Engineered enzymes flip a molecular switch to control ester bond placement

Chemists have long struggled to attach ester bonds to exactly the right spot on a molecule, especially when the reaction site is a bulky secondary alcohol sitting alongside a more reactive primary one. A team led by Xiaoguang Lei reports in Nature Chemistry that it has addressed this selectivity problem by reprogramming an ordinary metabolic enzyme into a family of ester-forming catalysts, using a small molecule as a switch to dictate which alcohol gets acylated. The starting point was an aldehyde dehydrogenase, a classical hydride-transfer enzyme that normally oxidizes aldehydes rather than building esters.

Through structure-guided protein engineering, the researchers reshaped the enzyme so that it could perform oxidative esterification, joining an alcohol and a carboxyl substrate while the oxidation chemistry supplies the driving force. They named the resulting catalysts OxiEs, for oxidative ester synthases. The engineering produced two complementary catalyst classes with divergent preferences.

The first class, called OxiEs1, depends on imidazole and favours primary alcohols, the easier and more reactive targets that conventional chemistry already handles reasonably well. The second class, OxiEs2, works without imidazole and shows exclusive selectivity for sterically demanding secondary alcohols, precisely the substrates that have made regioselective esterification such a formidable challenge. The most striking finding is mechanistic.

Imidazole, a small nitrogen-containing molecule, acts as a molecular switch that allosterically tunes the geometry of the active site. When imidazole is present, the enzyme's architecture favours primary alcohols; when it is absent, the reshaped active site accommodates and selectively acylates secondary alcohols instead. In other words, a single protein scaffold can be steered between two opposite regioselectivities by controlling one small effector molecule.

This switchable control matters because esters are everywhere. The ester bond underpins pharmaceuticals, agrochemicals, polymers and many functional materials, and installing it at the correct hydroxyl group in a multifunctional molecule often determines whether a synthesis route succeeds. The engineered enzymes demonstrate a broad substrate scope, acylating a wide range of secondary alcohols directly and with high selectivity.

According to the authors, the platform also extends beyond regioselectivity: the catalysts can control enantioselectivity, distinguishing between mirror-image forms of chiral substrates, and they support redox-neutral synthesis, in which the overall oxidation state of the product is balanced rather than requiring external oxidants or reductants. The practical credentials of the method rest on scale. The team prepared valuable ester products on gram scale under mild, sustainable conditions, an important benchmark for enzymatic chemistry moving from demonstration to application.

The authors present the work as establishing a strategy for regioselective control in esterification, transforming a classical hydride-transfer enzyme into a tunable platform for ester bond formation under gentle reaction conditions. Conceptually, the work shows that one protein scaffold can be redirected between primary and secondary alcohol substrates by adjusting a single allosteric input, an approach the authors describe as a general route to regioselective control in esterification. The imidazole-switch principle offers a concrete design rule for programming where, and on which functional group, an engineered enzyme builds an ester bond.

Subject of Research: Engineering aldehyde dehydrogenases into oxidative ester synthases with imidazole-controlled regioselectivity

Article Title: Enzymatic oxidative esterification with an unconventional regioselective control

Article References: Qiu, X., Hu, K., Yang, J., Li, P., Zhong, J., Dong, H., Han, Y., & Lei, X. (2026). Enzymatic oxidative esterification with an unconventional regioselective control. Nature Chemistry. https://doi.org/10.1038/s41557-026-02288-2

Image Credits: AI Generated

DOI: 10.1038/s41557-026-02288-2

Keywords: biocatalysis, enzyme engineering, regioselectivity, esterification, aldehyde dehydrogenase, Nature Chemistry, green chemistry, Enzymatic, oxidative, unconventional, regioselective, control