Dec 9 2019
A number of organic molecules are found to be chiral, implying that they cannot be superimposed on their mirror image. The mirror images are known as enantiomers, which could have different properties when they interact with other chiral entities, such as biomolecules.
The motorized catalyst. Image Credit: Dr Ruth Dorel/University of Groningen.
The selective production of the correct enantiomer is vital in fields such as pharmaceuticals. At present, chemists Ruth Dorel and Ben Feringa from the University of Groningen have formulated a method that not just realizes this but also controls which version is being synthesized using light. The study outcomes have been published online in the Angewandte Chemie journal on November 17th, 2019.
Helical Structure
The new method involves using a molecular motor developed by Professor Feringa. The 2016 Nobel Prize in Chemistry was awarded to Professor Feringa for developing the motor molecule. This molecule was employed to synthesize the first switchable catalyst for asymmetric anion-binding catalysis.
We attached anion-binding arms on both sides of the motor molecule to create an anion receptor that can act as a catalyst. This receptor will adopt a helical structure in the presence of anions that, depending on the relative position of the arms, will exist in different forms.
Dr Ruth Dorel, Chemist, University of Groningen
In this research, the researchers used a very slow-turning motor molecule to enable the use of different stages of the rotation cycle in catalysis. The molecular motor is composed of two identical halves, which are connected by a double carbon-carbon bond that acts as the axle. Unidirectional rotation around the axle is realized by sequential exposure of the molecule to UV light and heat.
As a result, the anion-binding groups on both the halves of the motor can transform from being isolated from each other (trans) to being located close to each other on the same side of the motor molecule (cis). The arms can take up two different configurations in the cis configuration, resulting in two different helices with opposite handedness.
The helicity dictates the enantiomer of the product that this catalyst will produce.
Dr Ruth Dorel, Chemist, University of Groningen
Drugs
The researchers tested the new catalyst on a standard reaction for anion-binding catalysis. “We now have a proof of principle,” explained Dorel. Although there is still a long way before the new catalyst can be practically used, it could potentially be used in basic research and in the synthesis of polymers or drugs.
For various drugs, only one of the mirror images acts as the active substance—the other may either have no role or can cause side effects. “And in polymer production, a catalyst like this could alter the shape and properties of the polymer chain on demand.”