A biocatalytic approach toward linear aliphatic nitriles being widely used as industrial bulk chemicals has been developed that runs at high substrate loadings of up to 1.4 kg/L as demonstrated for the synthesis of n-octanenitrile. This substrate loading is one of the highest ever reported in biocatalysis and to best of our knowledge the highest obtained for a water-immiscible product in aqueous medium. It is noteworthy that the biotransformation at such a high substrate loading was achieved by means of a metalloprotein bearing an iron-containing heme subunit in the active site. In detail, an aldoxime dehydratase from Bacillus sp. OxB-1 was used as a biocatalyst for a dehydration of aldoximes as readily available starting materials due to their easy preparation from aliphatic aldehydes through spontaneous condensation with hydroxylamine as bulk chemical. Excellent conversions toward the nitriles in the two-phase system were achieved and the products are easily separated from the reaction mixture without the need for further purification. Aliphatic nitriles are used in industry as solvents and intermediates for the production of surfactants and life sciences products.

A current challenge in catalysis is the development of methodologies for the production of bulk chemicals needed at levels of tens and hundreds of thousands of tons per year with the requirement to be produced at very low costs often being in the single-digit US dollar range. At the same time, such methodologies should address challenges raised by current manufacturing processes. Within this research area, a cyanide-free approach toward aliphatic nitriles used as industrial chemicals was developed starting from readily accessible n-alkenes as starting materials available in bulk quantities. This chemoenzymatic process concept is exemplified for the synthesis of nonanenitrile (as an n-/iso-mixture) and runs in water at low to moderate temperatures without the need for any types of cyanide sources. The process is based on a combination of a metal-catalyzed hydroformylation as the world-leading production technology for alkyl aldehydes with an emerging enzyme technology, namely, the recently developed transformation of aldoximes into nitriles through dehydration by means of aldoxime dehydratases. As a missing link, an efficient aldoxime formation with subsequent removal of remaining traces of hydroxylamine as an enzyme-deactivating component was found, which enabled the merging of these three steps, hydroformylation, aldoxime formation, and enzymatic dehydration, toward a nitrile synthesis without the need for purification of intermediates.

In recent years, there has been an increasing tendency to use biocatalysts in industrial chemistry, especially in the pharma and fine chemical sector. Preferably, enzymes or whole cells, applied as catalysts for a specific biotransformation, are utilized in aqueous reaction media since water is the natural medium for enzymes. In numerous examples of biocatalytic systems, however, a major problem is the insolubility of hydrophobic substrates in such aqueous reaction media. Apart from lipases, many enzymes are highly sensitive to organic solvents and are inactivated by an organic medium. Therefore, a change of solvent for biotransformations from water to organic solvents is usually challenging. In this study, we investigated the synthesis of nitriles by an organic solvent‐labile aldoxime dehydratase in pure organic solvents, exemplified for the dehydration of n‐octanaloxime to n‐octanenitrile. We present a method for applications in batch as well as flow mode based on an “immobilized aqueous phase” bearing the whole cells in a superabsorber as solid phase, thus enabling the use of a purely organic solvent as “mobile phase” and reaction medium.

The amide moiety of peptides can be replaced for example by a triazole moiety, which is considered to be bioisosteric. Therefore, the carbonyl moiety of an amino acid has to be replaced by an alkyne in order to provide a precursor of such peptidomimetics. As most amino acids have a chiral center at Cα, such amide bond surrogates need a chiral moiety. Here the asymmetric synthesis of a set of 24 N-sulfinyl propargylamines is presented. The condensation of various aldehydes with Ellman’s chiral sulfinamide provides chiral N-sulfinylimines, which were reacted with (trimethylsilyl)ethynyllithium to afford diastereomerically pure N-sulfinyl propargylamines. Diverse functional groups present in the propargylic position resemble the side chain present at the Cα of amino acids. Whereas propargylamines with (cyclo)alkyl substituents can be prepared in a direct manner, residues with polar functional groups require suitable protective groups. The presence of particular functional groups in the side chain in some cases leads to remarkable side reactions of the alkyne moiety. Thus, electron-withdrawing substituents in the Cα-position facilitate a base induced rearrangement to α,β-unsaturated imines, while azide-substituted propargylamines form triazoles under surprisingly mild conditions. A panel of propargylamines bearing fluoro or chloro substituents, polar functional groups, or basic and acidic functional groups is accessible for the use as precursors of peptidomimetics.

Pickering emulsion systems have emerged as platforms for the synthesis of organic molecules in biphasic biocatalysis.H erein, the catalytic performance was evaluated for biotransformation using whole cells exemplified for the dehydration of n-octanaloxime to n-octanenitrile catalysed by an aldoxime dehydratase (OxdB) overexpressed in E. coli. This study was carried out in Pickering emulsions stabilised solely with silica particles of different hydrophobicity.W e correlate,for the first time,the properties of the emulsions with the conversion of the reaction, thus gaining an insight into the impact of the particle wettability and particle concentration. When comparing two emulsions of different type with similar stability and droplet diameter,t he oil-in-water (o/w) system displayed ah igher conversion than the water-in-oil (w/o) system, despite the conversion in both cases being higher than that in a"classic" two-phase system. Furthermore,anincrease in particle concentration prior to emulsification resulted in an increase of the interfacial area and hence ahigher conversion.