Whole-cell catalysts design / construction

For the synthesis of (7 )-alcohols by reduction of the corresponding ketones, an E. coli whole-cell catalyst was constructed based on an ADH from L. kefir. Some preparative examples using these designer cells are summarized in section 9.4. 

For Baeyer-Villiger oxidations of ketones into lactones, recombinant whole-cell catalysts were constructed using the CHMO from A. calcoaceticus and cells of S. cerevisiae [127-129] or E. coli [130-132] as host system. These designer cells were used for example for the biotransformation of bicyclo[3.2.0]-hept-2-ene-6-one [133-136], In order to avoid the substrate and product inhibition, an adsorber... 

Based on the (/ )-specific ADH from L. kefir, a recombinant E. coli strain was constructed as a whole-cell biocatalyst, and co-expressed GDH was used for regeneration of NADPH [157]. These designer cells were applied for the reduction of 4-fluoroacetophenone to the corresponding optically active (/ )-4-fluorophe-nylethan-l-ol at 0.5 M educt concentration [158]. After a reaction time of 23 h, a conversion of >95% has been achieved, and the purified isolated chiral alcohol showed an ee value of >99% (87% yield). (S)-p-Halohydrins were obtained with this whole-cell catalyst by means of an enantioselective reduction of the corresponding ketones with both high conversions of >95% and enantioselectivities of >99% (Fig. 40). Base-induced cyclization of the [S-halohydrin led to enantiomeri-cally pure (S)-epoxides in high yield and enantiomeric purity (>99% ee) [159]. 

The photographs show a Diamond Shamrock MDC 55 cell. It is designed on the toast rack principle where a number of DSA anodes are bolted to the cell base (Fig. 3.8(a)) and the cathode assembly (Fig. 3.8(b)) is designed so that each anode is totally surrounded by cathode when it is lifted into place. It is dropped down from above over the fixed anodes. The cell is then completed (Fig. 3.9) by attachment of electrical connections, electrolyte feeds and product take-off pipes. The cathode assembly shown in Fig. 3.8(b) has seventeen cathode tubes which extend from one side of the cell body to the other. The body of each tube (see Fig. 3.10) and the internal faces of the cell sides are constructed from steel mesh (maybe covered by nickel cathode catalyst) and the asbestos-based diaphragjm is deposited onto the mesh by dipping the whole cathode assembly into an asbestos slurry. The caustic soda and hydrogen are collected from inside the tubes. The MDC 55 cell produces approximately 5 tons of CI2 per day and has the dimensions 3 m X 1.6 m X 2 m. Its dry weight is almost 7 tons. 

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