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The principle of click chemistry

Click chemistry constitutes a novel approach for easy, effective labeling and detection of biomolecules in vitro and in vivo. It is based on the use of biologically unique tags as reaction partners. This chemistry uses the most energetic pre-formed carbon-carbon bonds1. The premier candidates for a click reaction are alkynes and azides to yield triazoles, which form a stable covalent bond. This reaction is based on the azide alkyne Huisgen cycloaddition, which was described by Rolf Huisgen in the 1970s. The addition of the Cu(I) catalyst changes the reaction conditions to room temperature and allows the presence of water eliminating unwanted products. Figure 1 shows the reaction scheme of the click-reaction.

Figure 1: Principle of the click reaction between an azide (R1) and alkyne (R2).

Figure 1: The principle of the click reaction between an azide (R1) and alkyne (R2).

Click chemistry greatly facilitated the synthesis of biomolecular tools by overcoming three mayor challenges: natures limitation for use of reactive functional groups, the potential for disrupting protein function by the altering functional groups, and manipulation of molecules under biocompatible conditions (temperature sensitivity, solvent, and pH)3. Furthermore, the click chemistry reaction conditions were improved by omitting the requirement for a copper catalyst. Now this is a simple two-component reaction, still requiring an azide, but now pairing it with a cyclic alkyne containing a “ring strain”2. The ring strain is released upon the reaction of the alkyne with azide, generating the required conditions to complete the reaction.

Learn more about click chemistry and the recent “2022 Nobel Prize in Chemistry” winners for these chemical transformations.


Advantages of click chemistry

Using azide or alkyne tags for labeling proteins, nucleic acids, lipids or sugars has the advantage that neither moiety occurs in nature, and neither reacts with other molecules in cellular systems. Because of its high selectivity, bio-orthogonal click-chemistry can be used for detection in complex biological samples: one of the reaction partners is integrated into the molecule of interest, while the second tag containing a fluorescent label is covalently attached by performing the click-reaction. As the reaction is highly specific and proceeds rapidly towards completion, click chemistry can also be used to synthesize large substances.


Bio-orthogonal labeling with fluorescent Chromeo™ Dyes

Chromeo™ Dyes – Chromeo 488, Chromeo 494, Chromeo 546 and Chromeo 642 – exhibit superior fluorescent properties, broad Stokes shifts, stability towards photobleaching and pH, and low cell toxicity. In addition, they are compatible with most excitation sources including diode lasers, LEDs, tungsten lamps and xenon arc lamps. For bio-orthogonal labeling, Chromeo Dyes are offered as click-reactive azide or alkyne.

Figure 2: Click labeling with Chromeo Dye azides

Figure 2: Click labeling with Chromeo Dye azides.

 

Chromeo™ Azide and Alkyne advantages

  • High fluorescent intensity
  • Photostability – enables multiple exposures and increased exposure time
  • pH insensitive
  • Low background
  • Ready to use in click-reactions

References

  1. Zeglis, Brian M., and Jason S. Lewis. "Click for Better Chemistry." The New England Journal of Medicine, 15 Dec. 2022, pp. 2291-93.
  2. Zayas, Jessica, et al. "Strain Promoted Click Chemistry of 2- or 8-Azidopurine and 5-Azidopyrimidine Nucleoside and 8-Azidoadenosine Triphosphate with Cyclooctynes. Application to Living Cell Fluorescent Imaging." National Library of Medicine, pp. 1519-32, https://doi.org/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4826778/.
  3. Kolb, Hartmuth C., and K. B. Sharpless. "The growing impact of click chemistry on drug discovery." National Library of Medicine, vol. 8, 24 Nov. 2003, pp. 1128-37.