Henri Kagan and Kenso Soai win the 2026 Nobel Prize in Chemistry

Henri Kagan and Kenso Soai share the 2026 Nobel Prize in Chemistry for showing how a reaction that starts almost perfectly balanced between two mirror-image molecules can end up heavily lopsided toward one. The Royal Swedish Academy of Sciences announced the award on Oct. 7 and divided 12 million Swedish kronor equally between the two men.

Kagan, born in 1930 in Boulogne-Billancourt, France, is professor emeritus at the former Université Paris-Sud. Soai, born in 1950 in Hiroshima, is professor emeritus at Tokyo University of Science. The citation reads “for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis.”

Kagan’s Non-Linear Effect, 1986

Before 1986, the working assumption was that a catalyst passes its handedness to the product in direct proportion, so a 50:50 mix of left- and right-handed catalyst should yield a 50:50 mix of product. Kagan proposed otherwise, and the Academy’s popular-science background lays out his logic: a metal atom in the catalyst binds at least two chiral molecules, so mixing the two forms produces three catalyst species, left-left, right-right and left-right. The mixed left-right species reacts much more slowly.

Because that slow species is effectively sidelined, a partly mixed catalyst can favor one product mirror image more strongly than its composition would predict, and a plot of product ratio against catalyst ratio bends into a curve instead of a straight line. Kagan reported three such asymmetric reactions in 1986, according to the Academy’s announcement, and the idea gave chemists a way to extract far more single-handed product from a catalyst that was itself only partly pure. That was a practical surprise as much as a theoretical one, since it meant an imperfect catalyst could outperform what its own purity implied.

Soai’s Self-Copying Alkanol

In the early 1990s, Soai noticed that the catalyst and the product of an asymmetric reaction showing a strong non-linear effect looked structurally alike, and he asked whether a reaction could manufacture its own catalyst. After extensive trial and error he found a chiral compound, a 5-pyrimidyl alkanol, that does exactly that. His 1995 paper in Nature, which his university profile lists as volume 378, page 767, began from a 2% excess of one mirror image and finished with an 87% excess.

That reaction reinforced itself but stopped short of purity. In 2003, the Academy’s press release says, Soai presented a reaction that formed only one of the two possible mirror images, and the announcement adds that “other than life itself, no one had previously achieved this feat.” The popular-science background puts the endpoint at 99.99% of one enantiomer, with chance at the start deciding which one wins, so repeating the experiment can tip the result the other way.

Nature’s news team notes that this realizes a 1953 proposal by the physicist Charles Frank, who imagined a reaction that builds its own chiral catalyst and thereby reinforces a single mirror image. Jonathan Clayden of the University of Bristol told the journal that Kagan showed how it could work in principle, while Soai’s reaction supplied the first real example.

Drug Manufacturing and the Origin of Handedness

The practical stake sits in pharmaceutical plants, where a wrong-handed molecule is waste at best. Often only one mirror image of a drug molecule does the intended job, and the Academy says the laureates’ discoveries have been decisive for chemists designing the reactions that make medicines. Nature’s report adds that the same logic is used in building materials and perfumes, and recalls that the 2001 chemistry prize went to William Knowles, Ryoji Noyori and Barry Sharpless for chiral catalysts that steer reactions toward one mirror image.

The larger puzzle is biological. DNA twists right-handed and amino acids are left-handed, and Heiner Linke, chair of the Nobel Committee for Chemistry, said Kagan and Soai “have provided a solution to a chemical mystery that is over a century old.” Mónica Pérez-Temprano of the Institute of Chemical Research of Catalonia told Nature the work changes how chemists think about designing reactions.

Caveats came from the same reporting. Furkan Öztürk of the California Institute of Technology pointed out that the Soai reaction needs conditions, such as an environment without water, that do not match the early Earth, though its principles may still help explain how life settled on one handedness. Stephen Fletcher of the University of Oxford said the prize could spark renewed research into the reaction’s biological relevance.

Soai said he was shopping near his home when the call came and described it as one of the most exciting days of his life.

Olivier Riant of the Catholic University of Louvain, who trained with Kagan, called his former mentor very modest and uninterested in fame. The measured endpoints of the two men’s work remain the starkest summary of what the committee honored: a 2% head start grown to 87% in 1995, and a reaction that reached 99.99% by 2003.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

More from Morning Overview