Nobel Prize in Chemistry 2026 rewards a reaction that makes molecules pick one hand

Every protein in your body is built from left-handed amino acids, yet when chemists make those same molecules in a flask they get left and right versions in equal amounts. Henri B. Kagan and Kenso Soai showed how a reaction can break that tie, letting a tiny surplus of one mirror image grow until it takes over almost completely. The Royal Swedish Academy of Sciences has awarded them the Nobel Prize in Chemistry for it, and the work now sits behind how drug makers chase the right version of a medicine.

Many molecules come in two forms that are mirror images of each other, like a left and a right hand. Chemists call such molecules chiral, and the two versions enantiomers. They contain the same atoms joined in the same order, but they do not fit the same biological locks, so one form of a drug can heal while its twin does nothing or causes harm. Life is what chemists call homochiral: it uses only one hand of its amino acids and only one hand of the sugars in its DNA, and nobody has fully explained how it got that way.

Kagan, a French chemist at what was then Université Paris-Sud, and Soai, a Japanese chemist at the Tokyo University of Science, were cited “for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis.” They split 12 million Swedish kronor equally. “Henri Kagan and Kenso Soai have provided a solution to a chemical mystery that is over a century old: how homochirality can emerge spontaneously. The chemical reactions they have developed are spectacular,” said Heiner Linke, chair of the Nobel Committee for Chemistry.

The puzzle a physicist wrote down for chemists

The Nobel committee traces the prize back to Louis Pasteur, who sorted crystals of tartaric acid with tweezers under a microscope and found two mirror forms that bent polarised light in opposite directions. He later noticed that bacteria fermented only one of them. That was the first hint that the chemistry of life plays favourites.

Ordinary chemistry does not. A reaction that can form both mirror images, left to itself, makes a 50-50 mix, which chemists call a racemate. The trick for making more of one hand is a chiral catalyst, a helper substance that is not used up and that steers the reaction toward one version. Early attempts produced only a tiny bias.

Then the British theoretical physicist Charles Frank, at the University of Bristol, sketched on paper what a reaction would need to drive a mixture all the way to one hand. It needed a chiral catalyst, a way of boosting one mirror image while suppressing the other, and a product that catalyses its own formation, a property called autocatalysis. Frank closed his short paper by noting that a laboratory demonstration was not impossible. For decades, nobody managed it, and the problem became a classroom puzzle.

How they did it

Kagan attacked the second of Frank’s conditions by asking a question nobody had bothered with. Chemists assumed that the purity of the product simply mirrored the purity of the catalyst: feed in a catalyst that is 50 percent one hand, and you get a product with about half the bias you would get from a pure one. Kagan suspected the metal at the heart of these catalysts grabbed at least two chiral molecules at once, which would create three kinds of catalyst: left-left, right-right and a mixed left-right pair.

If the mixed pair worked more slowly than the matched ones, it would quietly soak up the minority hand and leave the majority catalysts to do most of the work. His team tested three reactions and found exactly that kind of break from the straight line. In one of them, a widely used oxidation developed by Barry Sharpless, the product came out purer than the catalyst that made it. Chemists named the phenomenon a non-linear effect, and it spread fast. In a related zinc reaction studied by Ryoji Noyori, a catalyst that was only 15 percent enriched in one hand delivered a product that was 98 percent enriched.

Soai went after Frank’s last condition, autocatalysis. Working on reactions that add zinc compounds to aldehydes, he noticed that the product looked a lot like the catalyst and wondered whether the product could become its own catalyst. His first self-copying reaction did copy itself, but the purity eroded each round: a catalyst 86 percent enriched gave a product only 35 percent enriched.

The breakthrough came with a pyrimidine alcohol, a molecule built around a ring of carbon and nitrogen atoms that forms when a zinc compound called diisopropylzinc reacts with a matching aldehyde. A catalyst made from a batch of that alcohol with only a 5 percent surplus of one hand produced new alcohol with a 55 percent surplus. Fed back in, that product became the catalyst for the next run, which reached 87 percent, and after five runs the purity plateaued around 90 percent. A refined version later took a sample whose imbalance was just 0.00005 percent and pushed it above 99.5 percent in three rounds, an amplification of the ratio between the two hands by a factor of 630,000. This amplifying self-copying chemistry is now called the Soai reaction.

A coin flip that picks a side

The most striking run used no chiral ingredient at all. Soai’s team started from molecules with no handedness and let the reaction go. Random fluctuations always leave one hand very slightly ahead, and the Soai reaction is sensitive enough to seize on that sliver and amplify it. In a series of 37 experiments, 18 ended with one hand dominant and 19 with the other, with purities ranging from 15 to 91 percent. Daniel Singleton, working independently in the United States, showed the same symmetry breaking.

That outcome looks a lot like what the young Earth would have needed: a reaction that picks a side by chance and then locks it in. The Nobel committee calls it the first laboratory experiment to confirm Frank’s model without any outside chiral influence, and the first time since the dawn of life that anyone had created handedness from a mix of molecules that had none.

Why your medicine cabinet cares

The thalidomide disaster of the early 1960s, when a sedative caused severe birth defects in thousands of children, made drug makers acutely aware that the two hands of a molecule can act very differently in the body. Investigators later concluded that the drug’s mirror form was responsible for the harm, although the body converts one form of thalidomide into the other, so even a pure dose would not have been safe. Today regulators expect companies to know which form of a chiral drug they are selling and what the other one does.

Kagan’s non-linear effects became an everyday diagnostic tool. If a reaction behaves non-linearly, that tells chemists how many chiral pieces gather around the catalyst, which helps them redesign the process for a purer product. The committee lists pharmaceuticals, flavours, scents, agricultural chemicals and some new materials among the industries that depend on this. Erick Carreira’s group used an asymmetric autocatalytic step to make a key building block of efavirenz, an HIV drug.

What the prize does not settle

The prize does not explain why life chose left-handed amino acids. The committee’s own scientific background says Frank’s model is only one possible route among several to an event that happened about 3.5 to 4 billion years ago, and that we will probably never have a definitive answer. The Soai reaction runs on zinc compounds that would not survive in water, so it is a proof of concept, not a re-creation of early Earth chemistry.

The Soai reaction also works on a narrow set of molecules. Only a handful of other systems show the same amplifying self-copying behaviour, and none has been found for amino acids or sugars. Even the mechanism is contested. One group led by Scott Denmark explains the amplification through a four-zinc cluster that only fits molecules of one hand, while Oliver Trapp’s team proposes a different intermediate and a kinetic bottleneck. The committee notes that both models might hold for different molecules, which also means neither has won.

Common questions about the 2026 Nobel Prize in Chemistry

Who won the Nobel Prize in Chemistry 2026?

Henri B. Kagan of the former Université Paris-Sud in France and Kenso Soai of the Tokyo University of Science in Japan share the prize equally. They were honoured for discovering non-linear effects and autocatalysis in asymmetric organic synthesis.

What does chiral mean in chemistry?

A chiral molecule cannot be superimposed on its mirror image, the way your left hand cannot be laid perfectly on your right. The two mirror versions, called enantiomers, can behave very differently inside living things.

What is the Soai reaction?

It is a reaction in which the product acts as a catalyst for making more of itself and favours its own handedness. A tiny surplus of one mirror image snowballs over successive rounds until almost all of the product has one hand.

Why does chirality matter for medicines?

Many drug molecules come in two mirror forms, and often only one has the intended effect while the other is inactive or harmful. Making the right form efficiently depends on asymmetric catalysis, the field these discoveries reshaped.

When it happened, and what comes next

Frank published his model in 1953. Kagan, who was born in 1930 in Boulogne-Billancourt, described the first non-linear effects in 1986. Soai, born in 1950 in Hiroshima, reported his first self-copying reaction in 1990, the amplifying version in the journal Nature in 1995, and the spontaneous symmetry breaking in 2003. The prize builds on two earlier chemistry Nobels for asymmetric catalysis, in 2001 and 2021.

Laboratories around the world are now trying to do for amino acids and sugars what Soai did for his pyrimidine alcohol. Kagan and Soai will receive their medals in Stockholm on 10 December.

Reference: Soai, K.; Shibata, T.; Morioka, H.; Choji, K., “Asymmetric autocatalysis and amplification of enantiomeric excess of a chiral molecule,” Nature, 1995. DOI: 10.1038/378767a0

Tags: Nobel Prize, amino acids, chemistry, chirality, Henri Kagan, Kenso Soai