Reaction engineering analysis of the asymmetric synthesis of chiral alcohols with Lactobacillus kefir

Maya Amidjojo, doctoral thesis Technische Universität München, 2004

Chiral alcohols are important building blocks for the synthesis of pharmaceuticals, flavour components and agrochemicals. An effective way for the biosynthesis of chiral alcohols is the enantioselective reduction of prochiral ketones using whole cells as biocatalysts. However, the substrates (partly also the products) oftentimes possess a low water solubility. This results in low conversion rates and yields. The biotransformations are therefore frequently performed in two-phase liquid/liquid-systems: a water-immiscible organic phase, containing the substrate, is brought in contact with the aqueous phase, containing the biocatalyst. Yet, the applied organic solvents, on their part, lead to a rapid deactivation of the biocatalysts and elevate the safety-related expenditures. Aim of the project was therefore the reaction engineering characterisation of selected asymmetric syntheses without the use of a water-immiscible organic phase as substrate reservoir and in-situ extracting agent. Lactobacillus kefir was chosen as biocatalyst, due to its number of oxidoreductases, which facilitate various asymmetric syntheses at high enantioselecitivities. With Lactobacillus kefir as whole-cell biocatalyst new processes were developed for the effective enantioselective syntheses of (R)-1-(4-chlorophenyl)-ethanol, tert-butyl (3R,5S)-6-chloro-dihydroxyhexanoate and ethyl (S) 4 chloro-3-hydroxybutanoate from their corresponding prochiral ketones, without the additional use of organic solvents. For this, the substrates were provided “microdispersive” as pure phase in the bioreactor.


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