What is Click Chemistry?

Click Chemistry has been used prominently in pharmaceutical and biotech R&D. It has become increasingly popular due its biocompatibility and its faster reaction speeds.¹ Click Chemistry can be categorized as one of three generations.

The 1^st generation of Click Chemistry uses a Cu(I) catalyst in the reaction between a terminal alkyne and an azide. Although the coupling reaction is successful, the addition of a Cu(I) catalyst can cause damage to the biomolecule.

The 2^nd generation Click Chemistry utilizes the reaction between cyclooctyne and an azide via strain-promoted azide-alkyne Click Chemistry. This reaction is copper-free and proceeds due to the high-activation energy of the strained molecule. In this copper-free Click Chemistry, commonly used reagents include DBCO, OCT and BCN. The use of reagents such as BCN, prevents the production of regioselective mixtures.

The 3^rd generation of Click Chemistry involves the ligation between a tetrazine and trans-Cyclooctene (TCO) without the use of a Cu(I) catalyst. The omission of the Cu(I) catalyst is ideal for in vivo cell labelling while still enabling a high-speed reaction.² This has been found to allow protein modification at lower concentrations.³

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The introduction of a PEG linker to Click Chemistry reagents enhances its water-solubility properties and makes it more convenient for biolabeling in aqueous buffers. 

Reference

¹ Biocojug Chem. 2008 December; 19(12):2297-2299. Doi: 10.1021/bc8004446.

² Biocojug Chem. 2008 December; 19(12):2297-2299. Doi: 10.1021/bc8004446.

³ J. Am. Chem. Soc. 2008, 130, 13518-13519.