engleski

Biocatalytic synthesis of enantioenriched product – reaction engineering approach

Optically pure fluorinated organic nitriles are synthetically valuable building blocks in the pharmaceutical and fine chemical industries. Since direct fluorination is challenging from both economic and environmental perspectives, the development of methods to modify existing fluorinated synthons is a prized alternative. Halohydrin dehalogenases (HHDHs) are synthetically valuable enzymes because they can accept numerous anionic nucleophiles such as cyanide, cyanate, azide and others in epoxide ring-opening reactions. HHDHs exhibit enantioselectivity or enantiopreference in a wide range of reactions and provide the ability to perform kinetic resolution of fluorinated building blocks, resulting in higher value products, i.e., optically pure β-substituted alcohols and unreacted enantiomers of substrates. However, if the enzyme is not completely enantioselective, the optical purity of the final products depends largely on the reaction conditions and reactor design. In this work, the HHDH-catalysed synthesis of (S)-3-(4-fluorophenyl)-3-hydroxypropanenitrile was investigated from a reaction engineering point of view. Since both enantiomers of 2-(4-fluorophenyl)oxirane are accepted in the biocatalytic reaction with cyanide ions, the reaction was kinetically studied in detail starting from the individual enantiomers of the substrate. In addition, the inevitable hydrolysis of the substrate was kinetically characterised. The effect of all concentrations of the reaction components on the enzyme activity was investigated. Differences were found between the enzyme affinities toward (R)- and (S)-2-(4-fluorophenyl)oxirane, as well as the presence of different inhibitions in both biocatalytic reactions. These effects are expressed numerically by Vm, Km and Ki values. In addition to activity, the stability of the enzyme in the presence of compounds from the reaction mixture was also evaluated, and as a result, a co-dependence of the operational stability decay on the initial substrate concentration was found. The mathematical model for the synthesis of (S)-3-(4-fluorophenyl)-3-hydroxypropanenitrile was developed and used as a guide for the detection and minimization of reaction bottlenecks. Through mathematical modelling, it is possible to manipulate the outcome of the reaction in the desired direction within the limitations of the enzyme. Process simulations were used to select suitable conditions for the synthesis of a product with high optical purity and yield.

fluorinated building blocks ; halohydrin dehalogenases ; enantioselectivity ; enzyme kinetics ; mathematical modelling ; process simulations

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