Cucurbiturils Substituted on the Methylene Bridge

Challenges and Opportunities of Functionalized Cucurbiturils for Biomedical Applications

Cucurbit[n]uril (CB[n]) macrocycles (especially CB[5] to CB[8]) have shown exceptional attributes since their discovery in 2000. Their stability, water solubility, responsiveness to several stimuli, and remarkable binding properties have enabled a growing number of biological applications. Yet, soon after their discovery, the challenge of their functionalization was set. Nevertheless, after more than two decades, a myriad of CB[n] derivatives has been described, many of them used in cells or in vivo for advanced applications. This perspective summarizes key advances of this burgeoning field and points to the next opportunities and remaining challenges to fully express the potential of these fascinating macrocycles in biology and biomedical sciences.

Construction of cucurbit[n]uril-based supramolecular frameworks via host-guest inclusion and functional properties thereof

Frameworks utilizing cucurbit[n]uril-based chemistry build on the rapid developments in the fields of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and supramolecular organic frameworks (SOFs), and as porous materials have found...

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Cucucrbituril (CB) belongs to a family of macrocycles that are easily accessible. Their structural specificity provides excellent molecular recognition capabilities, with the ability to be readily chemically modified. Because of these properties, researchers have found CB to be a useful molecular carrier for delivering drug molecules and therapeutic biomolecules. Their significance lies in the fact that CB not only increases the solubility and stability of an encapsulated guest but also provides the possibility to achieve targeted delivery of the guest molecule. Therefore, the emergence of CB undoubtedly provides opportunities for the development of targeted drug delivery in an era where intelligent drugs have attracted considerable attention. It has also been found that CB can enhance fluorescent dyes, allowing the preparation of biosensors with enhanced sensitivity for use in clinical settings. In the present review, the acquisition, properties, and structural modifications of CB are first comprehensively described, and then the value of this macrocycle in applications within the medical field is discussed. In addition, we have also summarized patent applications of CB in this field over recent years, aiming to illustrate the current status of developments of this molecule. Finally, we discuss the challenges faced by CB in the medical field and future trends in its development.

A Modular Synthetic Strategy for Functional Macrocycles

Reported here is a molecule-Lego synthetic strategy for macrocycles with functional skeletons, involving one-pot and high-yielding condensation between bis(2,4-dimethoxyphenyl)arene monomers and paraformaldehyde. By changing the blocks, variously functional units (naphthalene, pyrene, anthraquinone, porphyrin, etc.) can be conveniently introduced into the backbone of macrocycles. Interestingly, the macrocyclization can be tuned by the geometrical configuration of monomeric blocks. Linear (180°) monomer yield cyclic trimers and pentamers, while V-shaped (120°, 90° and 60°) monomers tend to form dimers. More significantly, even heterogeneous macrocycles are obtained in moderate yield by co-oligomerization of different monomers. This series of macrocycles have the potential to be prosperous in the near future.

Glycoluril derived cucurbituril analogues and the emergence of the most recent example: tiarauril

Cucurbituril analogues can bear some of the chemical and physical characteristics of their parental origin and are derived wholly or in part from glycolurils (including homologues).

Supramolecular chemistry of substituted cucurbit[n]urils

This review covers important advances in the field of substituted cucurbit[n]urils.

Synthesis and separation of cucurbit[n]urils and their derivatives

Cucurbit[n]uril chemistry has become an important part of contemporary supramolecular chemistry since cucurbit[n]urils (Q[n]s) are not only able to encapsulate various guests, but are also capable of coordinating to a wide range of metal ions, leading to the establishment of Q[n]-based host-guest chemistry and coordination chemistry. Each of these impressive developments can be attributed to the growth of protocols for obtaining Q[n]s. In this review, we survey synthetic procedures for obtaining cucurbit[n]urils and their substituted derivatives together with the separation and purification of these remarkable compounds. The coverage is aimed at both existing workers in the field as well as at those requiring an "entry" into Q[n]-based research.

Dimeric molecular clips based on glycoluril

Phenylene-bridged glycoluril dimers are used for the construction of supramolecular host molecules with high affinity towards methylviologen in water.

Template-directed synthesis of cucurbituril analogues using propanediurea as a building block

Cucurbituril-like macrocycles were prepared in moderate yields by condensing propanediurea with formaldehyde, using, respectively, CaCl₂ and BaCl₂ as templates.

Helianthus-like cucurbit[4]uril and cucurbit[5]uril analogues

Two cucurbituril-like macrocycles were synthesized by condensing cyclopentano-substituted propanediurea with formaldehyde in the presence and absence of Ca²⁺.

The smallest cucurbituril analogue with high affinity for Ag+

The smallest cucurbituril analogue with four repeated bi-uredio units was firstly synthesized and it binds selectively towards Ag⁺.

Adducts of aqua complexes of Ln3+with hexahydroxyhexamethylcucurbit[6]uril: potential application in the isolation of heavy lanthanides

The interactions between a series of Ln³⁺and HHQ[6] were investigated. X-ray crystallography analysis revealed that HHQ[6] selectively interacts with certain Ln ions. The experimental results point to a possible means of isolating lighter or heavier Ln cations.

Acyclic cucurbit[n]uril-type molecular containers: influence of glycoluril oligomer length on their function as solubilizing agents

We present the synthesis of a series of six new glycoluril derived molecular clips and acyclic CB[n]-type molecular containers (1–3) that all feature SO3(−) solubilizing groups but differ in the number of glycoluril rings between the two terminal dialkoxyaromatic sidewalls. We report the X-ray crystal structure of 3b which shows that its dialkoxynaphthalene sidewalls actively define a hydrophobic cavity with high potential to engage in π–π interactions with insoluble aromatic guests. Compounds 1–3 possess very good solubility characteristics (≥38 mM) and undergo only very weak self-association (Ks < 92 M(−1)) in water. The weak self-association is attributed to unfavorable SO3(−)···SO3(−) electrostatic interactions in the putative dimers 12–42. Accordingly, we created phase solubility diagrams to study their ability to act as solubilizing agents for four water insoluble drugs (PBS-1086, camptothecin, β-estradiol, and ziprasidone). We find that the containers 3a and 3b which feature three glycoluril rings between the terminal dialkoxy-o-xylylene and dialkoxynaphthalene sidewalls are less efficient solubilizing agents than 4a and 4b because of their smaller hydrophobic cavities. Containers 1 and 2 behave as molecular clip type receptors and therefore possess the ability to bind to and thereby solubilize aromatic drugs like camptothecin, ziprasidone, and PBS-1086.

Vladimir Sindelar

"Science is fun because … it is an adventure with unexpected results." This and more about Vladimir Sindelar can be found on page 1583.

Hydrophobic monofunctionalized cucurbit[7]uril undergoes self-inclusion complexation and forms vesicle-type assemblies

We report the synthesis of hydrophobic monofunctionalized CB[7] derivative 1 that forms self-assembled vesicles in combination with guests 1 and 2; release of encapsulated rhodamine 6G is triggered by addition of Triton X-100.

A cucurbit[5]uril analogue from dimethylpropanediurea–formaldehyde condensation

A new cucurbit[5]uril-like macrocycle has been synthesized and shows good solubility in water and organic solvents.

Cucurbiturils: from synthesis to high-affinity binding and catalysis

Major developments in the synthesis of cucurbiturils and applications related to their high-affinity binding and catalysis have recently taken place.

Supramolecular assembly of a methyl-substituted cucurbit[6]uril and its potential applications in selective sorption

Assembly of a methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril (HMeQ[6]) has been studied. We have demonstrated potential applications of this system based on the selective sorption of volatile alcohols in the polar channels, especially methanol.

Cucurbituril-based supramolecular engineered nanostructured materials

Nanostructured materials, including nanoparticles, nanocomposites, vesicles, and rods, have been prepared by taking advantage of the interesting features of cucurbituril homologues.