BARAC - yet another strain-promoted copper-free click chemistry

Believe it or not, this one is called BARAC. 

Click chemistry is certainly not "done". This time, instead of electronic properties, Bertozzi group looked at the strain energy by introducing some level of double bond nature into the octyne ring structure. The choice was amide bond which displays well-known partial double bond nature (C=N). "Brushing against the line between stability and reactivity without crossing it", this is another beautiful example of "rational design" in physical organic chemistry. "Gratifying", The click reaction rate was superior, 12-fold faster than DIFO the difluoro-version. The group then evaluated BARAC derivatives in their "traditional" cell glycobiology imaging where cell surface carries glycan azide. It demonstrates superior performance than DIFO and DIBO. Modular and scalable synthesis of BARAC offers more opportunities and wider applications of this new copper-free click chemistry. 

Champagne finished, time to work on the next click chemistry.

Journal of the American Chemical Society, 2010, DOI 10.1021/ja100014q

Bioorthogonal click chemistry - Carolyn Bertozzi the champion

Chem. Soc. Rev., 2010 DOI: 10.1039/b901970g

Carolyn Bertozzi et al clearly defined the bioorthognal click chemistry. They used this figure to illustrate a general bioorthogonal reaction. Best described: "we must first look at an organic chemistry textbook and remove any reaction that is sensitive to water. Second, with an abundant supply of thiols and amines in the cell, we must also remove reagents that are prone to nucleophilic attack. Third, because of the reducing environment in the cytosol, we have to remove reactions that are sensitive to redox chemistry. If a reaction requires heat (above 37 °C), pressure, or high concentrations to work then it is also unacceptable. Lastly, some functionalities can be digested by cellular enzymes that have an ase in their name (e.g., esterase, phosphatase, sulfatase, etc.). Add reagent toxicity to this list and you will find a select few reactions that remain viable for performance in living systems."

Indeed one needs to be very picky in picking a good bioothogonal reaction from the already- small click chemistry tool box. The review covers the most viable reactions up-to-date, lists their pros and cons, and potentials. The chemistry aspects are detailed, with great insights and perspectives from a mechanistic point of view.

And did I mention the secret - go back to the old dusty organic chemistry toolbox and find treasures, such as click chemistry?