What is Soai reaction? How Kenso Soai and Henri B. Kagan helped solve mirror-image mystery to win the Nobel Prize in Chemistry 2026

Soai reaction is an asymmetric autocatalytic reaction, which was developed by Japanese chemist Kenso Soai. His research demonstrated how a small initial imbalance between two mirror-image molecules can be amplified, helping chemists understand how one molecular form can become dominant.

Soai and French chemist Henri B. Kagan were awarded the 2026 Nobel Prize in Chemistry for "for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis."

What Are Mirror-Image Molecules Explained

Some molecules exist in two forms that are mirror images of one another, these forms are known as enantiomers.


This is particularly important in chemistry involving living organisms. Amino acids, for example, exist in two mirror-image forms, but only one is found in the proteins in our cells. The sugar molecules that are part of DNA also have two possible mirror-image forms, while life uses only one.

Chemists refer to this one-sidedness as homochirality. How homochirality can emerge has been a longstanding question in chemistry.

How Did Kenso Soai Develop the Soai Reaction

Soai studied an asymmetric chemical reaction that showed a major non-linear effect. When he examined the structures of the reaction’s catalyst and the product formed, he noticed significant similarities between them.

That led him to consider whether he could design a reaction in which the catalyst formed itself through an autocatalytic process.

After experimenting with different molecules Soai found a chiral substance called '5-pyrimidyl alkanol' that could participate in such reaction.

What Happened in the 1995 Soai Experiment

In research published in 1995, Soai and his colleagues demonstrated that autocatalysis could amplify a small initial enantiomeric excess.

They began with 5-pyrimidyl alkanol containing a 2% excess of one enantiomer. The reaction amplified that imbalance, ending with an excess of 87%.

The Royal Swedish Academy of Sciences says the reaction was self-reinforcing and fulfilled the criteria of a model proposed by Frank for how autocatalysis and inhibition could allow a small initial imbalance to become strongly one-sided. However, the experiment, did not reach 100% enantiomeric purity.

The original Nature paper reported that the 5-pyrimidyl alkanol underwent an autocatalytic reaction that generated more of the alkanol and enhanced the enantiomeric excess.

What Was the 2003 Soai Breakthrough

Soai continued his search for an autocatalytic process that could go further.

In 2003, he presented a reaction in which chiral molecules were created from a non-chiral combination of molecules and only one of the two possible mirror images formed. The Royal Swedish Academy of Sciences describes this as something previously achieved only by life itself.

At the beginning of the reaction, both enantiomers were created. Because chance could result in slightly more of one enantiomer being formed, that small excess could then be amplified through autocatalysis.

According to the Academy, the favoured enantiomer could ultimately comprise 99.99% of the product. When the reaction was repeated, the other enantiomer could instead become dominant; which one prevailed depended on what happened by chance at the beginning of the reaction.

Why Is the Soai Reaction Important

The importance of the Soai reaction is that it provided a chemical example of how a small initial imbalance in chirality could be amplified through autocatalysis.

The reaction also generated new interest in research into the chemical origins of life and the emergence of homochirality.

However, the Soai reaction is artificial and differs from the chemistry of life. It should therefore not be described as proof of how life originated. The Royal Swedish Academy specifically distinguishes the reaction from the chemistry of life.

How Did Soai’s Work Contribute to the 2026 Nobel Prize

Soai’s work was part of a broader chain of discoveries recognised by the 2026 Nobel Prize in Chemistry.

In 1986, Kagan discovered a way of manipulating chemical reactions that allowed a greater excess of one mirror image to be created than previously thought possible. His work demonstrated what chemists call non-linear effects.

Soai subsequently built on this area of research. His 1995 work demonstrated amplification of a small enantiomeric excess, while his 2003 work demonstrated the formation of chiral molecules from a non-chiral combination in which only one of the two possible mirror images formed.

The discoveries recognised by the Nobel Prize have given chemists tools for designing asymmetric reactions. The Royal Swedish Academy says these are important in areas including pharmaceuticals, flavours, scents, agricultural chemicals and some new materials.

The 2026 Nobel Prize therefore recognises the broader discoveries of Kagan and Soai, rather than the Soai reaction alone. Its official citation is: “for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis.”