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A new method for the preparation of chiral molecules

Many of the organic compounds exist in two slightly different structural forms called enantiomers, and they may have different properties in biological systems

A chiral molecule. University of Gothenburg.
A chiral molecule. University of Gothenburg.

Many of the organic compounds exist in two slightly different structural forms called enantiomers, and they may have different properties in biological systems. The big challenge is the control of the particular form obtained - a problem that has proven to be significant in the pharmaceutical industry. Researchers from the Swedish University of Gothenburg have now succeeded in developing a new method to control the process.

"Organic chemists believe that it is not possible to produce only one of the enantiomers without adding a component with a certain optical activity into the reaction, but we succeeded," says Theonitsa Kokoli from the Department of Chemistry at the University of Gothenburg, Sweden. "Our approach provides the industry with a method to produce one of the two forms without the need for catalysts."

The property that gives rise to several different structural forms of molecules is called chirality. The two enantiomers can be likened to two hands: they are not overlapping mirror images. The consequences of different properties in biological systems are that the molecule behaves like Dr. Jekyll and Mr. Hyde. The difference in these properties of the enantiomers may be harmless, as in the limonene molecule - one of the enantiomers emits an aroma of orange and the other an aroma of lemon.

The drug Thalidomide is a good example of a case where different forms of the same molecule can lead to devastating and even fatal results - one of the enantiomers led to relaxation and relief of nausea in pregnant women, while the other enantiomer led to severe damage to fetuses. The thalidomide disaster is one of the reasons for the extensive research invested in the field of chirality, since it is especially necessary to control the resulting enantiomer form. Over the years, research into chirality has led to several Nobel Prizes.

In the field of biomolecules, such as DNA and proteins, only one of the enantiomers exists in nature. Unlike biomolecules, this is not the case when chiral compounds are produced synthetically in the laboratory. Normally, equal amounts of each enantiomer are obtained. One way to create an excess amount of one of them is by using a chiral catalyst, but this component only passes on the original properties that were already present in it.

"We used instead a completely asymmetric synthesis, in which optical activity is "created," explains the researcher. "This method is considered impossible by many organic chemists. In our study we used crystals for our reactions, where the two forms crystallize as distinct crystals. The product obtained at the end of the reactions contained only one enantiomer."

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