A family of seven topologically isomeric calix[4]arene glycoconjugates was prepared through the synthesis of a series of alkyne-derivatised calix[4]arene precursors that are suitable for the attachment of sugar moieties by microwave-assisted copper(I)-catalysed azide-alkyne cycloaddition (CuAAC). The glycoconjugates thus synthesised comprised one mono-functionalised derivative, two 1,2- or 1,3-divalent regioisomers, one trivalent and three tetravalent topoisomers in the cone, partial cone or 1,3-alternate conformations. The designed glycoconjugates were evaluated as ligands for the galactose-binding lectin PA-IL from the opportunistic bacterium Pseudomonas aeruginosa, a major causative agent of lung infections in cystic fibrosis patients. Binding affinities were determined by isothermal titration calorimetry (ITC), and the interaction with the lectin was shown to be strongly dependant on both the valence and the topology. Whereas the trivalent conjugate displayed enhanced affinity when compared to a monosaccharide model, the tetravalent conjugates are to-date the highest-affinity ligands measured by ITC. The topologies presenting carbohydrates on both faces of calixarene are the most potent ones with dissociation constants of approximately 200 nM. Molecular modelling suggests that such a multivalent molecule can efficiently chelate two of the binding sites of the tetrameric lectin; this explains the 800-fold increase of affinity achieved by the tetravalent molecule. Surface plasmon resonance (SPR) experiments confirmed that this glycoconjugate is the strongest inhibitor for binding of PA-IL to galactosylated surfaces for potential applications as an anti-adhesive agent.

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The design of multivalent glycoclusters requires the conjugation of biologically relevant carbohydrate epitopes functionalized with linker arms to multivalent core scaffolds. The multigram-scale syntheses of three structurally modified triethyleneglycol analogues that incorporate amide moiety(ies) and/or a phenyl ring offer convenient access to a series of carbohydrate probes with different water solubilities and rigidities. Evaluation of flexibility and determination of preferred conformations were performed by conformational analysis. Conjugation of the azido-functionalized carbohydrates with tetra-propargylated core scaffolds afforded a library of 18 tetravalent glycoclusters, in high yields, by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The compounds were evaluated for their ability to bind to PA-IL (the LecA lectin from the opportunistic pathogen Pseudomonas aeruginosa). Biochemical evaluation through inhibition of hemagglutination assays (HIA), enzyme-linked lectin assays (ELLA), surface plasmon resonance (SPR), and isothermal titration microcalorimetry (ITC) revealed improved and unprecedented affinities for one of the monovalent probes (K(d)=5.8 μM) and also for a number of the tetravalent compounds that provide several new nanomolar ligands for this tetrameric lectin.

Pseudomonas aeruginosa lung infections are a major cause of death in cystic fibrosis and hospitalized patients. Treating these infections is becoming difficult due to the emergence of conventional antimicrobial multiresistance. While monosaccharides have proved beneficial against such bacterial lung infection, the design of several multivalent glycosylated macromolecules has been shown to be also beneficial on biofilm dispersion. In this study, calix[4]arene-based glycoclusters functionalized with galactosides or fucosides have been synthesized. The characterization of their inhibitory properties on Pseudomonas aeruginosa aggregation, biofilm formation, adhesion on epithelial cells, and destruction of alveolar tissues were performed. The antiadhesive properties of the designed glycoclusters were demonstrated through several in vitro bioassays. An in vivo mouse model of lung infection provided an almost complete protection against Pseudomonas aeruginosa with the designed glycoclusters.

The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) is described. The fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd(2+) and Zn(2+) over other metal ions. Addition of Cd(2+) and Zn(2+) to the solution of 8 results in ratiometric measurement.

A rapid synthetic route to a nontoxic fluorescently labeled water-soluble calixarene has been developed. Investigation of the cellular uptake of the labeled calixarene, via confocal microscopy, through coincubation with uptake inhibitors demonstrates that uptake is not through the common clathrin coated pits or caveolae (lipid raft) endocytic pathways and that the calixarene derivative localizes within the cytoplasm and does not enter the nucleus. The study demonstrates the power of fluorescent labeling for investigation of interactions between calixarenes and biological systems and the potential for calixarene based intracellular imaging agents

A new class of cryptand-like ionophore based on a bis calix[4]arene structure has been developed. These molecules proved highly selective for complexation of potassium over all group I metal cations and barium. A range of symmetric and asymmetric calix[4]tubes featuring either alkyl or phenyl substituents at the upper rim have been synthesized in exceptional yield. Alteration of the calix[4]arene upper rim environment enables fine-tuning of the rate of potassium uptake, which can be evaluated through the conformational change on binding by NMR studies. Selectivity of potassium complexation has been demonstrated using NMR and electrospray mass spectral techniques. Molecular modeling studies, derived from crystallographic data, confirm that the potassium metal cation is complexed via the axial route, passing through the calix[4]arene annulus, and provide evidence for complexation rate and selectivity.

The synthesis and the spectroscopic studies of the amidourea based calix[4]arene sensors 1 and 2 are described. The 4-nitrophenyl based sensor 1 was synthesized in two steps from the corresponding calix [4]arene tetraethyl ester and shown to give rise to color changes in the UV-vis spectra in DMSO upon recognition of pyrophosphate and fluoride. Fitting the changes in the absorption spectra using nonlinear regression analysis indicated strong binding of several anions by 1 such as acetate and hydrogen phosphate in 1:1 (Host:Guest) stoichiometry, and at higher concentration in 1:2 stoichiometry. The preorganized calix-cavity was, however, not found to host chlorine while binding of bromide was determined. At high concentrations of these anions, significant colorimetric changes were also observed that were clearly visible to the naked eye for both pyrophosphate and fluoride. The phenyl analogue 2 was made to enable analysis of the anion recognition using 1H NMR titrations and showed that ions such as phosphate were bound in 1:1 stoichiometry, whereas the "urea" protons were shown to be significantly affected upon coordination to the anion.