The three Nobel Laureates in Chemistry 2022 have brought chemistry into the era of functionalism and created a new genre in chemical biology.

The Royal Swedish Academy of Sciences decided to award the 2022 Nobel Prize in Chemistry to Carolyn R. Bertozzi, Morten Meldal and K. Barry Sharpless, for the development of click chemistry and bioorthogonal chemistry.

“This year’s Prize in Chemistry deals with not overcomplicating matters, instead working with what is easy and simple. Functional molecules can be built even by taking a straightforward route,” said Johan Åqvist, Chair of the Nobel Committee for Chemistry at the time of the announcement.

Morten Meldal and Barry Sharpless (this is his second Nobel Prize in Chemistry) laid the foundations for what today is known as click chemistry, a functional form of chemistry in which molecular building blocks snap together quickly and efficiently; think Lego for chemists. Carolyn Bertozzi took click chemistry to a new dimension when she started to utilize it in living organisms to map cells.

“This is a very well deserved award, honoring methods that will be useful within many areas. The simplified ways to build new and even complex molecules have great significance and facilitates and enables previously difficult and impossible projects and experiments.”

“This is a very well deserved award, honoring methods that will be useful within many areas. The simplified ways to build new and even complex molecules have great significance and facilitates and enables previously difficult and impossible projects and experiments,” says Gunnar C. Hansson, Professor at the Department of Medical Biochemistry and Cell Biology at the University of Gothenburg to NLS. “We are now looking forward to welcoming Carolyn Bertozzi to Sweden and Gothenburg so that we get more time to discuss common scientific interests.”

 

Gunnar C Hansson, Professor, University of Gothenburg. Photo: Johan Wingborg

 

Simple, reliable and green

The concept of click chemistry was coined by Barry Sharpless, currently W. M. Keck Professor at Scripps Research, La Jolla, CA, USA, around the year 2000. He described a form of simple and reliable chemistry, where reactions occur quickly and where unwanted by-products are avoided. Joining two molecules is often a slow process that leads to a variety of products that must be separated, so by taking small biomolecules that already have a complete carbon frame and linking them together using bridges of nitrogen or oxygen atoms, which are easier to control, Sharpless found a more robust method of building molecules.

Even if click chemistry cannot provide exact copies of natural molecules, it will be possible to find molecules that fulfill the same functions, Sharpless concluded, and he was convinced that click chemistry could generate pharmaceuticals that were as fit for purpose as those found in nature, and which could be produced on an industrial scale. In his publication from 2001 he listed several criteria that should be fulfilled for a chemical reaction to be called click chemistry, describes the Royal Swedish Academy of Sciences. One of these is that the reaction should be able to occur in the presence of oxygen and in water, which is a cheap and environmentally friendly solvent.

Shortly after the concept of click chemistry came about, in 2002, both Sharpless and Morten Meldal, currently Professor at University of Copenhagen, Denmark, independently of each other described the copper catalyzed azide-alkyne cycloaddition (CuAAC), what is now called the crown jewel of click chemistry. The known reaction of combining an alkyne with an acyl halide was efficient and had few unwanted side reactions, but it required a large amount of heat.

Meldal had been working on adding chemical handles to short proteins, i.e., peptides. He had constructed enormous molecular libraries that he screened to see if any of them could block pathogenic processes. He started to experiment with the azide-alkyne combination, and in his reaction the alkyne reacted with the wrong end of the acyl halide molecule. At the opposite end was a chemical group called an azide. Together with the alkyne, the azide created a ring-shaped structure, a triazole, a very useful and desirable chemical building block. Meldal realized that the copper irons had controlled the reaction so that, in principle, only one substance was formed.

“Both Meldal and Sharpless discovered that copper accelerated the reaction and reduced the need for adding extra heat.”

At the same time Sharpless published similar findings, that the copper catalyzed reaction between azides and alkynes, showing that the reaction works in water and is reliable. Both Meldal and Sharpless discovered that copper accelerated the reaction and reduced the need for adding extra heat.

Sharpless described it as an “ideal” click reaction. If chemists want to link two different molecules they can now introduce an azide in one molecule and an alkyne in the other. They then snap the molecules together with the help of some copper ions, describes the Royal Swedish Academy of Sciences.

This chemical reaction is today in widespread use, for example in the development of pharmaceuticals and for mapping DNA.

“The impact is enormous, since the simplicity of the process allows scientists who lack training in organic or medicinal chemistry to perform this synthetic transformation on their own.”

“From a drug development perspective, click chemistry makes it possible to create large molecular libraries quickly and with high purity. The impact is enormous, since the simplicity of the process allows scientists who lack training in organic or medicinal chemistry to perform this synthetic transformation on their own,” commented Per I Arvidsson, Platform Director, SciLifeLab Drug Discovery and Development Platform (DDD) in a SciLifeLab press release.

 

Illustrations of Carolyn R. Bertozzi, Morten Meldal, and K. Barry Marshall: © Nobel Prize Outreach. Ill. Niklas Elmehed

 

Copper-free click chemistry

Carolyn Bertozzi, currently Anne T. and Robert M. Bass Professor at Stanford University, CA, USA, took click chemistry into new dimensions by developing click reactions to work inside living organisms. In 2000 Bertozzi had coined the concep and developed the method of bioorthogonal reactions to map important but elusive biomolecules on the surface of cells, glycans, without disrupting the normal chemistry of the cell.

The problem when working with living cells is that copper, used by Meldal and Sharpless in the click chemistry, is toxic. However Bertozzi found that it had been shown in 1961 that azides and alkynes can react in an almost explosive manner, without the help of copper, if the alkyne is forced into a ring-shaped chemical structure. The strain creates so much energy that the reaction runs smoothly. It worked, and in 2004 she published her copper-free click reaction, called the strain-promoted alkyne-azide cycloaddition.

“Unlike click chemistry, Bertozzi’s bioorthogonal chemistries have opened a new genre in chemical biology, enabling selective and efficient chemical bond formation in complex biological mixtures including living cells or even the human body.”

Unlike click chemistry, Bertozzi’s bioorthogonal chemistries have opened a new genre in chemical biology, enabling selective and efficient chemical bond formation in complex biological mixtures including living cells or even the human body, explains Simon Elsässer, Group Leader at Science for Life Laboratory and Associate Professor at the department of Medicinal Biochemistry and Biophysics at Karolinska Institutet.

“Bioorthogonal chemistry has found many applications in basic biomedical research, by enabling researchers to attach tiny chemical handles onto their favorite molecules, be it carbohydrates (sugars), lipids or proteins. These handles can be utilized in the living cell to attach fluorescent dyes or other kinds of probes, or fish the tagged biomolecule out of the complex mixture of molecules within a cell,” says Simon Elsässer.

He and his research colleagues are using chemical biology to probe and manipulate proteins in the living cell and bioorthogonal chemistry is their go-to technology to label proteins that cannot otherwise be labeled, for example because they are processed or modified in complex ways.

“Using this technology, we have been able to visualize tiny proteins in mitochondria, study the processing of APP, a protein involved in Alzheimer’s disease, or illuminate membrane receptors,” he says.

Gunnar C. Hansson also says that his research group at the University of Gothenburg and others involved in medical research have made great use of Bertozzi’s discovery. “We have for example learned that the some tenths of a millimeter thick protective mucus layer in the large intestine that keeps bacteria away from us is renewed within one hour. Incredibly much faster than we could imagine.”

 

Simon Elsässer, Group Leader, SciLifeLab. Photo: Johannes Frandsén

 

A new class of biologics and smart therapies

In the pharmaceutical industry, both click and bioorthogonal chemistries are driving a new class of biologics, foremost antibody-drug-conjugates in oncology, describes Simon Elsässer. “Here, cytotoxic drugs are attached to an antibody that binds to the target tumor cell. The benefit over traditional chemotherapy is that the toxic effect is concentrated to kill the tumor cell, while sparing other tissues and organs,” he says.

Because bioorthogonal chemistry is highly efficient under physiologic conditions and non-toxic to human cells, new smart therapies are also currently being developed that utilize chemical reactions to precisely deliver drugs in the human body, he adds.

“When antibody and drug meet on the tumor cell, a bioorthogonal reaction is triggered that activates the drug in place to kill the tumor cell. This may sound like science fiction but there are actually Phase I clinical trials ongoing for such therapies.”

“A strategy termed ‘pre-targeting’ uses antibodies to ‘mark’ the target cell, e.g., the tumor. The cytotoxic agent is delivered in a second step, e.g., in an encapsulated form that prevents the drugs from killing healthy cells. When antibody and drug meet on the tumor cell, a bioorthogonal reaction is triggered that activates the drug in place to kill the tumor cell. This may sound like science fiction but there are actually Phase I clinical trials ongoing for such therapies,” says Simon Elsässer.

In 2020 California-based biotech Shasqi initiated this first human use of bioorthogonal chemistry, starting a Phase 1/2 clinical trial of a doxorubicin prodrug that exploits the tetrazine–TCO chemistry that Fox developed and Robillard adapted. The treatment is based on the pre-injection of a tetrazine-loaded hydrogel into the tumor site, followed by infusions of the doxorubicin prodrug. Only where the two components meet, at the tumor site, is the drug unleashed.

Several of the technologies developed in Bertozzi’s lab have been adapted for commercial use and she has launched seven companies in 12 years, all rooted in her extensive knowledge of modifying sugar structures.

Featured illustration: Johan Jarnestad