Kagan and Soai share chemistry Nobel for controlling molecular handedness

Henri B. Kagan and Kenso Soai won the 2026 Nobel Prize in Chemistry on 7 October for discoveries that help chemists favour one mirror-image form of a molecule, the Royal Swedish Academy of Sciences announced in Sweden. The work gives researchers ways to control a property that matters when making compounds for pharmaceuticals, while leaving open how that preference first arose in living systems.

The Academy awarded the prize for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis. Kagan, of France, and Soai, of Japan, will share the 12 million Swedish kronor award equally. Their findings describe different routes by which a small preference for one molecular form can grow into a much larger one.

Why molecular handedness matters for medicines

Some molecules exist in two forms that relate to each other as a left hand does to a right hand. The Academy calls this property chirality. It says amino acids can have either mirror-image form, yet the proteins in living cells contain one of them. For chemists designing compounds that interact with living organisms, the distinction can matter even when the two forms look closely related on paper.

The Academy says the laureates’ discoveries enabled chemists to steer reactions towards homochirality, a predominance of one mirror-image form. It identifies pharmaceutical manufacturing as one application of this control. Its account also describes Kagan’s findings as useful for obtaining purer forms of compounds used in flavours, scents, agricultural chemicals and some materials.

How Kagan and Soai amplified a chemical preference

Kagan’s contribution concerned how a catalyst’s composition affects the balance between a reaction’s two possible mirror-image products. In work the Academy dates to 1986, he showed that the relationship could be non-linear: a change in the catalyst’s balance could yield a larger than expected excess of one product. That gave chemists a way to understand and improve reactions seeking a particular molecular form.

Soai’s work took a different route. The Academy says a reaction he published in 1995 was autocatalytic, meaning its product helped drive further production of itself. In the example it gives, an initial 2% excess of one form rose to 87%. The figures illustrate amplification within that reaction; they do not describe the composition of naturally occurring amino acids or a medicine.

The Academy dates Soai’s successful reaction producing only one of the two possible mirror-image forms to 2003. It says the reaction could amplify a tiny chance imbalance, while the form that became dominant varied between repetitions. The result offered an experimental way to study how a chemical system might develop a strong preference without starting with a large one.

What the prize does not establish about life’s origins

The question predates both laureates. In its historical account, the Academy traces research on molecular handedness through Louis Pasteur’s 19th-century work on tartaric acid and a 1953 theoretical model by Charles Frank. Frank proposed that autocatalysis could reinforce an excess of one form. The later experiments gave chemists concrete reactions with which to investigate such behaviour.

The Academy also draws an explicit boundary around the finding: Soai’s reaction is artificial and differs from life’s chemistry. Researchers are working on related approaches involving homochiral amino acids and sugars, but these results alone do not show how living systems acquired their preference for particular molecular forms. The origin of biological homochirality remains an open question on the evidence described by the Academy.

Heiner Linke, chair of the Nobel Committee for Chemistry, called the emergence of homochirality a chemical mystery more than a century old and described the laureates’ reactions as spectacular, according to AP. Soai told AP that there were still fascinating unknowns and more to discover. Their award recognises an experimentally powerful way to control molecular handedness, while research into its role at life’s beginnings continues.