The synthesis of nitriles is of utmost importance for preparative organic chemistry. The classical routes are often associated with disadvantages such as toxicity of the reagents and drastic conditions. The uses of enzymes like aldoxime dehydratases (Oxds) and hydroxynitrile lyases constitute attractive benign alternatives. In this review, we summarize the recent trends regarding Oxds. Thousands of oxd genes were sequenced but less than thirty Oxds were investigated on protein level. We give an overview of these Oxds, their sequence analysis, conditions required for their overexpression, and their purification and assays. We then focus on the use of Oxds especially in multistep reactions combining the chemical or chemoenzymatic synthesis of aldoximes from different starting materials with the enzymatic dehydration of aldoximes to nitriles, possibly followed by the hydration of nitriles to amides. Progress in Oxd immobilization is also highlighted. Based on data published mainly in the last 5 years, we evaluate the industrial prospects of these enzyme processes in comparison with some other innovations in nitrile synthesis. KEY POINTS: • Aldoxime dehydratases (Oxds) are promising for cyanide-free routes to nitriles • A comprehensive overview of wet-lab explored Oxds is provided • Recent trends include combining Oxds with other enzymes or chemical catalysts.

• Klíčová slova
• Aldoxime dehydratase, Biocatalyst, Immobilization, Multistep reaction, Nitrile synthesis,
• MeSH
• dehydratasy * metabolismus   genetika   MeSH
• enzymy imobilizované * metabolismus   genetika   MeSH
• nitrily * metabolismus   MeSH
• oximy metabolismus   chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• aldoxime dehydratase MeSH Prohlížeč
• dehydratasy * MeSH
• enzymy imobilizované * MeSH
• nitrily * MeSH
• oximy MeSH

Various widely applied compounds contain cyano-groups, and this functional group serves as a chemical handle for a whole range of different reactions. We report a cyanide free chemoenzymatic cascade for nitrile synthesis. The reaction pathway starts with a reduction of carboxylic acid to aldehyde by carboxylate reductase enzymes (CARs) applied as living cell biocatalysts. The second - chemical - step includes in situ oxime formation with hydroxylamine. The final direct step from oxime to nitrile is catalyzed by aldoxime dehydratases (Oxds). With compatible combinations of a CAR and an Oxd, applied in one-pot two-step reactions, several aliphatic and aryl-aliphatic target nitriles were obtained in more than 80% conversion. Phenylacetonitrile, for example, was prepared in 78% isolated yield. This chemoenzymatic route does not require cyanide salts, toxic metals, or undesired oxidants in contrast to entirely chemical procedures.

• Klíčová slova
• aldoxime dehydratase (Oxd), carboxylic acid reductase (CAR), chemoenzymatic synthesis, cyanide-free nitrile synthesis, nitriles, oxidoreductases,
• Publikační typ
• časopisecké články MeSH

In plants, aldoximes per se act as defense compounds and are precursors of complex defense compounds such as cyanogenic glucosides and glucosinolates. Bacteria rarely produce aldoximes, but some are able to transform them by aldoxime dehydratase (Oxd), followed by nitrilase (NLase) or nitrile hydratase (NHase) catalyzed transformations. Oxds are often encoded together with NLases or NHases in a single operon, forming the aldoxime-nitrile pathway. Previous reviews have largely focused on the use of Oxds and NLases or NHases in organic synthesis. In contrast, the focus of this review is on the contribution of these enzymes to plant-bacteria interactions. Therefore, we summarize the substrate specificities of the enzymes for plant compounds. We also analyze the taxonomic and ecological distribution of the enzymes. In addition, we discuss their importance in selected plant symbionts. The data show that Oxds, NLases, and NHases are abundant in Actinobacteria and Proteobacteria. The enzymes seem to be important for breaking through plant defenses and utilizing oximes or nitriles as nutrients. They may also contribute, e.g., to the synthesis of the phytohormone indole-3-acetic acid. We conclude that the bacterial and plant metabolism of aldoximes and nitriles may interfere in several ways. However, further in vitro and in vivo studies are needed to better understand this underexplored aspect of plant-bacteria interactions.

• Klíčová slova
• aldoxime dehydratase, aldoxime-nitrile pathway, indole-3-acetic acid, nitrilase, nitrile hydratase, phytohormone, plant aldoxime, plant defense, plant-bacteria interaction,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

We report a new chemoenzymatic cascade starting with aldehyde synthesis by carboxylic acid reductase (CAR) followed by chemical in situ oxime formation. The final step to the nitrile is catalyzed by aldoxime dehydratase (Oxd). Full conversions of phenylacetic acid and hexanoic acid were achieved in a two-phase mode.

• Publikační typ
• časopisecké články MeSH