Niklas Elmehed © Nobel Prize Outreach. Left to right: Bertozzi, Meldal, Sharpless

Nobel Prize in Chemistry 2022: Click Chemistry and Bioorthogonal Chemistry

There are no chemists, biochemists and biologists that do not know the basic features of “click chemistry” and the great advantages of this new strategy for connecting molecules, even complex ones, in a simple, efficient, selective way under mild aqueous conditions. The 2022 Nobel Prize in Chemistry awarded to Barry Sharpless (The Scripps Research Institute, La Jolla California), Morten Meldal (University of Copenhagen) and Carolyn Bertozzi (University of Stanford) is the recognition of the fundamental importance of this new synthetic methodology for connecting two molecular fragments, even very complex ones like biomolecules and biopolymers. The story of “click chemistry” is not very old compared to other great discoveries in chemistry, in fact in about 20 years we moved from the first examples published to the award of the Nobel prize.

In 2001 Sharpless, that the same year was awarded with the Nobel Prize in Chemistry for the studies on the asymmetric catalysis, proposed the term “click chemistry” related to “a series of nearly perfect spring-loaded reactions” particularly interesting for making new chemical bonds with minimal by-product formation, high atom efficiency, high yield and simple purification. In the same period serendipitously Meldal observed that in particular one of these reactions, the 1,3-dipolar Huisgen cycloaddition between alkynes and organic azides providing 1H-[1,2,3]-triazoles derivatives, could be efficiently catalyzed by small amounts of copper salts selectively leading to the 1.4-regioisomer under mild experimental conditions. More importantly, he underlined the peculiarity of the reaction to be insensitive to the presence of many different functional groups. 

The orthogonality of the reaction combined to its high efficiency, ease of use, compatibility with multiple organic solvents, including the aqueous environment, and reproducibility under different temperature and pH conditions instantly stimulated interest in the use of this conjugation for the functionalization of biomolecules present in complex biological systems. However, the use of click chemistry for such applications was limited by the toxicity of copper ions to cells and living organisms. It was therefore essential to identify conditions that avoided the use of copper, a challenge that Bertozzi's research group faced immediately with outstanding results. It was Bertozzi herself in 2003 who coined the term “bioorthogonal chemistry”. To modify selectively and under physiological conditions the biomolecules present in living organisms, without interrupting or interfering with the surrounding vital cellular processes, the key functional groups azide and alkyne were maintained but made intrinsically more reactive to eliminate copper while ensuring a high selectivity, activity, yield and orthogonality with respect to most biomolecules.

The combination of "click chemistry" and "bioorthogonal chemistry" have had a huge impact in multiple areas. For example, the use of "click chemistry" and "bioorthogonal chemistry" has allowed the mapping and understanding of the role of biomolecules present on the surface of cells and involved in cell recognition and intercellular communication. Over the past 20 years, the application of these methodologies has allowed the development of new precision biotherapies for the treatment of diseases such as cancer and inflammatory disorders such as arthritis. The selectivity of this reaction has also allowed the development of point-of-care diagnostic systems for the rapid identification of pathogens, such as tuberculosis.

"Click chemistry" and "bioorthogonal chemistry" have also been used for the design of advanced next-generation biomaterials for multiple biomedical applications such as tissue engineering, regenerative medicine, precision imaging, cell therapy and drug delivery. Finally, these methodologies have allowed the development of new herbicides, photostabilizers, corrosion retardants, brightening agents and multiple macromolecular materials such as gels and polymers.

The story of this Nobel prize in chemistry teaches a couple of important lessons for chemists: it is crucial to pay attention to unexpected results that sometimes pop-up when performing scientific experiments, rather than ignoring them because not desired, since they can eventually lead to great discoveries. It is also fundamental to recognize the potentialities of a new result, and only with an interdisciplinary vision it is possible to bring such result to a higher degree of complexity, making a real step forward for the scientific community and for the entire humankind.

Written by Alessandro Angelini and Alessandro Scarso, Department of Molecular Sciences and Nanosystems.