Hydrazides of glycine-containing decasubstituted pillar[5]arenes: Synthesis and encapsulation of Floxuridine

Recent Updates on Supramolecular-Based Drug Delivery - Macrocycles and Supramolecular Gels

Supramolecules-based drug delivery has attracted significant recent research attention as it could enhance drug solubility, retention time, targeting, and stimuli responsiveness. Among the different supramolecules and assemblies, the macrocycles and the supramolecular hydrogels are the two important categories investigated to a greater extent. Here, we provide the most recent advancements in these categories. Under macrocycles, reports on drug delivery by cyclodextrins, cucurbiturils, calixarenes/pillararenes, crown ethers and porphyrins are detailed. The second category discusses the supramolecular hydrogels of macrocycles/polymers and low molecular weight gelators. The updated information provided could be helpful to advance R & D in this vital area.

Molecular Recognition by Pillar[5]arenes: Evidence for Simultaneous Electrostatic and Hydrophobic Interactions

The formation of inclusion complexes between alkylsulfonate guests and a cationic pillar[5]arene receptor in water was investigated by NMR and ITC techniques. The results show the formation of host-guest complexes stabilized by electrostatic interactions and hydrophobic effects with binding constants of up to 10⁷ M⁻¹ for the guest with higher hydrophobic character. Structurally, the alkyl chain of the guest is included in the hydrophobic aromatic cavity of the macrocycle while the sulfonate groups are held in the multicationic portal by ionic interactions.

Water-soluble pillar[5]arene sulfo-derivatives self-assemble into biocompatible nanosystems to stabilize therapeutic proteins

Pillar[5]arenes containing sulfonate fragments have been shown to form supramolecular complexes with therapeutic proteins to facilitate targeted transport with an increased duration of action and enhanced bioavailability. Regioselective synthesis was used to obtain a water-soluble pillar[5]arene containing the fluorescent label FITC and nine sulfoethoxy fragments. The pillar[5]arene formed complexes with the therapeutic proteins binase, bleomycin, and lysozyme in a 1:2 ratio as demonstrated by UV-vis and fluorescence spectroscopy. The formation of stable spherical nanosized macrocycle/binase complexes with an average particle size of 200 nm was established by dynamic light scattering and transmission electron microscopy. Flow cytometry demonstrated the ability of macrocycle/binase complexes to penetrate into tumor cells where they exhibited significant cytotoxicity towards A549 cells at 10^-5-10^-6 M while maintaining the enzymatic activity of binase.

Supramolecular Amphiphiles Based on Pillar[5]arene and Meroterpenoids: Synthesis, Self-Association and Interaction with Floxuridine

In recent years, meroterpenoids have found wide biomedical application due to their synthetic availability, low toxicity, and biocompatibility. However, these compounds are not used in targeted drug delivery systems due to their high affinity for cell membranes, both healthy and in cancer cells. Using the approach of creating supramolecular amphiphiles, we have developed self-assembling systems based on water-soluble pillar[5]arene and synthetic meroterpenoids containing geraniol, myrtenol, farnesol, and phytol fragments. The resulting systems can be used as universal drug delivery systems. It was shown by turbidimetry that the obtained pillar[5]arene/synthetic meroterpenoid systems do not interact with the model cell membrane at pH = 7.4, but the associates are destroyed at pH = 4.1. In this case, the synthetic meroterpenoid is incorporated into the lipid bilayer of the model membrane. The characteristics of supramolecular self-assembly, association constants and stoichiometry of the most stable pillar[5]arene/synthetic meroterpenoid complexes were established by UV-vis spectroscopy and dynamic light scattering (DLS). It was shown that supramolecular amphiphiles based on pillar[5]arene/synthetic meroterpenoid systems form monodisperse associates in a wide range of concentrations. The inclusion of the antitumor drug 5-fluoro-2'-deoxyuridine (floxuridine) into the structure of the supramolecular associate was demonstrated by DLS, 19F, 2D DOSY NMR spectroscopy.

Towards Universal Stimuli-Responsive Drug Delivery Systems: Pillar[5]arenes Synthesis and Self-Assembly into Nanocontainers with Tetrazole Polymers

In this work, we have proposed a novel universal stimulus-sensitive nanosized polymer system based on decasubstituted macrocyclic structures-pillar[5]arenes and tetrazole-containing polymers. Decasubstituted pillar[5]arenes containing a large, good leaving tosylate, and phthalimide groups were first synthesized and characterized. Pillar[5]arenes containing primary and tertiary amino groups, capable of interacting with tetrazole-containing polymers, were obtained with high yield by removing the tosylate and phthalimide protection. According to the fluorescence spectroscopy data, a dramatic fluorescence enhancement in the pillar[5]arene/fluorescein/polymer system was observed with decreasing pH from neutral (pH = 7) to acidic (pH = 5). This indicates the destruction of associates and the release of the dye at a pH close to 5. The presented results open a broad range of opportunities for the development of new universal stimulus-sensitive drug delivery systems containing macrocycles and nontoxic tetrazole-based polymers.

Metallo-Supramolecular Coordination Polymers Based on Amidopyridine Derivatives of Pillar[5]arene and Cu(II) and Pd(II) Cations: Synthesis and Recognition of Nitroaromatic Compounds

Decasubstituted pillar[5]arenes containing amidopyridine fragments have been synthesized for the first time. As was shown by UV-vis spectroscopy, the pillar[5]arenes with p-amidopyridine fragments form supramolecular associates with Cu(II) and Pd(II) cations in methanol in a 2:1 ratio. Using a sol-gel approach these associates are transformed into metallo-supramolecular coordination polymers (supramolecular gels) which were characterized as amorphous powders by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The powders are able to selectively adsorb up to 46% of nitrophenols from water and were incorporated into an electrochemical sensor to selectively recognize them in aqueous acidic solution.

Progress in the Chemistry of Macrocyclic Meroterpenoids

In the last decade, the chemistry of meroterpenoids—conjugated molecules formed from isoprenyl fragments through biosynthetic pathways—has developed rapidly. The class includes some natural metabolites and fully synthetic fragments formed through nonbiological synthesis. In the field of synthetic receptors, a range of structures can be achieved by combining fragments of different classes of organic compounds into one hybrid macrocyclic platform which retains the properties of these fragments. This review discusses the successes in the synthesis and practical application of both natural and synthetic macrocycles. Among the natural macrocyclic meroterpenoids, special attention is paid to isoprenylated flavonoids and phenols, isoprenoid lipids, prenylated amino acids and alkaloids, and isoprenylpolyketides. Among the synthetic macrocyclic meroterpenoids obtained by combining the “classical” macrocyclic platforms, those based on cyclodextrins, together with meta- and paracyclophanes incorporating terpenoid fragments, and meroterpenoids obtained by macrocyclization of several terpene derivatives are considered. In addition, issues related to biomedical activity, processes of self-association and aggregation, and the formation of host–guest complexes of various classes of macrocyclic merotenoids are discussed in detail.

Self-Assembly of Supramolecular Architectures by the Effect of Amino Acid Residues of Quaternary Ammonium Pillar[5]arenes

Novel water-soluble multifunctional pillar[5]arenes containing amide-ammonium-amino acid moiety were synthesized. The compounds demonstrated a superior ability to bind (1S)-(+)-10-camphorsulfonic acid (S-CSA) and methyl orange dye depending on the nature of the substituent, resulting in the formation one-to-one complexes with both guests. The formation of host-guest complexes was confirmed by ultraviolet (UV), circular dichroism (CD) and 1H NMR spectroscopy. This work demonstrates the first case of using S-CSA as a chiral template for the non-covalent self-assembly of architectures based on pillar[5]arenes. It was shown that pillar[5]arenes with glycine or L-alanine fragments formed aggregates with average hydrodynamic diameters (d) of 165 and 238 nm, respectively. It was established that the addition of S-CSA to the L-alanine-containing derivative led to the formation of micron-sized aggregates with d of 713 nm. This study may advance the design novel stereoselective catalysts and transmembrane amino acid channels.

Towards new nanoporous biomaterials: self-assembly of sulfopillar[5]arenes with vitamin D3 into supramolecular polymers

Novel water-soluble, deca-substituted pillar[5]arenes containing thiasulfate and thiacarboxylate fragments were synthesized and characterized. UV-vis, 2D 1H-1H NOESY and DOSY NMR spectroscopy revealed the ability of pillar[5]arenes containing thiasulfate fragments to form an inclusion complex with cholecalciferol (vitamin D3) in a 1 : 2 ratio (lg Kass = 2.2). Using DLS and SEM it was found that upon concentration and/or evaporation of the solvent, the supramolecular polymer (pillar[5]arene/vitamin D3 (1 : 2)) forms a porous material with an average wall diameter of 53 nm. It was shown that the supramolecular polymer is stable during photolysis by UV radiation (k1 = 1.7 × 10-5 s-1).

Nanoparticles based on the zwitterionic pillar[5]arene and Ag+: synthesis, self-assembly and cytotoxicity in the human lung cancer cell line A549

For the first time, stable pillar[5]arene/Ag+ nanoparticles, consisting of water-soluble pillar[5]arene containing γ-sulfobetaine fragments and Ag+ ions without Ag-Ag bonds, were synthesized and characterized. The pillar[5]arene/Ag+ (ratio 1:10) nanoparticles obtained were cubic with a rib length of 100 nm and are less cytotoxic than Ag+ ions. The survival of the A549 model cells in the presence of pillar[5]arene/Ag+ (1:10) nanoparticles at a concentration of 30 and 40 μM was 76% and 55%, while in the absence of pillar[5]arene, the cell survival for free Ag+ ions at the same concentration was 30% and 10%, respectively. The results can be used to create new antibacterial materials and 2D biomedical coatings.

Silica bound co-pillar[4+1]arene as a novel supramolecular stationary phase

A novel co-pillar[4+1]arene incorporating two bromo-octyl substituents has been synthesised for the first time, using microwave irradiation in high yield (88%) in under four minutes, and bound to the surface of chromatographic silica particles. The resulting new stationary phase has been successfully utilised to separate xylene isomers via liquid chromatographic techniques.

Stimuli-responsive supramolecular polymer network based on bi-pillar[5]arene for efficient adsorption of multiple organic dye contaminants

A novel supramolecular polymer network gel has been successfully prepared via bi-pillar[5]arene and a tripodal guest, exhibiting multi-stimuli-responsiveness and efficient adsorption of organic dyes.

Supramolecular neuromuscular blocker inhibition by a pillar[5]arene through aqueous inclusion of rocuronium bromide

A water-soluble pillar[5]arene, decafunctionalized with thioether and carboxylate fragments, was synthesized as a structural analogue of Sugammadex. Its ability to restore the contraction of the diaphragm muscle by encapsulating the muscle relaxant rocuronium bromide was demonstrated. Using UV-vis, NMR and fluorescence spectroscopy, it was shown that the muscle relaxant is associated with the pillar[5]arene with an association constant of 4500 M-1 and a stoichiometry of 1 : 1. The structure of the inclusion complex of the pillar[5]arene with rocuronium bromide was additionally investigated by quantum chemical methods.

Monosubstituted pillar[5]arene functionalized with (amino)phosphonate fragments are “smart” building blocks for constructing nanosized structures with some s- and p-metal cations in the organic phase

Pillar[5]arenes with phosphonate- and 1-aminophosphonate-substituents form complexes with Na⁺, K⁺, Cs⁺ and Pb²⁺ with a 1 : 1 stoichiometry and lg K_a values between 2.0 and 4.8, and that Pb²⁺ is the most effectively bound cation.