Strain-promoted alkyne azide cycloaddition for the functionalization of poly(amide)-based dendrons and dendrimers

Metal-Free Click-Chemistry: A Powerful Tool for Fabricating Hydrogels for Biomedical Applications

Increasing interest in the utilization of hydrogels in various areas of biomedical sciences ranging from biosensing and drug delivery to tissue engineering has necessitated the synthesis of these materials using efficient and benign chemical transformations. In this regard, the advent of "click" chemistry revolutionized the design of hydrogels and a range of efficient reactions was utilized to obtain hydrogels with increased control over their physicochemical properties. The ability to apply the "click" chemistry paradigm to both synthetic and natural polymers as hydrogel precursors further expanded the utility of this chemistry in network formation. In particular, the ability to integrate clickable handles at predetermined locations in polymeric components enables the formation of well-defined networks. Although, in the early years of "click" chemistry, the copper-catalyzed azide-alkyne cycloaddition was widely employed, recent years have focused on the use of metal-free "click" transformations, since residual metal impurities may interfere with or compromise the biological function of such materials. Furthermore, many of the non-metal-catalyzed "click" transformations enable the fabrication of injectable hydrogels, as well as the fabrication of microstructured gels using spatial and temporal control. This review article summarizes the recent advances in the fabrication of hydrogels using various metal-free "click" reactions and highlights the applications of thus obtained materials. One could envision that the use of these versatile metal-free "click" reactions would continue to revolutionize the design of functional hydrogels geared to address unmet needs in biomedical sciences.

Peptide Dendrimer-Based Antibacterial Agents: Synthesis and Applications

Pathogenic bacteria cause the deaths of millions of people every year. With the development of antibiotics, hundreds and thousands of people's lives have been saved. Nevertheless, bacteria can develop resistance to antibiotics, rendering them insensitive to antibiotics over time. Peptides containing specific amino acids can be used as antibacterial agents; however, they can be easily degraded by proteases in vivo. To address these issues, branched peptide dendrimers are now being considered as good antibacterial agents due to their high efficacy, resistance to protease degradation, and low cytotoxicity. The ease with which peptide dendrimers can be synthesized and modified makes them accessible for use in various biological and nonbiological fields. That is, peptide dendrimers hold a promising future as antibacterial agents with prolonged efficacy without bacterial resistance development. Their in vivo stability and multivalence allow them to effectively target multi-drug-resistant strains and prevent biofilm formation. Thus, it is interesting to have an overview of the development and applications of peptide dendrimers in antibacterial research, including the possibility of employing machine learning approaches for the design of AMPs and dendrimers. This review summarizes the synthesis and applications of peptide dendrimers as antibacterial agents. The challenges and perspectives of using peptide dendrimers as the antibacterial agents are also discussed.

Development of Essential Oil Delivery Systems by 'Click Chemistry' Methods: Possible Ways to Manage Duchenne Muscular Dystrophy

Recently, rare diseases have received attention due to the need for improvement in diagnosed patients' and their families' lives. Duchenne muscular dystrophy (DMD) is a rare, severe, progressive, muscle-wasting disease. Today, the therapeutic standard for treating DMD is corticosteroids, which cause serious adverse side effects. Nutraceuticals, e.g., herbal extracts or essential oils (EOs), are possible active substances to develop new drug delivery systems to improve DMD patients' lives. New drug delivery systems lead to new drug effects, improved safety and accuracy, and new therapies for rare diseases. Herbal extracts and EOs combined with click chemistry can lead to the development of safer treatments for DMD. In this review, we focus on the need for novel drug delivery systems using EOs as the therapy for DMD and the potential use of click chemistry for drug delivery systems. New EO complex drug delivery systems may offer a new approach for improving muscle conditions and mental health issues associated with DMD. However, further research should identify the potential of these systems in the context of DMD. In this review, we discuss possibilities for applying EOs to DMD before implementing expensive research in a theoretical way.

Well-Defined Bifunctional Dendrimer Bearing 54 Nitric Oxide-Releasing Moieties and 54 Ursodeoxycholic Acid Groups Presenting High Anti-Inflammatory Activity

Nitric oxide (NO) and ursodeoxycholic acid (UDCA) are endogenous molecules involved in physiological processes associated with inflammation. Since inflammatory processes are present in the mechanisms of many diseases, these molecules are important for the development of new drugs. Herein, we describe the synthesis of a well-defined bifunctional dendrimer with 108 termini bearing 54 NO-releasing groups and 54 UDCA units (Dendri-(NO/UDCA)₅₄). For comparison, a lower-generation dendrimer bearing 18 NO-releasing groups and 18 UDCA units (Dendri-(NO/UDCA)₁₈) was also synthesized. The anti-inflammatory activity of these dendrimers was evaluated, showing that the bifunctional dendrimers have an inverse correlation between concentration and anti-inflammatory activity, with an effect dramatically pronounced for Dendri-(NO/UDCA)₅₄ 20, which at just 0.25 nM inhibited 76.1% of IL-8 secretion. Data suggest that nanomolar concentrations of these dendrimers aid in releasing NO in a safe and controlled way. This bifunctional dendrimer has great potential as a drug against multifactorial diseases associated with inflammatory processes.

A 3D Peptide/[60]Fullerene Hybrid for Multivalent Recognition

Fully substituted peptide/[60]fullerene hexakis-adducts offer an excellent opportunity for multivalent protein recognition. In contrast to monofunctionalized fullerene hybrids, peptide/[60]fullerene hexakis-adducts display multiple copies of a peptide in close spatial proximity and in the three dimensions of space. High affinity peptide binders for almost any target can be currently identified by in vitro evolution techniques, often providing synthetically simpler alternatives to natural ligands. However, despite the potential of peptide/[60]fullerene hexakis-adducts, these promising conjugates have not been reported to date. Here we present a synthetic strategy for the construction of 3D multivalent hybrids that are able to bind with high affinity the E-selectin. The here synthesized fully substituted peptide/[60]fullerene hybrids and their multivalent recognition of natural receptors constitute a proof of principle for their future application as functional biocompatible materials.

Multivalent Pyrrolidine Iminosugars: Synthesis and Biological Relevance

Recently, the strategy of multivalency has been widely employed to design glycosidase inhibitors, as glycomimetic clusters often induce marked enzyme inhibition relative to monovalent analogs. Polyhydroxylated pyrrolidines, one of the most studied classes of iminosugars, are an attractive moiety due to their potent and specific inhibition of glycosidases and glycosyltransferases, which are associated with many crucial biological processes. The development of multivalent pyrrolidine derivatives as glycosidase inhibitors has resulted in several promising compounds that stand out. Herein, we comprehensively summarized the different synthetic approaches to the preparation of multivalent pyrrolidine clusters, from total synthesis of divalent iminosugars to complex architectures bearing twelve pyrrolidine motifs. Enzyme inhibitory properties and multivalent effects of these synthesized iminosugars were further discussed, especially for some less studied therapeutically relevant enzymes. We envision that this comprehensive review will help extend the applications of multivalent pyrrolidine iminosugars in future studies.

Topological and Multivalent Effects in Glycofullerene Oligomers as EBOLA Virus Inhibitors

The synthesis of new biocompatible antiviral materials to fight against the development of multidrug resistance is being widely explored. Due to their unique globular structure and excellent properties, [60]fullerene-based antivirals are very promising bioconjugates. In this work, fullerene derivatives with different topologies and number of glycofullerene units were synthesized by using a SPAAC copper free strategy. This procedure allowed the synthesis of compounds 1–3, containing from 20 to 40 mannose units, in a very efficient manner and in short reaction times under MW irradiation. The glycoderivatives were studied in an infection assay by a pseudotyped viral particle with Ebola virus GP1. The results obtained show that these glycofullerene oligomers are efficient inhibitors of EBOV infection with IC₅₀s in the nanomolar range. In particular, compound 3, with four glycofullerene moieties, presents an outstanding relative inhibitory potency (RIP). We propose that this high RIP value stems from the appropriate topological features that efficiently interact with DC-SIGN.

An Accelerated Modular-Orthogonal Ni-Catalyzed Methodology to Symmetric and Nonsymmetric Constitutional Isomeric AB2 to AB9 Dendrons Exhibiting Unprecedented Self-Organizing Principles

Five libraries of natural and synthetic phenolic acids containing five AB₃, ten constitutional isomeric AB₂, one AB₄, and one AB₅ were previously synthesized and reported by our laboratory in 5 to 11 steps. They were employed to construct seven libraries of self-assembling dendrons, by divergent generational, deconstruction, and combined approaches, enabling the discovery of a diversity of supramolecular assemblies including Frank-Kasper phases, soft quasicrystals, and complex helical organizations, some undergoing deracemization in the crystal state. However, higher substitution patterns within a single dendron were not accessible. Here we report three libraries consisting of 30 symmetric and nonsymmetric constitutional isomeric phenolic acids with unprecedented sequenced patterns, including two AB₂, three AB₃, eight AB₄, five AB₅, six AB₆, three AB₇, two AB₈, and one AB₉ synthesized by accelerated modular-orthogonal Ni-catalyzed borylation and cross-coupling. A single etherification step with 4-(n-dodecyloxy)benzyl chloride transformed all these phenolic acids, of interest also for other applications, into self-assembling dendrons. Despite this synthetic simplicity, they led to a diversity of unprecedented self-organizing principles: lamellar structures of interest for biological membrane mimics, helical columnar assemblies from rigid-solid angle dendrons forming Tobacco Mosaic Virus-like assemblies, columnar organizations from adaptable-solid angle dendrons forming disordered micellar-like nonhelical columns, columns from supramolecular spheres, five body-centered cubic phases displaying supramolecular orientational memory, rarely encountered in previous libraries forming predominantly Frank-Kasper phases, and two Frank-Kasper phases. Lessons from these self-organizing principles, discovered within a single generation of self-assembling dendrons, may help elaborate design principles for complex helical and nonhelical organizations of synthetic and biological matter.

Self-Assembly of a Triazolylferrocenyl Dendrimer in Water Yields Nontraditional Intrinsic Green Fluorescent Vesosomes for Nanotheranostic Applications

The promising field of nanomedicine stimulates a continuous search for multifunctional nanotheranostic systems for imaging and drug delivery. Herein, we demonstrate that application of supramolecular chemistry's concepts in dendritic assemblies can enable the formation of advanced dendrimer-based nanotheranostic devices. A dendrimer bearing 81 triazolylferrocenyl terminal groups adopts a more compact shell-like structure in polar solvents with the ferrocenyl peripheral groups backfolding toward the hydrophobic dendrimer interior, while exposing the more polar triazole moieties as the dendritic shell. Akin to lipids, the compact dendritic structure self-assembles into uniform nanovesicles that in turn self-assemble into larger vesosomes in water. The vesosomes emit green nontraditional intrinsic fluorescence (NTIL), which is an emerging property as there are no classical fluorophores in the dendritic macromolecular structure. This work confirms the hypothesis that the NTIL emission is greatly enhanced by rigidification of the supramolecular assemblies containing heteroatomic subluminophores (HASLs) and by the presence of electron rich functional groups on the periphery of dendrimers. This work is the first one detecting NTIL in ferrocenyl-terminated dendrimers. Moreover, the vesosomes are stable in biological medium, are uptaken by cells, and show cytotoxic activity against cancer cells. Accordingly, the self-organization of these dendrimers into tertiary structures promotes the emergence of new properties enabling the same component, in this case, ferrocenyl group, to function as both antitumoral drug and fluorophore.

Double Arylation of the Indole Side Chain of Tri- and Tetrapodal Tryptophan Derivatives Renders Highly Potent HIV-1 and EV-A71 Entry Inhibitors†

We have recently described a new generation of potent human immunodeficiency virus (HIV) and EV-A71 entry inhibitors. The prototypes contain three or four tryptophan (Trp) residues bearing an isophthalic acid moiety at the C2 position of each side-chain indole ring. This work is now extended by both shifting the position of the isophthalic acid to C7 and synthesizing doubly arylated C2/C7 derivatives. The most potent derivative (50% effective concentration (EC₅₀) HIV-1, 6 nM; EC₅₀ EV-A71, 40 nM), 33 (AL-518), is a C2/C7 doubly arylated tetrapodal compound. Its superior anti-HIV potency with respect to the previous C2-arylated prototype is in consonance with its higher affinity for the viral gp120. 33 (AL-518) showed comparable antiviral activities against X4 and R5 HIV-1 strains and seems to interact with the tip and base of the gp120 V3 loop. Taken together, these findings support the interest in 33 (AL-518) as a useful new prototype for anti-HIV/EV71 drug development.

Glycodendritic structures as DC-SIGN binders to inhibit viral infections

DC-SIGN, a lectin discovered two decades ago, plays a relevant role in innate immunity. Since its discovery, it has turned out to be a target for developing antiviral drugs based on carbohydrates due to its participation in the infection process of several pathogens. A plethora of carbohydrate multivalent systems using different scaffolds have been described to achieve this goal. Our group has made significant contributions to this field, which are revised herein.

Real-time monitoring of caspase-3/8 activity by self-assembling nanofiber probes in living cells

Caspase-3/8 are key members of the cysteine-aspartyl protease family with pivotal roles in apoptosis. We have designed and synthesized self-assembling probes, Nap-GFFpYDEVD-AFC and Nap-GFFpYIETD-AFC, with fluorescence 'turn-on' properties for real-time monitoring of Caspase-3/8 activity in living cells.

A Survey of Strain-Promoted Azide-Alkyne Cycloaddition in Polymer Chemistry

Highly efficient reactions that enable the assembly of molecules into complex structures have driven extensive progress in synthetic chemistry. In particular, reactions that occur under mild conditions and in benign solvents, while producing no by-products and rapidly reach completion are attracting significant attention. Amongst these, the strain-promoted azide-alkyne cycloaddition, involving various cyclooctyne derivatives reacting with azide-bearing molecules, has gained extensive popularity in organic synthesis and bioorthogonal chemistry. This reaction has also recently gained momentum in polymer chemistry, where it has been used to decorate, link, crosslink, and even prepare polymer chains. This survey highlights key achievements in the use of this reaction to produce a variety of polymeric constructs for disparate applications.

Telodendrimers: Promising Architectural Polymers for Drug Delivery

Architectural complexity has played a key role in enhancing the efficacy of nanocarriers for a variety of applications, including those in the biomedical field. With the continued evolution in designing macromolecules-based nanoparticles for drug delivery, the combination approach of using important features of linear polymers with dendrimers has offered an advantageous and viable platform. Such nanostructures, which are commonly referred to as telodendrimers, are hybrids of linear polymers covalently linked with different dendrimer generations and backbones. There is considerable variety in selection from widely studied linear polymers and dendrimers, which can help tune the overall composition of the resulting hybrid structures. This review highlights the advances in articulating syntheses of these macromolecules, and the contributions these are making in facilitating therapeutic administration. Limited progress has been made in the design and synthesis of these hybrid macromolecules, and it is through an understanding of their physicochemical properties and aqueous self-assembly that one can expect to fully exploit their potential in drug delivery.

Side chain effect in the modulation of αvβ3/α5β1 integrin activity via clickable isoxazoline-RGD-mimetics: development of molecular delivery systems

Construction of small molecule ligand (SML) based delivery systems has been performed starting from a polyfunctionalized isoxazoline scaffold, whose αvβ3 and α5β1 integrins' potency has been already established. The synthesis of this novel class of ligands was obtained by conjugation of linkers to the heterocyclic core via Huisgen-click reaction, with the aim to use them as "shuttles" for selective delivery of diagnostic agents to cancer cells, exploring the effects of the side chains in the interaction with the target. Compounds 17b and 24 showed excellent potency towards α5β1 integrin acting as selective antagonist and agonist respectively. Further investigations confirmed their effects on target receptor through the analysis of fibronectin-induced ERK1/2 phosphorylation. In addition, confocal microscopy analysis allowed us to follow the fate of EGFP conjugated α5β1 integrin and 17b FITC-conjugated (compound 31) inside the cells. Moreover, the stability in water solution at different values of pH and in bovine serum confirmed the possible exploitation of these peptidomimetic molecules for pharmaceutical application.

A bio-orthogonal functionalization strategy for site-specific coupling of antibodies on vesicle surfaces after self-assembly

Attaching targeting ligands on the surface of self-assembled drug delivery systems is one of the key requests for a controlled transport of the drug to a desired location.

Scaffold Simplification Strategy Leads to a Novel Generation of Dual Human Immunodeficiency Virus and Enterovirus-A71 Entry Inhibitors

Currently, there are only three FDA-approved drugs that inhibit human immunodeficiency virus (HIV) entry-fusion into host cells. The situation is even worse for enterovirus EV71 infection for which no antiviral therapies are available. We describe here the discovery of potent entry dual inhibitors of HIV and EV71. These compounds contain in their structure three or four tryptophan (Trp) residues linked to a central scaffold. Critical for anti-HIV/EV71 activity is the presence of extra phenyl rings, bearing one or two carboxylates, at the C2 position of the indole ring of each Trp residue. The most potent derivatives, 22 and 30, inhibit early steps of the replicative cycles of HIV-1 and EV-A71 by interacting with their respective viral surfaces (glycoprotein gp120 of HIV and the fivefold axis of the EV-A71 capsid). The high potency, low toxicity, facile chemical synthesis, and great opportunities for chemical optimization make them useful prototypes for future medicinal chemistry studies.

Investigation of tetrazine reactivity towards C-nucleophiles: pyrazolone-based modification of biomolecules

Chemoselective, biocompatible ligation reactions are the key components for efficient and modular access to biomolecular scaffolds. Tetrazine ligation leads to the formation of a mixture of isomers, which makes reaction monitoring, purification and characterization of conjugates difficult. We report herein a modified tetrazine ligation strategy based on the use of a pyrazolone coupling partner, which provides a single molecule conjugate.

Dendronized Systems for the Delivery of Chemotherapeutics

This chapter reviews the use of dendronized systems as nanocarriers for the delivery of chemotherapeutic drugs. Dendronized systems include dendrimers prepared through convergent methods as well as other systems containing dendrons (e.g., polymers, nanoparticles, liposomes). The preparation of such systems is detailed, followed by the various conjugation techniques used for the transport of chemotherapeutic drugs and their specific delivery to tumor cells. In addition, the ability of dendronized systems to provide passive and active targeting to tumors is discussed. The efficacy of drug delivery using dendronized systems is also illustrated through specific examples of kinetic and biological studies. Finally, the newest trends in conjugation of the most common chemotherapeutics to dendronized systems are described. Overall, this chapter highlights dendronized systems as a way to improve the therapeutic efficiency of drugs for the treatment of cancer. All the recent developments in areas, such as biodegradable dendrimers, modifications to enhance biocompatibility, selectively cleavable drug conjugations, ligand-mediated targeting, and the potential for multifunctional properties, show promises for future advances in cancer therapy.

Multimerization of DAB-1 onto Au GNPs affords new potent and selective N-acetylgalactosamine-6-sulfatase (GALNS) inhibitors

Gold glyconanoparticles (Au GNPs) decorated with the natural iminosugar DAB-1 at different densities are reported.

Ultrafast and efficient aza- and thiol-Michael reactions on a polyester scaffold with internal electron deficient triple bonds

A polyester scaffold possessing electron deficient triple bonds in the main chain was prepared and utilized as a precursor for aza- and thiol-Michael addition reactions.

Continuous detection of HCl and NH3 gases with a high-performance fluorescent polymer sensor

A novel fluorescent triazine-based covalent organic polymer (COP-1) sensor for HCl and NH₃ gases has been designed and synthesized.

Nanoparticle-macrophage interactions: A balance between clearance and cell-specific targeting

The surface properties of nanoparticles (NPs) are a major factor that influences how these nanomaterials interact with biological systems. Interactions between NPs and macrophages of the reticuloendothelial system (RES) can reduce the efficacy of NP diagnostics and therapeutics. Traditionally, to limit NP clearance by the RES system, the NP surface is neutralized with molecules like poly(ethylene glycol) (PEG) which are known to resist protein adsorption and RES clearance. Unfortunately, PEG modification is not without drawbacks including difficulties with the synthesis and associations with immune reactions. To overcome some of these obstacles, we neutralized the NP surface by acetylation and compared this modification to PEGylation for RES clearance and tumor-specific targeting. We found that acetylation was comparable to PEGylation in reducing RES clearance. Additionally, we found that dendrimer acetylation did not impact folic acid (FA)-mediated targeting of tumor cells whereas PEG surface modification reduced the targeting ability of the NP. These results clarify the impact of different NP surface modifications on RES clearance and cell-specific targeting and provide insights into the design of more effective NPs.

Self-interrupted synthesis of sterically hindered aliphatic polyamide dendrimers

2,2-Bis(azidomethyl)propionic acid was prepared in four steps and 85% yield from the commercially available 2,2-bis(hydroxymethyl)propionic acid and used as the starting building block for the divergent, convergent, and double-stage convergent-divergent iterative methods for the synthesis of dendrimers and dendrons containing ethylenediamine (EDA), piperazine (PPZ), and methyl 2,2-bis(aminomethyl)propionate (COOMe) cores. These cores have the same multiplicity but different conformations. A diversity of synthetic methods were used for the synthesis of dendrimers and dendrons. Regardless of the method used, a self-interruption of the synthesis was observed at generation 4 for the dendrimer with an EDA core and at generation 5 for the one with a PPZ core, whereas for the COOMe core, self-interruption was observed at generation 6 dendron, which is equivalent to generation 5 dendrimer. Molecular modeling and molecular-dynamics simulations demonstrated that the observed self-interruption is determined by the backfolding of the azide groups at the periphery of the dendrimer. The latter conformation inhibits completely the heterogeneous hydrogenation of the azide groups catalyzed by 10% Pd/carbon as well as homogeneous hydrogenation by the Staudinger method. These self-terminated polyamide dendrimers are enzymatically and hydrolytically stable and also exhibit antimicrobial activity. Thus, these nanoscale constructs open avenues for biomedical applications.

A metal-free synthetic approach to peptide-based iminosugar clusters as novel multivalent glycosidase inhibitors

Oxime ligation allowed the preparation of a set of iminosugar clusters from which new Jack bean α-mannosidase inhibitors were identified.

Cyclooctyne [60]fullerene hexakis adducts: a globular scaffold for copper-free click chemistry

The synthesis of a new highly symmetric hexakis adduct of C₆₀ appended with 12 cyclooctyne moieties has been carried out.

Synthesis and characterization of Bi(iii) immobilized on triazine dendrimer-stabilized magnetic nanoparticles: a reusable catalyst for the synthesis of aminonaphthoquinones and bis-aminonaphthoquinones

A novel method for synthesis of aminonaphthoquinone derivatives using Fe₃O₄@TDSN–Bi(iii) is reported.

Strain-promoted azide–alkyne cycloaddition for protein–protein coupling in the formation of a bis-hemoglobin as a copper-free oxygen carrier

Conventional chemical approaches to protein–protein coupling present challenges due to the intrinsic competition between the desired interactions of reagents with groups of the protein as well as reactions with water.

Recent advances in click chemistry applied to dendrimer synthesis

Dendrimers are monodisperse polymers grown in a fractal manner from a central point. They are poised to become the cornerstone of nanoscale devices in several fields, ranging from biomedicine to light-harvesting. Technical difficulties in obtaining these molecules has slowed their transfer from academia to industry. In 2001, the arrival of the "click chemistry" concept gave the field a major boost. The flagship reaction, a modified Hüisgen cycloaddition, allowed researchers greater freedom in designing and building dendrimers. In the last five years, advances in click chemistry saw a wider use of other click reactions and a notable increase in the complexity of the reported structures. This review covers key developments in the click chemistry field applied to dendrimer synthesis from 2010 to 2015. Even though this is an expert review, basic notions and references have been included to help newcomers to the field.

Synthesis and biological properties of multivalent iminosugars

Clustering 1-deoxynojirimycin (DNJ), first isolated from white mulberry, and other iminosugars around various scaffolds gave strong glycosidase inhibitors.

The dendrimer paradox – high medical expectations but poor clinical translation

This review was written with the intention to critically evaluate the status of dendrimers as drug carriers and find answers as to why this class of compounds has not translated into the clinic despite 40 years of research.