Enzyme and photocatalyst juggle 3-component reaction

Reactions that can combine more than two molecular pieces in one go are a powerful way to build complexity quickly and save on costly isolation and purification. But the choreography for such a multicomponent arrangement is rarely simple.

Engineered enzymes and photocatalysts have proved over the past few years to be a powerful combination for wrangling radicals with precise three-dimensional control. Now, a team of researchers led by Xiaoqiang Huang of Nanjing University and Binju Wang of Xiamen University has expanded the menu of photobiocatalytic reactions to a three-piece combo (Nature 2024, DOI: 10.1038/s41586-024-08399-5). The reaction stitches together an aldehyde, an alkene, and an α-bromo ketone to create a single chiral ketone product.

Huang and Wang have been collaborating for the past 5 years on engineering enzymes for organic synthesis. “Our goal is to make photoenzymatic catalysis more powerful” to achieve things that neither nature nor existing chemical methods can currently do well, Huang says. This paper builds on work that Huang published last year on engineering thiamine-dependent enzymes for radical chemistry.

The researchers engineered a benzaldehyde lyase enzyme from Pseudomonas fluorescens bacteria to work with a visible light-activated ruthenium catalyst to perform the new-to-nature transformation they sought. Wang’s team used computational modeling to pinpoint which amino acids in the active site to try substituting, as well as to probe the likely reaction mechanism. Ultimately, the researchers designed a mutant that turned out their desired product with a 70% yield and near-perfect stereoselectivity. They were also pleased to see that it tolerates a variety of different building blocks, something that’s often challenging in enzymatic reactions.

Rudi Fasan, who researches stereoselective biocatalysis at the University of Texas at Dallas and was not involved in the work, calls it “a beautiful piece of work and a remarkable achievement in biocatalysis.” He notes that the N-heterocyclic carbene catalysts used for similar radical reactions were originally inspired by thiamine cofactors, so Huang and coworkers’ choice to use engineered thiamine-dependent enzymes brings the field full circle. And, he adds, it presents plenty of opportunities to explore what else this broad class of enzymes can be engineered to do.

Yang Yang of the University of California, Santa Barbara, who researches photoenzymatic reactions and was also not involved in this work, says in an email to C&EN that the paper “beautifully illustrates the synthetic potential” of engineered enzymes coupled with photochemistry.

Huang says he and Wang will continue to collaborate on ways to push the boundaries of biocatalysis. For example, they’re starting to work on using protein design to craft new enzymes from scratch.