PUB - Publikationen an der Universität Bielefeld

Nitriles belong to the product classes, which are mostly needed and produced by the chemical industry, playing a major role in various industry segments ranging from high-volume low-price sectors such as polymers to low-volume high-price sectors such as the chiral pharma drugs. A common industrial technology for nitrile production is ammonoxidation as a gas phase reaction at high temperature. A further popular approach are substitution or addition reactions with hydrogen cyanide or derivatives thereof. A major drawback, however, is the very high toxicity of cyanide. Recently, as a synthetic alternative, a novel enzymatic approach towards nitriles has been developed by means of so-called aldoxime dehydratases, which are capable to convert an aldoxime in one step via dehydration into nitriles. Since the aldoxime substrates are easily accessible, this route is of high interest for synthetic purposes. However, whenever a novel method is developed for organic synthesis, it raises the question of substrate scope as one of the key criteria to be applied as a "synthetic platform technology". Thus, the scope of this review is to give an overview about the current state of the substrate scope of this enzymatic method for synthesizing nitriles by means of aldoxime dehydratases. Even being a recently emerged enzyme class, a range of substrates have already been studied so far, comprising non-chiral and chiral aldoximes. It turned out that this enzyme class of aldoxime dehydratases shows a broad substrate tolerance and accepts aliphatic and aromatic aldoximes as well as arylaliphatic aldoximes. Furthermore, aldoximes bearing a stereogenic center are recognized as well and in particular for 2-arylpropylaldoximes high enantioselectivities are found. It is further noteworthy that the enantiopreference turned out to depend on the (E)- and (Z)-isomer. Thus, opposite enantiomers are accessible although starting from the same racemic aldehyde and the same enzyme. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.