The novel formate oxidase from Aspergillus oryzae (AoFOx) is a useful catalyst to promote H2O2-dependent oxyfunctionalisation reactions. In this contribution we exploit the substrate promiscuity of AoFOx to fully oxidise methanol and formaldehyde to CO2 and drive peroxygenase-catalysed stereoselective oxyfunctionalisation reactions. The highly atom efficient H2O2 generation system also enabled high catalytic turnover of the peroxygenase production enzyme.@en

Elemental metals are shown to be suitable sacrificial electron donors to drive the stereoselective reduction of conjugated C=C double bonds using Old Yellow Enzymes as catalysts. Both direct electron transfer from the metal to the enzyme as well as mediated electron transfer is feasible, although the latter excels by higher reaction rates. The general applicability of this new chemoenzymatic reduction method is demonstrated, and current limitations are outlined.@en

The specific oxidation of 12α-OH group of hydroxysteroids is required for the preparation of cheno-and ursodeoxycholic acid (CDCA and UDCA, respectively). The C12 oxidation of hydroxysteroids into their 12-oxo derivatives can selectively be performed by employing 12α-hydroxysteroid dehydrogenases. These enzymes use NAD(P)+ as an electron acceptor, which has to be re-oxidized in a so-called “regeneration system”. Recently, the enzyme NAD(P)H oxidase (NOX) was applied for the regeneration of NAD+ in the enzymatic preparation of 12-oxo-CDCA from cholic acid (CA), which allows air to be used as an oxidant. However, the NOX system suffers from low activity and low stability. Moreover, the substrate loading is limited to 10 mM. In this study, the laccase/mediator system was investigated as a possible alternative to NOX, employing air as an oxidant. The laccase/mediator system shows higher productivity and scalability than the NOX system. This was proven with a preparative biotransformation of 20 g of CA into 12-oxo-CDCA (92% isolated yield) by employing a substrate loading of 120 mM (corresponding to 50 g/L). Additionally, the performance of the laccase/mediator system was compared with a classical ADH/acetone regeneration system and with other regeneration systems reported in literature.@en

Ursodeoxycholic acid (UDCA) is a pharmaceutical ingredient widely used in clinics. As bile acid it solubilizes cholesterol gallstones and improves the liver function in case of cholestatic diseases. UDCA can be obtained from cholic acid (CA), which is the most abundant and least expensive bile acid available. The now available chemical routes for the obtainment of UDCA yield about 30% of final product. For these syntheses several protection and deprotection steps requiring toxic and dangerous reagents have to be performed, leading to the production of a series of waste products. In many cases the cholic acid itself first needs to be prepared from its taurinated and glycilated derivatives in the bile, thus adding to the complexity and multitude of steps involved of the synthetic process. For these reasons, several studies have been performed towards the development of microbial transformations or chemoenzymatic procedures for the synthesis of UDCA starting from CA or chenodeoxycholic acid (CDCA). This promising approach led several research groups to focus their attention on the development of biotransformations with non-pathogenic, easy-to-manage microorganisms, and their enzymes. In particular, the enzymatic reactions involved are selective hydrolysis, epimerization of the hydroxy functions (by oxidation and subsequent reduction) and the specific hydroxylation and dehydroxylation of suitable positions in the steroid rings. In this minireview, we critically analyze the state of the art of the production of UDCA by several chemical, chemoenzymatic and enzymatic routes reported, highlighting the bottlenecks of each production step. Particular attention is placed on the precursors availability as well as the substrate loading in the process. Potential new routes and recent developments are discussed, in particular on the employment of flow-reactors. The latter technology allows to develop processes with shorter reaction times and lower costs for the chemical and enzymatic reactions involved.@en

The main objective of this study was to design a recyclable TEMPO (2,2,6,6-tetramethylpiperidinyl-N-oxyl) derivative that could be used as a catalyst in an ionic liquid solvent for the aerobic oxidation of alcohols by using NaNO2 and HCl as co-catalysts. To this end, a TEMPO derivative bearing a quaternary ammonium group, [4-Bu2MeN-TEMPO][PF6] (1), was prepared. It was subsequently shown that this ionic TEMPO derivative is an efficient catalyst for the aerobic oxidation of a variety of primary and secondary alcohols. It exhibits a synergistic effect with ionic liquid solvents and readily outperforms analogous oxidations in methylene chloride. Moreover, the ionic TEMPO could be recycled five times with no loss of activity.@en

The main objective of this study was to design a recyclable TEMPO (2,2,6,6-tetramethylpiperidinyl-N-oxyl) derivative that could be used as a catalyst in an ionic liquid solvent for the aerobic oxidation of alcohols by using NaNO2 and HCl as co-catalysts. To this end, a TEMPO derivative bearing a quaternary ammonium group, [4-Bu2MeN-TEMPO][PF6] (1), was prepared. It was subsequently shown that this ionic TEMPO derivative is an efficient catalyst for the aerobic oxidation of a variety of primary and secondary alcohols. It exhibits a synergistic effect with ionic liquid solvents and readily outperforms analogous oxidations in methylene chloride. Moreover, the ionic TEMPO could be recycled five times with no loss of activity.@en

The aerobic organocatalytic oxidation of alcohols was achieved by using water-soluble sodium anthraquinone sulfonate. Under visible-light activation, this catalyst mediated the aerobic oxidation of alcohols to aldehydes and ketones. The photo-oxyfunctionalization of alkanes was also possible under these conditions.@en

A photoenzymatic NADH regeneration system was established. The combination of deazariboflavin as a photocatalyst with putidaredoxin reductase enabled the selective reduction of NAD+ into the enzyme-active 1,4-NADH to promote an alcohol dehydrogenase catalysed stereospecific reduction reaction. The catalytic turnover of all the reaction components was demonstrated. Factors influencing the efficiency of the overall system were identified.@en

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.@en

Deazaflavins are potentially useful redox mediators for the direct, nicotinamide-independent regeneration of oxidoreductases. Especially the O2-stability of their reduced forms have attracted significant interest for the regeneration of monooxygenases. In this contribution we further investigate the photochemical properties of deazaflavins and investigate the scope and limitations of deazaflavin-based photoenzymatic reaction systems.@en

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.@en

The consecutive photooxidation and reductive amination of various alcohols in a cascade reaction were realized by the combination of a photocatalyst and several enzymes. Whereas the photocatalyst (sodium anthraquinone-2-sulfonate) mediated the light-driven, aerobic oxidation of primary and secondary alcohols, the enzymes (various ω-transaminases) catalyzed the enantio-specific reductive amination of the intermediate aldehydes and ketones. The system worked in a one-pot one-step fashion, whereas the productivity was significantly improved by switching to a one-pot two-step procedure. A wide range of aliphatic and aromatic compounds was transformed into the enantiomerically pure corresponding amines via the photo-enzymatic cascade.@en

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.@en

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.@en