Showing papers on "Click chemistry published in 2013"

Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology.

Abstract: Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States

Click to release: instantaneous doxorubicin elimination upon tetrazine ligation.

Abstract: Eliminated without a trace: The fastest click reaction, the highly selective inverse-electron-demand Diels-Alder reaction, has been modified to enable selective bioorthogonal release. Thus, the click reaction of a tetrazine with a drug-bound trans-cyclooctene caused the instantaneous release of the drug and CO2 (see scheme). One possible application is the chemically triggered release, and thereby activation, of a drug from a tumor-bound antibody-drug conjugate.

A general approach to DNA-programmable atom equivalents

Abstract: Nanoparticles can be combined with nucleic acids to programme the formation of three-dimensional colloidal crystals where the particles' size, shape, composition and position can be independently controlled. However, the diversity of the types of material that can be used is limited by the lack of a general method for preparing the basic DNA-functionalized building blocks needed to bond nanoparticles of different chemical compositions into lattices in a controllable manner. Here we show that by coating nanoparticles protected with aliphatic ligands with an azide-bearing amphiphilic polymer, followed by the coupling of DNA to the polymer using strain-promoted azide-alkyne cycloaddition (also known as copper-free azide-alkyne click chemistry), nanoparticles bearing a high-density shell of nucleic acids can be created regardless of nanoparticle composition. This method provides a route to a virtually endless class of programmable atom equivalents for DNA-based colloidal crystallization.

Bioorthogonal Click Chemistry: An Indispensable Tool to Create Multifaceted Cell Culture Scaffolds.

Abstract: Over the past decade, bioorthogonal click chemistry has led the field of biomaterial science into a new era of diversity and complexity by its extremely selective, versatile, and biocompatible nature. In this viewpoint, we seek to emphasize recent endeavors of exploiting this versatile chemistry toward the development of poly(ethylene glycol) hydrogels as cell culture scaffolds. In these cell-laden materials, the orthogonality of these reactions has played an effective role in allowing the creation of diverse biochemical patterns in complex biological environments that provide new found opportunities for researchers to delineate and control cellular phenotypes more precisely than ever.

(D)-Amino acid chemical reporters reveal peptidoglycan dynamics of an intracellular pathogen.

Abstract: Peptidoglycan (PG) is an essential component of the bacterial cell wall. Although experiments with organisms in vitro have yielded a wealth of information on PG synthesis and maturation, it is unclear how these studies translate to bacteria replicating within host cells. We report a chemical approach for probing PG in vivo via metabolic labeling and bioorthogonal chemistry. A wide variety of bacterial species incorporated azide and alkyne-functionalized d-alanine into their cell walls, which we visualized by covalent reaction with click chemistry probes. The d-alanine analogues were specifically incorporated into nascent PG of the intracellular pathogen Listeria monocytogenes both in vitro and during macrophage infection. Metabolic incorporation of d-alanine derivatives and click chemistry detection constitute a facile, modular platform that facilitates unprecedented spatial and temporal resolution of PG dynamics in vivo.

Two‐Color Glycan Labeling of Live Cells by a Combination of Diels–Alder and Click Chemistry

Abstract: Protein glycosylation is a complex form of posttranslational modification and has been shown to be crucial for the function of many proteins. Sialic acid is prominently positioned at the outer end of membrane glycoproteins. It plays a critical role for the regulation of a myriad of cellular functions and it forms a shield around the cell. Furthermore, it constantly interacts with the environment of cells and contributes to histocompatibility. This makes studying sialylation an interesting field of research, but monitoring sialic acid in vivo is challenging. While proteins are routinely labeled by genetic methods, such as expression as GFP fusion proteins, comparable methods are not available for secondary gene products, such as glycans of glycoconjugates. Metabolic oligosaccharide engineering (MOE) is a successful new strategy to visualize the localization of glycans in vitro and in vivo. In this approach, cells are cultivated in the presence of non-natural monosaccharide derivatives that carry a chemical reporter group and are nonetheless accepted by the biosynthetic machinery of a cell. For instance, peracetylated N-azidoacetylmannosamine (Ac4ManNAz) is taken up by the cell, deacetylated by cellular esterases, and owing to the promiscuity of the enzymes of sialic acid biosynthesis, is converted into N-azidoacetyl neuraminic acid and incorporated into sialoglycoconjugates. Once presented on the cell surface, the azide-containing sialylated glycan can be visualized through a bioorthogonal ligation reaction. Besides Ac4ManNAz, several monosaccharide derivatives of N-acetylgalactosamine, N-acetylglucosamine, and l-fucose are suitable for MOE providing further insights into the role of cellular structures and functions of glycans in the cell. Currently, mainly Staudinger ligation and azide–alkyne [3+2] cycloaddition (copper-catalyzed or strain-promoted, also known as the click reaction) are applied as ligation reactions in MOE. However, both of them rely on the reaction of azides and thus cannot be used for the concurrent detection of two different metabolically incorporated carbohydrates. A labeling strategy that can be carried out in the presence of azides and alkynes would significantly expand the scope of chemical labeling reactions in living cells and is thus highly desirable. Recently, it was shown that the Diels–Alder reaction with inverse electron demand (DARinv) of 1,2,4,5-tetrazines with strained dienophiles, such as trans-cyclooctenes, cyclobutenes, norbornenes, 13] cyclooctynes, and substituted cyclopropenes, fulfills the requirements of a bioorthogonal ligation reaction and furthermore is orthogonal to the azide–alkyne cycloaddition. However, these cyclic alkenes or kinetically stable tetrazines are expected to be too large for being efficiently metabolized by the sialic acid biosynthetic pathway, starting from the corresponding Nacylmannosamine derivative. In search for smaller dienophiles suitable for MOE, we identified monosubstituted (terminal) alkenes as a new class of chemical reporters. We recently reported the successful application of the DARinv between terminal alkenes and 1,2,4,5-tetrazines in the preparation of carbohydrate microarrays. The fact that terminal alkenes are hardly found in biological systems and are completely absent in proteins makes them a promising reporter group. Herein, we show that ManNAc derivatives containing a terminal alkene in the acyl side chain are metabolically incorporated into cell-surface sialic acids and can subsequently be labeled by the DARinv (Figure 1). Moreover, we demonstrate that double labeling of two differently modified, metabolically incorporated monosaccharides is possible by combining the DARinv with strainpromoted azide–alkyne cycloaddition (SPAAC). As the reaction rate of the DARinv of acyclic olefins with tetrazines is very sensitive to steric hindrance, double bonds with more than one substituent react very slowly. Terminal alkenes, on the other hand, can react rapidly without any further activation. This prompted us to design mannosamine derivatives 2 and 4 (Figure 2) that were synthesized in three steps from mannosamine hydrochloride (see the Supporting Information). Based on previous work by Keppler et al., we expected both derivatives to be accepted by cells with Npentenoylmannosamine 2 (owing to the shorter acyl side chain) being incorporated with higher efficiency. On the other [*] Dipl.-Chem. A. Niederwieser, M. Sc. A.-K. Sp te, M. Sc. C. J ngst, Prof. Dr. V. Wittmann University of Konstanz, Department of Chemistry and Konstanz Research School Chemical Biology (KoRS-CB) 78457 Konstanz (Germany) E-mail: mail@valentin-wittmann.de

Chemical Methods for Peptide and Protein Production

Abstract: Since the invention of solid phase synthetic methods by Merrifield in 1963, the number of research groups focusing on peptide synthesis has grown exponentially. However, the original step-by-step synthesis had limitations: the purity of the final product decreased with the number of coupling steps. After the development of Boc and Fmoc protecting groups, novel amino acid protecting groups and new techniques were introduced to provide high quality and quantity peptide products. Fragment condensation was a popular method for peptide production in the 1980s, but unfortunately the rate of racemization and reaction difficulties proved less than ideal. Kent and co-workers revolutionized peptide coupling by introducing the chemoselective reaction of unprotected peptides, called native chemical ligation. Subsequently, research has focused on the development of novel ligating techniques including the famous click reaction, ligation of peptide hydrazides, and the recently reported α-ketoacid-hydroxylamine ligations with 5-oxaproline. Several companies have been formed all over the world to prepare high quality Good Manufacturing Practice peptide products on a multi-kilogram scale. This review describes the advances in peptide chemistry including the variety of synthetic peptide methods currently available and the broad application of peptides in medicinal chemistry.

Silver‐Catalyzed Nitrogenation of Alkynes: A Direct Approach to Nitriles through CC Bond Cleavage

Abstract: The transformation of alkynes is a fundamental method that has been widely used in organic synthesis. Alkyne chemistry can be dated back to the early nineteenth century. The hydration of alkynes to ketones (Scheme 1a) and the addition reactions of alkynes (Scheme 1b) are early examples. Subsequently, various catalytic systems were developed. For example, the Pd-catalyzed Wacker-type oxidation to generate 1,2-diketones (Scheme 1c) is one of the most important industrial processes. The development of cyclization reactions such as click chemistry (Scheme 1d) has established new perspectives for the use of alkynes in drug discovery, materials science, supramolecular chemistry, polymer chemistry, and biotechnology. Furthermore, the coupling of terminal alkynes, such as the Sonogashira coupling (Scheme 1e), provides important methods for C C bond formation. The catalytic cleavage of C C bonds to produce carboxylic acids and new alkynes has also been disclosed (Scheme 1 f,g). Because of the significance and wide applications of such chemistry in organic synthesis, the exploration for new types of alkyne transformations is very attractive to researchers. Nitriles are one of the most common structural motifs in nature, and are versatile building blocks in the synthesis of natural products, pharmaceuticals, agricultural chemicals, materials, and dyes. Their importance in synthetic and medicinal chemistry has attracted considerable attention for the development of new synthetic strategies for these compounds. Azides have been widely used in organic reactions, but recent progress on the direct transformation of simple hydrocarbons into N-containing compounds through a nitrogenation strategy encouraged us to try the direct transformation of alkynes. Although metal-catalyzed C C bond cleavage involving alkyne metathesis has been disclosed, direct C C bond cleavage to form nitriles (Scheme 1h) is still unknown and remains both challenging and of great value. Herein, we report a novel and direct silver-catalyzed nitrogenation reaction of alkynes to nitriles through C C bond cleavage (Scheme 1h). The significance of the present chemistry is threefold: 1) It is the first example of a direct transformation from terminal alkynes to nitriles. 2) The application of selective C C bond cleavage in organic synthesis presents one of the most attractive and challenging projects. This chemistry provides a novel means of C C bond cleavage. 3) Compared to traditional gold salt p-acid catalysts, the silver catalyst plays a key role in this transformation. This research not only provides a new application for alkynes in organic synthesis, but also offers valuable mechanistic insights into this novel nitrogenation chemistry, which may promote the discovery of other new types of nitrogenation reactions for the construction of N-containing compounds. The initially investigated substrate for the direct nitrogenation of acetylenes was para-methoxy phenylacetylene. When the reaction is performed in the presence of Ag2CO3 using azidotrimethylsilane (TMSN3) as the nitrogen source, p-methoxy-benzonitrile (2a) was obtained in 58% yield (Table 1, entry 1). Reactions catalyzed by other transition metals, such as AuCl3, NiCl2, FeCl2, Cu(OAc)2, and Pd(OAc)2, either did not proceed or gave poor yields (Table 1, entries 2 and 3; see also the Supporting Information). Product 2a was obtained in 81% yield when DMSO was employed as the Scheme 1. Direct transformations of alkynes.

Functional Iron Oxide Magnetic Nanoparticles with Hyperthermia‐Induced Drug Release Ability by Using a Combination of Orthogonal Click Reactions

Abstract: Click and drug: A combination of orthogonal click reactions is employed for the preparation of functional iron oxide nanoparticles (IONPs) that show unprecedented hyperthermia-induced drug release through a magnetically stimulated retro-Diels-Alder (rDA) process. Magnetic stimulation induces sufficient local energy in close proximity to the cycloadduct to initiate the rDA process

Click Chemistry in Peptide-Based Drug Design

Abstract: Click chemistry is an efficient and chemoselective synthetic method for coupling molecular fragments under mild reaction conditions. Since the advent in 2001 of methods to improve stereochemical conservation, the click chemistry approach has been broadly used to construct diverse chemotypes in both chemical and biological fields. In this review, we discuss the application of click chemistry in peptide-based drug design. We highlight how triazoles formed by click reactions have been used for mimicking peptide and disulfide bonds, building secondary structural components of peptides, linking functional groups together, and bioconjugation. The progress made in this field opens the way for synthetic approaches to convert peptides with promising functional leads into structure-minimized and more stable forms.

A microgel construction kit for bioorthogonal encapsulation and pH-controlled release of living cells.

Abstract: pH-Cleavable cell-laden microgels with excellent long-term viabilities were fabricated by combining bioorthogonal strain-promoted azide–alkyne cycloaddition (SPAAC) and droplet-based microfluidics. Poly(ethylene glycol)dicyclooctyne and dendritic poly(glycerol azide) served as bioinert hydrogel precursors. Azide conjugation was performed using different substituted acid-labile benzacetal linkers that allowed precise control of the microgel degradation kinetics in the interesting pH range between 4.5 and 7.4. By this means, a pH-controlled release of the encapsulated cells was achieved upon demand with no effect on cell viability and spreading. As a result, the microgel particles can be used for temporary cell encapsulation, allowing the cells to be studied and manipulated during the encapsulation and then be isolated and harvested by decomposition of the microgel scaffolds.

The thiol‐ene (click) reaction for the synthesis of plant oil derived polymers

Abstract: This review covers the discovery and development of radical thiol-ene addition reactions as functionalization and polymerization method. First, some general and important developments within the field of polymer chemistry are introduced. However, the utilization of this efficient coupling procedure for the syntheses of materials derived from plant oils are the focus of this manuscript. Applications of this unique reaction will also be discussed in terms of green chemistry requirements as well as reaction conditions and efficiency.

Redox-Responsive, Core Cross-Linked Polyester Micelles

Abstract: Monomethoxy poly(ethylene glycol)-b-poly(Tyr(alkynyl)-OCA), a biodegradable amphiphilic block copolymer, was synthesized by means of ring-opening polymerization of 5-(4-(prop-2-yn-1-yloxy)benzyl)-1,3-dioxolane-2,4-dione (Tyr(alkynyl)-OCA) and used to prepare core cross-linked polyester micelles via click chemistry. Core cross-linking not only improved the structural stability of the micelles, but also allowed controlled release of cargo molecules in response to the reducing reagent. This new class of core cross-linked micelles can potentially be used in controlled release and drug delivery applications.

The click reaction as an efficient tool for the construction of macrocyclic structures.

Abstract: The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC, known as the click reaction) is an established tool used for the construction of complex molecular architectures. Given its efficiency it has been widely applied for bioconjugation, polymer and dendrimer synthesis. More recently, this reaction has been utilized for the efficient formation of rigid or shape-persistent, preorganized macrocyclic species. This strategy also allows the installment of useful functionalities, in the form of polar and function-rich 1,2,3-triazole moieties, directly embedded in the macrocyclic structures. This review analyzes the state of the art in this context, and provides some elements of perspective for future applications.

Organocatalytic triazole formation, followed by oxidative aromatization: regioselective metal-free synthesis of benzotriazoles.

Abstract: Herein we report on our studies on the sequential one-pot combinations of amine-catalyzed multicomponent reactions (MCRs). We have developed the copper-free synthesis of functionalized bicyclic N-aryl-1,2,3-triazole and N-arylbenzotriazole products 4 and 5 from the simple unmodified starting materials through [3+2]-cycloaddition ([3+2]-CA) and oxidative aromatization reactions in one pot under amine catalysis. The sequential one-pot reaction proceeds in good yields with high selectivity by using pyrrolidine as the catalyst from the simple unmodified substrates of enones, aryl azides, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Furthermore, we have demonstrated the medicinal applications of products 4 and 5 through simple organic reactions.

The Growing Impact of Bioorthogonal Click Chemistry on the Development of Radiopharmaceuticals

Abstract: Click chemistry has become a ubiquitous chemical tool with applications in nearly all areas of modern chemistry, including drug discovery, bioconjugation, and nanoscience. Radiochemistry is no exception, as the canonical Cu(I)-catalyzed azide-alkyne cycloaddition, strain-promoted azide-alkyne cycloaddition, inverse electron demand Diels-Alder reaction, and other types of bioorthogonal click ligations have had a significant impact on the synthesis and development of radiopharmaceuticals. This review will focus on recent applications of click chemistry ligations in the preparation of imaging agents for SPECT and PET, including small molecules, peptides, and proteins labeled with radionuclides such as 18F, 64Cu, 111In, and 99mTc.

A Chemo-Enzymatic Approach for Site-Specific Modification of the RNA Cap**

Abstract: Capped and gowned: A two-step approach can be used to site-specifically modify the 5'-cap of eukaryotic mRNAs. First, a trimethylguanosinesynthase variant recognizes the m(7)G cap structure and introduces bioorthogonal groups using S-adenosyl-L-methionine-based cosubstrates. Then, the enzymatically introduced reporter groups are further modified by thiol-ene or CuAAC click chemistry (see scheme).

A bioorthogonal ligation enabled by click cycloaddition of o-quinolinone quinone methide and vinyl thioether.

Abstract: There is an increasing interest in the use of bioorthogonal ligation to advance biomedical research through selective labeling of biomolecules in living systems. Accordingly, discovering new reactions to expand the toolbox of bioorthogonal chemistry is of particular interest to chemical biologists. Herein we report a new bioorthogonal ligation enabled by click hetero-Diels-Alder (HDA) cycloaddition of in situ-generated o-quinolinone quinone methides and vinyl thioethers. This reaction is highly selective and proceeds smoothly under aqueous conditions. The functionalized vinyl thioethers are small and chemically stable in vivo, making them suitable for use as bioorthogonal chemical reporters that can be effectively coupled to various biomolecules. We utilized this bioorthogonal ligation for site-specific labeling of proteins as well as imaging of bioactive small molecules inside live cells.

Effect of Click-Chemistry Approaches for Graphene Modification on the Electrical, Thermal, and Mechanical Properties of Polyethylene/Graphene Nanocomposites

Abstract: The effect of the type of chemical route used to functionalize graphene with short-chain polyethylene on the final properties of graphene-based high density polyethylene nanocomposites is reported. Three different click reactions, namely copper-catalyzed alkyne–azide (CuAAC), thiol–ene and thiol–yne have been addressed. The nanocomposites were prepared using a method that we denominate “gradient interphase”. The electrical and thermal conductivity and the mechanical properties strongly depend on the click reaction used to modify graphene, the thiol–ene reaction giving the best results. This study demonstrates that the election of the chemical strategy to provide graphene with functionalities common to the polymer matrix and the engineering of the interface are crucial to obtain nanocomposites with improved properties.

Exploring the Effect of Amphiphilic Polymer Architecture: Synthesis, Characterization, and Self-Assembly of Both Cyclic and Linear Poly(ethylene gylcol)-b-polycaprolactone

Abstract: While amphiphilic block copolymers have demonstrated their utility for a range of practical applications, the behavior of cyclic block copolymers remains largely unexplored due to limited synthetic access. To investigate their micelle formation, biocompatible cyclic amphiphilic poly(ethylene glycol)-polycaprolactone, c-(PEG-PCL), was synthesized by a combination of ring-opening polymerization (ROP) and click chemistry. In addition, exactly analogous linear block copolymers have been prepared as a control sample to elucidate the role of polymer architecture in their self-assembly and acid-catalyzed degradation.