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Iris Hilker

Publications and source records attributed to Iris Hilker.

5 recordsLinked to original sources
PubMed2006

On the influence of oxygen and cell concentration in an SFPR whole cell biocatalytic Baeyer-Villiger oxidation process.

Efficient whole cell biotransformations, in particular microbial whole cell Baeyer-Villiger oxidation with molecular oxygen, demand comprehension and optimization of the process details involved. Optimal provision of oxygen and control of bioprocess parameters are pivotal for their success. The interrelation of cell density and oxygen supply in an in situ substrate feeding and product removal (SFPR) whole cell Baeyer-Villiger oxidation process was investigated in detail. Both parameters were optimized with respect to practical considerations. The outcome of this study supports a schematic process model, allows estimation of optimum process conditions and exploration of its limits.

Bioreactors↗
PubMed2006

Directed evolution of an industrial biocatalyst: 2-deoxy-D-ribose 5-phosphate aldolase.

Aldolases are emerging as powerful and cost efficient tools for the industrial synthesis of chiral molecules. They catalyze enantioselective carbon-carbon bond formations, generating up to two chiral centers under mild reaction conditions. Despite their versatility, narrow substrate ranges and enzyme inactivation under synthesis conditions represented major obstacles for large-scale applications of aldolases. In this study we applied directed evolution to optimize Escherichia coli 2-deoxy-D-ribose 5-phosphate aldolase (DERA) as biocatalyst for the industrial synthesis of (3R,5S)-6-chloro-2,4,6-trideoxyhexapyranoside. This versatile chiral precursor for vastatin drugs like Lipitor (atorvastatin) is synthesized by DERA in a tandem-aldol reaction from chloroacetaldehyde and two acetaldehyde equivalents. However, E. coli DERA shows low affinity to chloroacetaldehyde and is rapidly inactivated at aldehyde concentrations useful for biocatalysis. Using high-throughput screenings for chloroacetaldehyde resistance and for higher productivity, several improved variants have been identified. By combination of the most beneficial mutations we obtained a tenfold improved variant compared to wild-type DERA with regard to (3R,5S)-6-chloro-2,4,6-trideoxyhexapyranoside synthesis, under industrially relevant conditions.

Aldehyde-Lyases↗
PubMed2005

Microbial transformations 59: first kilogram scale asymmetric microbial Baeyer-Villiger oxidation with optimized productivity using a resin-based in situ SFPR strategy.

This study is demonstrating the scale up of asymmetric microbial Baeyer-Villiger oxidation of racemic bicyclo[3.2.0]hept-2-en-6-one (1) to the kilogram scale using a 50 L bioreactor. The process has been optimized with respect to bottlenecks identified in downscaled experiments. A high productivity was obtained combining a resin-based in situ substrate feeding and product removal methodology (in situ SFPR), a glycerol feed control, and an improved oxygenation device (using a sintered-metal sparger). As expected both regioisomeric lactones [(-)-(1S,5R)-2 and (-)-(1R,5S)-3] were obtained in nearly enantiopure form (ee > 98%) and good yield. This represents the first example of such an asymmetric Baeyer-Villiger biooxidation reaction ever operated at that scale. This novel resin-based in situ SFPR technology therefore clearly opens the way to further (industrial) upscaling of this highly valuable (asymmetric) reaction.

Biomedical Engineering↗
PubMed2004

Microbiological transformations 57. Facile and efficient resin-based in situ SFPR preparative-scale synthesis of an enantiopure "unexpected" lactone regioisomer via a Baeyer-Villiger oxidation process.

[reaction: see text] The microbiological Baeyer-Villiger oxidation of (-)-bicyclo[3.2.0]hept-2-en-6-one allowed exclusive formation of the "unexpected" lactone regioisomer in 84% yield, high chemical purity, and enantiopure form. Substrate (25 g) was transformed in a 1 L bubble column reactor, following a in situ substrate feeding/product removal methodology, which afforded high volumetric productivity (1.2 g L(-)(1) h(-)(1)). This illustrates the high "sustainable chemistry" advantages of such a process, simply conducted in aqueous medium, at room temperature and using atmospheric oxygen.

Bioreactors↗