Laccase review maps oxygen-driven routes to greener organic synthesis

A comprehensive review finds that laccase enzymes can use molecular oxygen to drive a broad range of organic transformations under mild conditions, offering a greener alternative to conventional chemical oxidants. The analysis brings together evidence on how these multicopper oxidoreductases work, which substrates they can handle, and why mediators, protein engineering and reaction conditions determine whether laboratory reactions remain selective and practical.

Laccases are classified as benzenediol:oxygen oxidoreductases and belong to the multicopper oxidoreductase family. Unlike monooxygenases, which insert an oxygen atom into a substrate and commonly require reducing cofactors, and peroxidases, which use hydrogen peroxide, laccases oxidize substrates by transferring electrons directly to molecular oxygen and reducing it to water. Their catalytic machinery generally consists of four copper ions arranged at a Type 1 site and a trinuclear Type 2/Type 3 cluster, although some fungal laccases lack the Type 2 copper.

The catalytic cycle begins when a reducing substrate transfers an electron to the Type 1 copper. The electrons then move to the trinuclear cluster, where oxygen binds and is reduced in two stages. The first produces a peroxide intermediate, while a second two-electron transfer breaks the oxygen–oxygen bond and yields a native intermediate containing a bridging oxo group. This configuration supports the complete four-electron reduction of dioxygen to water and helps regenerate the reduced enzyme for another cycle. Over time, the native intermediate rearranges into a resting oxidized form that can still accept electrons at the Type 1 site but transfers them too slowly to sustain effective catalysis.

These enzymes are widespread but unevenly characterized. Fungi, especially white-rot species, are the most extensively studied sources and often produce several isoforms. Bacterial laccases occur in genera including Bacillus, Streptomyces, Klebsiella, Pseudomonas and Yersinia, while plant laccases are particularly associated with the resin canals of members of the Anacardiaceae family. Fungal laccases generally have higher redox potentials than bacterial enzymes. High-potential fungal laccases can oxidize compounds with redox potentials above 400 mV, including bisphenol A, p-nonylphenol and the azo dye BR114, whose listed potentials exceed 600 mV.

Laccases do not transform every substrate equally well. Direct oxidation is most suitable when the substrate can reach the active site and has a redox potential compatible with the Type 1 copper. Chemical mediators broaden that reach by acting as electron shuttles: the enzyme oxidizes the mediator, and the oxidized mediator then transfers electrons to the target compound. ABTS is associated with electron transfer; mediators containing N–OH groups, such as HBT, N-hydroxyacetanilide and NHPI, can generate reactive nitroxyl radicals that promote hydrogen-atom transfer; and TEMPO promotes an ionic oxidation pathway. Naturally occurring phenols such as acetosyringone, acetovanillone, ferulic acid, p-coumaric acid, syringaldehyde and vanillin can also serve as mediators.

The choice of mediator is not merely a reaction-engineering detail because it can redirect oxidation toward different products. In examples summarized by the review, ABTS and HBT promoted different outcomes in the oxidation of benzylic alcohols, while mediator selection also changed the conversion of vanillyl alcohol. Mediators can also improve productivity. In a reported trimerization of indole, TEMPO shortened the reaction from 48 to 24 hours and increased the isolated yield from 23% to 51%. Such results show that a mediator can extend the substrate range of a laccase while simultaneously affecting reaction time, yield and the likely oxidation pathway.

A particularly useful family of laccase reactions creates carbon–carbon bonds through oxidative coupling of aromatic substrates. The review describes laccase-mediated dimerization of salicylic esters in acetate buffer at pH 5 and room temperature, which produced a functionalized biaryl in 84% yield. Bisphenol A underwent predominantly C–C coupling in the presence of laccase from Trametes villosa. Other examples included selective formation of a bis-lactone lignan from sinapinic acid, while ferulic acid followed both C–O and C–C coupling routes. These contrasting outcomes underscore the importance of substrate structure, steric effects and the source of the enzyme.

Enzyme origin alone did not determine performance in every comparison. Laccase from Pycnoporus coccineus oxidized the monolignols isoeugenol and coniferyl alcohol at rates approximately three- to sevenfold higher than laccase from the lacquer tree Rhus vernicifera in an acetone–water mixture. In a related system, laccases from Myceliophthora thermophila and Trametes pubescens oxidized 3,5,4′-trihydroxystilbene in an n-butanol/phosphate buffer at pH 6.5, giving a dehydrodimer in 31% yield compared with 18% using the T. pubescens enzyme alone. These are measured reaction outcomes, but they also expose how strongly results depend on the particular substrate, medium and enzyme preparation.

Beyond dimerization, laccases can generate trimers, polymers and heterocycles. Oxidative trimerization of the phenolic antioxidant sesamol produced reported yields of 61% and 30% with laccases from Trametes versicolor and Agaricus bisporus, respectively. Laccase catalysis has also been used for phenolic polymerization, aniline polymerization, Diels–Alder-type cyclization and domino reactions that assemble benzofurans, benzopyranocoumarins, phenazines and related structures. Some reported transformations use molecular oxygen under ambient air and room-temperature conditions, while others require mediators or a Lewis acid, illustrating that “mild” does not mean identical for every substrate.

The review also documents oxidation cascades designed to functionalize sugars, alcohols, amines and pharmaceutical scaffolds. Trametes pubescens laccase combined with TEMPO selectively oxidized primary hydroxyl groups in mono- and disaccharides. A laccase from Fomes durissimus oxidized aromatic methyl groups to aldehydes without a chemical mediator, and oxidation of furfuryl alcohol supplied an acceptor aldehyde for a subsequent aldol reaction. Laccase-mediated derivatization produced penicillin, cephalosporin and carbacephem derivatives, while separate studies generated amino-acid derivatives, hydroquinone-coupled antibiotics, triazoles and other potentially bioactive compounds.

These results position laccases as a versatile platform rather than a universal replacement for established chemistry. Native enzymes can lose activity, become structurally unstable, perform poorly in solvent-rich media and be difficult to recover and reuse. Reaction outcomes can also suffer from competing products, and a transformation that works with one laccase may perform differently with another. The review therefore points to enzyme immobilization, protein engineering, mediator optimization and process design as necessary steps for translating laboratory chemistry into scaled manufacturing.

Overall, the review presents laccase catalysis as a route to milder, more selective oxidation chemistry with molecular oxygen as the terminal oxidant. The strongest evidence lies in reactions that couple, oxidize, cyclize or polymerize organic molecules under controlled conditions, sometimes with substantial yields and in water or mixed aqueous-organic media. The review is not a clinical study and reports no new clinical outcomes or datasets. Its central conclusion is that laccases offer an unusually broad enzymatic toolbox, while their practical value depends on matching the enzyme, mediator, substrate and operating conditions to the intended transformation.

Subject of Research: Review of laccase-catalysed organic transformations using molecular oxygen as the terminal oxidant

Article Title: Laccase catalyses sustainable organic transformations

Article References: Gupta, S., Kumar, G., & Narula, A. K. (2026). Laccase catalyses sustainable organic transformations. Discover Chemistry, 3(1), Article 586. https://doi.org/10.1007/s44371-026-01002-y

Image Credits: AI Generated

DOI: 10.1007/s44371-026-01002-y

Keywords: laccase, biocatalysis, organic synthesis, molecular oxygen, green chemistry, oxidative coupling, redox mediators, multicopper oxidoreductases, enzyme catalysis, sustainable chemistry, catalyses, sustainable