France's Henri Kagan and Japan's Kenso Soai on Wednesday won the Nobel Prize in Chemistry for solving the mystery of why only one form of certain molecules appears in nature, a discovery decisive for the manufacture of pharmaceuticals.
The pair were honoured "for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis", the jury said.
Like hands, molecules such as amino acids exist as two mirrored variants, but only one of them is found in the proteins in the body's cells, while the other is rarely found in nature.
The fact that only one appears is a phenomenon known as "homochirality", the Royal Swedish Academy of Sciences explained.
"Henri Kagan and Kenso Soai have provided a solution to a chemical mystery that is over a century old: how homochirality can emerge spontaneously," Heiner Linke, chair of the Nobel Committee for Chemistry, told a press conference.
"The chemical reactions they have developed are spectacular," Linke added.
Kagan, 95, is professor emeritus at the Universite Paris-Saclay in France while Soai, 76, is a professor at Tokyo University of Science.
Soai, who was out shopping when he received the call from Stockholm, said it was one of "the most exciting days in my life", when he was reached by the Nobel Foundation during Wednesday's press conference.
The Academy had not been able to reach Kagan to give him the news before the announcement.
French President Emmanuel Macron congratulated him on his prize on X, calling his achievement "a tremendous source of pride for the country".
Mirrored keys
The academy in a separate statement likened the chirality conundrum to a locksmith creating keys to order but whenever they produce them they get two mirrored variants.
"Only one of them fits the lock -- and the lock can be damaged if your customers try to unlock it with the other key."
One example of the potential danger of using the wrong key, or version, was the thalidomide scandal in the late 1950s and early 1960s, when thousands of children were born with birth defects.
"When researchers analysed what had happened, they realised that it was the active substance's mirror image that caused the harm," the academy said.
Phillip Broadwith, an editor at the Royal Society of Chemistry's Chemistry World magazine, explained that the duo's work "goes to the very fundamental level of understanding how we can control which 'hand' of a molecule we make".
Controlling "is crucial for making things like drugs or even flavours and fragrances", Broadwith said.
"It also helps to explain a possible way that all the chiral molecules on earth -– our proteins, sugars and biomolecules, settled into one specific handedness rather than the other," he said in an email sent to AFP by the society.
In the 1980s, Kagan found a new way of manipulating chemical reactions to create an excess of one of the mirror-image forms. Soai later took the next step and in 1995 published a key paper describing the design for "the first ever chemical reaction that had the potential to be homochiral", to create the chosen version of a molecule, the jury said.
In 2003, he succeeded.
"The Soai reaction is considered one of the most elegant chemical experiments ever conducted," the academy said.
Snubbed
Kagan had previously missed out on the Nobel prize.
In 2001, the chemistry prize was awarded to William Knowles, Ryoji Noyori and Barry Sharpless for their pioneering work in asymmetric catalysis.
That sparked controversy, with many French chemists outraged by the absence of the man regarded internationally as the "father" of the technique.
The chemistry prize follows the physics prize, which on Tuesday honoured Belgian physicist Francis Halzen for groundbreaking work using Antarctic ice to capture particles originating in the distant cosmos.
On Monday, the medicine prize was awarded to US psychiatrist and neurologist Karl Deisseroth and German scientists Peter Hegemann and Georg Nagel. The literature laureate will be revealed on Thursday, and perhaps the most keenly anticipated award — the peace prize — is due on Friday.
The economics prize wraps up the Nobel season on October 12.
