A molecule is said to be chiral (Greek hand (kheir), the hand) when it can take two forms, called enantiomers, with the same chemical composition, images of each other in a mirror and not superimposed. Just like our two hands. Two enantiomers share the same physical properties, except for the deflection of polarized light. On the other hand, two enantiomers in a biological environment sometimes have different chemical properties: one enantiomer of a drug may have therapeutic properties, while the other is toxic. So being able to have any of the enantiomers of a molecule turns out to be the case crucial but also regulatory, especially for the clinical testing of new medicines.

During their synthesis, the two enantiomers are usually produced in equal amounts, forming a so-called “racemic” mixture. It appears to be very difficult to selectively synthesize only one of the two enantiomers.. Subsequently, several strategies were developed to separate enantiomers from a racemic mixture. For example, one of the two enantiomers can be reacted selectively using a chiral catalyst: it is transformed while the other remains intact. The use of chiral membranes that act as filters to separate the two enantiomers is another research direction also being explored.

Scientists from the Marseille Institute of Molecular Sciences (CNRS/Aix-Marseille University/Centrale Méditerranée) propose an original strategy to simultaneously prepare and physically separate two enantiomers of a molecule from a racemic substrate. This approach combines two chiral catalysts, mirror images of each other working in parallel and separated by a non-chiral membrane with selective permeability. Successfully tested on Jacobsen’s HKR model reaction, which allows obtaining chiral 1,2-diols* from racemic epoxides**, it could be extended to other reactions that lead to important chiral building blocks in organic or pharmaceutical synthesis. Results can be found in the Journal of the American Chemical Society.

*A diol is an organic compound that carries two hydroxyl groups (-OH).

** Functional group in which two carbon atoms are connected by an oxygen atom.

Editor: CCdM

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