The 2026 Nobel Prize in Chemistry was awarded to French and Japanese scientists for deciphering chemical asymmetry. What is chemical chirality? What contributions did their discoveries make?

This year’s Chemistry Prize is truly chemistry! In one sentence: the two laureates studied the chiral amplification effect in asymmetric catalysis. On the occasion of its 125th anniversary, the journal *Science* published a list of the 125 most challenging scientific questions—among them, a question directed at chemistry asked: “Why does life require chirality?” Some molecules—such as amino acids—exist in two mirror-image forms. Yet only one of these mirror-image variants appears in living organisms. Chemists have long been puzzled about how this chemical asymmetry arises. Henri Kagan and Kensō Soai have been awarded the 2026 Nobel Prize in Chemistry for solving this puzzle. I. First, a quick refresher: What is chirality? (Readers familiar with my earlier article, “What do you consider the most ‘artistic’ chemical discovery?” may skip this section—but this time I’ll clarify points left insufficiently explained before.) Chirality, put plainly, means: an object and its mirror image cannot be superimposed by any combination of rotations or translations. The term originates from the Greek word χείρ (cheir), meaning “hand.” In the late 19th century, Lord Kelvin gave it the definition still used today: “Any geometrical figure or point group is chiral if its mirror image cannot be brought into coincidence with itself.” For example, when you pick up a seashell on the beach, it elegantly coils to the right—and even after searching the entire shoreline, you’re unlikely to find its left-coiling mirror counterpart. Raise your hands: your left and right hands are mirror images, yet you cannot fit a left-hand glove onto your right hand. The wonder of chemistry lies in the fact that molecules, too, possess chirality. When you peel an orange, the fresh, zesty aroma wafting toward you comes primarily from a molecule called limonene. Intriguingly, another limonene molecule—with identical atoms and identical connectivity—smells sharply of turpentine instead. A more classic example is carvone: (R)-(−)-carvone smells like spearmint (the cool, refreshing scent of mint gum), whereas (S)-(+)-carvone smells like caraway (the pungent, spicy aroma of cumin and coriander seeds). Though they share the same molecular formula, these two enantiomers deliver entirely distinct olfactory experiences. Why do these chemical twins trigger such radically different responses in your nose? Because your olfactory receptor proteins themselves are chiral—they are chiral enzymes and receptors. When encountering two enantiomers, they behave like left hands shaking only left hands, generating distinct neural signals and thus distinct perceptions. II. A painful lesson: biological systems are chiral recognition machines Before the 1960s, humanity had not fully grasped that biological systems themselves function as chiral recognition machines. The cost was devastating. Thalidomide, a sedative launched in 1957, contained equal amounts of its (R)- and (S)-enantiomers. The (R)-enantiomer conferred the desired sedative effect, while the (S)-enantiomer caused severe birth defects. Shortly after thalidomide’s market release in 1957, its potential teratogenicity became apparent. Although Grünenthal GmbH swiftly recalled all stock, over 3 million tablets had already been sold worldwide—impacting more than 10,000 infants. Countless miscarriages, premature births, and stillbirths were also attributed to thalidomide.

The 2026 Nobel Prize in Chemistry was awarded for ‘chirality.’ Are drug names containing ‘left’ or ‘right’ (e.g., levofloxacin and eszopiclone) applications of this principle?

Eszopiclone (marketed as ‘right’-eszopiclone) is a similar case. Ordinary zopiclone contains a racemic mixture of two mirror-image molecules; ‘right’-eszopiclone isolates the (+)-(S)-enantiomer.[2] That is, levofloxacin is ‘left-rotating’ and belongs to the S-configuration; eszopiclone is ‘right-rotating’—yet it, too, belongs to the S-configuration. This involves two distinct nomenclature systems: ・‘Left-rotating’ and ‘right-rotating’ refer to how a molecule rotates plane-polarized light—clockwise (+) or counterclockwise (–).[3] ・R and S denote the three-dimensional spatial arrangement of atoms within the molecule. II. Mirror-image molecules can indeed exhibit vastly different pharmacological effects Although enantiomers share nearly identical chemical compositions, their differing three-dimensional shapes affect how they bind to target sites—leading to significant differences in efficacy. Ofloxacin is a racemic mixture comprising levofloxacin (S-enantiomer) and R-(+)-ofloxacin (R-enantiomer, literally translatable as ‘dextrofloxacin’). ・One study comparing 801 microbial strains found that levofloxacin’s antibacterial activity was generally comparable to, or up to ~4-fold higher than, that of ofloxacin; another study involving 506 Gram-positive bacterial strains showed levofloxacin’s overall antibacterial activity to be approximately twice that of ofloxacin.[4,5] ・Moreover, the S-enantiomer’s antibacterial activity can be up to ~100-fold greater than that of the R-enantiomer—primarily due to differences in their ability to inhibit bacterial DNA gyrase.[6] A similar phenomenon occurs with eszopiclone. ・According to FDA review documents, the S-enantiomer (i.e., eszopiclone) binds to the GABA_A receptor complex with roughly 50-fold greater affinity than its R-counterpart.[2] III. This year’s Nobel Prize research focuses on ‘selecting and amplifying’ one handedness We already know that enantiomers often differ markedly in biological effect. Yet chemical reactions producing chiral molecules typically yield both mirror-image forms equally. For pharmaceuticals, fragrances, pesticides, and other products, however, we frequently desire only one enantiomer. The 2026 Nobel Prize in Chemistry was awarded to Henri B. Kagan and Kensō Soai “for discovering nonlinear effects and autocatalysis in asymmetric organic synthesis.”[7] Kagan discovered that certain asymmetric reactions can amplify minute initial imbalances. Soai later identified a special reaction in which the chiral product itself acts as a catalyst to produce more of the same enantiomer. In his landmark 1995 experiment, starting from just 2% enantiomeric excess of one form, he amplified it to 87%.[8] This addresses the fundamental question: “How can one mirror-image form become increasingly dominant?” Thus, a more precise statement is: Levofloxacin, eszopiclone, and the 2026 Nobel Prize in Chemistry all fall under the broad umbrella of chiral chemistry. The ‘left’ and ‘right’ in drug names illustrate *why* chirality affects drug efficacy; this year’s Nobel Prize, by contrast, illuminates *how* chemists selectively generate—and amplify—one specific chiral form during synthesis. References [1] U.S. Food and Drug Administration. LEVAQUIN (levofloxacin) Prescribing Information. 2020.

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