No abstract

Peroxygenases are an emerging new class of enzymes allowing selective oxyfunctionalisation reactions in a cofactor-independent way different from well-known P450 monooxygenases. Herein, we focused on recent developments from organic synthesis, molecular biotechnology and reaction engineering viewpoints that are devoted to bring these enzymes in industrial applications. This covers natural diversity from different sources, protein engineering strategies for expression, substrate scope, activity and selectivity, stabilisation of enzymes via immobilisation, and the use of peroxygenases in low water media. We believe that peroxygenases have much to offer for selective oxyfunctionalisations and we have much to study to explore the full potential of these versatile biocatalysts in organic synthesis.

Biocatalysis community has witnessed a drastic increase in the number of studies for the use of enzymes in continuously operated flow reactors. This significant interest arose from the possibility of...

Cofactor-dependent enzymes catalyze a broad range of synthetically useful transformations. However, the cofactor requirement also poses economic and practical challenges for the application of these biocatalysts. For three decades, considerable research effort has been devoted to the development of reliable in situ regeneration methods for the most commonly employed cofactors, particularly NADH and NADPH. Today, researchers can choose from a plethora of options, and oxidoreductases are routinely employed even on industrial scale. Nevertheless, more efficient cofactor regeneration methods are still being developed, with the aim of achieving better atom economy, simpler reaction setups, and higher productivities. Besides, cofactor dependence has been recognized as an opportunity to confer novel reactivity upon enzymes by engineering their cofactors, and to couple (redox) biotransformations in multi-enzyme cascade systems. These novel concepts will help to further establish cofactor-dependent biotransformations as an attractive option for the synthesis of biologically active compounds, chiral building blocks, and bio-based platform molecules.

Teaching old dogs new tricks: Alcohol dehydrogenases (ADHs) may be established redox biocatalysts but they still are good for a few surprises. ADHs can be used to oxidize aldehydes, and this was demonstrated by the oxidative dynamic kinetic resolution of profens. In the presence of a suitable cofactor regeneration system, this reaction can occur with high selectivity.

The use of oxidoreductases (EC1) in non‐conventional reaction media has been increasingly explored. In particular, deep eutectic solvents (DESs) have emerged as a novel class of solvents. Herein, an in‐depth study of bioreduction with an alcohol dehydrogenase (ADH) in the DES glyceline is presented. The activity and stability of ADH in mixtures of glyceline/water with varying water contents were measured. Furthermore, the thermodynamic water activity and viscosity of mixtures of glyceline/water have been determined. For a better understanding of the observations, molecular dynamics simulations were performed to quantify the molecular flexibility, hydration layer, and intraprotein hydrogen bonds of ADH. The behavior of the enzyme in DESs follows the classic dependence of water activity (aW) in non‐conventional media. At low aW values (<0.2), ADH does not show any activity; at higher aW values, the activity was still lower than that in pure water due to the high viscosities of the DES. These findings could be further explained by increased enzyme flexibility with increasing water content.

A bi‐enzymatic cascade consisting of a Baeyer–Villiger monooxygenase and an alcohol dehydrogenase (ADH) was designed in a convergent fashion to utilise two molar equivalents of cyclohexanone (CHO) and one equivalent of 1,6‐hexanediol as a ‘double‐smart cosubstrate’ to produce ε‐caprolactone (ECL) with water as sole by‐product. The convergent enzymatic cascade reaction reported herein, is performed at ambient conditions in water, is self‐sufficient with respect to cofactor, and incorporates all starting materials into the desired product, ECL. Among different enzymes explored, the reaction catalysed by cyclohexanone monooxygenase from Acinetobacter sp. NCIMB 9871 coupled with ADH from Thermoanaerobacter ethanolicus showed the best results, reaching 91 % conversion of CHO after 24 h with a product titre of 2 g L−1. Scale‐up of the coupled system (50 mL) performed better than the small‐scale reactions and >99 % conversion of CHO and ECL concentration of 20 mM were achieved within 18 h.

Cyanobacteria have the capacity to use photosynthesis to fuel their metabolism, which makes them highly promising production systems for the sustainable production of chemicals. Yet, their dependency on visible light limits the cell‐density, which is a challenge for the scale‐up. Here, it was shown with the example of a light‐dependent biotransformation that internal illumination in a bubble column reactor equipped with wireless light emitters (WLEs) could overcome this limitation. Cells of the cyanobacterium Synechocystis sp. PCC 6803 expressing the gene of the ene‐reductase YqjM were used for the reduction of 2‐methylmaleimide to (R)‐2‐methylsuccinimide with high optical purity (>99 % ee). Compared to external source of light, illumination by floating wireless light emitters allowed a more than two‐fold rate increase. Under optimized conditions, product formation rates up to 3.7 mm h−1 and specific activities of up to 65.5 U gDCW−1 were obtained, allowing the reduction of 40 mm 2‐methylmaleimide with 650 mg isolated enantiopure product (73 % yield). The results demonstrate the principle of internal illumination as a means to overcome the intrinsic cell density limitation of cyanobacterial biotransformations, obtaining high reaction rates in a scalable photobioreactor.