Simplifying the synthesis of dendrimers: accelerated approaches

Multivalent polymers for drug delivery and imaging: the challenges of conjugation

Multivalent polymers offer a powerful opportunity to develop theranostic materials on the size scale of proteins that can provide targeting, imaging, and therapeutic functionality. Achieving this goal requires the presence of multiple targeting molecules, dyes, and/or drugs on the polymer scaffold. This critical review examines the synthetic, analytical, and functional challenges associated with the heterogeneity introduced by conjugation reactions as well as polymer scaffold design. First, approaches to making multivalent polymer conjugations are discussed followed by an analysis of materials that have shown particular promise biologically. Challenges in characterizing the mixed ligand distributions and the impact of these distributions on biological applications are then discussed. Where possible, molecular-level interpretations are provided for the structures that give rise to the functional ligand and molecular weight distributions present in the polymer scaffolds. Lastly, recent strategies employed for overcoming or minimizing the presence of ligand distributions are discussed. This review focuses on multivalent polymer scaffolds where average stoichiometry and/or the distribution of products have been characterized by at least one experimental technique. Key illustrative examples are provided for scaffolds that have been carried forward to in vitro and in vivo testing with significant biological results.

RAFT-mediated control of nanogel structure and reactivity: chemical, physical and mechanical properties of monomer-dispersed nanogel compositions

OBJECTIVE

This study examines how nanogel structure correlates with photopolymerization and key polymer properties upon addition of nanogels with latent reactivity into a monomer dispersant to produce polymer/polymer composites.

METHODS

Two nanogels that retained RAFT functionality based on the synthetic approach were prepared to have different branching densities. These reactive nanogels were dispersed in triethylene glycol dimethacrylate at 0-40 wt%. Reaction kinetics, volumetric shrinkage and shrinkage stress associated with the photopolymerization of nanogel-modified formulations were measured in real time with mechanical properties of the polymers also evaluated. The basic structure of RAFT-derived nanogel particles was examined by the preparation of a separate nanogel constructed with degradable disulfide crosslinking groups. The model nanogel molecular weight and polydispersity were compared before and after degradation.

RESULTS

Despite the controlled radical synthetic approach, the nanogels, which are composed of multiple interconnected, short primary chains, presented relatively high polydispersity. Through addition of the reactive nanogels to a monomer that both infiltrates and disperses the nanogels, the photopolymerization rate was moderately reduced with the increase of nanogel loading levels. Volumetric shrinkage decreased proportionally with nanogel concentration; however, a greater than proportional reduction of polymerization-induced stress was observed. Mechanical properties, such as flexural strength, storage modulus were maintained at the same levels as the control resin for nanogel systems up to 40 wt%.

SIGNIFICANCE

This study demonstrated that beyond the use of RAFT functionality to produce discrete nano-polymeric structures, the residual chain end groups are important to maintain reactivity and mechanical properties of nanogel-modified resin materials.

Combination of Orthogonal ABB and ABC Multicomponent Reactions toward Efficient Divergent Synthesis of Dendrimers with Structural Diversity

Synthesis of dendrimers has been directed toward process efficiency and structural diversity. We report a divergent approach to the preparation of dendrimers with both ABC and ABB branching structures from nonbranching monomers by combination of efficient orthogonal ABC Passerini multicomponent reaction (MCR) and ABB thiol-yne MCR. Two kinds of dendrimers were synthesized efficiently: (1) dendrimers with two generations in three steps and (2) dendrimers with two generations containing one kind of internal functional group and two kinds of surface functional groups in five steps. This new synthetic method offers an efficient access to dendrimers with structural diversity.

Dendrimer-surfactant interactions

In this article, we reviewed the interactions between dendrimers and surfactants with particular focus on the interaction mechanisms and physicochemical properties of the yielding dendrimer-surfactant aggregates. In order to provide insight into the behavior of dendrimers in biological systems, the interactions of dendrimers with bio-surfactants such as phospholipids in bulk solutions, in solid-supported bilayers and at the interface of phases or solid-states were discussed. Applications of the dendrimer-surfactant aggregates as templates to guide the synthesis of nanoparticles and in drug or gene delivery were also mentioned.

Dendritic architectures based on bis-MPA: functional polymeric scaffolds for application-driven research

Dendritic polymers are highly branched, globular architectures with multiple representations of functional groups. These nanoscale organic frameworks continue to fascinate researchers worldwide and are today under intensive investigation in application-driven research. A large number of potential application areas have been suggested for dendritic polymers, including theranostics, biosensors, optics, adhesives and coatings. The transition from potential to real applications is strongly dictated by their commercial accessibility, scaffolding ability as well as biocompatibility. A dendritic family that fulfills these requirements is based on the 2,2-bismethylolpropionic acid (bis-MPA) monomer. This critical review is the first of its kind to cover most of the research activities generated on aliphatic polyester dendritic architectures based on bis-MPA. It is apparent that these scaffolds will continue to be in the forefront of cutting-edge research as their structural variations are endless including dendrons, dendrimers, hyperbranched polymers, dendritic-linear hybrids and their hybridization with inorganic surfaces.

Benzylic viologen dendrimers: a review of their synthesis, properties and applications

Dendrimers containing benzylic viologen branching units, their guest complexation, photophysical and biological applications has been reviewed.

“Onion peel” dendrimers: a straightforward synthetic approach towards highly diversified architectures

We report herein a novel “onion peel strategy” for the divergent construction of glycodendrimers using different building blocks at each layer of the dendritic growth.

Rapid, semi-automated convergent synthesis of low generation triazine dendrimers using microwave assisted reactions

Microwave assisted synthesis allows for the rapid access of low generation triazine dendrimers in high yields.

Reactive imidazole intermediates: simplified synthetic approach to functional aliphatic cyclic carbonates

Reactive imidazole intermediates based on AB₂ and A₃ monomers, i.e. bis(methylol) propionic acid (bis-MPA) and trimethylolpropane (TMP) have successfully been synthesized and isolated on a 100 gram scale via a facile synthetic protocol using 1,1′-carbonyldiimidazole (CDI) as a key reagent.

The first peripherally masked thiol dendrimers: a facile and highly efficient functionalization strategy of polyester dendrimers via one-pot xanthate deprotection/thiol–acrylate Michael addition reactions

We present the first xanthate surface functional dendrimers which undergo rapid one-pot deprotection to thiols and subsequent acrylate Michael addition .

Bis(benzylamine) monomers: One-pot preparation and application in dendrimer scaffolds for removing pyrene from aqueous environments

Bisimine and bisamine AB₂ monomers have been synthesized from 3,5-diaminobenzoic acid and benzaldehyde derivatives without the need for protective groups or purification. This monomer preparation is universal for various electron-donating and electron-withdrawing benzaldehyde substrates. To demonstrate the versatility of these previously unreported AB₂ monomers in the formation of high molecular weight structures, novel first-generation dendrimers and hybrid second-generation dendrimers have been synthesized. Using fluorescence spectroscopy, pyrene was shown to be removed from an aqueous environment upon exposure to thin dendrimer films, with the first-generation dendrimer removing 70% of the pyrene within 30 min and the hybrid second-generation dendrimers removing 38–52%. Inclusion formation constants were calculated to be on the order of 10⁹–10¹¹ M⁻¹ and are comparable to the values of previously reported macromolecules. These results illustrate that size may not influence pyrene removal as effectively as composition.

Dendrimers with large nonlinear optical performance by introducing isolation chromophore, utilizing the Ar/ArF self-assembly effect, and modifying the topological structure

By the combination of divergent and convergent approach, a new series of NLO dendrimers (G1-PFPh-NS-GL to G3-PFPh-NS-GL) was conveniently prepared with satisfied yields through the powerful "click chemistry" reaction, in which perfluoroaromatic rings were introduced in the periphery, two types of chromophores were arranged with regular AB structure, and their topological structure was improved to a more spherical shape. All the dendrimers demonstrated good processability, and G1-PFPh-NS-GL exhibited the highest NLO effect of 221 pm/V among the three dendrimers.

Theoretical and computational studies of dendrimers as delivery vectors

It is a great challenge for nanomedicine to develop novel dendrimers with maximum therapeutic potential and minimum side-effects for drug and gene delivery. As delivery vectors, dendrimers must overcome lots of barriers before delivering the bio-agents to the target in the cell. Extensive experimental investigations have been carried out to elucidate the physical and chemical properties of dendrimers and explore their behaviors when interacting with biomolecules, such as gene materials, proteins, and lipid membranes. As a supplement of the experimental techniques, it has been proved that computer simulations could facilitate the progress in understanding the delivery process of bioactive molecules. The structures of dendrimers in dilute solutions have been intensively investigated by monomer-resolved simulations, coarse-grained simulations, and atom-resolved simulations. Atomistic simulations have manifested that the hydrophobic interactions, hydrogen-bond interactions, and electrostatic attraction play critical roles in the formation of dendrimer-drug complexes. Multiscale simulations and statistical field theories have uncovered some physical mechanisms involved in the dendrimer-based gene delivery systems. This review will focus on the current status and perspective of theoretical and computational contributions in this field in recent years. (275 references).

Extending the limits of precision polymer synthesis: giant polyphenylene dendrimers in the megadalton mass range approaching structural perfection

The catalyst-free Diels-Alder synthesis of polyphenylene dendrimers with a chromophore core has now been demonstrated to achieve the seventh to ninth generations upon divergent growth. Since standard analytical tools such as size-exclusion chromatography do not provide realistic molecular weights, MALDI-TOF mass spectrometry was applied to characterize the complete series of nine generations. Perfection and monodispersity were thus elucidated at such high masses. Transmission electron microscopy imaging was used to determine the size of these molecularly defined nanosized "particles" with diameters of up to 33 nm.

Dendrimer and cancer: a patent review (2006-present)

INTRODUCTION

Dendrimers were widely used in cancer diagnosis and therapy during the past decade. The surface functionalities allow bioactive molecules such as imaging probes, therapeutic compounds, targeting ligands to be present on dendrimer surface in a multivalent fashion. In addition, the interior pockets as well as the charged surface of dendrimer can be encapsulated/bound with anti-cancer drugs or therapeutic DNAs/siRNAs.

AREAS COVERED

The combination of dendrimer chemistry and new cancer therapy techniques such as radiotherapy, photodynamic therapy, neuron capture therapy, and photothermal therapy provides promising strategies in future cancer therapy. Here, we focused on recent advances on this topic in the patents (2006 - present) and discussed the advantages of dendrimer technology in these inventions.

EXPERT OPINION

The challenges and perspectives of dendrimer-based theranostics for cancer diagnosis and therapy are discussed. Future efforts in this area should be focused on designing materials to solve problems such as cancer metastasis, multidrug resistance (MDR) in cancer cells, and early-stage cancer diagnosis.

Use of Nanotechnology to Develop Multi-Drug Inhibitors For Cancer Therapy

Therapeutic agents that inhibit a single target often cannot combat a multifactorial disease such as cancer. Thus, multi-target inhibitors (MTIs) are needed to circumvent complications such as the development of resistance. There are two predominant types of MTIs, (a) single drug inhibitor (SDIs) that affect multiple pathways simultaneously, and (b) combinatorial agents or multi-drug inhibitors (MDIs) that inhibit multiple pathways. Single agent multi-target kinase inhibitors are amongst the most prominent class of compounds belonging to the former, whereas the latter includes many different classes of combinatorial agents that have been used to achieve synergistic efficacy against cancer. Safe delivery and accumulation at the tumor site is of paramount importance for MTIs because inhibition of multiple key signaling pathways has the potential to lead to systemic toxicity. For this reason, the development of drug delivery mechanisms using nanotechnology is preferable in order to ensure that the MDIs accumulate in the tumor vasculature, thereby increasing efficacy and minimizing off-target and systemic side effects. This review will discuss how nanotechnology can be used for the development of MTIs for cancer therapy and also it concludes with a discussion of the future of nanoparticle-based MTIs as well as the continuing obstacles being faced during the development of these unique agents.’