Kagan and Soai share the chemistry Nobel for mirror-image reactions

Henri Kagan and Kenso Soai won the 2026 Nobel Prize in Chemistry on Wednesday for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis. The Royal Swedish Academy of Sciences said the work shows how a reaction can be driven toward one molecular mirror image. Kagan, 95, is French and a professor emeritus at Paris-Saclay, formerly Paris-Sud. Soai, 76, is Japanese, at the Tokyo University of Science. They share 12 million Swedish kronor, about 1.2 million dollars at 10.0309 kronor to the dollar.

The problem is older than either man. Louis Pasteur, in the nineteenth century, saw that tartaric acid comes in two crystal forms that are mirror images, and that a mould ferments only one of them. Living cells are built the same way. Amino acids and sugars in the body are almost all of one handedness. Chemists call that homochirality. A reaction in a flask, left alone, usually makes both hands in equal amount. A drug can need only one. The other can be useless, or harmful. The Academy pointed to thalidomide in the early 1960s, when one mirror image of a sedative was tied to birth defects in thousands of children. Peter Somfai, of the Nobel Committee for Chemistry, said the left-handed form of a drug can have one effect and the right-handed form another, and that chemists need ways to make only the form they want. He called the laureates' findings powerful tools for that work, and one experiment probably the coolest in organic chemistry.

Kagan has worked on chirality since the 1960s. His non-linear effects showed that a small excess of one mirror image in a catalyst can produce a much larger excess in the product. The relationship is not a straight line. A little imbalance at the start becomes a large imbalance at the end. Soai then showed a reaction that amplifies itself. In autocatalysis, the product is also the catalyst. If the product is chiral, the hand that appears first can speed its own making and suppress the other. Somfai described this as making one mirror image from almost nothing. That is the link the Academy drew to the origin of biological handedness. A tiny chance imbalance, repeated, can become the single hand life uses.

The prize also closes a long French argument. In 2001 the chemistry Nobel went to William Knowles, Ryoji Noyori and Barry Sharpless for asymmetric catalysis. The French research minister at the time complained to the Nobel Foundation that Kagan had been left out. Wednesday's award does not revise 2001. It gives Kagan the prize 25 years later, at 95, for the non-linear effects that sat beside that earlier work. Soai learned of the call while he was out buying groceries. He told the Stockholm press conference it was the most exciting day of his life, and that he was glad to share it with Kagan. From Tokyo he said the mystery is not fully solved and that he would keep at the research. His daughter is not the family voice in the record. Kagan's daughter, Veronique Le Deunff, said she was very happy, and that the creativity of the work had opened new lines of research.

The political notes were short. President Emmanuel Macron congratulated the laureates and called the prize an honour for France and a fit recognition of a life of research. Prime minister Sanae Takaichi telephoned Soai and said that, as a Japanese, she was proud of him. The medals will be handed over by King Carl XVI Gustaf on 10 December in Stockholm, followed by the banquet at City Hall.

For a chemist in a plant the takeaway is practical. A process that can be seeded with a small excess, or that amplifies its own product, uses less of an expensive chiral catalyst and wastes less of the unwanted hand. For anyone reading the citation, the two names do different jobs. Kagan showed the non-linear jump. Soai showed the reaction that runs away toward one hand. The Academy gave them one prize because the second result sits on the first.