High Density Orthogonal Surface Immobilization via Photoactivated Copper-Free Click Chemistry

Strain-promoted alkyne-azide cycloadditions (SPAAC) reveal new features of glycoconjugate biosynthesis

We have shown that 4-dibenzocyclooctynol (DIBO), which can easily be obtained by a streamlined synthesis approach, reacts exceptionally fast in the absence of a Cu(I) catalyst with azido-containing compounds to give stable triazoles. Chemical modifications of DIBO, such as oxidation of the alcohol to a ketone, increased the rate of strain promoted azide-alkyne cycloadditions (SPAAC). Installment of a ketone or oxime in the cyclooctyne ring resulted in fluorescent active compounds whereas this property was absent in the corresponding cycloaddition adducts; this provides the first example of a metal-free alkyne-azide fluoro-switch click reaction. The alcohol or ketone functions of the cyclooctynes offer a chemical handle to install a variety of different tags, and thereby facilitate biological studies. It was found that DIBO modified with biotin combined with metabolic labeling with an azido-containing monosaccharide can determine relative quantities of sialic acid of living cells that have defects in glycosylation (Lec CHO cells). A combined use of metabolic labeling/SPAAC and lectin staining of cells that have defects in the conserved oligomeric Golgi (COG) complex revealed that such defects have a greater impact on O-glycan sialylation than galactosylation, whereas sialylation and galactosylation of N-glycans was similarly impacted. These results highlight the fact that the fidelity of Golgi trafficking is a critical parameter for the types of oligosaccharides being biosynthesized by a cell. Furthermore, by modulating the quantity of biosynthesized sugar nucleotide, cells might have a means to selectively alter specific glycan structures of glycoproteins.

Recent developments of cyclopropene chemistry

This critical review discusses recent developments in the field of cyclopropene chemistry. Although several excellent reviews that mainly focused on the thermolysis and pyrolysis as well as metal-mediated reactions of cyclopropenes have been published, significant new developments have also been achieved in recent years. This brand new review provides an overview of the progress from 2007 to 2011 on the syntheses and transformations of cyclopropenes as well as their related mechanistic studies (238 references).

Synthesis of thiol-clickable and block copolypeptide brushes via nickel-mediated surface initiated polymerization of α-amino acid N-carboxyanhydrides (NCAs)

We describe the synthesis of homo-, block, and clickable copolypeptide brushes from low surface area substrates using nickel-mediated surface-initiated polymerization of α-amino N-carboxyanhydrides.

Spatial and temporal control of the alkyne-azide cycloaddition by photoinitiated Cu(II) reduction

The click reaction paradigm is focused on the development and implementation of reactions that are simple to perform while being robust and providing exquisite control of the reaction and its products. Arguably the most prolific and powerful of these reactions, the copper-catalysed alkyne-azide reaction (CuAAC) is highly efficient and ubiquitous in an ever increasing number of synthetic methodologies and applications, including bioconjugation, labelling, surface functionalization, dendrimer synthesis, polymer synthesis and polymer modification. Unfortunately, as the Cu(I) catalyst is typically generated by the chemical reduction of Cu(II) to Cu(I), or added as a Cu(I) salt, temporal and spatial control of the CuAAC reaction is not readily achieved. Here, we demonstrate catalysis of the CuAAC reaction via the photochemical reduction of Cu(II) to Cu(I), affording comprehensive spatial and temporal control of the CuAAC reaction using standard photolithographic techniques. Results reveal the diverse capability of this technique in small molecule synthesis, patterned material fabrication and patterned chemical modification.

One-pot tandem copper-catalyzed library synthesis of 1-thiazolyl-1,2,3-triazoles as anticancer agents

One-pot multicomponent synthesis to assemble compounds has been an efficient method for constructing a compound library. We have developed one-pot tandem copper-catalyzed azidation and CuAAC reactions that afford 1-thiazolyl-1,2,3-triazoles with anticancer activity. By utilizing this one-pot synthetic strategy, we constructed a library of 1-thiazolyl-1,2,3-triazoles in search of the potent lead compound. Furthermore, 1-thiazolyl-1,2,3-triazoles were evaluated for anticancer activity against the multidrug-resistant cancer cells MES-SA/Dx5. Most of the 1-thiazolyl-1,2,3-triazoles revealed cytotoxic effect against cancer cells at micromolar to low micromolar range. Testing some of the most potent compounds (5{4,2-4} and 5{5,1-3}) against the normal cell line Vero showed no significant toxicity (except 5{4,2}) to normal cells. This result indicates that compounds 5{4,3-4} and 5{5,1-3} possessed good potency and selectivity to cancer cells over normal cells.

Selective surface chemistry using alumina nanoparticles generated from block copolymers

Developing orthogonal surface chemistry techniques that perform at the nanoscale is key to achieving precise control over molecular patterning on surfaces. We report the formation and selective functionalization of alumina nanoparticle arrays generated from block copolymer templates. This new material provides an alternative to gold for orthogonal surface chemistry at the nanometer scale. Atomic force microscopy and X-ray photoelectron spectroscopy confirm these particles show excellent selectivity over silica for phosphonic and carboxylic acid adsorption. As this is the first reported synthesis of alumina nanoparticles from block copolymer templates, characterizations via Fourier transform infrared spectroscopy, Auger electron spectroscopy, and transmission electron microscopy are presented. Reproducible formation of alumina nanoparticles was dependent on a counterintuitive synthetic step wherein a small amount of water is added to an anhydrous toluene solution of block copolymer and aluminum chloride. The oxidation environment of the aluminum in these particles, as measured by Auger electron spectroscopy, is similar to that of native aluminum oxide and alumina grown by atomic layer deposition. This discovery expands the library of available surface chemistries for nanoscale molecular patterning.

Metal-free sequential [3 + 2]-dipolar cycloadditions using cyclooctynes and 1,3-dipoles of different reactivity

Although metal-free cycloadditions of cyclooctynes and azides to give stable 1,2,3-triazoles have found wide utility in chemical biology and material sciences, there is an urgent need for faster and more versatile bioorthogonal reactions. We have found that nitrile oxides and diazocarbonyl derivatives undergo facile 1,3-dipolar cycloadditions with cyclooctynes. Cycloadditions with diazocarbonyl derivatives exhibited similar kinetics as compared to azides, whereas the reaction rates of cycloadditions with nitrile oxides were much faster. Nitrile oxides could conveniently be prepared by direct oxidation of the corresponding oximes with BAIB, and these conditions made it possible to perform oxime formation, oxidation, and cycloaddition as a one-pot procedure. The methodology was employed to functionalize the anomeric center of carbohydrates with various tags. Furthermore, oximes and azides provide an orthogonal pair of functional groups for sequential metal-free click reactions, and this feature makes it possible to multifunctionalize biomolecules and materials by a simple synthetic procedure that does not require toxic metal catalysts.