Henri B. Kagan

Henri B. Kagan (born December 15, 1930, Boulogne-Billancourt, France) is a French chemist who was awarded the 2026 Nobel Prize for Chemistry for his work on nonlinear effects in asymmetric chemical reactions. He shared the prize with Japanese chemist Kenso Soai.

Kagan received a bachelor’s in chemical engineering from the École Nationale Supérieure de Chimie de Paris in 1954 and a doctorate from the Collège de France in 1960. He then became a research associate at the Collège de France. In 1967 he became an assistant professor at the Université de Paris-Sud, where he spent the remainder of his career. In 1999 he became an emeritus professor at the Université de Paris-Sud.

The molecules that make up living things have two forms (or enantiomers) that are mirror images of each other. However, life only uses one of these forms; life is homochiral, Greek for “same” and “hand.” How a chemical reaction that makes more of one form than the other (that is, an asymmetric reaction) could happen was the subject of Kagan’s Nobel Prize-winning work.

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Chemists knew that for such a reaction to occur, the catalyst (the substance that drives the reaction) would have to have a specific chirality (handedness) itself. Chemists also thought that the chirality of the catalyst would be directly reflected in the chirality of the products. Kagan began wondering in the late 1960s if that relation between the chirality of the catalyst and that of the products was true.

In 1986 Kagan and his collaborators published a paper describing three different asymmetric reactions. The catalyst had two pieces: a metal ion and left- or right-handed forms of some chiral molecule. Two of the chiral molecules would bond to the metal ion to form the catalyst. This meant that there would be three types of catalyst: right-metal ion-right, left-metal ion-left, and left-metal ion-right. Kagan’s realization that the left- and right-handed forms had an affinity for one another (instead of their own type) led to his finding that the left-handed form (the minor enantiomer) is sequestered by the catalytically inactive left-metal-right form (the less-reactive heterochiral catalyst). The resulting right-metal-right catalyst was then able to react, allowing for the formation of a product having very high optical purity.

Kagan’s discovery ultimately allowed for the generation of safer and more effective single-handed molecules by the pharmaceutical industry; previously, drugs with the incorrect mirror image were either very toxic or simply inactive. His work further offered a mathematical basis for a possible explanation of handedness observed among essential molecules of life (e.g., left-handed amino acids and right-handed sugar molecules).

Among Kagan’s honors for his work are the Silver Medal of the French National Centre for Scientific Research (1974), the Wolf Prize in Chemistry (2001, shared with K. Barry Sharpless and Noyori Ryōji), and the Franklin Institute’s Bower Award and Prize for Achievement in Science (2005). He was named a chevalier of the Legion of Honour in 2002.

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