麻豆淫院

Amides and thioesters are ubiquitous compounds in chemistry, used for the production of medicines, natural products, and advanced materials. Traditionally, their synthesis is a messy business, involving wasteful reagents, toxic metals, or energy-intensive conditions.

The use of enzymes can offer an environmentally friendly and efficient alternative here. However, established biocatalytic methods commonly require expensive cofactors (helper molecules) like ATP that support the enzymatic conversion. In addition, the scope of the enzymatic conversion can be rather limited so that only a few structural varieties of the desired product are obtained.

In the study now in Angewandte Chemie International Edition, the biocatalysis researchers reveal how amides and thioesters can be produced in a relatively straightforward manner using alcohol dehydrogenase (ADH) enzymes. They were also able to extend the scope of this enzymatic conversion using enzyme engineering.

Teaching ADH enzymes a new trick

In nature, alcohol dehydrogenases catalyze the oxidation of an alcohol to a carbonyl compound, hence their name. Since this is a reversible conversion, ADHs can also catalyze the reduction of carbonyl compounds to alcohols. The "reduction direction" is in fact the most common application of ADHs in industry, in particular for producing chiral secondary alcohols starting from prochiral ketones. As a consequence, the enzymes are also referred to as carbonyl reductases or ketoreductases.

The current research by the HIMS Biocat researchers now adds to the industrial toolbox by exploiting the forward pathway of alcohol oxidation. In their paper, the team describes how they have been able to "teach ADHs a new trick": forging direct links between alcohols and amines or thiols.

Effective, clean synthesis

So what is the trick? When an ADH oxidizes an alcohol to an aldehyde, the aldehyde can react on the spot with an amine or a thiol, which acts as a nucleophile. This additional reaction creates intermediates called hemiaminal or hemithioacetal, respectively.

Instead of stopping there, the enzyme goes on to carry out a second oxidation step on these intermediates. The result is the formation of an amide or a thioester, respectively, which are both highly valuable compounds in industrial synthesis.

By testing a range of ADHs, the researchers were able to reveal the novel "oxidative coupling" in about half of the cases. Yields reached up to 99% by only using 0.1 mol% of the enzyme compared to the alcohol substrate. The scalability of the reaction was also proven.

As a result, this application of ADHs paves the way towards an effective, clean synthesis of amides and thioesters. Without the need for costly ATP, activated intermediates or harsh reaction conditions鈥攋ust the enzyme, air, and aqueous buffer.

Broadening the scope

To broaden the scope further, the researchers used protein engineering. By mutating key residues and opening up the active site, the engineered enzyme allowed for the acceptance of bulkier amines and thiols, enabling the synthesis of even more challenging amides and thioesters. The researchers expect the scope to become much broader in future by performing more protein engineering and testing other ADHs.

This work shows how exploring and tweaking the "hidden reactivity" of known enzymes can lead to new, useful biotransformations. This green and versatile method provides a sustainable platform for synthesizing building blocks central to pharmaceuticals, agrochemicals, and biomaterials, greatly contributing to cleaner industrial chemistry.