Click chemistry is a chemical paradigm introduced by K. Barry Sharpless in 2001 [10] and describes chemical reactions that generate substances quickly, reliably and in quantitative yield by joining small building blocks under mild conditions. This is inspired by the fact that chemical reactions in nature also generate substances by joining small modular units.

Advantages of click chemistry labeling: Labeling by simple, efficient reactions High labeling yield (nearly quantitative) Allows introduction of sensitive labels (mild conditions) Highly modular system (combinatorial approach) Orthogonal to conventional methods Bioorthogonal reaction (no azides or alkynes in natural systems) Labeling of all bases possible (G, A, C, T, U) Broad range of marker- and dye-azides available Also adaptable to linking beads, microarrays, nanoparticles, peptides etc.

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Alkyne-containing Reagents for Cu(I)-catalyzed Click Reactions

One of the most popular reactions within the click chemistry paradigm is the Cu(I)-catalyzed 1,3-dipolar Huisgen cycloaddition of alkynes and azides, using a Copper (Cu) catalyst at room temperature. This reaction proceeds with great efficiency and selectivity in aqueous media and yields a triazole moiety.

In contrast to many crosslinking methods used in biological research, this reaction depends upon a pair of unique groups with very specific reactivity to one another. Since neither alkynes nor azides occur in cells, they react only with each other in biological media, resulting in minimal background or side reactions. The Cu(I)-catalyzed azide-alkyne ligation reaction has endless applications where toxicity is irrelevant, from probing enzyme activity, visualizing biomolecules in fixed cells to detection of DNA synthesis in proliferating cells and to selective attachment of flourophores to viruses. However, in many biological applications the presence of Cu(I) is unacceptable due to its toxicity.

Assay Kits Click Chemistry Kits Alkyne-containing Nucleosides Alkyne-containing Nucleotides Alkyne-containing CEPs Alkyne-containing CPGs

Alkyne-containing Fluorescent Dyes Alkyne-containing Spacers Alkyne-containing Chemical Modification Reagents Auxiliary Reagents

DBCO-containing Reagents for Copper-free Click Reactions

The strain-promoted or Cu(I)-free [2+3] cycloaddition strategy relies on the use of strained cyclooctynes. Their use decreases the activation energy for the cycloaddition click reaction, enabling it to be carried out without the need for catalysis at low temperatures with an efficiency greater than that of the Cu(I)-catalyzed ligation.

Diarylcyclooctynes are thermally stable compounds with very narrow and specific reactivity toward azides. The ligation reaction is very fast and results in almost quantitative yield of stable triazoles.

The strain-promoted Click reaction and the so called Staudinger ligation (phosphine-azide) are competing technologies for chemoselective ligation. Both reactions are chemoselective and do not require copper, so both do not damage biomolecules. However, the rate of Staudinger ligation is about 100fold lower than the rate of the DBCO cycloaddition, which makes the Staudinger ligation hardly useful for studying dynamic biological systems. Only in cases where the speed of ligation is irrelevant, both reactions can be used with about equal efficiency.

DBCO-containing Chemical Modification Reagents DBCO-containing Biotinylation Reagents DBCO-containing PEGylation Reagents

DBCO-containing Spacers DBCO-containing Fluorescent Dyes DBCO-containing Nucleotides DBCO-containing Phosphoramidites

Azide-containing Reagents for Click Reactions

Azide-containing reagents are used in Copper-catalyzed cycloadditions as well as in Copper-free click reactions. They are selective reagents towards triple bonds (alkynes or cycloalkynes), yielding stable triazoles in almost quantitative yield under mild conditions.

Non-Fluorescent Azides Biotin Azides PEG and Spacer Azides Azides of Amino Acids

Azides of Fluorescent Dyes Azides of Quencher Dyes Nucleotide Azides Nucleoside Azides

Alkene-Tetrazine Click Chemistry

The cyclooctene/tetrazine chemistry constitutes a new and superior way to link molecules in a "click" manner. It features high reaction speed and nearly quantitative yield under physiological conditions. The resulting products contain a stable Dihydropyrazine moiety, providing bio-compatibility and low steric hindrance.

Cyclooctene-containing Chemical Modification Reagent

Tetrazine-containing Chemical Modification Reagent Tetrazine-containing Fluorescent Dyes