Leipzig researchers develop efficient process for chemical synthesis of terpenes

This allows the targeted production of these important substances using simple and readily available starting materials. To this end, the team has replicated the enzymatic processes that occur in nature with the help of fluorinated alcohol catalyst solutions. The process can be widely used in existing laboratories. The research results have now been published in the journal "Nature Communications".

Broad range of terpenes in nature

Terpenes give pine needles their scent and beer and orangeade their flavour. They play a key role in the communication of living beings, such as insects, but also us humans, and in defence mechanisms, for example of plants against animal predators, fungi and bacteria. In human biology, terpenes also play an important role in metabolic processes.  

Terpenes have long been used industrially on a large scale: in the production of food and food supplements, in perfumes and in medicines, for example in cancer or COVID-19 drugs. We need many tonnes of different terpenes every year and that means we have to be able to produce them efficiently and sustainably synthetically - that is a big problem," says Prof. Dr. Tanja Gulder, Chair of Biomimetic Catalysis at the University of Leipzig.

In nature, enzymes form terpenes through targeted folding
„Because nature makes these molecular compounds in a unique variant in each case,

explains Gulder. „Terpene cyclases, proteins with 100 to 1,000 amino acids, are used for this. These enzymes press simple and mobile carbon chains into a specific three-dimensional shape, which determines the appearance of the product," Gulder continues. Once the reaction has taken place, the shape of the respective terpene remains unchangeable. The reaction takes place in a so-called „enzyme pocket“ in the active centre of the enzyme, which contains a blueprint of the form to be created. Once the reaction is complete, the enzyme releases the finished product and the process is repeated with the next building block. „You can imagine this as a fast-paced molecular production machine“, says Gulder.  

There are terpenes that are similar in terms of the type and number of their atomic compounds– but whose spatial arrangements are different. „In a simple case, such atomic differences determine whether something tastes like caraway or orange“, explains Gulder. However, such differences could also mean that one terpene has a completely different effect on the human organism than the other. Errors here can have fatal consequences.
And depending on how the carbon chains are placed in the enzyme pocket, different terpenes come out, which is also part of the complexity of nature,
says Gulder.
Previously, it has been difficult to produce terpenes in the laboratory, but this has required very different and harsh starting conditions, such as a very acidic environment or low temperatures, says the researcher. This is neither effective nor environmentally friendly for large-scale production. The extraction of terpenes from organisms such as plants, animals and fungi also has its limits. „You can't harvest all the Pacific yew trees to isolate taxol for a cancer drug. You would need the bark of 12 full-grown trees of this less common tree species for 1 gram of the active ingredient," says Gulder. Currently, a precursor of the desired terpene is extracted from the needles of another tree species and then processed further.

Therefore, we wanted to see how we could replicate nature's processes in a test tube and achieve the greatest possible flexibility and efficiency.

The solution: liquid construction kit with fluorinated alcohol
The team succeeded in recreating a precisely fitting, enzyme-like environment for the formation of terpenes, which consists of easily available chemical substances. This can be used like a construction kit: By adding different starting materials and additives that act as catalysers, different terpenes can be produced artificially. The pivotal point of the new approach is the properties of fluorinated alcohol: „We had discovered that if hydrogen atoms in alcohols are replaced with fluorine atoms, the resulting fluorinated alcohol has extreme binding forces: In such solutions, molecules form helices or rings that stack up to form rings," explains Prof Gulder. The size and structure of these structures can be specifically influenced by chemical additions. „Basically, we have recreated an artificial enzyme pocket in the form of a structured solution into which our respective starting material can fold. Just as in nature, the forms remain after the reaction.“

Computer simulations were also used to develop the method. Our colleagues Philipp Dullinger and Professor Dominik Horinek from the University of Regensburg calculated which three-dimensional structures, i.e. forms, the alcohols form with the respective additives used. This was important in order to identify suitable catalysts that would lead us to the desired terpenes," reports Prof Dr Tanja Gulder.

Implementable in common chemistry laboratories
The method does not require any additional infrastructure, it can be implemented in chemistry laboratories without additional effort and can be easily scaled up for large-scale production. The process also requires no heavy metals or precious metals. „This makes it widely applicable and more sustainable than previous methods“, says Gulder, who was a Heisenberg professor at the Technical University of Munich before joining the University of Leipzig. „It is an example of the future-oriented research focus on multifunctional catalysis at the University of Leipzig and the recently approved large-scale research centre CTC in the Leipzig area.“ Its focus will be on sustainable catalysis in an industrial context.