2021 Chemistry Nobel Prize for the discovery of New Organic Catalysts

Industrial Catalysts are tools for building new molecules selectively. Many industries depend on molecules that can form elastic and durable materials, store energy in solar batteries or inhibit the progression of diseases. Plastic, pharmaceutical, perfume, and food industries heavily depend upon the use of safe and efficient catalysts. Products synthesized by catalysis are responsible for about 35% of the world’s GDP.

Catalysts in cars neutralize toxic substances in exhaust fumes. The human body contains thousands of catalysts in the form of enzymes. Enzymes construct the molecular complexes that give living beings their shapes, colors, and functions. There are some others such as cholesterol, chlorophyll, or the toxin called strychnine, which are the most complex molecules known. When trying to copy nature’s products in the laboratory,  one often ends up with lots of unwanted by-products. Earlier, it had been difficult to find efficient methods to overcome this problem.

Asymmetric Organo-catalysts,  discovered by Benjamin List and David MacMillan, efficiently speed up some organic reactions.  Organic substances have stable carbon atoms, to which more active elements such as oxygen, nitrogen, sulfur, phosphorus, or their groups can attach. Often two different asymmetric molecules with the same chemical composition but different structures, are formed simultaneously. However, only one of these is required, particularly when producing pharmaceuticals. The other has to be separated as it causes side effects.

Benjamin List worked with catalytic antibodies; molecules that are built from amino acids and enzymes. Normally, antibodies attach to foreign viruses or bacteria in our bodies, but the researchers isolated these. Many such reactions are controlled by one or more individual amino acids in the enzyme. Benjamin found that the amino acid proline is an efficient catalyst and assists asymmetric catalysis.  In its case, out of two mirror images,  one comprises more than 90 % and is the useful component. Others include cholesterol, chlorophyll, or the toxin strychnine.

David MacMillan designed simple organic molecules which (just like metals) could temporarily loosen the bonds between atoms. He selected a reaction, which chemists use to build (organic compound) rings of carbon atoms. Some of these organic molecules are also excellent for asymmetric catalysis with mostly one type of desired structural configuration.

These scientists designed cheap and stable organic catalysts, which can be used to accelerate a variety of chemical reactions. They work just like nature’s enzymes.  Previously,  it was necessary to isolate and purify each intermediate product, otherwise, the volume of by-products becomes too great. This led to some of the substances being lost at every step. Organo-catalysts work in an unbroken sequential reaction, which can considerably reduce waste in chemical manufacturing.

Strychnine is a toxic compound used as a pesticide. Its synthesis is an example of how organo-catalysis has led to more efficient molecular constructions. Earlier, it required more than two dozen chemical reactions, and less than  0.001 percent of the initial material formed strychnine, the rest was wasted.  With organo-catalysts it is built in just a few steps, and the production process is much more efficient.

Organo-catalysis is most important in the pharmaceuticals industry.  Researchers can now make large volumes of different asymmetric molecules in a simple way. For example, they can now artificially produce potentially curative substances that were otherwise isolated only in small amounts from rare plants or deep-sea organisms. At pharmaceutical companies, this method is also useful to streamline their existing products. Two examples of this are paroxetine, which is used to treat anxiety and depression, and the antiviral medication oseltamivir, which is used to treat respiratory infections.

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Professor Dr. Surjit Singh Bhatti, Calgary, Canada  (surjitsinghhatti@gmail.com)

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