Terminal Azide Research Articles

New polynitrogen hyperbranched polymers

A method for the preparation of new representatives of polynitrogen hyperbranched polymers of heterocyclic series was developed involving polymerization of monomeric 2,4-diazido-6-propynyloxy-1,3,5-triazine by 1,3-dipolar cycloaddition. Kinetics of polymerization of diazidoacetylene monomer was compared with the kinetic data of polymerization of its closest analog, 2-azido-4,6-bis(propynyloxy)-1,3,5-triazine monomer. Properties of hyperbranched poly(1,2,3-triazole-1,3,5-triazine)s with terminal azide groups and terminal triple bonds were compared, as well.

Coiled Coil Peptides as Universal Linkers for the Attachment of Recombinant Proteins to Polymer Therapeutics

We have designed, synthesized, and characterized peptides containing four repeats of the sequences VAALEKE (peptide E) or VAALKEK (peptide K). While the peptides alone adopt in aqueous solutions a random coil conformation, their equimolar mixture forms heterodimeric coiled coils as confirmed by CD spectroscopy. 5-Azidopentanoic acid was connected to the N-terminus of peptide E via a short poly(ethylene glycol) spacer. The terminal azide group enabled conjugation of the peptide with a synthetic drug carrier based on the N-(2-hydroxypropyl)methacrylamide copolymer containing propargyl groups using "click" chemistry. When incorporated into the polymer drug carrier, peptide E formed a stable noncovalent complex with peptide K belonging to a recombinant single-chain fragment (scFv) of the M75 antibody. The complex thereby mediates a noncovalent linkage between the polymer drug carrier and the protein. The recombinant scFv antibody fragment was selected as a targeting ligand against carbonic anhydrase IX-a marker overexpressed by tumor cells of various human carcinomas. The antigen binding affinity of the polymer-scFv complex was confirmed by ELISA. This approach offers a well-defined, specific, and nondestructive universal method for the preparation of protein (antibody)-targeted polymer drug and gene carriers designed for cell-specific delivery.

Click to Join Peptides/Proteins Together

Copper(I) is able to catalyze Huisgen 1,3-dipolar cycloaddition in a "click" fashion. This copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction presents excellent chemoselectivity and occurs over a wide-range of reaction conditions. It shows tolerance to variation in both pH and solvent polarity, thereby facilitating the ligation of peptides and proteins to produce peptidomimetics and synthetic proteins. In addition, the only product formed is a 1,4-disubstituted-1,2,3-triazole moiety, in many aspects resembling the natural peptide bond, including hydrogen-bonding capability, planarity, distance between the 1 and 4 substituents, and conformational restriction of the peptide backbone; thus the triazole-backbone-modified peptide, in which a triazole replaces the amide bond, may be anticipated to present a secondary structure similar to that of its natural counterpart. This Focus Review describes the scope and applications of copper(I)-catalyzed alkyne–azide cycloaddition in synthetic peptide/protein chemistry.

Dendritic surface functionalization of biodegradable polymer assemblies

The functionalization of nanomaterials with dendritic surface moieties was recently demonstrated to be an effective means of displaying biological ligands and potentially modulating the biological properties of these materials. With the aim of extending this surface functionalization approach to biodegradable polymer assemblies, poly(ethylene oxide)-polycaprolactone (PEO-PCL) block copolymers with terminal azide or methoxy groups were prepared and were assembled to form micelles or vesicles with varying loadings of surface azides. Dendrons bearing peripheral amines, guanidines, or hydroxyls were prepared and conjugated to the assemblies, and the conjugation yields were measured and compared as a function of azide loading and assembly type (micelle versus vesicle). A small molecule rhodamine derivative was also conjugated, allowing the effect of sterics to be studied. The effects of the surface functionalization on the aggregation state of the assemblies were studied by light scattering and transmission electron microscopy. Overall, the results revealed interesting differences between the two systems with respect to both the reaction yields and the stabilities. Furthermore, micelles functionalized with dendrons bearing peripheral guanidines were found to exhibit enhanced cell uptake relative to control micelles, demonstrating that this approach can be used to modulate the biological properties of the materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

ChemInform Abstract: Three‐Component Assembly and Divergent Ring‐Expansion Cascades of Functionalized 2‐Iminooxetanes.

AbstractReactions of α‐keto esters with N‐sulfonylketimines, prepared in situ from terminal alkynes and azide (III), proceeds via 2‐iminooxetane intermediates such as (VII) which are transformed into maleimide derivatives or 5‐iminopyrrolidinones.

Bis(2-amino-1,3-thia-zole-κN)diazido-zinc.

In the title complex, [Zn(N3)2(C3H4N2S)2], the ZnII atom is tetra­hedrally coordinated by two terminal azide ligands and by the ring N atoms of two different 2-amino­thia­zole ligands. Intra­molecular N—H⋯N hydrogen bonds between the amino groups of both 2-amino­thia­zole ligands and the N atom of one of the azide ligands ensure that the heterocyclic rings are oriented in the same direction. Inter­molecular N—H⋯N hydrogen bonds link the mol­ecules into zigzag sheets in the ac plane.

Hyaluronic Acid-Based Hydrogels Crosslinked by Copper-Catalyzed Azide-Alkyne Cycloaddition with Tailorable Mechanical Properties

Biopolymers of the extracellular matrix are attractive starting materials for providing degradable and biocompatible biomaterials. In this study, hyaluronic acid-based hydrogels with tunable mechanical properties were prepared by the use of copper- catalyzed azide-alkyne cycloaddition (known as "click chemistry"). Alkyne-functionalized hyaluronic acid was crosslinked with linkers having two terminal azide functionalities, varying crosslinker density as well as the lengths and rigidity of the linker molecules. By variation of the crosslinker density and crosslinker type, hydrogels with elastic moduli in the range of 0.5-4 kPa were prepared. The washed materials contained a maximum of 6.8 mg copper per kg dry weight and the eluate of the gel crosslinked with diazidostilbene did not show toxic effects on L929 cells. The hyaluronic acid-based hydrogels have potential as biomaterials for cell culture or soft tissue regeneration applications.

Clickable molecularly imprinted nanoparticles

Terminal alkynyl and azide groups are introduced on the surface of molecularly imprinted core-shell nanoparticles using precipitation polymerization. These clickable groups enable simple nanoparticle conjugation and surface modification under mild reaction conditions, opening new opportunities for nanoparticle-based assays and chemical sensing.

Rhodamine-B decorated superparamagnetic iron oxide nanoparticles: preparation, characterization and their optical/magnetic properties

The paper reports on covalent clicking of rhodamine-B (RhB) bearing a terminal azide group to alkyne-terminated silica coated superparamagnetic iron oxide nanoparticlesvia the copper(I)-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction. The course of the reaction was followed the use of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, fluoroscopy, and magnetics. The RhB labelled Fe3O4@SiO2 nanoparticles exhibit stable fluorescence and no detectable leakage of the fluorescent dye because the resulting 1,4-disubstituted 1,2,3-triazole ring formed via click reaction is thermally stable and relatively inert to hydrolysis, oxidation, and reduction. Due to the superparamagnetic property of the Fe3O4 and the RhB molecule covalently decorated in the Fe3O4@SiO2 framework, the nanoparticles are endowed with properties of a contrast agent in magnetic resonance imaging (MRI) and optical imaging modality. The cytotoxicity tests indicate the bifunctional nanoparticles could be applied in biomedical or bioengineering field.

Syntheses, structures, and properties of two mononuclear cobalt(III) azido complexes containing a tetradentate N-donor Schiff base as end-capping ligand

Two hexacoordinated mononuclear Co(III) compounds of the type cis-[Co(L)(N3)2] X [1, X = ClO4; 2, X = PF6; L = N,N′-(bis(pyridine-2-yl)benzylidine)-1,4-butanediamine] have been synthesized and characterized by physicochemical and spectroscopic methods. The crystal structures of complexes 1 and 2 both have distorted octahedral geometry with two terminal azides in mutual cis orientations. In the crystalline state, two mononuclear units of 1 are associated by weak C–H…π interactions to produce a dimeric unit, which packs through C–H…O hydrogen bonds and π…π interactions leading to a 2-D continuum. The mononuclear units in 2 are engaged in weak cooperative intermolecular C–H…π interactions and multiple C–H…F hydrogen bonds giving rise to a 3-D network structure. These diamagnetic compounds are redox active and show luminescence in DMF solutions.

Three‐Component Assembly and Divergent Ring‐Expansion Cascades of Functionalized 2‐Iminooxetanes

Reactions of α-keto esters with N-sulfonylketimines, prepared in situ from terminal alkynes and azide (III), proceeds via 2-iminooxetane intermediates such as (VII) which are transformed into maleimide derivatives or 5-iminopyrrolidinones.

Synthesis of biodegradable multiblock copolymers by click coupling of RAFT-generated heterotelechelic polyHPMA conjugates

A new strategy for the synthesis of biodegradable high molecular weight N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymeric carriers has been designed. An enzyme-sensitive, alkyne-functionalized, chain transfer agent (CTA-GFLG-alkyne; N α -(4-pentynoyl)- N δ -(4-cyano-4-(phenylcarbonothioylthio)pentanoyl–glycylphenylalanylleucylglycyl)-lysine) was synthesized and used to mediate the reversible addition–fragmentation chain transfer (RAFT) polymerization and copolymerization of HPMA. Post-polymerization modification with 4,4′-azobis(azidopropyl 4-cyanopentanoate) resulted in the formation of heterotelechelic HPMA copolymers containing terminal alkyne and azide groups. Chain extension via click reaction resulted in high molecular weight multiblock copolymers. Upon exposure to papain, these copolymers degraded into the initial blocks. Similar results were obtained for copolymers of HPMA with N-methacryloylglycylphenylalanylleucylglycyl thiazolidine-2-thione and N-methacryloylglycylphenylalanylleucylglycyl-gemcitabine. The new synthetic method presented permits the synthesis of biocompatible, biodegradable high molecular weight HPMA copolymer–anticancer drug conjugates that possess long-circulation times and augmented accumulation in solid tumor tissue due to the enhanced permeability and retention effect.

Effect of water addition on the coupling of homopolymers by click chemistry

Homopolymers bearing terminal azide and alkyne groups can be coupled via click chemistry to yield diblock copolymers. When performed in solvents that dissolved both homopolymers, the click reaction was found in this study to be inefficient, probably due to the embedding of the reactive end groups inside the random coils of the polymers. The efficiency was only slightly affected by the addition of a small amount of water into the reaction mixture. However, the reaction efficiency increased dramatically near the water volume fraction where one or both of the reacting polymers began to precipitate. Further increases in water content caused the polymer(s) to undergo macroscopic phase separation and the click reaction efficiency decreased once again. A possible explanation for the observed effect of water on the polymer coupling reaction is proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Spectroscopic Characterization and Competitive Inhibition Studies of Azide Binding to a Functional NOR Model

AbstractAzide binding to a functional nitric oxide reductase (NOR) model has been investigated in its mixed‐valence (LFeIIIFeII and LFeIIFeIII) and fully oxidized (LFeIIIFeIII) forms. FTIR and EPR spectroscopic methods indicate that azide binds in a bridging mode between the heme iron and the non‐heme iron sites. Terminal azide binding at both heme and non‐heme centers is also identified with the reactions of azide and the dinuclear compounds LFeIII/ZnII and LZnII/FeIII: the bound azide at the ferric heme center exhibits a vibrational frequency at 2007 cm–1 in the FTIR, while the bound azide at the ferric non‐heme site shows a band at 2055 cm–1. The reactivity of nitric oxide with the model compounds in the presence of excess azide was investigated. It is demonstrated that azide does not inhibit NO binding to the fully reduced catalyst but binds the FeB tightly in both the mixed‐valence and the fully oxidized states. These results further support the proposal that a bis‐ferrous instead of a mixed‐valence state is the active form of NOR.

ChemInform Abstract: And If Everything Was as Easy as a “Click”: Cu(I)‐Catalyzed 1,3‐Dipolar Cycloaddition Between Terminal Alkynes and Azides

AbstractReview: 27 refs.

Uranium azide photolysis results in C–H bond activation and provides evidence for a terminal uranium nitride

Uranium nitride [U[triple bond]N](x) is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U[triple bond]N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U[triple bond]N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C(6)F(5))(3). These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

Systems Analysis of Protein Modification and Cellular Responses Induced by Electrophile Stress

Biological electrophiles result from oxidative metabolism of exogenous compounds or endogenous cellular constituents, and they contribute to pathophysiologies such as toxicity and carcinogenicity. The chemical toxicology of electrophiles is dominated by covalent addition to intracellular nucleophiles. Reaction with DNA leads to the production of adducts that block replication or induce mutations. The chemistry and biology of electrophile−DNA reactions have been extensively studied, providing in many cases a detailed understanding of the relation between adduct structure and mutational consequences. By contrast, the linkage between protein modification and cellular response is poorly understood.In this Account, we describe our efforts to define the chemistry of protein modification and its biological consequences using lipid-derived α,β-unsaturated aldehydes as model electrophiles. In our global approach, two large data sets are analyzed: one represents the identity of proteins modified over a wide range of electrophile concentrations, and the second comprises changes in gene expression observed under similar conditions. Informatics tools show theoretical connections based primarily on transcription factors hypothetically shared between the two data sets, downstream of adducted proteins and upstream of affected genes. This method highlights potential electrophile-sensitive signaling pathways and transcriptional processes for further evaluation.Peroxidation of cellular phospholipids generates a complex mixture of both membrane-bound and diffusible electrophiles. The latter include reactive species such as malondialdehyde, 4-oxononenal, and 4-hydroxynonenal (HNE). Enriching HNE-adducted proteins for proteomic analysis was a technical challenge, solved with click chemistry that generated biotin-tagged protein adducts. For this purpose, HNE analogues bearing terminal azide or alkyne functionalities were synthesized. Cellular lysates were first exposed to a single type of HNE analogue (azido- or alkynyl-HNE), and then click reactions were performed against the cognate alkynyl- and azido-biotin derivative. The resulting biotin-labeled proteins were captured and enriched over a streptavidin matrix for subsequent mass spectrometric analysis. We thereby identified a multitude of HNE targets. Simultaneous microarray analysis of changes in gene expression triggered by HNE also produced an abundance of data. Functional analysis of both data sets generated the hypothesis that an important pathway of cellular response derives from electrophile modification of protein chaperones, resulting in the release of transcription factors that are their clients. Informatic analysis of the protein modification and microarray data sets identified several transcription factors as potential mediators of the cellular response to HNE-adducted proteins. Among these, heat shock factor 1 (HSF1) was confirmed as a sensitive and robust effector of HNE-induced changes in gene expression. Activation of HSF1 appears, in part, to be mediated by the electrophilic adduction of Hsp70 and Hsp90, which normally maintain HSF1 in an inactive cytosolic complex.The identification of HSF1 as a mediator of biological effects downstream of HSF1 has provided new opportunities for research, illustrating the potential of our systems-based approach. Accordingly, we characterized HSF1-mediated gene expression in protecting against electrophile-induced toxicity. Among the genes induced by HSF1, Bcl-2- associated athanogene 3 (BAG3) is notable for its actions in promoting cell survival through stabilization of antiapoptotic Bcl-2 proteins, appearing to have a critical role in mediating cellular protection against electrophile-induced death.

Synthesis, molecular and crystalline architectures, and properties of novel bis(bidentate) and bis(tridentate) Schiff base bridged dinuclear mercury(II)pseudohalides: Control of coordination numbers by varying denticities

A tetracoordinated [Hg 2(L 1)(SCN) 4] ( 1) [L 1 = N,N′-(bis-(pyridin-2-yl)benzylidene)-1,2-ethanediamine] and two pentacoordinated [Hg 2(L 2)(X) 4] [L 2 = N-((1-pyridin-2-yl)formylidene)-N′-[2-(4-{2-[((1-pyridin-2-yl)formylidene) amino]ethyl}piperazin-1-yl)ethyl]amine; X = N 3 - , ( 2) and X = NCS −, ( 3)] dinuclear mercury(II) compounds have been prepared and characterized using microanalytical, spectroscopic, thermal and X-ray crystallographic results. Structural analyses reveal bis(bidentate) congregation behaviour of classical tetradentate L 1 and bis(tridentate) character of L 2 encapsulating two metal centers. Each mercury(II) center in 1 is in a distorted tetrahedral coordination environment with HgN 2S 2 chromophore. Hg(1) is attached with two N atoms of L 1 and two S atoms of two terminal thiocyanates whereas neighbouring Hg(1) is ligated to the other two N donor set of the same Schiff base completing its bis(bidentate) mode and two S atoms of thiocyanates. In 2 and 3 each mercury(II) center adopts a distorted square pyramidal geometry with MN 5 (in 2) and MN 3S 2 (in 3) chromophores and two metal(II) centers are encapsulated by bis(tridentate) congregation behaviour of L 2 through donation of three N donor set to each metal and the fourth and fifth positions are occupied by two N atoms of terminal azides in 2 and two S atoms of terminal thiocyanates in 3. In solid-state, dinuclear units of 1 pack through cooperative C–H⋯N and C–H⋯S hydrogen bonds and C–H⋯π interactions giving rise to a 3D network. Individual dinuclear units of 2 and 3 self-assemble through cooperative C–H⋯N hydrogen bondings and C–H⋯π interactions affording 3D network structure and 2D continuum, respectively. In DMF solutions at room temperature all the complexes display high-energy intraligand 1(π–π∗) fluorescence.

The application of CuAAC ‘click’ chemistry to catenane and rotaxane synthesis

The copper(I)-catalysed azide-alkyne cycloaddition (the CuAAC 'click' reaction) is proving to be a powerful new tool for the construction of mechanically interlocked molecular-level architectures. The reaction is highly selective for the functional groups involved (terminal alkynes and azides) and the experimental conditions are mild and compatible with the weak and reversible intermolecular interactions generally used to template the assembly of interlocked structures. Since the CuAAC reaction was introduced as a means of making rotaxanes by an 'active template' mechanism in 2006, it has proven effective for the synthesis of numerous different types of rotaxanes, catenanes and molecular shuttles by passive as well as active template strategies. Mechanistic insights into the CuAAC reaction itself have been provided by unexpected results encountered during the preparation of rotaxanes. In this tutorial review we highlight the rapidly increasing utility and future potential of the CuAAC reaction in mechanically interlocked molecule synthesis.

Miktoarm core-crosslinked star copolymers with biologically active moieties on peripheries

Miktoarm core-crosslinked star (CCS) copolymers featuring hydrophobic inner compartment based on poly(e-caprolactone) (PCL), and hydrophilic multivalent exterior consisting of L-lysine dendritic wedges and estradiol or ferrocene moieties have been synthesized. Ring-opening polymerization (ROP) of e-caprolactone (e-CL) initiated by functional alcohols provides alkyne or azide end-capped linear PCL chains. Further derivatization of the hydroxyl chain ends of these hetero-telechelic macromolecules by methacrylic acid (MA), and subsequent Cu(I) mediated “click” coupling of terminal alkyne and azide groups with azide-functionalized dendritic wedge, 17α-ethynylestradiol and ethynylferrocene afford well-defined linear-dendritic and linear macromonomers (MMs), respectively. Atom transfer radical polymerization (ATRP) of the MMs together with a difunctional monomer 1,4-butanediol dimethacrylate (BDMA) results in miktoarm CCS copolymers. Elucidation of the structure and composition of the intermediate and final products demonstrates effectiveness, versatility, and high degree of control displayed by the proposed synthetic sequence.