Biologically Active Heteroglycoclusters Constructed on a Pillar[5]arene-Containing [2]Rotaxane Scaffold

Pillararenes: a new frontier in antimicrobial therapy

Pillararenes have gained great interest among researchers in many fields due to their symmetric structure and facile functionalization. In this review, we summarize recent progress for pillararenes as antimicrobial agents, ranging from cationic pillararenes and peptide-modified pillararenes to sugar-functionalized pillararenes. Moreover, their structure-activity relationships are presented, and their mechanisms of action are discussed. As a state-of-the-art technology, their opportunities and outlook are also outlined in this emerging field. Overall, their potent inhibitory activity and high biocompatibility give them potential for the development of novel antimicrobial agents.

Proton- versus Cation-Selective Transport of Saccharide Rim-Appended Pillar[5]arene Artificial Water Channels

Transport of water across cell membranes is a fundamental process for important biological functions. Herein, we focused our research on a new type of symmetrical saccharide rim-functionalized pillar[5]arene (PA-S) artificial water channels with variable pore structures. To point out the versatility of PA-S channels, we systematically varied the nature of anchoring/gate keepers d-mannoside, d-mannuronic acid, or sialic acid H-bonding groups on lateral pillar[5]arene (PA) arms, known as good membrane adhesives, to best describe the influence of the chemical structure on their transport activity. The control of hydrophobic membrane binding-hydrophilic water binding balance is an important feature influencing the channels' structuration and efficiency for a proper insertion into bilayer membranes. The glycosylated PA channels' transport performances were assessed in lipid bilayer membranes, and the channels were able to transport water at high rates (∼106-107 waters/s/channel within 1 order of magnitude as for aquaporins), serving as selective proton railways with total Na+ and K+ rejection. Molecular simulation substantiates the idea that the PAs can generate supramolecular pores, featuring hydrophilic carbohydrate gate-keepers that serve as water-sponge relays at the channel entrance, effectively absorbing and redirecting water within the channel. The present channels may be regarded as a rare biomimetic example of artificial channels presenting proton vs cation transport selectivity performances.

Pillararenes as Promising Carriers for Drug Delivery

Since their discovery in 2008 by N. Ogoshi and co-authors, pillararenes (PAs) have become popular hosts for molecular recognition and supramolecular chemistry, as well as other practical applications. The most useful property of these fascinating macrocycles is their ability to accommodate reversibly guest molecules of various kinds, including drugs or drug-like molecules, in their highly ordered rigid cavity. The last two features of pillararenes are widely used in various pillararene-based molecular devices and machines, stimuli-responsive supramolecular/host-guest systems, porous/nonporous materials, organic-inorganic hybrid systems, catalysis, and, finally, drug delivery systems. In this review, the most representative and important results on using pillararenes for drug delivery systems for the last decade are presented.

A Fucosylated Lactose-Presenting Tetravalent Glycocluster Acting as a Mutual Ligand of Pseudomonas aeruginosa Lectins A (PA-IL) and B (PA-IIL)-Synthesis and Interaction Studies

The Gram-negative bacterium Pseudomonas aeruginosa is an important opportunistic human pathogen associated with cystic fibrosis. P. aeruginosa produces two soluble lectins, the d-galactose-specific lectin PA-IL (LecA) and the l-fucose-specific lectin PA-IIL (LecB), among other virulence factors. These lectins play an important role in the adhesion to host cells and biofilm formation. Moreover, PA-IL is cytotoxic to respiratory cells in the primary culture. Therefore, these lectins are promising therapeutic targets. Specifically, carbohydrate-based compounds could inhibit their activity. In the present work, a 3-O-fucosyl lactose-containing tetravalent glycocluster was synthesized and utilized as a mutual ligand of galactophilic and fucophilic lectins. Pentaerythritol equipped with azido ethylene glycol-linkers was chosen as a multivalent scaffold and the glycocluster was constructed by coupling the scaffold with propargyl 3-O-fucosyl lactoside using an azide-alkyne 1,3-dipolar cycloaddition reaction. The interactions between the glycocluster and PA-IL or PA-IIL were investigated by isothermal titration microcalorimetry and saturation transfer difference NMR spectroscopy. These results may assist in the development of efficient anti-adhesion therapy for the treatment of a P. aeruginosa infection.

Multivalent glycocyclopeptides: conjugation methods and biological applications

Click chemistry was extensively used to decorate synthetic multivalent scaffolds with glycans to mimic the cell surface glycocalyx and to develop applications in glycosciences. Conjugation methods such as oxime ligation, copper(I)-catalyzed alkyne-azide cycloaddition, thiol-ene coupling, squaramide coupling or Lansbury aspartylation proved particularly suitable to achieve this purpose. This review summarizes the synthetic strategies that can be used either in a stepwise manner or in an orthogonal one-pot approach, to conjugate multiple copies of identical or different glycans to cyclopeptide scaffolds (namely multivalent glycocyclopeptides) having different size, valency, geometry and molecular composition. The second part of this review will describe the potential of these structures to interact with various carbohydrate binding proteins or to stimulate immunity against tumor cells.

Structural Considerations for Building Synthetic Glycoconjugates as Inhibitors for Pseudomonas aeruginosa Lectins

Pseudomonas aeruginosa is a pathogenic bacterium, responsible for a large portion of nosocomial infections globally and designated as critical priority by the World Health Organisation. Its characteristic carbohydrate-binding proteins LecA and LecB, which play a role in biofilm-formation and lung-infection, can be targeted by glycoconjugates. Here we review the wide range of inhibitors for these proteins (136 references), highlighting structural features and which impact binding affinity and/or therapeutic effects, including carbohydrate selection; linker length and rigidity; and scaffold topology, particularly for multivalent candidates. We also discuss emerging therapeutic strategies, which build on targeting of LecA and LecB, such as anti-biofilm activity, anti-adhesion and drug-delivery, with promising prospects for medicinal chemistry.

Copillar[5]arene Chemistry: Synthesis and Applications

Research on pillar[n]arenes has witnessed a very quick expansion. This emerging class of functionalized macrocyclic oligoarenes not only offers host–guest properties due to the presence of the central cavity, but also presents a wide variety of covalent functionalization possibilities. This short review focuses on copillararenes, a subfamily of pillar[n]arenes. In copillararenes, at least one of the hydroquinone units bears different functional groups compared to the others. After having defined the particular features of copillararenes, this short review compares the different synthetic strategies allowing their construction. Some key applications and future perspectives are also described.

1 Introduction

2 General Features of Pillar[5]arenes

3 Synthesis of Functionalized Copillar[4+1]arenes

4 Concluding Remarks

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

Pillar[n]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral inversion. These advantages have enabled the high-yield synthesis and rational design of pillar[n]arene-based mechanically interlocked molecules (MIMs). In particular, new types of pillar[n]arene-based MIMs that can dynamically convert between interlocked and unlocked states through unit rotation have been produced. The highly symmetrical pillar-shaped structures of pillar[n]arenes result in simple NMR spectra, which are useful for studying the motion of pillar[n]arene wheels in MIMs and creating sophisticated MIMs with higher-order structures. The creation and application of polymeric MIMs based on pillar[n]arenes is also discussed.

Nano-Theranostics for the Sensing, Imaging and Therapy of Prostate Cancers

We highlight hereby recent developments in the emerging field of theranostics, which encompasses the combination of therapeutics and diagnostics in a single entity aimed for an early-stage diagnosis, image-guided therapy as well as evaluation of therapeutic outcomes of relevance to prostate cancer (PCa). Prostate cancer is one of the most common malignancies in men and a frequent cause of male cancer death. As such, this overview is concerned with recent developments in imaging and sensing of relevance to prostate cancer diagnosis and therapeutic monitoring. A major advantage for the effective treatment of PCa is an early diagnosis that would provide information for an appropriate treatment. Several imaging techniques are being developed to diagnose and monitor different stages of cancer in general, and patient stratification is particularly relevant for PCa. Hybrid imaging techniques applicable for diagnosis combine complementary structural and morphological information to enhance resolution and sensitivity of imaging. The focus of this review is to sum up some of the most recent advances in the nanotechnological approaches to the sensing and treatment of prostate cancer (PCa). Targeted imaging using nanoparticles, radiotracers and biomarkers could result to a more specialised and personalised diagnosis and treatment of PCa. A myriad of reports has been published literature proposing methods to detect and treat PCa using nanoparticles but the number of techniques approved for clinical use is relatively small. Another facet of this report is on reviewing aspects of the role of functional nanoparticles in multimodality imaging therapy considering recent developments in simultaneous PET-MRI (Positron Emission Tomography-Magnetic Resonance Imaging) coupled with optical imaging in vitro and in vivo, whilst highlighting feasible case studies that hold promise for the next generation of dual modality medical imaging of PCa. It is envisaged that progress in the field of imaging and sensing domains, taken together, could benefit from the biomedical implementation of new synthetic platforms such as metal complexes and functional materials supported on organic molecular species, which can be conjugated to targeting biomolecules and encompass adaptable and versatile molecular architectures. Furthermore, we include hereby an overview of aspects of biosensing methods aimed to tackle PCa: prostate biomarkers such as Prostate Specific Antigen (PSA) have been incorporated into synthetic platforms and explored in the context of sensing and imaging applications in preclinical investigations for the early detection of PCa. Finally, some of the societal concerns around nanotechnology being used for the detection of PCa are considered and addressed together with the concerns about the toxicity of nanoparticles–these were aspects of recent lively debates that currently hamper the clinical advancements of nano-theranostics. The publications survey conducted for this review includes, to the best of our knowledge, some of the most recent relevant literature examples from the state-of-the-art. Highlighting these advances would be of interest to the biomedical research community aiming to advance the application of theranostics particularly in PCa diagnosis and treatment, but also to those interested in the development of new probes and methodologies for the simultaneous imaging and therapy monitoring employed for PCa targeting.

Homo- and Heterovalent Neoglycoproteins as Ligands for Bacterial Lectins

Click chemistry gives access to unlimited set of multivalent glycoconjugates to explore carbohydrate-protein interactions and discover high affinity ligands. In this study, we have created supramolecular systems based on a carrier protein that was grafted by Cu(I)-catalyzed azide-alkyne cycloaddition with tetravalent glycodendrons presenting αGal, βGal and/or αFuc. Binding studies of the homo- (4 a-c) and heterovalent (5) neoglycoproteins (neoGPs) with the LecA and LecB lectins from P. aeruginosa has first confirmed the interest of the multivalent presentation of glycodendrons by the carrier protein (IC50 up to 2.8 nM). Moreover, these studies have shown that the heterovalent display of glycans (5) allows the interaction with both lectins (IC50 of 10 nM) despite the presence of unspecific moieties, and even with similar efficiency for LecB. These results demonstrate the potential of multivalent and multispecific neoGPs as a promising strategy to fight against resistant pathogens.

Pillar[5]arene-Based Polycationic Glyco[2]rotaxanes Designed as Pseudomonas aeruginosa Antibiofilm Agents

Pseudomonas aeruginosa (P.A.) is a human pathogen belonging to the top priorities for the discovery of new therapeutic solutions. Its propensity to generate biofilms strongly complicates the treatments required to cure P.A. infections. Herein, we describe the synthesis of a series of novel rotaxanes composed of a central galactosylated pillar[5]arene, a tetrafucosylated dendron, and a tetraguanidinium subunit. Besides the high affinity of the final glycorotaxanes for the two P.A. lectins LecA and LecB, potent inhibition levels of biofilm growth were evidenced, showing that their three subunits work synergistically. An antibiofilm assay using a double ΔlecAΔlecB mutant compared to the wild type demonstrated that the antibiofilm activity of the best glycorotaxane is lectin-mediated. Such antibiofilm potency had rarely been reached in the literature. Importantly, none of the final rotaxanes was bactericidal, showing that their antibiofilm activity does not depend on bacteria killing, which is a rare feature for antibiofilm agents.

Dendritic-Like Molecules Built on a Pillar[5]arene Core as Hole Transporting Materials for Perovskite Solar Cells

Multi-branched molecules have recently demonstrated interesting behaviour as charge-transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer-like compounds, which have been used as hole-transporting materials (HTMs) for PSCs. The performances of the solar cells containing these novel compounds have been extensively investigated. Interestingly, a positive dendritic effect has been evidenced as the hole transporting properties are improved when going from the first to the second-generation compound. The stability of the devices based on the best performing pillar[5]arene material has been also evaluated in a high-throughput ageing setup for 500 h at high temperature. When compared to reference devices prepared from spiro-OMeTAD, the behaviour is similar. An analysis of the economic advantages arising from the use of the pillar[5]arene-based material revealed however that our pillar[5]arene-based material is cheaper than the reference.

Applications of Discrete Synthetic Macromolecules in Life and Materials Science: Recent and Future Trends

In the last decade, the field of sequence-defined polymers and related ultraprecise, monodisperse synthetic macromolecules has grown exponentially. In the early stage, mainly articles or reviews dedicated to the development of synthetic routes toward their preparation have been published. Nowadays, those synthetic methodologies, combined with the elucidation of the structure-property relationships, allow envisioning many promising applications. Consequently, in the past 3 years, application-oriented papers based on discrete synthetic macromolecules emerged. Hence, material science applications such as macromolecular data storage and encryption, self-assembly of discrete structures and foldamers have been the object of many fascinating studies. Moreover, in the area of life sciences, such structures have also been the focus of numerous research studies. Here, it is aimed to highlight these recent applications and to give the reader a critical overview of the future trends in this area of research.

Synthesis of functionalized copillar[4+1]arenes and rotaxane as heteromultivalent scaffolds

In this study, novel copillar[4+1]arenes were used as central heteromultivalent scaffolds via orthogonal couplings with a series of biologically relevant molecules such as carbohydrates, α-amino acids, biotin and phenylboronic acid. Further modifications by introducing maleimides or cyclooctyne groups provided molecular probes adapted to copper-free click chemistry. An octa-azidated fluorescent rotaxane bearing two distinct ligands was also generated in a fully controlled manner.

Antimicrobial Activity of Calixarenes and Related Macrocycles

Calixarenes and related macrocycles have been shown to have antimicrobial effects since the 1950s. This review highlights the antimicrobial properties of almost 200 calixarenes, resorcinarenes, and pillararenes acting as prodrugs, drug delivery agents, and inhibitors of biofilm formation. A particularly important development in recent years has been the use of macrocycles with substituents terminating in sugars as biofilm inhibitors through their interactions with lectins. Although many examples exist where calixarenes encapsulate, or incorporate, antimicrobial drugs, one of the main factors to emerge is the ability of functionalized macrocycles to engage in multivalent interactions with proteins, and thus inhibit cellular aggregation.

Diversity Oriented Preparation of Pillar[5]arene-Containing [2]Rotaxanes by a Stopper Exchange Strategy

Rotaxane building blocks bearing 3,5-bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillar[5]arene derivative, 3,5-bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10-decanediol and 1,12-dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers.

Carbohydrate supramolecular chemistry: beyond the multivalent effect

(Hetero)multivalency acts as a multichannel switch that shapes the supramolecular properties of carbohydrates in an intrinsically multifactorial biological context.

Heteroglycoclusters With Dual Nanomolar Affinities for the Lectins LecA and LecB From Pseudomonas aeruginosa

Multivalent structures displaying different instead of similar sugar units, namely heteroglycoclusters (hGCs), are stimulating the efforts of glycochemists for developing compounds with new biological properties. Here we report a four-step strategy to synthesize hexadecavalent hGCs displaying eight copies of αFuc and βGal. These compounds were tested for the binding to lectins LecA and LecB from Pseudomonas aeruginosa. While parent fucosylated (19) and galactosylated (20) homoclusters present nanomolar affinity with LecB and LecA, respectively, we observed that hGCs combining these sugars (11 and 13) maintain their binding potency with both lectins despite the presence of an unspecific sugar. The added multivalency is therefore not a barrier for efficient recognition by bacterial receptors and it opens the route for adding different sugars that can be selected for their immunomodulatory properties.

Functionalization at Will of Rim-Differentiated Pillar[5]arenes

The development of an efficient synthetic route toward rim-differentiated C₅-symmetric pillar[5]arenes (P[5]s), whose two rims are decorated with different chemical functionalities, opens up successive transformations of this macrocyclic scaffold. This paper describes a gram-scale synthesis of a C₅-symmetric penta-hydroxy P[5] precursor, and a range of highly efficient reactions that allow functionalizing either rim at will via, e.g., sulfur(VI) fluoride exchange (SuFEx) reactions, esterifications, or Suzuki–Miyaura coupling. Afterward, BBr₃ demethylation activates another rim for similar functionalizations.

Recent advances in the development of rotaxanes and pseudorotaxanes based on pillar[n]arenes: from construction to application

This article summarizes recent advances in the development of rotaxanes and pseudorotaxanes based on pillar[n]arenes: from construction to application.

The study of multivalent carbohydrate-protein interactions by bio-layer interferometry

The study of complex multivalent carbohydrate-protein interactions remains highly complicated and sometimes rendered impossible due to aggregation problems. In this study, we demonstrate that bio-layer interferometry is an excellent complementary method to standard techniques such as SPR and ITC. Using tetra- and hexadecavalent GalNAc glycoconjugates and Helix pomatia agglutinin (HPA) as a model lectin, we were able to measure reliable kinetic and thermodynamic parameters of multivalent interactions going from the micro to the nanomolar range.

Sugared biomaterial binding lectins: achievements and perspectives

Lectins, a distinct group of glycan-binding proteins, play a prominent role in the immune system ranging from pathogen recognition and tuning of inflammation to cell adhesion or cellular signalling. The possibilities of their detailed study expanded along with the rapid development of biomaterials in the last decade. The immense knowledge of all aspects of glycan-lectin interactions both in vitro and in vivo may be efficiently used in bioimaging, targeted drug delivery, diagnostic and analytic biological methods. Practically applicable examples comprise photoluminescence and optical biosensors, ingenious three-dimensional carbohydrate microarrays for high-throughput screening, matrices for magnetic resonance imaging, targeted hyperthermal treatment of cancer tissues, selective inhibitors of bacterial toxins and pathogen-recognising lectin receptors, and many others. This review aims to present an up-to-date systematic overview of glycan-decorated biomaterials promising for interactions with lectins, especially those applicable in biology, biotechnology or medicine. The lectins of interest include galectin-1, -3 and -7 participating in tumour progression, bacterial lectins from Pseudomonas aeruginosa (PA-IL), E. coli (Fim-H) and Clostridium botulinum (HA33) or DC-SIGN, receptors of macrophages and dendritic cells. The spectrum of lectin-binding biomaterials covered herein ranges from glycosylated organic structures, calixarene and fullerene cores over glycopeptides and glycoproteins, functionalised carbohydrate scaffolds of cyclodextrin or chitin to self-assembling glycopolymer clusters, gels, micelles and liposomes. Glyconanoparticles, glycan arrays, and other biomaterials with a solid core are described in detail, including inorganic matrices like hydroxyapatite or stainless steel for bioimplants.

Microarray Analysis of Oligosaccharide-Mediated Multivalent Carbohydrate-Protein Interactions and Their Heterogeneity

Carbohydrate-protein interactions (CPIs) are involved in a wide range of biological phenomena. Hence, the characterization and presentation of carbohydrate epitopes that closely mimic the natural environment is one of the long-term goals of glycosciences. Inspired by the multivalency, heterogeneity and nature of carbohydrate ligand-mediated interactions, we constructed a combinatorial library of mannose and galactose homo- and hetero-glycodendrons to study CPIs. Microarray analysis of these glycodendrons with a wide range of biologically important plant and animal lectins revealed that oligosaccharide structures and heterogeneity interact with each other to alter binding preferences.

The aqueous supramolecular chemistry of cucurbit[n]urils, pillar[n]arenes and deep-cavity cavitands

This tutorial review summarizes the continuing exploration of three prominent water-soluble hosts: cucurbiturils, pillar[n]arenes and deep-cavity cavitands. As we describe, these hosts are revealing how orchestrating the hydrophobic effect can lead to a broad range of properties and applications, from: nano-reactors, supramolecular polymers, stimuli-responsive biointerfaces, switches, and novel purification devices. We also describe how their study is also revealing more details about the properties of water and aqueous solutions.

Biological and related applications of pillar[n]arenes

Pillar[n]arenes are a new class of synthetic supramolecular macrocycles streamlined by their particular pillar-shaped architecture which consists of an electron-rich cavity and two fine-tuneable rims. The ease and diversity of the functionalization of the two rims open possibilities for the design of new architectures, topological isomers, and scaffolds. Significantly, this emerging class of macrocyclic receptors offers a unique platform for biological purposes. This review article covers the most recent contributions from the pillar[n]arene field in terms of artificial membrane transport systems, controlled drug delivery systems, biomedical imaging, biosensors, cell adhesion, fluorescent sensing, and pesticide detection based on host-guest interactions. The review also uniquely describes the properties of sub-units that make pillar[n]arenes suitable for biological applications and it provides a detailed outline for the design of new innovative pillar-like structures with specific properties to open up a new avenue for pillar[n]arene chemistry.

Fullerene hexa-adduct scaffolding for the construction of giant molecules

Hexa-substituted fullerenes are unique scaffolds for the fast construction of globular dendrimers. Efficient synthetic methodologies based on the post-functionalization of pre-constructed fullerene hexa-adduct derivatives have been reported in recent years and dendrimers difficult or even impossible to prepare by classical fullerene chemistry are now easily accessible. Fullerodendrimers for various applications have been thus prepared. Examples include liquid crystalline materials, non-viral gene delivery systems and bioactive glycoclusters. On the other hand, fullerene hexa-adduct building blocks have been used for the ultra-fast synthesis of giant dendrimers. Indeed, the resulting dendrimers of first generation are already surrounded by 120 peripheral functional groups. This strategy has been used to prepare giant glycoclusters with anti-viral activity and multivalent glycosidase inhibitors.

A Rotaxane Scaffold Bearing Multiple Redox Centers: Synthesis, Surface Modification and Electrochemical Properties

A rotaxane scaffold incorporating two dithiolane anchoring units for the modification of gold surfaces has been functionalized with multiple copies of a redox unit, namely ferrocene. Surface modification has been first assessed at the single molecule level by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) imaging, while tip enhanced Raman spectroscopy (TERS) provided the local vibrational signature of the ferrocenyl subunits of the rotaxanes grafted onto the gold surface. Finally, oxidation of the redox moieties within a rotaxane scaffold grafted onto gold microelectrodes has been investigated by ultrafast cyclic voltammetry. Intramolecular electron hopping is indeed extremely fast in this system. Moreover, the kinetics of charge injection depends on the molecular coverage due to the influence of intermolecular contacts on molecular motions.

A Rotaxane Scaffold for the Construction of Multiporphyrinic Light-Harvesting Devices

A sophisticated photoactive molecular device has been prepared by combining recent concepts for the preparation of multifunctional nanomolecules (click chemistry on multifunctional scaffolds) with supramolecular chemistry (self-assembly to prepare rotaxanes). Specifically, a clickable [2]rotaxane scaffold incorporating a free-base porphyrin stopper has been prepared and functionalized with ten peripheral Zn(II)-porphyrin moieties. Electrochemical investigations of the final compound revealed a peculiar behavior resulting from the intramolecular coordination of the Zn(II) porphyrin moieties to 1,2,3-triazole units. Finally, steady state investigations of the compound combining Zn(II) and free-base porphyrin moieties have shown that this compound is a light-harvesting device capable of channeling the light energy from the peripheral Zn(II)-porphyrin subunits to the core by singlet-singlet energy transfer.

Preparation of Pillar[5]arene-Based [2]Rotaxanes by a Stopper-Exchange Strategy

A pillar[5]arene-containing rotaxane building block bearing exchangeable stoppers has been prepared in multigram scale quantities with high yields from the reaction of 2,4-dinitrophenol (DNP) with the inclusion complex resulting from the association of dodecanedioyl chloride with 1,4-diethoxypillar[5]arene. Stopper exchange reactions have been achieved by treatment of the resulting DNP diester with various amines through an addition-elimination mechanism preventing the unthreading of the axle component during the reaction and thus preserving the [2]rotaxane structures. The resulting diamide [2]rotaxane derivatives have thus been obtained in good to excellent yields. Importantly, [2]rotaxanes difficult or impossible to prepare by direct introduction of the two stoppers in a single synthetic step are now easily available.

“Onion peel” glycodendrimer syntheses using mixed triazine and cyclotriphosphazene scaffolds

An expeditious synthetic protocol for the construction of glycodendrimers is illustrated using the newly discovered “onion peel” strategy. The onion peel approach and orthogonal coupling strategies were accomplished with rationally design sequential modifications of cyanuric acid. Carefully chosen building blocks and their effective attachment by chemoselective atom economical click reactions, namely Cu (I) azide–alkyne cycloaddition reaction (CuAAC) and photocatalyzed thiol-ene reaction (TEC), allowed rapid build-up of glycodendrimers in contrast to traditional dendrimers syntheses that are based on the repetitive use of identical building blocks to form each layer. The newly formed glycodendrimers were evaluated for their capacity to cross-link carbohydrate-lectin interactions using dynamic light scattering (DLS). Rapid increase in particle size was observed as a function of time when compared to their monomer counterparts resulting from the multivalent lectin cross-linking ability of the new glycodendrimers.

Coordination-Driven Folding in Multi-ZnII -Porphyrin Arrays Constructed on a Pillar[5]arene Scaffold

Pillar[5]arene derivatives bearing peripheral porphyrin subunits have been efficiently prepared from a deca-azide pillar[5]arene building block (17) and Zn^II -porphyrin derivatives bearing a terminal alkyne function (9 and 16). For the resulting deca-Zn^II -porphyrin arrays (18 and 20), variable temperature NMR studies revealed an intramolecular complexation of the peripheral Zn^II -porphyrin moieties by 1,2,3-triazole subunits. As a result, the molecules adopt a folded conformation. This was further confirmed by UV/Vis spectroscopy and cyclic voltammetry. In addition, we have also demonstrated that the coordination-driven unfolding of 18 and 20 can be controlled by an external chemical stimulus. Specifically, addition of an imidazole derivative (22) to solution of 18 or 20 breaks the intramolecular coordination at the origin of the folding. The resulting molecular motions triggered by the addition of the imidazole ligand mimic the blooming of a flower.

Multivalency as an action principle in multimodal lectin recognition and glycosidase inhibition: a paradigm shift driven by carbon-based glyconanomaterials

The last decade has witnessed a series of discoveries that question the traditional paradigm of multivalency as a "safe" strategy to enhance the binding affinity of a lectin receptor to its cognate carbohydrate ligand. Upon following the initial reports on the supplementary effects operating in the presence of a third carbohydrate species (heteromultivalent effect), the observation of functional promiscuity of glyco(mimetic)ligands elicited by (hetero)multivalency, spreading from lectins to glycoprocessing enzymes (inhibitory multivalent effect), has raised concerns about the potential consequences of glyconanomaterials binding to non-cognate proteins and creating messiness or noise in the processes they participate in. Carbon-based glycomaterials, specifically glyconanodiamonds and glycofullerenes, have been instrumental in increasing our awareness of the frequency of these lectin-enzyme crosstalk behaviours elicited by multivalency, driving a reformulation of the rules and concepts in glycoscience towards a "generalized multivalency" scenario.

Construction of giant glycosidase inhibitors from iminosugar-substituted fullerene macromonomers

An ultra-fast synthetic procedure based on grafting of twelve fullerene macromonomers onto a fullerene hexa-adduct core was used for the preparation of a giant molecule with 120 peripheral iminosugar residues. The inhibition profile of this giant iminosugar ball was evaluated against various glycosidases. In the particular case of the Jack bean α-mannosidase, a dramatic enhancement of the glycosidase inhibitory effect was observed for the giant molecule with 120 peripheral subunits as compared to that of the corresponding mono- and dodecavalent model compounds.

The Impact of Heteromultivalency in Lectin Recognition and Glycosidase Inhibition: An Integrated Mechanistic Study

The vision of multivalency as a strategy limited to achieve affinity enhancements between a protein receptor and its putative sugar ligand (glycotope) has proven too simplistic. On the one hand, binding of a glycotope in a dense glycocalix-like construct to a lectin partner has been shown to be sensitive to the presence of a third sugar entity (heterocluster effect). On the other hand, several carbohydrate processing enzymes (glycosidases and glycosyltransferases) have been found to be also responsive to multivalent presentations of binding partners (multivalent enzyme inhibition), a phenomenon first discovered for iminosugar-type inhibitory species (inhitopes) and recently demonstrated for multivalent carbohydrate constructs. By assessing a series of homo- and heteroclusters combining α-d-glucopyranosyl-related glycotopes and inhitopes, it was shown that multivalency and heteromultivalency govern both kinds of events, allowing for activation, deactivation or enhancement of specific recognition phenomena towards a spectrum of lectin and glycosidase partners in a multimodal manner. This unified scenario originates from the ability of (hetero)multivalent architectures to trigger glycosidase binding modes that are reminiscent of those harnessed by lectins, which should be considered when profiling the biological activity of multivalent architectures.

Myeloid C-Type Lectin Receptors in Viral Recognition and Antiviral Immunity

Recognition of viral glycans by pattern recognition receptors (PRRs) in innate immunity contributes to antiviral immune responses. C-type lectin receptors (CLRs) are PRRs capable of sensing glycans present in viral pathogens to activate antiviral immune responses such as phagocytosis, antigen processing and presentation, and subsequent T cell activation. The ability of CLRs to elicit and shape adaptive immunity plays a critical role in the inhibition of viral spread within the host. However, certain viruses exploit CLRs for viral entry into host cells to avoid immune recognition. To block CLR interactions with viral glycoproteins, antiviral strategies may involve the use of multivalent glycan carrier systems. In this review, we describe the role of CLRs in antiviral immunity and we highlight their dual function in viral clearance and exploitation by viral pathogens.

Heterolayered hybrid dendrimers with optimized sugar head groups for enhancing carbohydrate–protein interactions

Novel heterolayered (“onion peel”) hybrid glycodendrimers containing optimised sugar head groups with galactoside and mannoside units with affinities for two different lectins.

Mechanistic Insight into Heptosyltransferase Inhibition by using Kdo Multivalent Glycoclusters

The synthesis of unprecedented multimeric Kdo glycoclusters based on fullerene and calix[4]arene central scaffolds is reported. The compounds were used to study the mechanism and scope of multivalent glycosyltransferase inhibition. Multimeric mannosides based on porphyrin and pillar[5]arenes were also generated in a controlled manner. Twelve glycoclusters and their monomeric ligands were thus assayed against heptosyltransferase WaaC, which is an important bacterial glycosyltransferase that is involved in lipopolysaccharide biosynthesis. It was first found that all the multimers interact solely with the acceptor binding site of the enzyme even when the multimeric ligands mimic the heptose donor. Second, the novel Kdo glycofullerenes displayed very potent inhibition (Ki =0.14 μm for the best inhibitor); an inhibition level rarely observed with glycosyltransferases. Although the observed "multivalent effects" (i.e., the enhancement of affinity of a ligand when presented in a multimeric fashion) were in general modest, a dramatic effect of the central scaffold on the inhibition level was evidenced: the fullerene and the porphyrin scaffolds being by far superior to the calix- and pillar-arenes. We could also show, by dynamic light scattering analysis, that the best inhibitor had the propensity to form aggregates with the heptosyltransferase. This aggregative property may contribute to the global multivalent enzyme inhibition, but probably do not constitute the main origin of inhibition.

Synthesis of a New Series of Sialylated Homo- and Heterovalent Glycoclusters by using Orthogonal Ligations

The synthesis of heteroglycoclusters (hGCs) is being subjected to rising interest, owing to their potential applications in glycobiology. In this paper, we report an efficient and straightforward convergent protocol based on orthogonal chemoselective ligations to prepare structurally well-defined cyclopeptide-based homo- and heterovalent glycoconjugates displaying 5-N-acetyl-neuraminic acid (Neu5Ac), galactose (Gal), and/or N-acetyl glucosamine (GlcNAc). We first used copper-catalyzed azide-alkyne cycloaddition and/or thiol-ene coupling to conjugate propargylated α-sialic acid 3, β-GlcNAc thiol 5, and β-Gal thiol 6 onto cyclopeptide scaffolds 7-9 to prepare tetravalent homoglycoclusters (10-12) and hGCs (13-14) with 2:2 combinations of sugars. In addition, we have demonstrated that 1,2-diethoxycyclobutene-3,4-dione can be used as a bivalent linker to prepare various octavalent hGCs (16, 19, and 20) in a controlled manner from these tetravalent structures.

Toward the Rational Design of Galactosylated Glycoclusters That Target Pseudomonas aeruginosa Lectin A (LecA): Influence of Linker Arms That Lead to Low-Nanomolar Multivalent Ligands

Anti-infectious strategies against pathogen infections can be achieved through antiadhesive strategies by using multivalent ligands of bacterial virulence factors. LecA and LecB are lectins of Pseudomonas aeruginosa implicated in biofilm formation. A series of 27 LecA-targeting glycoclusters have been synthesized. Nine aromatic galactose aglycons were investigated with three different linker arms that connect the central mannopyranoside core. A low-nanomolar (Kd =19 nm, microarray) ligand with a tyrosine-based linker arm could be identified in a structure-activity relationship study. Molecular modeling of the glycoclusters bound to the lectin tetramer was also used to rationalize the binding properties observed.

Glycomaterials for probing host-pathogen interactions and the immune response

The initial engagement of host cells by pathogens is often mediated by glycan structures presented on the cell surface. Various components of the glycocalyx can be targeted by pathogens for adhesion to facilitate infection. Glycans also play integral roles in the modulation of the host immune response to infection. Therefore, understanding the parameters that define glycan interactions with both pathogens and the various components of the host immune system can aid in the development of strategies to prevent, interrupt, or manage infection. Glycomaterials provide a unique and powerful tool with which to interrogate the compositional and functional complexity of the glycocalyx. The objective of this review is to highlight some key contributions from this area of research in deciphering the mechanisms of pathogenesis and the associated host response.

Pentavalent pillar[5]arene-based glycoclusters and their multivalent binding to pathogenic bacterial lectins

Anti-adhesive glycoclusters offer potential as therapeutic alternatives to classical antibiotics in treating infections. Pillar[5]arenes functionalised with either five galactose or five fucose residues were readily prepared using CuAAC reactions and evaluated for their binding to three therapeutically relevant bacterial lectins: LecA and Lec B from Pseudomonas aeuruginosa and BambL from Burkholderia ambifaria. Steric interactions were demonstrated to be a key factor in achieving good binding to LecA with more flexible galactose glycoclusters showing enhanced activity. In contrast binding to the fucose-selective lectins confirmed the importance of topology of the glycoclusters for activity with the pillar[5]arene ligand proving a selective ligand for BambL.

Pillar[5]arene-Based Glycoclusters: Synthesis and Multivalent Binding to Pathogenic Bacterial Lectins

The synthesis of pillar[5]arene-based glycoclusters has been readily achieved by CuAAC conjugations of azido- and alkyne-functionalized precursors. The lectin binding properties of the resulting glycosylated multivalent ligands have been studied by at least two complementary techniques to provide a good understanding. Three lectins were selected from bacterial pathogens based on their potential therapeutic applications as anti-adhesives, namely LecA and LecB from Pseudomonas aeruginosa and BambL from Burkholderia ambifaria. As a general trend, multivalency improved the binding to lectins and a higher affinity can be obtained by increasing to a certain limit the length of the spacer arm between the carbohydrate subunits and the central macrocyclic core.