Acetylenic cyclodextrins for multireceptor architectures: cups with sticky ends for the formation of extension wires and junctions

Preparation of 6-Monohalo-β-cyclodextrin Derivatives with Selectively Methylated Rims via Diazonium Salts

A series of 6-monohalo (Cl, Br, and I) β-cyclodextrin derivatives with various types of methylations were synthesized via a diazotization/nucleophilic displacement reaction from the corresponding methylated cyclodextrin amines. All four starting compounds (6A-amino-6A-deoxy derivatives of native β-CD, per-6-O-methyl-, per-2,3-O-methyl-, and per-2,3,6-O-methyl-β-CD) were found to have different reactivities under the same reaction conditions. Unsubstituted and fully per-O-methylated cyclodextrin amines undergo fast transformation, giving lower yields of the monohalogenated product. The selectively methylated cyclodextrin amines react remarkably slower and provide almost complete conversion into the desired monohalogenated compound. A pure product was, in several cases, successfully isolated with simple purification techniques (extraction and precipitation), allowing large-scale preparations. This new method opens the way for preparing poorly investigated monofunctionalized selectively methylated cyclodextrins.

Arsenic(V) Removal from Water by Resin Impregnated with Cyclodextrin Ligand

More rigorous environmental rules on hazardous metals release require the implementation of diverse methods to remove them from contaminated streams. The adsorption process is the most attractive method for removal of toxic metal ions from different aqueous solutions. In the present study, batch and fixed bed column experiments were carried out to investigate the performance of permethylated β-cyclodextrin impregnated resin for the removal of As(V) ions from aqueous solutions. Sorption of As(V) ions was performed in groups under a variety of pH and metal concentrations. It was noted that removal efficiency was the highest (98%) at pH 6.0, and at an initial As(V) concentration equal to 0.1 mg/L. Sorption model use for experimental data indicates that the removal mechanism of As(V) by the permethylated β-cyclodextrin impregnated resin was the physical sorption. The adsorption capacity of the cyclodextrin ligand immobilized onto Amberlite XAD-4 resin was 19 mg/g. In addition, the impregnated resin was regenerable, thus was able to be used over and over.

Pharmacological Chaperones for the Treatment of α-Mannosidosis

α-Mannosidosis (AM) results from deficient lysosomal α-mannosidase (LAMAN) activity and subsequent substrate accumulation in the lysosome, leading to severe pathology. Many of the AM-causative mutations compromise enzyme folding and could be rescued with purpose-designed pharmacological chaperones (PCs). We found that PCs combining a LAMAN glycone-binding motif based on the 5 N,6 O-oxomethylidenemannojirimycin (OMJ) glycomimetic core and different aglycones, in either mono- or multivalent displays, elicit binding modes involving glycone and nonglycone enzyme regions that reinforce the protein folding and stabilization potential. Multivalent derivatives exhibited potent enzyme inhibition that generally prevailed over the chaperone effect. On the contrary, monovalent OMJ derivatives with LAMAN aglycone binding area-fitting substituents proved effective as activity enhancers for several mutant LAMAN forms in AM patient fibroblasts and/or transfected MAN2 B1-KO cells. This translated into a significant improvement in endosomal/lysosomal function, reverting not only the primary LAMAN substrate accumulation but also the additional downstream consequences such as cholesterol accumulation.

Xylylene Clips for the Topology-Guided Control of the Inclusion and Self-Assembling Properties of Cyclodextrins

The topology of β-cyclodextrin can be molded, from toroidal to ovoid basket-shaped, by the installation of an o- or m-xylylene moiety connecting two consecutive d-glucopyranosyl units through the secondary O-2(I) and O-3(II) positions. This strategy can be exploited advantageously to precast the cavity for preferential inclusion of globular or planar guests as well as to privilege dimeric or monomeric species in water solution.

Halogen bonding rotaxanes for nitrate recognition in aqueous media

Incorporating halogen bonding into an interlocked [2]rotaxane anion host system results in unprecedented nitrate recognition in 90% water.

Multichannel Detection and Differentiation of Explosives with a Quantum Dot Array

The sensing and differentiation of explosive molecules is key for both security and environmental monitoring. Single fluorophores are a widely used tool for explosives detection, but a fluorescent array is a more powerful tool for detecting and differentiating such molecules. By combining array elements into a single multichannel platform, faster results can be obtained from smaller amounts of sample. Here, five explosives are detected and differentiated using quantum dots as luminescent probes in a multichannel platform: 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), tetryl (2,4,6-trinitrophenylmethylnitramine), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN). The sharp, variable emissions of the quantum dots, from a single excitation wavelength, make them ideal for such a system. Each color quantum dot is functionalized with a different surface receptor via a facile ligation process. These receptors undergo nonspecific interactions with the explosives, inducing variable fluorescence quenching of the quantum dots. Pattern analysis of the fluorescence quenching data allows for explosive detection and identification with limits-of-detection in the ppb range.

Cyclodextrin and phosphorus(iii): a versatile combination for coordination chemistry and catalysis

The relevance of cyclodextrins equipped with P(iii) atoms in coordination chemistry and homogeneous catalysis is discussed.

Staudinger ligation towards cyclodextrin dimers in aqueous/organic media. Synthesis, conformations and guest-encapsulation ability

β-Cyclodextrin (β-CD) dimers have been prepared using the bioorthogonal Staudinger ligation for the first time. In addition to a known linker, methyl 2-(diphenylphosphanyl)terephthalate, a doubly active linker was specifically developed that enabled connection of two β-CD units in a single step and in aqueous/organic media, under mild conditions and with good yields. A three-carbon spacer between the β-CD torus and the azido group was required for facile dimer formation. The products, as studied by NMR spectroscopy, were found to adopt closed conformations by intramolecular self-inclusion. On the other hand, association via intermolecular binding was also observed in aqueous solution, confirmed by DOSY NMR experiments. Despite self-inclusion, the β-CD cavities were capable of guest encapsulation, as shown by titration experiments: the binding constant with 1-adamantylamine was similar to that of natural β-CD. Theoretical calculations for isolated molecules (PM3 level of theory) and in the presence of solvent [water, PM3(COSMO)] as well as DFT calculations suggested that the compounds prefer to adopt conformations which bring the phenyl groups either inside the β-CD cavity (inclusion) or over its narrow side (vicinal). Thus, Staudinger ligation could be the method of choice for linking CDs exhibiting (i) ease of preparation in aqueous media, in short steps, under mild conditions and in good yields, (ii) satisfactory aqueous solubility and independent binding capacity of the cavities.

Study of near-symmetric cyclodextrins by compressed sensing 2D NMR

The compressed sensing NMR (CS-NMR) is an approach to processing of nonuniformly sampled NMR data. Its idea is to introduce minimal l(p) -norm (0 < p ≤ 1) constraint to a penalty function used in a reconstruction algorithm. Here, we demonstrate that 2D CS-NMR spectra allow the full spectral assignment of near-symmetric β-cyclodextrin derivatives (mono-modified at the C6 position). The application of CS-NMR ensures experimental time saving and the resolution improvement, necessary because of very low chemical shift dispersion. In the overnight experimental time, the set of properly resolved 2D NMR spectra required for the unambiguous assignment of mono(6-deoxy-6-(1-1,2,3-triazo-4-yl)-1-propane-3-O-(phenyl)) β-cyclodextrin was obtained. The highly resolved HSQC spectrum was reconstructed from 5.12% of the data. Moreover, reconstructed 2D HSQC-TOCSY spectrum yielded information about the correlations within one sugar unit, and 2D HSQC-NOESY technique allowed the sequential assignment of the glucosidic units.

New and old NMR experiments for the resonance assignment of complex oligosaccharides--application to a cyclodextrin derivative

The complete assignment of the (1)H and (13)C sugar resonances in mono-3,6-anhydro-heptakis(2,3-O-methyl)-hexakis(6-O-methyl)-β-cyclodextrin, an asymmetrically functionalized β-cyclodextrin, was carried out by means of 2D NMR experiments. The TOCSY and the homonuclear multiple relay COSY spectra provided most of the (1)H assignments. The multiplicity edited HSQC and a set of F(1) selective HSQC-TOCSY and multiple relay HSQC-COSY spectra gave access to most of the (13)C chemical shifts. The latter were fully and accurately determined by means of a pair of complementary, highly folded HSQC-TOCSY spectra. The TOCSY-ROESY and ROESY-TOCSY spectra yielded the sequential assignment of the sugar units. A high resolution F(1) selective F(1) decoupled version of the TOCSY-ROESY experiment was recorded.

β-Cyclodextrin dimers linked through their secondary faces with rigid spacer arms as hosts for bile salts

A convenient synthesis of β-cyclodextrin dimers in which the two cyclodextrin units are linked by rigid tethers of relatively short length through their secondary sides is reported. Compounds hexa-2,4-diynediyl- and 1,4-phenylenediethyne-briged β-cyclodextrin dimers are obtained in good yields from mono-2-O-propargyl-β-cyclodextrin through Pd-mediated oxidative homo- and heterocoupling reactions. Isothermal titration calorimetry and NMR spectroscopy (PGSE and 2D-ROESY) are used to determine the thermodynamic parameters (K, ΔH, and TΔS°) for the complexation of such β-cyclodextrin dimers with sodium cholate, deoxycholate, and chenodeoxycholate as well as to estimate the size of the supramolecular structures. The binding of bile salts is enhanced relative to that of native β-cyclodextrin. Although chenodeoxycholate salt binds in a 1:1 fashion, cholate and deoxycholate salts bind in a 1:2 sequential mode.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Cationic heteroleptic cyclometalated iridium(III) complexes containing phenyl-triazole and triazole-pyridine clicked ligands

Novel heteroleptic iridium complexes containing the 1-substituted-4-phenyl-1H-1,2,3-triazole (phtl) cyclometalating ligand have been synthesized. The 3+2 Huisgen dipolar cycloaddition method (‘click’ chemistry) was utilized to prepare a class of bidentate ligands (phtl) bearing different substituents on the triazole moiety. By using various ligands (phtl-R₁ and pytl-R₂) (R₁=adamantane, methyl and R₂=adamantane, methyl, β-cyclodextrin, ursodeoxycholic acid), we prepared a small library of new luminescent ionic iridium complexes [Ir(phtr-R₁)₂(pytl-R₂)]Cl and report on their photophysical properties. The flexibility of the clicking approach allows a straightforward control on the chemical-physical properties of the complexes by varying the nature of the substituent on the ligand.

New cyclodextrin dimers and trimers capable of forming supramolecular adducts with shape-specific ligands

Bridged cyclodextrin dimers and trimers, in which respectively two and three hydrophobic cavities lie in close proximity, display much higher binding affinities and molecular selectivities than do parent cyclodextrins (CDs). By joining betaCD units with links inserted at different positions (2-2', 3-2', 6-2' or 6-2'-6'') and interposing spacers of different lengths and shapes, multicavity structures can be synthesized that are precisely tailored to fit specific guest molecules. This enzyme-mimicking strategy can also be used to generate stable supramolecular adducts. A series of CD dimers and trimers was prepared in good yields by carrying out the critical synthetic steps under power ultrasound (US) or microwave (MW) irradiation. Starting from azide and acetylenic CD derivatives, we exploited an efficient MW-promoted Huisgen 1,3-dipolar cycloaddition in the presence of Cu(I) salts. The resulting bridged CD derivatives gave stable adducts with magnetic-resonance-imaging contrast agents (MRI CAs) containing gadolinium(III) chelates. These inclusion complexes were found to be 2 to 3 orders of magnitude more stable than those formed by betaCD and to be endowed with high relaxivity values.

Efficient synthesis of a fluorescent tripod detection system for pesticides by microwave-assisted click chemistry

A new tripod molecule containing an aromatic core bearing three peracetylated cyclodextrins was synthesized via a microwave-assisted Huisgen 1,3-dipolar cycloaddition and was studied by fluorescence spectroscopy. The photoluminescent properties of complexation phenomena with different pesticides were evaluated in acetonitrile. Fluorescence titrations have been performed to calculate binding constants, sensitivity factors, and limit of detection of the resulting complexes. 2D NMR experiments confirmed the inclusion of pesticide in the hydrophobic cavity of the macrocycle and validated the supramolecular association responsible for the quenching of the fluorescence.