A recent discovery made by researchers at the University of California at Los Angeles (UCLA) overturns a well-established law of organic chemistry: Bredt's rule. Nearly a century old, it asserted that it was impossible to create certain types of specific organic molecules due to their instability. The discovery by the UCLA team is a game-changer: it makes it possible to envisage new molecular structures that were previously inaccessible and could revolutionize certain fields such as pharmaceutical research.
What is Bredt's rule and why is it so important?
To understand the impact of this discovery, it is helpful to first explain some organic chemistry basics. Organic chemistry mainly studies molecules composed of carbonlike those found in living beings. Among them, certain molecules, called olefins or alkenes, have doubles liaisons between two carbon atoms. This double bond confers a specific geometry: the atoms and groups of atoms linked to it are generally found in the same plane, a characteristic which makes these structures quite rigid.
In 1924, the German chemist Julius Bredt states a rule for certain molecular structures called bridged bicyclic molecules. These molecules have a complex structure with several rings that share common atoms, much like two bracelet loops that intersect. Bredt's rule states that these molecules cannot have a double bond in a position called a bridgeheadthat is to say where the two cycles come together. This rule is explained by geometric reasons: a double bond at the head of the bridge would cause a structural constraint so great that the molecule would become unstable, or even impossible to create.
This law remained indisputable in organic chemistry for almost 100 yearsimposing limits on scientists in the molecular structures they could envisage. In other words, it seemed impossible to create molecules of this type, called anti-Bredt olefins (or ABOs). Chemists and pharmacologists have therefore abandoned these structures, which has limited the field of possibilities for certain scientific and industrial applications.
A major breakthrough from UCLA: making impossible molecules
Now, UCLA chemists, led by Professor Neil Garg, have challenged this seemingly inescapable rule. Their study, published in the prestigious journal Science, demonstrates that it is in fact possible to create olefins anti-Bredt. The team not only proved that these molecules could exist, but also developed a method to make them, opening the door to a whole new category of organic compounds.
To circumvent the constraint imposed by Bredt's rule, the UCLA researchers used silyl halidesa type of chemical compound, to generate reactions that lead to the formation of ABOs. Since these molecules are very unstable, the team added another chemical to trap these structures and make them usable for analyzes and applications. The results show that it is not only possible to create anti-Bredt olefins, but also to stabilize them sufficiently to study them and use them in chemical reactions.
According to Neil Garg, this discovery shows that certain rules of chemistry should not be taken as absolute truths, but rather as guidelines. By freeing chemists from this imposed limitation, they can now consider more varied and complex molecular structures.
The implications of this discovery for scientific research
The questioning of Bredt's rule marks a turning point in the history of organic chemistry. The UCLA team emphasizes the importance of this advance in that it makes it possible to design molecules that were until now theoretically impossible to create. This means that chemists now have an additional tool to innovate and design unique structures with new chemical functions.
Anti-Bredt olefins could notably play an essential role in cutting-edge fields such as pharmaceutical research. In the development of new drugs, the ability to manipulate three-dimensional molecular structures is indeed crucial. These molecules, due to their unique shapes, can indeed interact more specifically with biological targets, which can lead to more effective drugs with fewer side effects.
This study not only opens the way to new drugs: it also illustrates a fundamental principle in science: that of questioning dogmas. What we thought impossible yesterday can become achievable today thanks to scientific progress and methodological innovations.
