Chemoselective Electrochemical Cleavage of Sulfonimides as a Direct Way to Sulfonamides.

A new method for selective cleavage of sulfonimides into sulfonamides in high yields using a simple electrochemical approach is shown. As revealed by the electrochemical study, the aromatic sulfonimides can be selectively cleaved by electrolysis of the starting compound at a given potential (only -0.9 V vs SCE for the nosyl group). The high chemoselectivity was confirmed by preparative electrolysis, and the results were supported with DFT calculations of a set of substances bearing different sulfonimide functions. Moreover, various experimental setups together with other attempts to simplify the procedure were tested. Finally, the removal of the p-nosyl group from the corresponding sulfonimides proceeds smoothly regardless of the number of nosyl groups and the overall shape of the complex molecule. Thus, the method is interesting for use in the field of multifunctional molecules such as calix[n]arenes.

Transport of Anions across the Dialytic Membrane Induced by Complexation toward Dendritic Receptors.

A novel approach to inducing anion transport over the dialytic membrane was proposed and successfully tested using the dihydrogen phosphate anion. The anion receptor based on isophthalamide was anchored on a dendritic skeleton, resulting in a macromolecular structure with a limited possibility to cross the dialytic membrane. The dendritic receptor was placed in a compartment separated from a mother anion solution by a membrane. The resulting anion complexation reduced the actual concentration of the anion and induced the anion transfer across the membrane. The anion concentration in mother solution decreased, while it was found to be increased in the compartment with the dendritic receptor. This phenomenon was observed using dendritic receptors with four and eight complexation sites. A detailed analysis of a series of dialytic experiments by 1H NMR spectroscopy enabled an assessment of the complexation behavior of both receptors and an evaluation of the dendritic effect on the anion complexation.

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation.

The introduction of chiral alkyl substituents into the lower rim of calix[4]arene immobilised in the 1,3-alternate conformation led to a system possessing a preorganised ureido cavity hemmed with chiral alkyl units in the near proximity. As shown by the 1H NMR titration experiments, these compounds can be used as receptors for chiral anions in DMSO-d 6. The chiral recognition ability can be further strengthened by the introduction of another chiral moiety directly onto the urea N atoms. The systems with double chiral units being located around the binding ureido cavity showed better stereodiscrimination, with the highest selectivity factor being 3.33 (K L/K D) achieved for N-acetyl-ʟ-phenylalaninate. The structures of some receptors were confirmed by single crystal X-ray analysis.

5,11,17,23,29,35-Hexa-tert-butyl-37,38,39,40,41,42-hexa-kis-(eth-oxy-carbonyl-meth-oxy)calix[6]arene acetonitrile disolvate.

In the title compound, C(90)H(120)O(18)·2CH(3)CN, the calix[6]arene has a 1,2,3-alternate conformation and possesses inversion symmetry. It crystallizes as an acetonitrile disolvate, with a half-mol-ecule of calix[6]arene and one mol-ecule of solvent in the asymmetric unit. In the crystal, the two solvent mol-ecules are enclosed in voids between the calix[6]arene mol-ecules. They form weak C-H⋯O hydrogen bonds involving an O atom of the lower rim substituent. The cavity of the calix[6]arene itself is enclosed by two opposite phenol rings, which are turned into the cavity due to the presence of a C-H⋯π inter-action. The calix[6]arene mol-ecule exhibits disorder of one substituent on its lower rim [occupancy ratio 0.897 (3):0.103 (3)].

Solvent Extraction of Some Divalent Metal Cations into Nitrobenzene by Using a Synergistic Mixture of Strontium Dicarbollylcobaltate and p-tert-Butylcalix[4]arene-tetrakis (N,N-Diethylacetamide).

From extraction experiments and g-activity measurements, the exchange extraction constants corresponding to the general equilibrium M2+(aq) + 1•Sr2+(nb) <-> 1•M2+(nb) + Sr2+(aq) taking place in the two-phase water-nitrobenzene system (M2+ = Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Pb2+, UO22+, Mn2+, Co2+, Ni2+; 1 = p-tert-butylcalix[4]arene-tetrakis(N,N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) were determined. Further, the stability constants of the 1•M2+ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the series of Cu2+ < Ba2+ < Zn2+ < Ni2+ < UO22+ < Co2+ < Mn2+ < Cd2+ < Ca2+ < Pb2+.

5,11,17,23,29-Penta-tert-butyl-31,32,33,34,35-penta-propoxycalix[5]arene dichloro-methane hemisolvate.

The title compound, tert-butyl-propoxycalix[5]arene, C(70)H(100)O(5)·0.5CH(2)Cl(2), crystallizes as a solvate with two mol-ecules of calix[5]arene in 1,2-alternate conformations and one mol-ecule of dichloro-methane in the asymmetric unit. One tert-butyl group in one of the mol-ecules and two in the other are disordered over two positions with occupancy factors fixed at 0.5917:0.4083, 0.5901:0.4099 and 0.8535:0.1465, respectively, in the final refinement. The C atoms of a prop-oxy group in each of the mol-ecules are also disordered over two positions with occupancies of 0.7372:0.2628 and 0.5027:0.4973. The mol-ecules form intra-molecular hydrogen bonds between prop-oxy O atoms and an adjacent CH(2) group in a neighbouring prop-oxy chain. In the crystal, inter-molecular C-H⋯O and C-H⋯Cl inter-actions occur involving the dichloro-methane mol-ecule.

Meta nitration of thiacalixarenes.

Nitration of thiacalix[4]arene, immobilized in the 1,3-alternate conformation, leads regioselectively to meta-substituted products. Depending on the reaction conditions, mono- and dinitro-derivatives can be isolated in acceptable yields. This unique substitution pattern is inaccessible in classical calixarene chemistry, and yields inherently chiral compounds, which makes thiacalixarenes very attractive as building blocks or molecular scaffolds.

Cooperative interaction of hydronium ion with an ethereally fenced hexaarylbenzene-based receptor: an NMR and theoretical study.

Using (1)H and (13)C NMR and DFT calculations, the structure and interactions of the symmetric ethereally fenced hexaarylbenzene receptor 1 with hydronium ions were studied. Both 1 and its equimolecular complex 1.H(3)O(+) exhibit C(3v) symmetry. According to DFT, two similar optimal structures of the complex exist, the more stable one being 15.4 kJ/mol lower in energy. The equilibrium between 1 and 1.H(3)O(+) complexes is characterized by the stabilization constant K = 1.97 x 10(6) (i.e., the binding constant eta = 6.3) according to both proton and carbon NMR spectra. The exchange dynamics between 1 and the complex measured by the delay-varied CPMG sequence had to be corrected for the internal exchange processes in both 1 (conformation change) and the complex (vacillation between the two minima). After this correction, the correlation time of exchange was found to be 4.76 x 10(-5) s. Such relatively fast exchange can be explained only by it being mediated by the excess water molecules present in the system.

25,26,27,28-Tetra-propoxycalix[4]arene-5,17-dicarbonitrile.

In the title compound, C(42)H(46)N(2)O(4), both crystallographically independent mol-ecules display a 1,3-alternate conformation. Their crystal packing is stabilized by non-classical C-H⋯N hydrogen bonds. The dihedral angles between the planes of the aromatic rings and the mean plane through the methyl-ene C atoms bridging the aromatic rings are 78.10 (13), 80.74 (14), 81.89 (12) and 79.05 (14)° for the first mol-ecule, and 71.65 (11), 76.60 (13), 77.97 (14) and 74.76 (13)° for the second mol-ecule. Both mol-ecules have three C atoms of one prop-oxy chain disordered over two set of sites; the site-occupancy factors are 0.7/0.3 and 0.6/0.4, respectively.

Interaction of hydrated protons with trioctylphosphine oxide: NMR and theoretical study.

Interaction of trioctylphosphine oxide (TOPO) with fully ionized hydrated protons (HP) was studied in acetonitrile-d(3) and nitrobenzene-d(5) using (1)H, (13)C, and (31)P NMR, PFG NMR, and magnetic relaxation, and the experimental results were confronted with high-precision ab initio DFT calculations. Relative chemical shifts of NMR signals of TOPO (0.02 mol/L) under the presence of HP in the molar ratio beta = 0-2.0 mol/mol show binding between TOPO and HP. Self-diffusion measurements using (1)H PFG NMR demonstrate that larger complexes with higher content of TOPO are generally formed at beta < 0.75. Analyzing the dependence of (31)P NMR chemical shifts on beta by the use of program LETAGROP, we obtained very good fitting for the assumed coexistence of three complexes (TOPO)(i).HP (named C(i)), where i = 1, 2, 3. The logarithms of the respective stabilization constants log K(i) were found to be 3.63, 4.67, and 7.23 in acetonitrile and 3.91, 6.04, and 7.92 in nitrobenzene. The (31)P NMR chemical shifts Deltadelta(i) corresponding to these complexes are 39.35, 29.51, and 19.72 ppm in acetonitrile and 38.37, 28.47, and 18.63 ppm in nitrobenzene. These values and the calculated values of alpha(i) =[C(i)]/[TOPO](0) were utilized in the analysis of the system dynamics. This was done by measuring the transverse (31)P NMR relaxation by the CPMG sequence with varying delays t(p) between the pi pulses in the mixtures with beta = 0.5, 1.25, and 1.5. Calculating the probabilities of imaginable exchange processes shows that only three of them can have significant influence on relaxation rate R(2), namely C(1) <--> TOPO, C(2) <--> C(1), and C(3) <--> C(2). Using the slopes of the R(2)-t(p)(-1) dependences in the above three mixtures, the following correlation times were obtained: tau(10) = 2.5 x 10(-6), tau(21) = 7.4 x 10(-5), tau(32) = 11.3 x 10(-5) s. The DFT calculations support the hypothesis that complexes C(1) to C(3) are the main species in the mixtures of TOPO with HP, with the only exception that additional water molecules are bound to the complexes in the case of C(1) and C(2). Schematically, the compositions of the three stable complexes is [3TOPO.H(3)O](+), [2TOPO.H(3)O.H(2)O](+), and [TOPO.H(3)O.2H(2)O](+). The relative (31)P NMR shifts calculated for the optimized structures of C(1), C(2), and C(3) are in very good agreement with the experimentally observed values.

NMR and theoretical study of the cooperative interaction of hydrated proton with dibenzo-24-crown-8.

Interaction of hydrated protons (HPs) with dibenzo-24-crown-8 (DBC in nitrobenzene-d(5) was studied by (1)H and (13)C NMR under assistance of ab initio-density functional theory (DFT) quantum calculations. HPs were afforded by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) with 3.5 M excess of H(2)O. The forming of a complex between HP and DBC leads to marked and additive relative shifts of both (1)H and (13)C signals. This was utilized for the estimation of the stabilization constant K of the complex. Its value is at least 10(6) l/mol, which agrees with the result of independent extraction method (log K = 6.3). Using absolute integral intensities of the HP signal in a water-saturated system, it was shown that the form of HP present in the complex must be H(5)O(2)(+), in accord with formerly published structure of the complex in crystalline form. The investigation of the dynamics of exchange between bound and free DBC by transverse relaxation using variably spaced pulses in the Carr-Purcell-Meiboom-Gill (CPMG) sequence or on-resonance rotating-frame relaxation with variable spin-lock field intensity was partly hampered by the fast relaxation of some signals in the complex because of relative immobilization of its internal motions. In order to remove these effects, a pulse sequence dipolar interaction-free transverse relaxation (DIFTRE) for static DIFTRE was devised and the MLEV17 pulse sequence with high intensity of electromagnetic field was used in a separate series of experiments. Using the results of these latter experiments, the correlation time of exchange was established to be about 0.8 ms, which complied with the shape of the spectra. The accompanying ab initio DFT calculations showed that the apparent symmetry of the molecules of both DBC and its complex with H(5)O(2)(+) was probably the result of averaging of energetically close conformations (five for DBC and four for the complex). Both NMR and the calculations show that the basic mode of binding of the ion in the complex is analogous to that found in crystal but the most pronounced conformation is slightly different.

Interaction of hydronium ion with dibenzo-18-crown-6: NMR, IR, and theoretical study.

Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.

Simple synthesis of calix[4]arenes in a 1,2-alternate conformation.

The least accessible calix[4]arene conformers-1,2-alternates-can be very easily prepared using a proximal dialkylation and subsequent peralkylation reaction sequence.

Cooperative interaction of n-butylammonium ion with 1,3-alternate tetrapropoxycalix [4]arene: NMR and theoretical study.

The interaction of 1,3-alternate tetrapropoxycalix[4]arene (1) with n-butylammonium ion (2) in CD(2)Cl(2) was examined using (1)H, (13)C and (14)N NMR spectroscopy and DFT (density functional theory) calculations. NMR shows that 1 forms with 2 an equimolecular hydrogen-bonded complex with the equilibrium constant 5.91 x 10(3) l/mol at 296 K. The structure of the complex can be shown to be asymmetric at 203 K, with 2 interacting by hydrogen bonds with the two ethereal oxygen atoms of one half of 1 and with the pi system of the other half, but is rapidly averaged to an apparent C(4h) symmetry by chemical exchange at higher temperatures. Using two related but independent techniques based on transverse and rotating-frame proton relaxation, it is shown that only an intermolecular exchange of 2 between the bound and free states takes place, in contrast to previously studied interaction of 1 with H(3)O(+). Its correlation time is 0.169 ms. It is shown by DFT calculations that such swift exchange is not possible without a cooperative interaction of both 2 and 1 with several molecules of water present. Similarities and contrasts between the exchange processes of 2 and H(3)O(+) bound to 1 are discussed, in particular with respect to the apparent quantum tunneling of the latter inside the molecule of the complex.

Cooperative interaction of H3O+ with 1,3-alternate tetrapropoxycalix[4]arene: NMR and theoretical study.

Interaction of H3O+ or H5O2+ with 1,3-alternate tetrapropoxycalix[4]arene (1) was studied in nitrobenzene and dichloromethane using 1H and 13C NMR including transverse and rotating-frame relaxations and density functional level of theory (DFT) quantum calculations. According to NMR, the ion forms an equimolecular complex with 1 with the equilibrium constant K being 3.97 x 10(3) L.mol(-1) at 296 K. The ions are bound by strong hydrogen bonds to the phenoxy-oxygen atoms of one half of 1 and by a medium-strong hydrogen bond to the pi system of the aromatic rings of the other half. The complex appears to have C(4h) symmetry in NMR even when cooling its solution down to 213 K, which could be due either to a genuine symmetry of the complex (if the ion is H5O2+) or to fast structure averaging by ion exchange processes (if the ion is H3O+). Therefore, the dynamics of the system was studied. Using two independent NMR methods (transverse and rotating-frame relaxation), two different exchange processes were discerned with correlation times 25 x 10(-6) and 5 x 10(-6) s, the first being clearly intermolecular and the other being apparently intramolecular. The energetic aspects of the possible exchange processes were examined by DFT quantum calculations. Rotation of H3O+ ion within one binding site with the energy barrier 8.13 kcal/mol is easily possible. Intermolecular exchange by freeing the ion from the complex has too high a barrier but cooperative interaction of the ion with additional water molecules makes it viable. The intramolecular exchange (or hopping) of the H3O+ ion between the two sites of the molecule is not viable in the classical manner, the barrier being 25.6 kcal/mol. Quantum tunneling of the ion is highly improbable, too. Alternative mechanisms including concerted two-ion intermolecular exchange and cooperative interaction with another bound water molecule including complexation with proton dihydrate H5O2+ are discussed.

N-acetyl-D-glucosamine substituted calix[4]arenes as stimulators of NK cell-mediated antitumor immune response.

A series of calixarenes substituted with 2-acetamido-2-deoxy-beta-D-glucopyranose linked by a thiourea spacer was prepared and tested for binding activity to heterogeneously expressed activation receptors of the rat natural killer cells NKR-P1, and the receptor CD69 (human NK cells, macrophages). In the case of NKR-P1, the binding affinity of beta-D-GlcNAc-substituted calixarenes carrying two or four sugar units was in a good agreement with the inhibitory potencies of the linear chitooligomers (chitobiose to chitotetraose) reported previously. The influence of GlcNAc substitution of the calixarene skeleton on binding affinity for CD69 receptor was more profound and the 5,11,17,23-tetrakis[N-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-thioureido]-25,26,27,28-tetrapropoxycalix[4]arene (cone) (1) proved to be the best CD69 ligand identified to date. Lower GlcNAc substitution led to dramatic decrease of the binding activity (by about 1.5 order of magnitude per one GlcNAc unit). The immunostimulating activity results with the newly synthesized GlcNAc tetramers on calixarene scaffolds exhibited stimulation of natural cytotoxicity of human PBMC in concentrations 10(-4) and 10(-8)M. These calix-sugar compounds were superior to the previously tested PAMAM-GlcNAc(8)5.

Anion recognition by alpha-arylazo-N-confused calix[4]pyrroles.

The first example of substitution reaction in the free alpha-position of N-confused calix[4]pyrroles is reported: azo-coupling with various arenediazonium salts. The obtained azocompounds were used for studies of their anion-binding properties by UV-Vis spectroscopy.

Two structural types of 1,3-alternate tetrapropoxycalix[4]arene derivatives in the solid state.

The solid state structures of seven tetrapropoxycalix[4]arene derivatives immobilised in a 1,3-alternate conformation were determined using single-crystal X-ray crystallography. The cavity shapes of investigated derivatives (upper rim unsubstituted, distally di-substituted and tetra-substituted) and the nature of intermolecular interactions in molecular packing were compared. The results indicate that there are only two structural types adopted by basic tetrapropoxycalix[4]arene derivatives in the 1,3-alternate conformation.