Petra Cuřínová

Systematic approach to new ligands for anion recognition based on ureido-calix[4]arenes

Mono, di-, tri- and tetraureido-calix[4]arenes in the cone, partial cone and 1,3-alternate conformations have been synthesised and their complexation ability towards selected anions has been studied. The structure–anion complexation ability relationship has been systematically monitored. A new type of very efficient ligands based on diureido-calix[4]arene in a 1,3-alternate conformation with pronounced bonding ability towards carboxylates was designed.

Anion recognition by diureido-calix[4]arenes in the 1,3-alternate conformation

A series of diureido-calix[4]arenes immobilised in the 1,3-alternate conformation was synthesised and systematically studied for their complexation ability. As revealed by 1H NMR and UV/vis titrations, this structural motif leads to very efficient ligands for anion recognition with high binding constants in nonpolar solvents. The comparison with the corresponding ligands possessing the cone conformation indicates that diureido-calix[4]arene in a 1,3-alternate conformation are very promising anion receptors with pronounced binding ability towards carboxylates.

Various Extraction Methods for Obtaining Stilbenes from Grape Cane of Vitis vinifera L.

Grape cane, leaves and grape marc are waste products from viticulture, which can be used to obtain secondary stilbene derivatives with high antioxidant value. The presented work compares several extraction methods: maceration at laboratory temperature, extraction at elevated temperature, fluidized-bed extraction, Soxhlet extraction, microwave-assisted extraction, and accelerated solvent extraction. To obtain trans-resveratrol, trans-ε-viniferin and r2-viniferin from grape cane of the V. vinifera variety Cabernet Moravia, various conditions were studied: different solvents, using powdered versus cut cane material, different extraction times, and one-step or multiple extractions. The largest concentrations found were 6030 ± 680 µg/g dry weight (d.w.) for trans-resveratrol, 2260 ± 90 µg/g d.w. for trans-ε-viniferin, and 510 ± 40 µg/g d.w. for r2-viniferin. The highest amounts of stilbenes (8500 ± 1100 µg/g d.w.) were obtained using accelerated solvent extraction in methanol.

Chiral anion recognition by a ureido-thiacalix[4]arene ligand immobilized in the 1,3-alternate conformation

While all the alkylation methods commonly used in the chemistry of classical calixarenes failed, tetranitrothiacalix[4]arene was easily alkylated using various alcohols under Mitsunobu reaction conditions. The products thus obtained were immobilized in the 1,3-alternate conformation as suggested by 1H NMR and proven unequivocally by X-ray analysis. The introduction of chiral alkyl substituents into the lower rim of thiacalixarene gave us an opportunity to form well-preorganized ureido cavities on both sites of the system. As revealed by 1H NMR titration experiments, such compounds were capable of chiral anion recognition even in DMSO-d6 which is a highly competitive solvent towards hydrogen bonding interactions. The highest chiral discrimination was achieved for free serine with a selectivity factor of 3.13 for the D-isomer.

Phosphonium carbosilane dendrimers for biomedical applications – synthesis, characterization and cytotoxicity evaluation

We report the synthesis and cytotoxicity evaluation of a completely new class of cationic carbosilane dendrimers functionalized with several different phosphonium peripheral groups and an ammonium functionalised one as a reference. The carbosilane dendrimers with NMe3, PMe3, P(Et2)2(CH2)3OH, PBu3, P(C6H4-OMe)3 and P(Ph)3 peripheral substituents were synthesized, thoroughly characterized and modelled by computer simulations. The cytotoxicities of the dendrimers were investigated in vitro on three model cell lines (B14, BRL and NRK cells) by MTT and CV assay methods. Generally, the cytotoxicities of PMe3 carbosilane dendrimers were similar or slightly lower when compared with NMe3 dendrimers. The substitution of methyl groups in PMe3 carbosilane dendrimers with more hydrophobic and bulky alkyl substituents (PBu3 and P(Et2)2(CH2)3OH dendrimers) resulted in an increase of cytotoxicity. The P(C6H4-OMe)3 dendrimer showed exceptionally low cytotoxicity across all cell lines or assay methods used. Generally, phosphonium carbosilane dendrimers could represent a valuable alternative to ammonium ones in gene therapy applications due to comparable or lower cytotoxicities, the presence of positive charge for nucleic acid electrostatic binding and in the cases of P(C6H4-OMe)3 and P(Ph)3 dendrimers high potential of mitochondrial targeting.

Anion receptors based on ureidocalix[4]arenes immobilised in the partial cone conformation

A novel method enabling the synthesis of receptors based on the calix[4]arenes immobilized in the partial cone conformation is reported. The application of a protection/deprotection strategy using nosyl groups enables the regioselective introduction of functional groups (NO2 and NH2) into the upper rim of calix[4]arenes, leading finally to the substitution pattern so far inaccessible to calixarene chemistry. The introduction of two ureido functions at the para positions of the partial cone conformer yields a novel type of receptor which can bind anions even in a highly competitive solvent (DMSO). This revealed that the partial cone conformation, so far rather ignored in supramolecular chemistry, can be also very useful in design of novel anion receptors.

Calix[4]arenes containing a ureido functionality on the lower rim as highly efficient receptors for anion recognition

The introduction of nosyl moieties onto the lower rim of the calix[4]arene skeleton led to the formation of compounds immobilised in cone conformations. Subsequent reduction of the nitro group and reaction with aryl isocyanates enabled the construction of new calixarene-based ligands for anion recognition. As proven by NMR and UV/vis titration experiments, diaryl urea moieties with electron-withdrawing substituents on both sides represent very efficient tools for the complexation of selected anions (AcO−, BzO−, H2PO4−) even in highly competitive solvents such as DMSO-d6.

C,N-Chelated organotin(iv) azides: synthesis, structure and use within click chemistry

A set of tri- and diorganotin(IV) azides bearing 2-(N,N-dimethylaminomethyl)phenyl as a C,N-chelating ligand (LCN) has been prepared and structurally characterized. Triorganotin(IV) azides of the type LCNR2SnN3 (R = n-Bu (1) and Ph (2)) and (LCN)2(n-Bu)SnN3 are monomeric both in solution and in the solid state. The central tin atom in these species is five-coordinated with distorted trigonal bipyramidal geometry. Diorganotin(IV) azides of the type LCNRSn(N3)2 (R = n-Bu and Ph) are monomeric with trigonal bipyramidal geometry around the tin atom as well. Finally, (LCN)2Sn(N3)2 contains a six-coordinated tin atom with heavily distorted octahedral geometry due to the presence of two LCN units. The potential use of selected organotin(IV) azides 1 and 2 as useful building blocks within click chemistry was investigated. The reactions of 1 and 2 with various nitriles resulted in the formation of corresponding triorganotin(IV) tetrazolides (i.e. κ-N1: LCN(n-Bu)2Sn(5-MeCN4), LCNPh2Sn(5-MeCN4), LCN(n-Bu)2Sn(5-Me2NCH2CN4), LCNPh2Sn(5-Me2NCH2CN4); and κ-N2: LCN(n-Bu)2Sn(5-t-BuCN4), LCNPh2Sn(5-t-BuCN4), LCN(n-Bu)2Sn(5-PhCN4), LCNPh2Sn(5-PhCN4)). Similarly, the reaction of 1 and 2 with cyclooctyne provided corresponding C,N-chelated di-n-butyl/diphenyltin(IV) κ-N1 4,5,6,7,8,9-hexahydrocycloocta[d][1,2,3]triazol-1-ides. All azido complexes and products of the [3+2] cycloaddition reactions were characterized by the combination of elemental analysis, mass spectrometry, IR spectroscopy, multinuclear NMR spectroscopy and, in the case of crystalline materials, XRD analysis. In addition, DFT calculations were carried out within the click chemistry reactions in order to corroborate the preferred formation of the respective tetrazolide regioisomer.

Evaluation of toxicological and teratogenic effects of carbosilane glucose glycodendrimers in zebrafish embryos and model rodent cell lines

Abstract Glycodendrimers (Glyco-DDMs) represent a rapidly growing class of nanoparticles with promising properties for biomedical applications but concerns regarding the impact on human health and environment are still justified. Here we report, for the first time, the comparative study of in vivo developmental toxicity of carbosilane Glyco-DDMs and their cytotoxicity in vitro. Carbosilane Glyco-DDMs (generation 1–3) containing 4, 8, and 16 β-d-glucopyranosyl units at the periphery (DDM1Glu, DDM2Glu, and DDM3Glu) were synthesized and characterized by 1H, 13C and 29Si NMR, mass spectrometry, dynamic light scattering, atomic force microscopy (AFM), and computer modeling. In vitro cytotoxicity assay (MTT) of DDM1–3Glu was performed on three different rodent cell lines (Cricetulus griseus) – B14 (ATCC, CCL-14.1), BRL 3A (ATCC, CRL-1442), and NRK 52E (ATCC, CRL-1571). Overall, very low cytotoxicity was observed with calculated IC50 in mM range with slight difference between each cell line and DDM generation investigated. Modified fish embryo test (FET) was further used for DDM3Glu developmental toxicity testing on zebrafish (Danio rerio) embryos. While seemingly harmless to intact embryos, adverse effects of DDMs on the embryonic development become evident after chorion removal (LD50=2.78 µM at 96 hpe). We summarized that the modified FET test showed a two to three orders of magnitude difference between the in vitro cytotoxicity and in vivo developmental toxicity of DDM3Glu. While, in general, the Glyco-DDMs show great promises as efficient vectors in targeted drug delivery or as therapeutic molecules itself, we suggest that their developmental toxicity should be thoroughly investigated to exclude safety risks associated with their potential biomedical use.

ESI-TOF mass spectrometry of cationic carbosilane dendrimers: A potent tool for characterization of structural defects

Macromolecular polyelectrolytes are gaining considerable attention for the application in medicine that implies their detailed characterization. We have successfully applied electrospray ionization mass spectrometry (ESI MS) to the analysis of defects in the structure of three generations of polycationic carbosilane dendrimers bearing series of quarternary phosphonium groups at their periphery. Besides expected defects caused by incomplete conversion of particular reaction steps during the synthesis of dendritic scaffold and subsequent peripheral functionalization, also, several products of side reactions were observed together with defects created in the course of measurement (particularly ion exchange products). Defective molecules can be to some extent separated by means of gel permeation chromatography that proves that they are not products of in source fragmentation processes. Within the reaction sequence used for the synthesis of dendrimers under study, hydrosilylation was the source of most defects; the effectivity of quarternization depends on the type of phosphine. Results confirm high sensitivity of ESI MS towards defects, stability of the carbosilane skeleton towards fragmentation under the conditions of ESI ionization, and capability to detect both lower- and higher-molecular weight impurities arising from the synthetic sequence in the same m/z range as the target dendrimer, thus providing valuable view of the polydispersity.