Aromatic hydroxylation reactions catalyzed by heme-thiolate enzymes proceed via an epoxide intermediate. These aromatic epoxides could be valuable building blocks for organic synthesis giving access to a range of chiral trans-disubstituted cyclohexadiene synthons. Here, we show that naphthalene epoxides generated by fungal peroxygenases can be subjected to nucleophilic ring opening, yielding non-racemic trans-disubstituted cyclohexadiene derivates, which in turn can be used for further chemical transformations. This approach may represent a promising shortcut for the synthesis of natural products and APIs.

The pilot-scale production of the peroxygenase from Agrocybe aegerita (rAaeUPO) is demonstrated. In a fed-batch fermentation of the recombinant Pichia pastoris, the enzyme was secreted into the culture medium to a final concentration of 0.29 g L-1 corresponding to 735 g of the peroxygenase in 2500 L of the fermentation broth after 6 days. Due to nonoptimized downstream processing, only 170 g of the enzyme has been isolated. The preparative usefulness of the so-obtained enzyme preparation has been demonstrated at a semipreparative scale (100 mL) as an example of the stereoselective hydroxylation of ethyl benzene. Using an adjusted H2O2 feed rate, linear product formation was observed for 7 days, producing more than 5 g L-1 (R)-1-phenyl ethanol. The biocatalyst performed more than 340.000 catalytic turnovers (942 g of the product per gram of rAaeUPO).

Invited for this month's cover is the group of Prof. Dr. Frank Hollmann at Delft University of Technology in the Netherlands. The Front Cover shows the vanadium-dependent haloperoxidase from the marine organism Curcuvaria inaequalis, which efficiently activates halides as hypohalites that can then initiate spontaneous halo-lactonization and halo-etherification reactions. The Communication itself is available at 10.1002/cssc.201902240.

H₂O₂ can be accepted by several peroxygenases as a clean oxidant, able to supply both the necessary electrons and oxygen atom at the same time. The biocatalysts, in turn, are able to catalyse an array of interesting oxygen insertion reactions at enantio- and regio-selectivities hard to attain with classical chemical methods. The sensitivity of most peroxygenases towards H₂O₂, however, requires this oxidant to be generated in situ. Here, we suggest the application of (modified) sulfite oxidases to couple the oxidation of sulfites to the reduction of oxygen. This enables us to use calcium sulfite, an industrial waste product from scrubbing flue gases, as an electron donor to reduce oxygen. This will supply the required peroxide in a controlled manner and enables us to perform these challenging reactions at the expense of simple salts.

Peroxygenases have long inspired the selective oxyfunctionalization of various aliphatic and aromatic compounds, because of their broad substrate spectrum and simplicity of catalytic mechanism. This study provides a proof-of-concept of piezobiocatalysis by demonstrating peroxygenase-catalyzed oxyfunctionalization reactions fueled by piezocatalytically generated H₂O₂. Bismuth oxychloride (BiOCl) generated H₂O₂ in situ via an oxygen reduction reaction under ultrasonic wave conditions. Through the simple combination of water, ultrasound, recombinant, evolved unspecific peroxygenase from Agrocybe aegerita (rAaeUPO), and BiOCl, the piezobiocatalytic platform accelerated selective hydroxylation of ethylbenzene to enantiopure (R)-1-phenylethanol [total turnover number of rAaeUPO (TTN_rAaeUPO), 2002; turnover frequency, 77.7 min^-1 >99% enantiomeric excess (ee)]. The BiOCl-rAaeUPO couple also catalyzed other representative substrates (e.g., propylbenzene, 1-chloro-4-ethylbenzene, cyclohexane, and cis-β-methylstyrene) with high turnover frequency and selectivity. We alleviated the oxidative stress of piezocatalytically generated OH^- on rAaeUPO by spatial separation of rAaeUPO and BiOCl, which resulted in greatly enhanced TTN_rAaeUPO of >3900 and the notable prolongation of reaction time. Overall, the BiOCl-rAaeUPO couple serves as a mechanical-to-chemical energy conversion platform for driving peroxygenase-catalyzed reactions under ultrasonic conditions.

By mimicking the role of human liver P450 monooxygenases, fungal unspecific peroxygenases (UPOs) can perform a range of highly selective oxyfunctionalization reactions on pharmacological compounds, including O-dealkylations and hydroxylations, thereby simulating drug metabolism. Here we have benchmarked human drug metabolite (HDM) synthesis by several evolved UPO mutants, focusing on dextromethorphan, naproxen and tolbutamide. The HDM from dextromethorphan was prepared at the semi-preparative scale as a proof of production. The structural analysis of mutations involved in the synthesis of HDMs highlights the heme access channel as the main feature on which to focus when designing evolved UPOs. These variants are becoming emergent tools for the cost-effective synthesis of HDMs from next-generation drugs.

A set of dual functional small molecules (DFSMs) containing different amino acids has been synthesized and employed together with three different variants of the cytochrome P450 monooxygenase P450BM3 from Bacillus megaterium in H2O2-dependent oxidation reactions. These DFSMs enhance P450BM3 activity with hydrogen peroxide as an oxidant, converting these enzymes into formal peroxygenases. This system has been employed for the catalytic epoxidation of styrene and in the sulfoxidation of thioanisole. Various P450BM3 variants have been evaluated in terms of activity and selectivity of the peroxygenase reactions.

An increasing number of biocatalytic oxidation reactions rely on H ₂ O ₂ as a clean oxidant. The poor robustness of most enzymes towards H ₂ O ₂ , however, necessitates more efficient systems for in situ H ₂ O ₂ generation. In analogy to the well-known formate dehydrogenase to promote NADH-dependent reactions, we here propose employing formate oxidase (FOx) to promote H ₂ O ₂ -dependent enzymatic oxidation reactions. Even under non-optimised conditions, high turnover numbers for coupled FOx/peroxygenase catalysis were achieved.

Biocatalytic oxyfunctionalisation reactions are traditionally conducted in aqueous media limiting their production yield. Here we report the application of a peroxygenase in neat reaction conditions reaching product concentrations of up to 360 mM.

We report visible light-driven, asymmetric hydrogenation of C=C bonds using an ene-reductase from Thermus scotoductus SA-01 (TsOYE) and a light-harvesting dye (rose bengal, RB) co-immobilized in an alginate hydrogel. Highly efficient encapsulation of RB in alginate hydrogel was achieved using the intrinsic affinity between TsOYE and RB, which allowed for the construction of robust RB-TsOYE-loaded alginate capsules. In the absence of NADH, the photobiocatalytic system facilitated asymmetric reduction of 2-methylcyclohexenone to an enantiopure (R)-2-methylcyclohexanone (ee > 99%; max. conversion, 70.4%; turnover frequency, 1.54 min ^-1 turnover number, 300.2) under illumination. A series of stability tests revealed a significant enhancement of TsOYE's robustness in alginate hydrogel against heat and chemical denaturants. This study provides insight into a greener and sustainable approach of cofactor-free OYE catalysis for producing value-added chemicals using light energy.

Nicotinamide adenine dinucleotide (NAD⁺) is a key redox compound in all living cells responsible for energy transduction, genomic integrity, life-span extension, and neuromodulation. Here, we report a new function of NAD⁺ as a molecular photocatalyst in addition to the biological roles. Our spectroscopic and electrochemical analyses reveal light absorption and electronic properties of two p-conjugated systems of NAD⁺. Furthermore, NAD⁺ exhibits a robust photostability under UV-Vis-NIR irradiation. We demonstrate photocatalytic redox reactions driven by NAD⁺, such as O₂ reduction, H₂O oxidation, and the formation of metallic nanoparticles. Beyond the traditional role of NAD⁺ as a cofactor in redox biocatalysis, NAD⁺ executes direct photoactivation of oxidoreductases through the reduction of enzyme prosthetic groups. Consequently, the synergetic integration of biocatalysis and photocatalysis using NAD⁺ enables solar-to-chemical conversion with the highest-ever-recorded turnover frequency and total turnover number of 1263.4 hour⁻¹ and 1692.3, respectively, for light-driven biocatalytic trans-hydrogenation.

Photoenzymatic cascades can be used for selective oxygenation of C−H-Bonds under mild conditions circumventing the hydrogen peroxide mediated peroxygenase inactivation via in situ H₂O₂ generation. Here, we report the “on demand” production of hydrogen peroxide via methanol assisted reduction of molecular oxygen using UV-illuminated titanium dioxide (Aeroxide P25) combined with the enantioselective hydroxylation of ethylbenzene to (R)-1-phenylethanole catalyzed by the Unspecific Peroxygenase from Agrocybe Aegerita. For the application of the system it is important to understand the influence of the reaction parameters to be able to optimize the system. Therefore, we systematically investigated product formation and enzyme inactivation as well as ROS formation (H₂O₂, ^.OH and ^.O₂⁻) applying different light intensities and temperatures. As a result, Turnover Numbers up to 220 000, photonic efficiencies up to 13.6 % and production rates up to 0.9 mM h⁻¹ were achieved.

Peroxygenases require a controlled supply of H₂O₂ to operate efficiently. Here, we propose a photocatalytic system for the reductive activation of ambient O₂ to produce H₂O₂ which uses the energy provided by visible light more efficiently based on the combination of wavelength-complementary photosensitizers. This approach was coupled to an enzymatic system to make formate available as a sacrificial electron donor. The scope and current limitations of this approach are reported and discussed.

Peroxygenases catalyze selective oxyfunctionalization of hydrocarbons with high conversion efficiencies using H₂O₂ as a key cosubstrate. Here, we report an unbiased photoelectrochemical (PEC) tandem structure consisting of a FeOOH/BiVO₄ photoanode, a Cu(In,Ga)Se₂ solar absorber, and a graphitic carbon nitride/reduced graphene oxide hybrid cathode for light-driven peroxygenase catalysis. Powered by sufficient photovoltage generated by the solar absorber, the PEC platform generates H₂O₂ in situ through reductive activation of molecular oxygen using water as an electron donor in the absence of external bias. The peroxygenase from Agrocybe aegerita catalyzed the stereoselective hydroxylation of ethylbenzene to (R)-1-phenylethanol with total turnover numbers over 43 300 and high enantioselectivity (ee > 99%) in the unbiased PEC tandem system.

A chemoenzymatic method for the halocyclization of unsaturated alcohols and acids by using the robust V-dependent chloroperoxidase from Curvularia inaequalis (CiVCPO) as catalyst has been developed for the in situ generation of hypohalites. A broad range of halolactones and cyclic haloethers are formed with excellent performance of the biocatalyst.

The E-factor has become an important measure for the environmental impact of (bio)chemical reactions. However, summing up the obvious wastes generated in the laboratory neglects energy-related wastes (mostly greenhouse gases) which are generated elsewhere. To estimate these wastes, we propose to extend the E-factor by an energy-term (E⁺-factor). At the example of a lab-scale enzyme fermentation, we demonstrate that the E⁺-factor can constitute a multiple of the classical E-factor and therefore must not be neglected striving for a holistic estimation of the environmental impact.

The selective oxidation of trans-2-hexen-1-ol to the corresponding aldehyde using a recombinant aryl alcohol oxidase from Pleurotus eryngii (PeAAOx) is reported. Especially using the two liquid phase system to overcome solubility and product inhibition issues enabled to achieve more than 2.200.000 catalytic turnovers for the production enzyme as well as molar product concentrations, pointing towards an economic feasible reaction.

Peroxygenases are very interesting catalysts for specific oxyfunctionalization chemistry. Instead of relying on complicated electron transport chains, they rely on simple hydrogen peroxide as the stoichiometric oxidant. Their poor robustness against H₂O₂ can be addressed via in situ generation of H₂O₂. Here we report that simple graphitic carbon nitride (g-C₃N₄) is a promising photocatalyst to drive peroxygenase-catalyzed hydroxylation reactions. The system has been characterized by outlining not only its scope but also its current limitations. In particular, spatial separation of the photocatalyst from the enzyme is shown as a solution to circumvent the undesired inactivation of the biocatalyst. Overall, very promising turnover numbers of the biocatalyst of more than 60.000 have been achieved.

The biocatalytic preparation of trans-hex-2-enal from trans-hex-2-enol using a novel aryl alcohol oxidase from Pleurotus eryngii (PeAAOx) is reported. As O₂-dependent enzyme PeAAOx-dependent reactions are generally plagued by the poor solubility of O₂ in aqueous media and mass transfer limitations resulting in poor reaction rates. These limitations were efficiently overcome by conducting the reaction in a flow-reactor setup reaching unpreceded catalytic activities for the enzyme in terms of turnover frequency (up to 38 s^-1) and turnover numbers (more than 300000) pointing towards preparative usefulness of the proposed reaction scheme.

Light-driven activation of redox enzymes is an emerging route for sustainable chemical synthesis. Among redox enzymes, the family of Old Yellow Enzyme (OYE) dependent on the nicotinamide adenine dinucleotide cofactor (NADH) catalyzes the stereoselective reduction of α,β-unsaturated hydrocarbons. Here, we report OYE-catalyzed asymmetric hydrogenation through light-driven regeneration of NADH and its analogues (mNADHs) by N-doped carbon nanodots (N-CDs), a zero-dimensional photocatalyst. Our spectroscopic and photoelectrochemical analyses verified the transfer of photo-induced electrons from N-CDs to an organometallic electron mediator (M) for highly regioselective regeneration of cofactors. Light triggered the reduction of NAD⁺ and mNAD⁺s with the cooperation of N-CDs and M, and the reduction behaviors of cofactors were dependent on their own reduction peak potentials. The regenerated cofactors subsequently delivered hydrides to OYE for stereoselective conversions of a broad range of substrates with excellent biocatalytic efficiencies.