Kagan and Soai win chemistry Nobel for mirror-molecule work
The academy says Kenso Soai’s reaction was the first in which only one of two possible mirror images formed, a feat no one but life had achieved.
Henri B. Kagan and Kenso Soai have won the 2026 Nobel Prize in Chemistry for work on molecules that come in two mirror-image forms, the Royal Swedish Academy of Sciences announced on 7 October 2026.
The academy gave the prize “for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis”. Kagan is Professor Emeritus at the then Université Paris-Sud in France. Soai is Professor Emeritus at Tokyo University of Science in Japan.
The puzzle is why life uses only one of two mirror-image versions of its molecules. Amino acids exist as two such variants, but only one is found in the proteins in human cells. In test tubes, chemists’ reactions that could form both always gave equal proportions.
The question matters for medicine. According to the academy’s popular-science account, one mirror image of a drug molecule can have the therapeutic effect while the other can cause sometimes harmful side effects.
“Henri Kagan and Kenso Soai have provided a solution to a chemical mystery that is over a century old: how homochirality can emerge spontaneously,” said Heiner Linke, chair of the Nobel Committee for Chemistry.
The academy traces the idea to the mid-19th century, when Louis Pasteur found that crystals of tartaric acid, a substance important for wine production, existed in two variants that were each other’s mirror image. A reaction that makes its own catalyst, known as autocatalysis, was one of the conditions in a 1953 model.
Kagan took the first step in 1986. Chemists had assumed that the purity of the product followed directly from the purity of the catalyst. Kagan reasoned that a mixed catalyst would exist in three forms, and the mixed form drove the reaction far more slowly than the other two. The product ended up with a greater excess of one mirror image than the catalyst had.
Soai took the next step, which the academy calls the first reaction in which only one mirror image formed. No one but life had achieved that before. A 1995 publication described a self-creating substance, 5-pyrimidyl alkanol, and a reaction that started with a 2% excess of one mirror image. It ended with an excess of 87%, short of the 100% purity found in life.
In 2003, Soai presented a reaction in which a small excess of one mirror image formed copies of itself. Chance decided which version took over, and the winner could make up 99.99% of the product.
The academy says the Soai reaction is artificial and different to the chemistry of life, and researchers are now trying to repeat the achievement with amino acids and sugars. It adds that Kagan’s non-linear effects help chemists design reactions for pharmaceuticals, flavours, scents and agricultural chemicals.