthesis of M2NH3 which is a tetracationic analogue of our prototypical acyclic CB[n]-type molecular container M2. Both M1NH3 and M2NH3 possess excellent solubility in D2O and do not undergo intermolecular self-association processes that would impinge on their molecular recognition properties. Compounds M1NH3 and M2NH3 do, however, undergo an intramolecular self-complexation process driven by ion-dipole interactions between the ureidyl C=O portals and the OCH2CH2NH3 arms along with inclusion of one aromatic wall in its own hydrophobic cavity. The Ka values for M1NH3 and M2NH3 toward seven nucleotides were determined by 1H NMR titration and found to be quite modest (Ka in the 102 - 103 M-1 range) although M2NH3 is slightly more potent. The more highly charged guests (e.g. ATP) form stronger complexes with M1NH3 and M2NH3 than the less highly charged guest (e.g. ADP, AMP). The work highlights the dominant influence of the ureidyl C=O portals on the molecular recognition behavior of acyclic CB[n]-type receptors and suggests routes (e.g. more highly charged arms) to enhance their recognition behavior toward anions.

Synthesis of giant globular multivalent glycofullerenes as potent inhibitors in a model of Ebola virus infection.

The use of multivalent carbohydrate compounds to block cell-surface lectin receptors is a promising strategy to inhibit the entry of pathogens into cells and could lead to the discovery of novel antiviral agents. One of the main problems with this approach, however, is that it is difficult to make compounds of an adequate size and multivalency to mimic natural systems such as viruses. Hexakis adducts of [60]fullerene are useful building blocks in this regard because they maintain a globular shape at the same time as allowing control over the size and multivalency. Here we report water-soluble tridecafullerenes decorated with 120 peripheral carbohydrate subunits, so-called 'superballs', that can be synthesized efficiently from hexakis adducts of [60]fullerene in one step by using copper-catalysed azide­alkyne cycloaddition click chemistry. Infection assays show that these superballs are potent inhibitors of cell infection by an artificial Ebola virus with half-maximum inhibitory concentrations in the subnanomolar range.

Acyclic Cucurbit[n]uril-Type Molecular Containers: Influence of Linker Length on Their Function as Solubilizing Agents.

Two acyclic cucurbit[n]uril (CB[n])-type molecular containers that differ in the length of the (CH2 )n linker (M2C2: n=2, M2C4: n=4) between their aromatic sidewalls and sulfonate solubilizing groups were prepared and studied. The inherent solubilities of M2C2 (68 mm) and M2C4 (196 mm) are higher than the analogue with a (CH2 )3 linker (M2, 14 mm) studied previously. (1) H NMR dilution experiments show that M2C2 and M2C4 do not self-associate in water, which enables their use as solubilizing excipients. We used phase solubility diagrams (PSDs) to compare the solubilizing capacities of M2, M2C2, M2C4, hydroxypropyl-ß-cyclodextrin (HP-ß-CD), and sulfobutylether-ß-cyclodextrin (SBE-ß-CD) toward 15 insoluble drugs. We found that M2C2 and M2C4-as gauged by the slope of their PSDs-are less potent solubilizing agents than M2. However, the higher inherent solubility of M2C2 allows higher concentrations of drug to be formulated using M2C2 than with M2 in several cases. The solubilizing ability of M2C2 and SBE-ß-CD were similar in many cases, with Krel values averaging 23 and 12, respectively, relative to HP-ß-CD. In vitro cytotoxicity and in vivo maximum tolerated dose studies document the biocompatibility of M2C2.

Acyclic Cucurbit[n]uril Dendrimers.

The synthesis of acyclic cucurbit[n]uril dendrimers G1-G3 that bear four dendrons on their aromatic sidewalls via thiolate S(N)2 chemistry is reported. G1-G3 are polycationic and can bind to pEGFP plasmid DNA as shown by dynamic light scattering (DLS), gel electrophoresis, and scanning electron microscopy (SEM). The gene delivery ability of G1-G3 is presented.

Mannoside Glycolipid Conjugates Display Anti-inflammatory Activity by Inhibition of Toll-like Receptor-4 Mediated Cell Activation.

Inhibition of excessive Toll-like receptor 4 (TLR4) signaling is a therapeutic approach pursued for many inflammatory diseases. We report that Mannoside Glycolipid Conjugates (MGCs) selectively blocked TLR4-mediated activation of human monocytes and monocyte-derived dendritic cells (DCs) by lipopolysaccharide (LPS). They potently suppressed pro-inflammatory cytokine secretion and maturation of DCs exposed to LPS, leading to impaired T cell stimulation. MGCs did not interfere with LPS and could act in a delayed manner, hours after LPS stimulation. Their inhibitory action required both the sugar heads and the lipid chain, although the nature of the sugar and the structure of the lipid tail could be modified. They blocked early signaling events at the cell membrane, enhanced internalization of CD14 receptors, and prevented colocalization of CD14 and TLR4, thereby abolishing NF-κB nuclear translocation. When the best lead conjugate was tested in a mouse model of LPS-induced acute lung inflammation, it displayed an anti-inflammatory action by suppressing the recruitment of neutrophils. Thus, MGCs could serve as promising leads for the development of selective TLR4 antagonistic agents for inflammatory diseases.

Differentially functionalized acyclic cucurbiturils: synthesis, self-assembly and CB[6]-induced allosteric guest binding.

We report the synthesis of mono- and difunctionalized acyclic cucurbit[n]uril-type containers (1HA, 1HDA, 2HDA) which bear hexylammonium and hexanediammonium arms. The intra- and intermolecular assembly processes of 1HA, 1HDA, 2HDA as well as the ability of CB[n] to trigger allosteric host­guest binding toward guests 9­11 are presented.

Polycationic pillar[5]arene derivatives: interaction with DNA and biological applications.

Dendritic pillar[5]arene derivatives have been efficiently prepared by grafting dendrons with peripheral Boc-protected amine subunits onto a preconstructed pillar[5]arene scaffold. Upon cleavage of the Boc-protected groups, water-soluble pillar[5]arene derivatives with 20 (13) and 40 (14) peripheral ammonium groups have been obtained. The capability of these compounds to form stable nanoparticles with plasmid DNA has been demonstrated by gel electrophoresis, transmission electron microscopy (TEM), and dynamic light scattering (DLS) investigations. Transfection efficiencies of the self-assembled 13/pCMV-Luc and 14/pCMV-Luc polyplexes have been evaluated in vitro with HeLa cells. The transfection efficiencies found for both compounds are good, and pillar[5]arenes 13 and 14 show very low toxicity if any.

Dynamic micelles of mannoside glycolipids are more efficient than polymers for inhibiting HIV-1 trans-infection.

Mannoside glycolipid conjugates are able to inhibit human immunodeficiency virus type 1 (HIV-1) trans-infection mediated by human dendritic cells (DCs). The conjugates are formed by three building blocks: a linear or branched mannose head, a hydrophilic linker, and a 24-carbon lipid chain. We have shown that, even as single molecules, these compounds efficiently target mannose-binding lectins, such as DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN) important for HIV-1 transmission. With the goal to optimize their inhibitory activity by supramolecular structure formation, we have compared saturated and unsaturated conjugates, as single molecules, self-assemblies of dynamic micelles, and photopolymerized cross-linked polymers. Surface plasmon resonance showed that, unexpectedly, polymers of trivalent conjugates did not display a higher binding affinity for DC-SIGN than single molecules. Interactions on a chip or in solution were independent of calcium; however, binding to DCs was inhibited by a calcium chelator. Moreover, HIV-1 trans-infection was mostly inhibited by dynamic micelles and not by rigid polymers. The inhibition data revealed a clear correlation between the structure and molecular assembly of a conjugate and its biological antiviral activity. We present an interaction model between DC-SIGN and conjugates-either single molecules, micelles, or polymers-that highlights that the most effective interactions by dynamic micelles involve both mannose heads and lipid chains. Our data reveal that trivalent glycolipid conjugates display the highest microbicide potential for HIV prophylaxis, as dynamic micelles conjugates and not as rigid polymers.

Synthesis of optically pure [60]fullerene e,e,e-tris adducts.

The reaction of readily available optically active Si-tethered tris(malonates) with C60 gave easily separable diastereoisomers differing by the absolute configuration of the inherently chiral addition pattern on the fullerene core. The absolute configuration of the e,e,e addition pattern has been unambiguously determined using X-ray crystal structure analysis.

Gene delivery with polycationic fullerene hexakis-adducts.

Polyplexes prepared from DNA and globular compact polycationic derivatives constructed around a fullerene hexakis-adduct core have shown remarkable gene delivery capabilities.