Braca

Photocatalytic cross-coupling: A redox-neutral photochemical method enables direct C(sp²)─C(sp²) bond formation between phenols and heteroaryl halides using an organic dye and base. Complementary radical generation allows efficient cross-coupling in up to 91% yield. Mechanistic studies, DFT, HTE, and machine learning rationalize and predict reactivity, offering a sustainable approach to this challenging transformation.

ABSTRACT

Developing sustainable methods for C(sp²)─C(sp²) bond formation that avoid transition-metals and prefunctionalized substrates remains a central goal in synthetic chemistry. Phenols and N-heteroarenes (azines) are abundantly available, yet their cross-coupling is hindered by mismatched redox properties and chemoselectivity issues. Herein, we report a photochemical strategy that couples phenols with heteroaryl halides under redox-neutral conditions using an organic dye photocatalyst and base. Concurrent oxidation of the phenol component and reduction of the azine component generates complementary radicals that cross-couple efficiently, delivering moderate to high yields (up to 91%) with high functional group tolerance. Mechanistic experiments and density functional theory (DFT) studies elucidate the radical reaction pathways, while substrate clustering, high-throughput experimentation (HTE), and machine learning (ML) enable prediction of C–C versus S_NAr reactivity across broad chemical space.

Nature Chemistry, Published online: 25 February 2026; doi:10.1038/s41557-026-02079-9

The enzymatic synthesis of azetidines is a prime example of the superiority natural systems often show over laboratory syntheses, but how nature achieves such difficult transformations in mild conditions is unclear. Now, two independent reports have revealed that the azetidine ring of polyoxamic acid arises from L-isoleucine via a dual-enzyme system that overcomes major energetic barriers through coordinated metalloenzyme chemistry.

Nature, Published online: 25 February 2026; doi:10.1038/d41586-026-00515-x

A protein reinforces the blood–brain barrier, which becomes leaky with age.

Nature Communications, Published online: 26 February 2026; doi:10.1038/s41467-026-69913-z

Using mutational scanning, this study maps how thousands of mutations alter substrate specificity in the promiscuous enzyme D-amino acid oxidase, and reveals catalytic-site and long-range effects that inform the design of highly selective biocatalysts.

Nature Synthesis, Published online: 27 February 2026; doi:10.1038/s44160-026-01003-w

Photoinduced ligand-to-metal charge transfer is used to enable abiotic cross-couplings in metalloenzymes. Engineering a 2-histidine metal site and substituting iron with nickel activates PsEFE for nickel-catalysed C(sp²)–S coupling reactions between thiols and aryl bromides. Directed evolution yielded metalloenzyme variants that can produce a range of thioethers with high efficiency.

We present a high-throughput selection system to engineer fluoroacetate dehalogenases (FAcDs). By challenging E. coli populations that produce diverse FAcD libraries to grow on non-natural organofluorides as their sole carbon source, we isolated a panel of FAcD variants with improved activity and altered substrate specificity.

ABSTRACT

The widespread use of organofluorides in modern society has inadvertently led to the bioaccumulation of harmful pollutants, most prominently per- and polyfluorinated alkyl substances (PFAS). In principle, tailored biocatalysts able to cleave C─F bonds represent an attractive strategy to combat this (emerging) environmental crisis. However, Nature is largely impartial to C─F bonds, with fluoroacetate dehalogenases (FAcDs) standing out by catalyzing the hydrolysis of single C─F bonds in fluoroacetate at high turnover rates. To harness its catalytic prowess for non-natural organofluorides, we designed and applied a robust growth-based selection strategy for large-scale FAcD engineering. Specifically, we demonstrate that FAcD-catalyzed C─F bond cleavage of (natural and) synthetic organofluorides generates metabolizable carbon sources for bacteria, enabling in vivo enrichment of active FAcD variants. By forcing populations expressing diverse FAcD-libraries to utilize various organofluorides as sole carbon source, we elicited a panel of FAcD variants with improved activities and altered substrate profiles for fluoroacetate, 2-fluoropropionate, and 2,2-difluoroacetate. In these efforts, we also identified a previously overlooked inhibition pathway, which impedes the conversion of gem-difluoride compounds. Overall, our study presents the first large-scale engineering campaign of FAcDs and introduces an operationally simple selection platform to adapt these enzymes for the sustainable degradation of contaminating organofluorides.

We report here a series of iron(III) porphyrin-phenoxide complexes where secondary-sphere H-bonding interactions exert a large influence on geometry, spin state and redox properties by shifting the Fe(III)/Fe(II) redox couples and 1e-oxidation toward more positive potentials and thereby offering insights into enzymatic regulation for biological activities.

ABSTRACT

Hydrogen bonding (H-bonding) plays a pivotal role in regulating the chemical and electrochemical properties of metalloproteins by influencing substrate recognition, binding orientation, and active-site geometry. In heme enzymes, conserved H-bonding networks are directly linked to catalytic efficiency by modulating redox potentials and spin states of the iron center. Despite extensive studies on biological systems, the molecular origin of H-bonding effects on the electronic structure and redox properties of heme groups remains underexplored. We report here iron(III) porphyrin–phenoxide complexes where secondary-sphere H-bonding interactions exert a large influence on geometry, spin state, and redox properties. The H-bonding interactions elongate the axial Fe─O bond, contract the porphyrin core, and stabilize the intermediate-spin (S = 3/2) state of iron, while the absence of H-bonding favors the high-spin (S = 5/2) state. Similar effects are also observed in the iron(III)-chloro complex in which the axial ligand is engaged in secondary-sphere H-bonding interactions. Electrochemical studies reveal positive shifts in the Fe(III)/Fe(II) couple and 1e⁻ oxidation, highlighting H-bonding as a regulator of redox noninnocence. Supported by computational studies, our findings provide fundamental insights into the interplay between H-bonding, spin state, and redox chemistry, thereby offering insight into enzymatic regulation for its biological functions.

Nature Chemistry, Published online: 25 February 2026; doi:10.1038/s41557-026-02079-9

The enzymatic synthesis of azetidines is a prime example of the superiority natural systems often show over laboratory syntheses, but how nature achieves such difficult transformations in mild conditions is unclear. Now, two independent reports have revealed that the azetidine ring of polyoxamic acid arises from L-isoleucine via a dual-enzyme system that overcomes major energetic barriers through coordinated metalloenzyme chemistry.

To overcome the limitation of toxic byproduct generation in NO removal, this work presents a biohybrid strategy that leverages natural enzymatic active sites to enhance exciton dissociation, thereby achieving efficient deep NO oxidation. By immobilizing cytochrome c on carbon nitride, the semi-artificial photoenzyme exhibits powerful internal electric field with a 2.4-fold increase in surface potential, enabling efficient deep NO oxidation.

ABSTRACT

Solar-driven catalysis holds promise in molecular oxygen activation and low-concentration NO_x elimination but achieving highly selective conversion of NO to nontoxic nitrate (NO₃ ⁻), while suppressing toxic NO₂ formation remains challenging. Here, we report a semi-artificial photoenzyme catalyst constructed by immobilizing mono-heme cytochrome c (cyt c) on carbon nitride (CN) to refine reactive species generation for deep NO oxidation. The hybrid photoenzyme catalyst establishes localized internal electric fields (IEF) between cyt c and CN that promote exciton dissociation, and creates polarized active sites on cyt c that preferentially adsorb O₂, and activate O₂ to active peroxides (•O₂ ⁻ and *O₂ ²⁻) via an electron transfer pathway with inhibiting ¹O₂ formation. The one-step NO oxidation to NO₃ ⁻ is boosted over cyt c/CN, showing exceptional 97.4% NO conversion with ultralow NO₂ selectivity (1.5%, 6.5 ppb) and long-term stability (98.1% after 300 min) at a weight hourly space velocity (WHSV) of 850 L g⁻¹·h⁻¹ across wide humidity ranges. The undesirable NO₂ generation is significantly lower than that of bare CN (17.0%, 104.7 ppb) and reported catalysts. The catalyst exhibits high activity in direct NO₂ removal (92.9%) and rapidly reduces NO levels to below the safe concentration (52 ppb) in a simulated environment chamber.

Nature Catalysis, Published online: 23 February 2026; doi:10.1038/s41929-026-01493-z

Despite its importance in medicinal chemistry, the sulfonamide functional group is rare in natural products and its biosynthesis is poorly understood. This study reveals the structure and mechanism of SbzM, a sulfonamide synthase essential for altemicidin biosynthesis.

Nature Communications, Published online: 23 February 2026; doi:10.1038/s41467-026-69968-y

L-Proline is a powerful organocatalyst widely applied in asymmetric synthesis due to its secondary amine functionality, however, in proteins, this functional group is locked in peptide bonds, rendering proline catalytically inactive. Here, the authors engineer the nonenzymatic protein scaffold LmrR into a new-tonature biocatalyst by exposing its native L-proline residue at the N-terminus to catalyze enantioselective aldol reactions.

Engineered hemoproteins enabled the stereoselective C–H amination of carboxylic esters to access enantioenriched aryl-β-amino esters. Directed evolution yielded variants with excellent chemoselectivity towards the use of O-pivaloylhydroxylamine triflic acid or hydroxylamine hydrochloride as aminating reagents. Through the collection of partial sequence-activity data, beneficial mutations to improve the final variants catalytic activity were identified.

ABSTRACT

Engineered biocatalysts can utilize nitrene precursors to access enantioenriched amination products, yet they have not been applied to produce valuable, enantiomerically enriched noncanonical β-amino esters. Current approaches to synthesizing β-amino acids rely on pre-oxidized precursors and multistep synthetic approaches involving various protecting groups. We engineered a platform of heme enzymes for stereoselective C–H bond amination of readily available carboxylic ester derivatives to install primary amines. A directed evolution campaign coupled with sequencing of over 1000 variants enabled us to develop engineered variants that use either O-pivaloylhydroxylamine triflic acid (PONT) or hydroxylamine hydrochloride (H₂NOH∙HCl) as aminating reagents. An analysis of the resulting sequence–activity dataset revealed additional improvements that could be made to the final variant, highlighting the utility of sequencing data to guide future steps in directed evolution campaigns. The evolved nitrene transferases expand the scope of accessible chiral β-amino acid building blocks for peptidomimetic applications and provide new starting points for the design and synthesis of enantioenriched β-amino acid motifs.

p-Benzoyl-l-phenylalanine (pBzF) integrates genetic code expansion with benzophenone photochemistry to enable proximity-based labeling, programmable biocatalysis, and biosafe microbial engineering, all from a single, site-specifically encoded amino acid.

ABSTRACT

p-Benzoyl-l-phenylalanine (pBzF) is a widely used noncanonical amino acid (ncAA) that expands the chemical repertoire of proteins. Its benzophenone (BP) chromophore undergoes near-quantitative intersystem crossing (ISC) to a triplet state, furnishing a highly efficient, site-addressable photoreactive handle. Beyond photochemistry, the bulky, hydrophobic side chain introduces distinct steric and electronic effects that enable new reactivity in protein active sites. Genetic incorporation of pBzF in vivo, including directed evolution, has unlocked applications ranging from site-specific photo-crosslinking for interaction mapping to engineering antibody fragments, sharpening monoclonal antibody (mAb) epitope recognition, and creating protein-based photocatalysts. pBzF has also proved powerful for mechanistic studies by stabilizing short-lived intermediates. More recently, pBzF-containing proteins have been leveraged in light-driven transformations, including [2+2] photocycloadditions, deracemizations, and dehalogenations, and in the construction of artificial photosynthetic systems. This review critically discusses these advances and establishes pBzF as a versatile photochemical and structural motif for building proteins with non-natural, light-responsive, and catalytically competent functions.

Biocatalytic stereo-controlled C–S bond formation unlocked! Engineered, cofactor-independent 4-oxalocrotonate tautomerase variants catalyze enantioselective thia-Michael additions of aliphatic thiols to cinnamaldehyde, affording (R)-β-thioenals with up to 99% conversion and high enantiopurity (up to 95:5 e.r.).

The thia-Michael addition is one of the most versatile and practical reactions for CS bond formation in organic synthesis, but remains a continuing challenge for biocatalysis. Here we report engineered cofactor-independent enzymes, based on the promiscuous enzyme 4-oxalocrotonate tautomerase, for the enantioselective synthesis of various (R)-β-thioenals via the nucleophilic addition of aliphatic thiols to cinnamaldehyde. These engineered enzymes efficiently promote the formation of the carbon–sulfur bond with good stereocontrol, affording the desired (R)-β-thioenal products with excellent conversions (up to 99%) and with moderate-to-high enantiopurity (e.r. up to 95:5). Our results highlight the power of catalytic promiscuity for expanding the biocatalytic repertoire for non-natural reactions.

Nature Synthesis, Published online: 02 February 2026; doi:10.1038/s44160-025-00987-1

A copper-catalysed, enantioconvergent coupling reaction between racemic tertiary electrophiles and cyclopropanols is reported. Employing a rationally designed N,N,N-ligand, this method facilitates the construction of quaternary stereocentres, offering a practical route to chiral C(sp3)-rich building blocks.

Science, Volume 391, Issue 6784, January 2026.

Nature Synthesis, Published online: 29 January 2026; doi:10.1038/s44160-025-00989-z

Macrocyclization typically proceeds via thioesterase mediation in type I polyketide synthases. Now, using genome mining and crystallographic analysis, an alternative mechanism for stereoselective macrocyclization in the akaeolide biosynthetic pathway is reported. The mechanism is proposed to proceed via an iminium-catalysed tandem Michael addition and Knoevenagel condensation, using nuclear transport factor 2-like enzymes.

Nature Catalysis, Published online: 23 January 2026; doi:10.1038/s41929-025-01470-y

Light-driven enzymatic catalysis has enabled important abiological transformations in vitro. Now a cellular ene-reductase photoenzyme is integrated with a de novo-designed olefin biosynthetic pathway for photoinduced hydroalkylation, hydroamination and hydrosulfonylation reactions within cells.

Asymmetric hydrogen-atom transfer (HAT) is challenging due to early, weakly organized transition states that lead to small energy differences and competing racemic pathways. This mini-review is intended to provide a mechanistically unified framework for asymmetric HAT by classifying strategies into five regimes according to where enantioselection is set: donation-controlled termination, radical-centered control, abstraction-controlled HAT, cooperative bimetallic catalysis, and enzyme-mediated HAT.

Abstract

Hydrogen-atom transfer (HAT) lies at the heart of radical chemistry, yet asymmetric HAT has been difficult because the high reactivity of radicals often forces H-transfer to proceed through early, weakly organized transition states, yielding small ΔΔG^‡ and allowing rapid racemic background pathways to compete. Recent advances across small-molecule, metalloradical, cooperative, peptide, and enzymatic catalysis show that high enantioselectivity is attainable when the catalyst is engineered to exert stereocontrol precisely at the H-transfer step that sets configuration. In this minireview, we organize asymmetric HAT into five regimes—donation-controlled termination, radical-centered control, abstraction-controlled HAT, cooperative bimetallic catalysis, and enzyme-mediated HAT—each specified by where chiral information is introduced during H-transfer. Through representative cases, we illustrate how catalysts achieve enantioselection by defining radical geometry, guiding H-delivery, enforcing selective hydrogen abstraction, or confining donor–acceptor pairs within organized chiral environments. This mechanistic framework provides a unified lens spanning synthetic and biocatalytic systems, clarifies the distinct stereochemical logics in each regime, and highlights emerging opportunities for expanding asymmetric radical chemistry through precisely orchestrated H-atom transfer.

Harnessing transient, unstabilized alkyl radical intermediates for the enantioselective construction of valueadded chemical entities remains a fundamental challenge in biocatalysis. Through the repurposing and directed evolution of pyridoxal phosphate (PLP)-dependent tryptophan synthases, we advanced an open-shell enzyme platform capable of intercepting transient alkyl radicals for the efficient and enantioselective synthesis of aliphatic non-canonical amino acids. Engineering an orthogonal pair of radical PLP enzymes allowed unstabilized alkyl radicals, generated from diverse aliphatic organoboronates, to undergo dehydroxylative C(sp3)-C(sp3) coupling with a common L-serine donor, affording either L- or D-amino acids with excellent enantiopurity in an enzyme-controlled fashion. Mechanistic and computational investigations employing radical clock substrates and unusual radical-mediated rearrangement processes revealed that the radical intermediates generated in this system exhibit unexpectedly long lifetimes, highlighting the power of this dual enzyme-photocatalyst platform to engage unactivated alkyl radicals. Collectively, these findings delineate a potentially general strategy for generating and utilizing unstabilized alkyl radicals and underscore the synthetic potential of radical pyridoxal biocatalysts for stereodivergent amino acid construction.

ABSTRACT

The design of artificial enzymes with non-canonical amino acids (ncAAs) capable of catalyzing non-natural reactions represents a promising frontier in biocatalysis. However, the synthetic challenges and high cost associated with ncAAs bearing catalytic residues have limited progress in this area. Here, we report the development of artificial Friedel–Crafts alkylases using a one-pot strategy that seamlessly integrates the biosynthesis of ncAAs with their site-specific incorporation into proteins via genetic code expansion. This innovative approach enables the functionalization of enzymes with novel catalytic properties tailored for stereoselective Friedel–Crafts alkylation. The artificial Friedel–Crafts alkylase exhibited efficient catalytic activity for the enantioselective Friedel–Crafts alkylation of enals and indoles via iminium activation, yielding a range of chiral indole alcohols with up to 98% enantiomeric excess (e.e.) and 99% yield following directed evolution. By demonstrating the feasibility and advantages of this one-pot strategy, we aim to establish a versatile platform for the design of artificial enzymes and to pave the way for broader applications in enzyme engineering and synthetic biology with in situ biosynthesized ncAAs.