STOCKHOLM, Oct 7 – French chemist Henri B. Kagan and Japanese scientist Kenso Soai have been awarded the Nobel Prize in Chemistry for discoveries that helped scientists understand and control the unusual mirror-image behavior of molecules, work that has become fundamental to modern drug development.
The two scientists were recognized for finding ways to make chemical reactions favor one particular version of a molecule over its mirror image. Although the two forms can have exactly the same atoms and chemical formula, their three-dimensional arrangements can be different enough to produce dramatically different effects.
The phenomenon is known as molecular chirality, a term derived from the Greek word for hand. The comparison is straightforward: a person’s right and left hands are mirror images of one another, but they cannot be perfectly superimposed. Molecules can display the same kind of handedness.
The difference can have major consequences in medicine. One version of a molecule may interact with a biological target in a useful way, while its mirror image may have a different effect. For researchers developing medicines, being able to control which form is produced can therefore be essential.
The Royal Swedish Academy of Sciences announced the chemistry prize in Stockholm on Wednesday, honoring Kagan, 95, who is affiliated with Université Paris-Sud in Orsay, France, and Soai, 76, of the Tokyo University of Science.
The prize recognizes decades of research into a problem that had challenged chemists for generations: how to persuade ordinary chemical reactions to consistently produce one molecular form rather than a mixture of both.
How mirror-image molecules changed chemistry and medicine
The importance of the discovery can be understood through examples found in everyday chemistry. Carvone, a molecule used in flavoring and fragrances, exists in two mirror-image forms. One has a smell associated with mint, while the other resembles the scent of caraway, a spice commonly used in foods such as rye bread.
The same principle becomes considerably more important when molecules interact with the human body. Biological systems are themselves highly selective about molecular shape. DNA, for example, has a characteristic right-handed structure, while proteins in the human body are built primarily from left-handed amino acids.
That selectivity means a molecule’s shape can determine how it behaves inside the body. A drug molecule must often fit into a particular biological target much like a key fitting into a lock. A mirror-image version may fit differently, fail to produce the intended effect or interact with another target.
Kagan’s research in the 1980s helped establish that chemists could deliberately design reactions to favor one molecular form. His work provided important evidence that molecular handedness could be controlled through chemical design rather than simply accepted as an unavoidable feature of reactions.
Soai later took the field further. His research produced what became known as the Soai reaction, a landmark chemical reaction capable of efficiently producing one mirror-image form of a molecule. The reaction became especially important in research into asymmetric synthesis and the mechanisms by which chemical reactions can become selective.
Peter Somfai, a member of the Nobel Committee for Chemistry, described the work as a major development in organic chemistry. He said the discoveries by Kagan and Soai had fundamentally changed scientists’ understanding of molecular chirality and how chemical reactions can be controlled.
The committee characterized the achievement as something that had previously been accomplished, in effect, by life itself. Living organisms routinely produce molecules in highly specific forms, but reproducing that kind of selectivity through artificial chemistry was a much more difficult challenge.
Rigoberto Hernandez, president of the American Chemical Society, also highlighted the broad significance of the research. He said modern medicines would not be possible without this area of chemistry, reflecting how deeply asymmetric chemical synthesis has become embedded in pharmaceutical research.
The influence of the work is not limited to one particular drug or class of medicines. Scientists use the principles of molecular selectivity when designing and manufacturing compounds intended to interact with biological systems. Understanding how catalysts and reactions control molecular shape has therefore become an important part of the broader process of developing medicines.
Somfai said it would be difficult to identify a single drug and attribute its development exclusively to the work recognized by the Nobel committee because the underlying chemistry is now used as a general tool. The techniques and understanding developed through this field have instead become part of the wider foundation on which pharmaceutical chemistry operates.
Kagan and Soai react to the Nobel recognition
The award also brought recognition to two scientists whose careers span different generations of modern chemistry.
Kagan, who is 95, has been affiliated with Université Paris-Sud in Orsay, France, and is a member of the French Academy of Sciences. The academy congratulated him and Soai after the announcement, expressing pride in Kagan’s contribution to the field.
Soai, 76, is affiliated with the Tokyo University of Science in Japan. Speaking by telephone to the Nobel committee and journalists, he said he was very excited by the news and described the moment as one of the most exciting days of his life.
The timing of the call caught him away from a laboratory or university office. Soai said he was shopping near his home when the Nobel committee reached him with the news.
The chemistry award is the third Nobel prize announced during this year’s series of awards, following the medicine prize on Monday and the physics prize on Tuesday.
The medicine prize was awarded to three scientists whose research contributed to the development of a light-based technique that allows researchers to investigate how the brain works. The physics prize recognized research involving neutrinos, elusive subatomic particles that have long presented difficult questions for physicists.
The Nobel announcements will continue through the week. The literature prize is scheduled for Thursday, followed by the Nobel Peace Prize on Friday. The Nobel Memorial Prize in Economic Sciences is due to be announced on Monday.
The chemistry prize awarded to Kagan and Soai carries the same financial award as the other Nobel categories this year, with prize money totaling 12 million Swedish kronor, roughly $1.2 million. The amount is shared when a prize is awarded to more than one laureate.
Beyond the financial award, the recognition places Kagan and Soai among scientists whose work has had a lasting influence far beyond their original experiments. Their research helped turn the mysterious handedness of molecules into something chemists could deliberately manipulate.
That ability has become particularly valuable in a world where medicines are expected to be increasingly precise. Rather than simply producing a chemical compound and testing whatever mixture emerges, researchers can now design reactions with greater control over the three-dimensional form of the molecules they seek.
The Nobel committee’s decision therefore recognizes not only an important discovery in organic chemistry but also a shift in how scientists approach the relationship between molecular structure and biological function. The work of Kagan and Soai helped make molecular “handedness” a controllable feature of chemistry, opening a path that has become central to the development of many modern medicines.