Braca

Herein, we describe a convenient and general method for the Markovnikov oxidation of unactivated olefins to alcohols and ketones using commercially available iron acetylacetonate (Fe(acac)₃) as catalysts, and cheap phenylsilane PhSiH₃ as reducing agent. All reactions proceed efficiently at room temperature with air as sole oxidant. The alcohols are formed smoothly in up to >80 % isolated yield and with 100 % regioselectivity for secondary alcohols formation, while the corresponding ketones were observed as by-products.

Abstract

Herein, we describe a simple and convenient protocol for the Markovnikov oxidation of unactivated olefins to alcohols and ketones using readily available iron salt Fe(acac)₃ as a catalyst, and phenylsilane PhSiH₃ as reducing material. All reactions proceed efficiently at mild conditions with air as terminal oxidant. This transformation has been applied to a variety of substrates, and is distinguished by its simplicity, mild temperatures and broad scope. The alcohols are formed smoothly in up to >80 % isolated yield and with 100 % regioselectivity for secondary alcohols formation, while the corresponding ketones were observed as by-products.

Nature, Published online: 24 March 2025; doi:10.1038/s41586-025-08887-2

Generalizing arene C−H alkylations by radical−radical cross-coupling

Photoenzymatic catalysis facilitates stereoselective new-to-nature chemistry under mild conditions. In addition to the rational design of artificial photoenzymes, naturally occurring redox enzymes have been repurposed for this approach. Most prominently, flavin-containing cofactors can promote photoredox catalysis in the chiral protein environment, with several examples of enantioselective C–C bond forming reactions reported in recent years. Here, we add another class of natural enzymes, which utilize the pyrroloquinoline quinone (PQQ) cofactor, to the toolbox of photobiocatalysis. Although structurally distinct from flavin, PQQ exhibits mechanistic similarities, as it also absorbs visible light and is capable of single-electron transfer. First, we established the trimethyl ester PQQMe3 as a stand-alone photoredox catalyst in pure organic solvent. Upon excitation, PQQMe3 enables the redox-neutral radical cyclization of an N-(bromoalkyl)-substituted indole. We then tested a panel of PQQ-dependent sugar and alcohol dehydrogenases for photoenzymatic catalysis in aqueous buffer, focusing on a redox-neutral radical reaction to form oxindoles. Under optimized reaction conditions, we obtained 69% yield and an 82:18 enantiomeric ratio. Our work thus demonstrates that PQQ enzymes are capable of stereoselective photoredox catalysis. Future enzyme engineering efforts based on computational modelling and directed evolution will fully unlock their synthetic potential.

In this study, a bispecific artificial metallopeptide was developed, consisting of a ruthenium catalyst, an Fc-binding peptide, and an albumin-binding ligand, to achieve catalytic activity control. This metallopeptide formed an artificial metalloenzyme (ArM) with human serum albumin but was displaced from the pocket of HSA in the presence of IgG, demonstrating catalytic activity changes depending on the binding protein.

Abstract

An artificial metalloenzyme (ArM) utilizing a human serum albumin (HSA) scaffold exhibits remarkable catalytic stability due to the presence of a catalytic center within the deep hydrophobic pocket, demonstrating potential in vivo applicability for disease treatment via a prodrug activation strategy. Additionally, the development of latent catalysts is an important consideration for catalyst therapy to suppress the undesired activation of prodrugs. In this study, we developed a catalytic activity control system using a bispecific artificial metallopeptide, composed of a CpRu catalyst, an Fc-binding peptide, and an albumin-binding ligand. This metallopeptide individually interacted with both HSA and IgG, exhibiting catalytic activity change depending on the binding protein. The catalytic activity was enhanced when the metallopeptide was displaced from the pocket by interaction with IgG compared to the ArM formed with HSA, whereas no activity change was observed in the traditional ArM lacking the Fc-binding peptide unit. This is the first report of the activity switching in an ArM by changing the binding place of the metal catalyst. We anticipated that this system could lead to further development of the concept for in vivo synthesis of drug molecules, termed “therapeutic in vivo synthetic chemistry” realizing the disease therapy without side effects of drugs.

Herein, we describe a novel method for producing highly sought-after fluorinated compounds through the integration of nitrilase enzymes and iridium photoredox catalysis in a convenient one-pot reaction. Our chemo- biocatalytic methodology delivers a range of fluorinated and fluoroalkylated products from simple nitrile precursors, in good yields, at room temperature under benign aqueous conditions.

Abstract

Fluorinated molecules are widely used as pharmaceuticals, agrochemicals, and as various functional materials. Traditional synthetic methods for introducing fluorine substituents into organic molecules involve deleterious chemicals and lack selectivity. Enzymes have evolved in nature which can halogenate a diverse range of substrates with high selectivity under aqueous conditions, using benign inorganic halides as the halogen source. Although there are many halogenase enzymes that can chlorinate or brominate diverse substrates, only one fluorinase enzyme has been discovered to date that produces a single fluorinated adenosine derivative in nature. Herein, we complement the lack of biocatalytic fluorination protocols and address the need for cleaner and more selective fluorination methods by merging chemo and biocatalysis to selectively fluorinate compounds in a single integrated reaction. Our approach relies on combining nitrilase enzymes with photoredox catalysis to transform cheap and abundant organonitrile compounds into highly sought-after fluorinated, trifluoromethylated, and perfluoroalkylated compounds.

Copper(II) and copper(III) trifluoromethyl complexes were used to elucidate the mechanism of Cu-mediated C(sp²)−H trifluoromethylation. For electron-rich substrates, a previously unidentified single electron transfer (SET) mechanism is followed, whereas electron-poor substrates follow CF₃ radical release/electrophilic aromatic substitution (S_EAr).

Abstract

We report copper(II) and copper(III) trifluoromethyl complexes supported by a pyridinedicarboxamide ligand (L) as a platform for investigating the role of electron transfer in C(sp²)−H trifluoromethylation. While the copper(II) trifluoromethyl complex is unreactive towards (hetero)arenes, the formal copper(III) trifluoromethyl complex performs C(sp²)−H trifluoromethylation of a wide range of (hetero)arenes. Mechanistic studies using the copper(III) trifluoromethyl complex suggest that the mechanism of arene trifluoromethylation is substrate-dependent. When the thermodynamic driving force for electron transfer is high, the reaction proceeds through a previously unidentified single electron transfer (SET) mechanism, where an initial electron transfer occurs between the substrate and oxidant prior to CF₃ group transfer. Otherwise, a CF₃ radical release/electrophilic aromatic substitution (S_EAr) mechanism is followed. These studies provide valuable insights into the role of strong oxidants and potential mechanistic dichotomy in Cu-mediated C(sp²)−H trifluoromethylation.

Under visible light, an enantioselective multicomponent reaction was achieved by exploiting natural enzyme diversity and biocompatible photochemistry.

Abstract

Despite remarkable advances in photoenzymatic methodologies, the development of photoenzymatic multicomponent reactions remains a significant challenge. In this Highlight, we showcase a recent breakthrough by Prof. Xiaoqiang Huang and co-workers, who achieved enantioselective triple-component radical sorting via visible light-induced biocatalysis under mild conditions. This innovative approach opens new avenues for the synthesis of complex molecules with high precision and efficiency, marking a remarkable advance in the field of enzymatic photocatalysis.

Polyamine-supported Co^II complexes catalyzed the oxidative fluorination of saturated hydrocarbons, in some instances selectively, when combined with Selectfluor and CsF, producing fluorinated products in near-quantitative yields. Mechanistic analysis supported the involvement of a Co^IV-(F)₂ oxidant in C−H activation and a Co^III−F F-atom donor for radical rebound.

Abstract

The heme paradigm where Fe=O acts as the C−H oxidant and Fe−OH rebounds with the formed carbon-centered radical guides the design of the prototypical synthetic hydroxylation catalyst. We are exploring methods to evolve beyond the metal-oxo oxidant and hydroxide rebound, to incorporate a wider array of functional group. We have demonstrated the application of Co^II(OTf)₂ (10 mol% catalyst; OTf=trimfluoromethanesulfonate) in combination with polydentate N-donor ligands (e. g. BPMEN=N,N′-dimethyl-N,N′-bis(pyrid-2-ylmethyl)ethane-1,2-diamine) and Selectfluor in the oxidative fluorination of saturated hydrocarbons in high yields. The addition of CsF to the reaction mixture induced near-quantitative yields of fluorinated saturated hydrocarbons (>90 % yield of fluorinated product). For 1-hydroxy, 1-acetyl, 1-carboxy-, and 1-acetamido-adamantane, we demonstrated selective fluorination at the 3-position. We propose two mechanisms for the Co^II-catalyzed reaction: either (i) an N-radical, derived from Selectfluor, acted as the C−H oxidant followed by radical rebound with Co^III−F; or (ii) a Co^IV−(F)₂ species was the C−H oxidant followed by radical rebound with Co^III−F. Our combined spectroscopic, kinetic, and chemical trapping evidence suggested that an N-radical was not the active oxidant. We concluded that a Co^IV−(F)₂ species was the likely active oxidant and Co^III−F was the likely F-atom donor to a carbon centered radical producing a C−F bond.

The ability to synthesize enantiopure materials is vital for pharmaceutical and agrochemical industries due to the inherently chiral nature of biological systems and the fact that two enantiomers can have drastically different biochemical properties within organisms and ecosystems. In particular, enantioselective preparation of atropisomers is of great interest due to their privileged status as chiral ligands and pharmacophores. Although chromatographic- or crystallization-based methods are commonly used to separate atropisomers, we urgently need more efficient and economical approaches to access enantioenriched atropisomers. The use of stereoconvergent methods to access molecules with point chirality is well established, but we have not yet tapped the potential of stereoconvergent catalytic methods to arrive at enantioenriched atropisomers. We recently discovered deracemization activity in a wild-type P450 enzyme and explored its ability to deliver a stereoconvergent route toward enantioenriched atropisomers. Using a curated set of P450 variants, we found that a wide variety of symmetric and non-symmetrically substituted 2,2ʹ-binaphthol (BINOL) building blocks can be deracemized to high enantiomeric purity. Further, we demonstrated that this deracemization activity is mechanistically distinct from activity of previously reported P450 enzymes, which operate through enantioselective bond formation to afford enantioenriched atropisomers, whereas, the deracemization process reported here is proposed to proceed through bond rotation. As engineered variants have complementary selectivity profiles and substrate scope, this biocatalytic platform should be readily tunable for any desired substitution pattern. We anticipate that these results will inspire new stereoconvergent approaches to synthesizing configurationally stable atropisomers.

Lytic polysaccharide monooxygenases (LPMOs) are Cu-containing enzymes that play a crucial role in lignocellulosic biomass degradation for use in biofuel production. These enzymes carry out the selective oxidation of C-H bonds in the sugar units, leading to the cleavage of the glycosidic bond. Creating LPMO mimics facilitates the study of the mechanism of action, the characterisation of the reactive species responsible for the C-H bond activation and the potential scale up for industrial application. Here we report the synthesis, characterisation and activity assays of two novel Cu-binding peptides that mimic the active site of LPMOs. CD, ATR-FTIR and EPR spectroscopic studies of the peptides and their corresponding copper complexes show that the sequences fold in a β-hairpin conformation and produce complexes with a single Cu ion bound in an LPMO-like environment, confirmed by computational studies. Activity assays were conducted with p-nitrophenyl-β-D-glucopyranoside (PNPG) and demonstrate that the Cu-complexes show LPMO-like activity on the model substrate. Furthermore, the Cu-hairpins can also perform light-driven oxidation of phosphoric acid swollen cellulose (PASC) in the presence of melanin, similarly to some LPMO enzymes, an activity that is unreported for any LPMO mimic characterised so far. This work is the first example of a β-hairpin LPMO mimic and paves the way to further exploration of small peptide mimics of this key class of metalloenzymes.

The nitrogen-nitrogen (N-N) bond motif comprises an important class of compounds for drug discovery. Synthetic methods are primarily based on the modification of N-N or N=N precursors, whereas selective methods for direct N-N coupling offer advantages in terms of atom economy and sustainability. In this context, enzymes such as piperazate synthases (PZSs), which naturally catalyze the N-N cyclization of L-N5-hydroxyornithine to the cyclic hydrazine L-piperazate, may allow an expansion of the current narrow range of chemical approaches for N-N coupling. In this study, we demonstrate that PZSs are able to catalyze the conversion of various N-hydroxylated diamines, which are different from the natural substrate. The N-hydroxylated diamines were obtained in situ using N-hydroxylating monooxygenases (NMOs), allowing subsequent cyclization by PZS, ultimately forming the N-N bond to yield various N-N bond-containing heterocycles. Using bioinformatic tools, we identified novel NMO and PZS homologs that exhibit distinct activity and stereoselectivity profiles. The screened panel yielded 17 hydroxylated diamines and new promiscuous NMOs, thereby expanding the substrate range of NMOs resulting in the formation of previously poorly accessible N-hydroxylated products as substrates for PZS. The subsequently investigated PZSs led to a series of 5- and 6-membered N-N bond-containing heterocycles, and the most promiscuous catalysts were used to scale up and optimize the synthesis, yielding the desired N-N bond-containing heterocycles with up to 45% isolated yield. Overall, our data provides essential insights into the substrate promiscuity and activity of NMOs and PZSs, further enhancing the potential of these biocatalysts for an expanded range of N-N coupling reactions.

HomeScienceVol. 387, No. 6738Prepare now for a potential H5N1 pandemicBack To Vol. 387, No. 6738 Full accessLetter Share on Prepare now for a potential H5N1 pandemicJesse L. Goodman [email protected], Norman W. Baylor, [...] , Rebecca Katz, Lawrence O. Gostin, [...] , Rick A. Bright, Nicole Lurie, and Bruce G. Gellin+4 authors +2 authors fewerAuthors Info & AffiliationsScience6 Mar 2025Vol 387, I…

An efficient artificial copper-dependent Michaelase featuring a metal-binding unnatural amino acid, e. g. bipyridyl alanine (BpyA), was optimized through directed evolution and applied in catalytic asymmetric additions of 2-acetyl azaarenes to nitroalkenes. Various chiral γ-nitro butyric acid derivatives were obtained in good yields with high enantioselectivities. Moreover, the reaction was performed at preparative scale and the product was used in follow-up derivatization reactions towards various high-value-added pharmaceutically relevant compounds.

Abstract

Artificial metalloenzymes (ArMs) are an attractive approach to achieving “new to nature” biocatalytic transformations. In this work, a novel copper-dependent artificial Michaelase (Cu_Michaelase) comprising a genetically encoded copper-binding ligand, i. e. (2,2-bipyridin-5-yl)alanine (BpyA), was developed. For the first time, such an ArM containing a non-canonical metal-binding amino acid was successfully optimized through directed evolution. The evolved Cu_Michaelase was applied in the copper-catalyzed asymmetric addition of 2-acetyl azaarenes to nitroalkenes, yielding various γ-nitro butyric acid derivatives, which are precursors for a range of high-value-added pharmaceutically relevant compounds, with good yields and high enantioselectivities (up to >99 % yield and 99 % ee). Additionally, the evolved variant could be further used in a preparative-scale synthesis, providing chiral products for diverse derivatizations. X-ray crystal structure analysis confirmed the binding of Cu(II) ions to the BpyA residues and showed that, in principle, there is sufficient space for the 2-acetyl azaarene substrate to coordinate. Kinetic studies showed that the increased catalytic efficiency of the evolved enzyme is due to improvements in apparent K _M for both substrates and a notable threefold increase in apparent k _cat for 2-acetyl pyridine. This work illustrates the potential of artificial metalloenzymes exploiting non-canonical metal-binding ligands for new-to-nature biocatalysis.

The biosynthesis of saturated bioisosteres of ortho-disubstituted benzenes was reported by the artificial photoenzyme harboring a genetic incorporated photosensor under the light with several examples after the directed evolution. Our work provides a biocatalytic strategy for the synthesis of saturated bioisosteres of ortho-disubstituted benzenes and expands the utility of artificial photoenzyme for abiological reactions.

Abstract

Saturated bioisosteres of ortho-substituted benzenes are of significant interest due to their enhanced pharmacokinetic properties, such as improved metabolic stability and reduced toxicity, making them valuable in drug design and development. However, efficient synthesis of them remains a challenge in organic chemistry. Herein, we report the biocatalytic synthesis of saturated bioisosteres of ortho-substituted benzenes using engineered artificial photoenzymes. The artificial photoenzyme, incorporating genetically encoded unnatural amino acids with benzophenone photosensitizer residue, facilitate the formation of chiral saturated bioisosteres with moderate enantiomeric excess via the energy transfer process. Our results demonstrate the versatility of artificial photoenzymes in mediating new-to-nature reactions that are difficult to achieve with conventional chemical or enzymatic methods.

Genetic incorporation of noncanonical amino acids (ncAAs) harboring catalytic side chains into proteins allows the creation of enzymes able to catalyze reactions that have no equivalent in nature. Here, we present for the first time the use of the ncAA 3-aminotyrosine (aY) as catalytic residue in a designer enzyme for iminium activation catalysis. Incorporation of aY into protein scaffold LmrR gave rise to an artificial Friedel-Crafts (FC) alkylase exhibiting complementary enantioselectivity to a previous FC-alkylase design using p-aminophenylalanine as catalytic residue in the same protein. The new FC-alkylase was optimized by directed evolution to afford a quadruple mutant that showed increased activity and excellent enantioselectivity (up to 95% ee). X-ray crystal structures of the parent and evolved designer enzymes suggest that the introduced mutations cause a narrowing of the active site and a reorientation of the catalytic -NH2 group. Furthermore, the evolved FC-alkylase was applied in whole-cell catalysis, facilitated by the straightforward incorporation of aY. Our work demonstrates that aY is a valuable addition to the biochemists toolbox for creating artificial enzymes.

Nature Catalysis, Published online: 06 February 2025; doi:10.1038/s41929-025-01294-w

Iminium-catalysed cycloaddition is a prominent example of organocatalytic reactivity, yet a biological counterpart has not been identified. Now, the authors report biochemical, structural and computational evidence for iminium catalysis by the natural Diels–Alderase SdnG.