Synthesis of DOTA-conjugated multivalent cyclic-RGD peptide dendrimers via 1,3-dipolar cycloaddition and their biological evaluation: implications for tumor targeting and tumor imaging purposes

This report describes the design and synthesis of a series of alpha(V)beta(3) integrin-directed monomeric, dimeric and tetrameric cyclo[Arg-Gly-Asp-d-Phe-Lys] dendrimers using "click chemistry". It was found that the unprotected N-epsilon-azido derivative of cyclo[Arg-Gly-Asp-d-Phe-Lys] underwent a highly chemoselective conjugation to amino acid-based dendrimers bearing terminal alkynes using a microwave-assisted Cu(I)-catalyzed 1,3-dipolar cycloaddition. The alpha(V)beta(3) binding characteristics of the dendrimers were determined in vitro and their in vivoalpha(V)beta(3) targeting properties were assessed in nude mice with subcutaneously growing human SK-RC-52 tumors. The multivalent RGD-dendrimers were found to have enhanced affinity toward the alpha(V)beta(3) integrin receptor as compared to the monomeric derivative as determined in an in vitro binding assay. In case of the DOTA-conjugated (111)In-labeled RGD-dendrimers, it was found that the radiolabeled multimeric dendrimers showed specifically enhanced uptake in alpha(V)beta(3) integrin expressing tumors in vivo. These studies showed that the tetrameric RGD-dendrimer had better tumor targeting properties than its dimeric and monomeric congeners.

A triazole-templated ring-closing metathesis for constructing novel fused and bridged triazoles

The feasibility of trapping the vinyl copper intermediate generated in situ from azide-[3 + 2] cycloadditions and viability of employing these triazoles as unique templates for ring-closing metathesis are described here; this work effectively combines the two powerful reactions for the first time to construct various de novo fused and bridged triazoles that are otherwise not trivial to synthesize.

Recent applications of the CuI-catalysed Huisgen azide–alkyne 1,3-dipolar cycloaddition reaction in carbohydrate chemistry

This article surveys recent applications of Cu(I)-catalysed 1,3-dipolar cycloaddition of azides and alkynes in carbohydrate chemistry, highlighting developments in the preparation of simple glycoside and oligosaccharide mimetics, glyco-macrocycles, glycopeptides, glyco-clusters and carbohydrate arrays.

[3 + 2] Cycloaddition of acetylenes with azides to give 1,4-disubstituted 1,2,3-triazoles in a modular flow reactor

The cycloaddition of acetylenes with azides to give the corresponding 1,4-disubstituted 1,2,3-triazoles is reported using immobilised reagents and scavengers in pre-packed glass tubes in a modular flow reactor.

A new azide staining reagent based on “click chemistry”

A new staining reagent was prepared and its ability to stain several azide-containing agents on TLC plates was determined.

Click multivalent neoglycoconjugates as synthetic activators in cell adhesion and stimulation of monocyte/machrophage cell lines

The efficient synthesis of fluorescent and non-fluorescent multivalent neoglycoconjugates is described by means of the Cu(i) catalyzed azide-alkyne 1,3-dipolar cycloaddition ("click-chemistry"). A well-defined glycopolymer, glycocyclodextrin or glycocluster architecture displaying galactose or lactose epitopes has been chosen. Cellular assays using U-937 and RAW 264.7 monocyte/macrophage cells showed that these glycocompounds have the capability to act as synthetic activators mimicking the lipopolysaccharide (LPS) effects. Thus, the click compounds promote cell adhesion and stimulation of monocytes, measured as an increase in the amount of TNFalpha, facilitating their differentiation to macrophages.

Solid-phase based synthesis of jasplakinolide analogs by intramolecular azide–alkyne cycloadditions

The synthesis of a focused library of jasplakinolide analogs with a 1,2,3-triazole in place of an E-configured double bond is described, featuring the Cu(I) catalyzed azide-alkyne cycloaddition reaction as an efficient macrocyclization tool.

Clicking polymers: a straightforward approach to novel macromolecular architectures

Living/controlled polymerization techniques have enabled the synthesis of a large variety of different well-defined (co)polymer structures. In addition, the use of click chemistry in polymer science is a quickly emerging field of research since it allows the fast and simple creation of well-defined and complex polymeric structures in yields that were previously unattainable. In this critical review, the application of the azide-alkyne 1,3-dipolar cycloaddition for the construction of well-defined polymer architectures will be discussed in detail, providing a comprehensive overview for all disciplines related to polymeric materials.

Polymer-supported proline-decorated dendrons: dendritic effect in asymmetric aldol reaction

The yield and enantioselectivity of an asymmetric aldol reaction, catalyzed by a proline derivative immobilized on polystyrene via dipolar cycloaddition, are remarkably improved by the dendronization of the support.

1,2,3-Triazoles as peptide bond isosteres: synthesis and biological evaluation of cyclotetrapeptide mimics

Since the discovery of Cu(I)-catalysed click chemistry, the field of peptidomimetics has expanded to include 1,4-connected 1,2,3-triazoles as useful peptide bond isosteres. Here, we report the synthesis of triazole-containing analogues of the naturally occurring tyrosinase inhibitor cyclo-[Pro-Val-Pro-Tyr] and show that the analogues retain enzyme inhibitory activity, demonstrating the effectiveness of a 1,4-connected 1,2,3-triazole as a trans peptide bond isostere.

The growing applications of click chemistry

Click chemistry, the subject of this tutorial review, is a modular synthetic approach towards the assembly of new molecular entities. This powerful strategy relies mainly upon the construction of carbon-heteroatom bonds using spring-loaded reactants. Its growing number of applications are found in nearly all areas of modern chemistry from drug discovery to materials science. The copper(I)-catalysed 1,2,3-triazole forming reaction between azides and terminal alkynes has become the gold standard of click chemistry due to its reliability, specificity and biocompatibility.

Synthesis of Functional Derivatives of 7,8-Dicarba-nido-undecaborate Anion by Ring-Opening of Its Cyclic Oxonium Derivatives

A new approach to synthesis of functional derivatives of 7,8-dicarba-nido-undecaborate anion based on ring-opening of its cyclic oxonium derivatives [10-(CH2)4O-7,8-C2B9H11] and [10-O(CH2CH2)2O-7,8-C2B9H11] with various nucleophiles was developed. Both cyclic oxonium derivatives can be obtained as single isomers by reaction of the parent anion [7,8-C2B9H12]- with mercury(II) chloride in the corresponding solvents. Mechanism of formation of the cyclic oxonium derivatives of 7,8-dicarba-nido-undecaborate anion was proposed. A series of 7,8-dicarba-nido-undecaborate derivatives with terminal carboxylic and azide functions were prepared by the ring-opening reactions of the cyclic oxonium derivatives with substituted phenolate and azide ions, respectively.

Poly(vinyl alcohol)-graft-poly(ethylene glycol) resins and their use in solid-phase synthesis and supported TEMPO catalysis

New poly(vinyl alcohol)-graft-poly(ethylene glycol) (PVA-g-PEG) resins with various PEG chain lengths, which have high loadings and good swelling both in water and organic solvents, have been prepared via an anionic polymerization of ethylene oxide onto PVA beads and applied in solid-phase synthesis, supported TEMPO catalysis and in HR-MAS 1H NMR spectral analysis.

Improved Protocols for Microwave-Assisted Cu(I)-Catalyzed Huisgen 1,3-Dipolar Cycloadditions

The Huisgen 1,3-dipolar cycloaddition of azides and acetylenes catalyzed by Cu(I) salts, leading to 1,2,3-triazoles, is one of the most versatile "click reactions". We have developed a series of optimized protocols and new applications of this reaction starting from several substrates, comparing heterogeneous vs homogeneous catalysis, conventional heating vs microwave irradiation or simultaneous microwave/ultrasound irradiation. Both non-conventional techniques strongly promoted the cycloaddition (bromide → azide → triazole), that could be conveniently performed in a one-pot procedure. This was feasible even with such bulky molecules as functionalized β-cyclodextrins (β-CD), starting from 61-O-tosyl-β-CD or from heptakis[6-O-(tert-butyldimethylsilyl)]-21-O-propargyl-β-CD. "Greener" heterogeneous catalysis with charcoal-supported Cu(II) or Cu(I) (prepared under ultrasound) was advantageously employed.

Peptidomimetics via copper-catalyzed azide–alkyne cycloadditions

This critical review concerns the impact of copper-mediated alkyne-azide cycloadditions on peptidomimetic studies. It discusses how this reaction has been used to insert triazoles into peptide chains, to link peptides to other functionalities (e.g. carbohydrates, polymers, and labels), and as a basis for evolution of less peptidic compounds as pharmaceutical leads. It will be of interest to those studying this click reaction, peptidomimetic secondary structure and function, and to medicinal chemists.

“Click” 1,2,3-triazoles as tunable ligands for late transition metal complexes

The potential of "click" 1,2,3-triazoles to act as mono-dentate ligands in late transition metal complexes is explored relative to other commonly-used Lewis bases and it is shown that their coordination strength, determined by their 1- and 4-substituents, is easily tunable.

Synthesis of bitriazolyl nucleosides and unexpectedly different reactivity of azidotriazole nucleoside isomers in the Huisgen reaction

Novel bitriazolyl nucleosides were synthesized via the Huisgen reaction, starting with 3-azidotriazole nucleoside (1). Surprisingly, its isomer, 5-azidotriazole nucleoside (1') did not yield the corresponding Huisgen reaction products efficiently because it was rapidly reduced to amine in the presence of Cu(II)-ascorbate. The significant differences between the reactivity of these two isomers in Cu(II)-ascorbate mediated reactions are mainly due to differences in their electronic properties and steric congestion as a result of different relative positions of the azido and the ribosyl moieties.

Click chemistry as a route to cyclic tetrapeptide analogues: synthesis of cyclo-[Pro-Val-psi(triazole)-Pro-Tyr]

Despite the plethora of techniques to cyclize small peptides, a synthesis of cyclo-[(L)Pro-(L)Tyr-(L)Pro-(L)Val], a potent tyrosinase inhibitor, remains elusive because of the unfavorable transition state leading to the cyclic product. Herein, we report the successful synthesis of its triazole analogue, cyclo-[(L)Pro-(L)Val-psi(triazole)-(L)Pro-(L)Tyr]. Attempted cyclization via peptide bond formation at room temperature fails to provide the desired product, but Cu(I)-catalyzed alkyne-azide coupling at 110 degrees C affords the triazole tetrapeptide in 70% yield, demonstrating the utility of "click" chemistry.

A convergent synthesis of new beta-turn mimics by click chemistry

Alkyne-azide cycloaddition ("click" chemistry) between two peptide strands derivatized with terminal azide and alkyne, respectively, provides an efficient convergent synthesis of triazole ring-based new beta-turn mimics.