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    Overcoming limitations of L-threonine aldolases in biocatalysis: Highly efficient applications via reaction engineering
    In this interdisciplinary tandem project by the working groups Liese (Bioprocess Engineering) and Gröger (Industrial Organic Synthesis), the aim is to generate a basic scientific understanding of efficient diastereoselective synthesis processes using L-threonine aldolases. These enzymes catalyze asymmetric aldol reactions to form a-amino ß-hydroxy carboxylic acids. Currently, the major disadvantage of this enzymatic reaction type is the unfavorable thermodynamic equilibrium, which leads to unwanted diastereomeric ratios of the products. Starting from a model reaction, a fundamental understanding of the competing thermodynamic and kinetic control of the biocatalytic reaction system will be developed. The establishment of inline (NMR) and offline (HPLC) analytical methods will allow a comprehensive kinetic and thermodynamic characterization depending on the reaction progress. Based on this, reaction and enzyme measures to overcome the thermodynamic and kinetic limitations are evaluated and implemented in a continuously operated reactor. At the end of this project, this comprehensive study should demonstrate that aldol reactions catalyzed by L-threonine aldolases are a worthy alternative to conventional chemical synthesis processes for the synthesis of alpha-amino beta-hydroxy carboxylic acids.
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    SPP 2240: Chemoenzymatic reaction cascade in an All-in-One electrochemical system with in situ supply of H2O2 for biosynthesis in aqueous and organic media
    Chemoenzymatic reaction cascades have a great potential for biosynthesis and sustainability, especially when coupled with the latest advances in electrochemical systems and material sciences. This envisaged project connects the expertise of three truly interdisciplinary groups in biocatalysis, bioprocess engineering, bioelectrochemical systems (BES) and nano-materials in a unique way to address fundamental challenges in developing a novel and individually optimizable platform for hydrogen peroxide-dependent enzymatic cascade reactions. H2O2 plays an important role as a green and powerful co-substrate or co-factor in the biosynthesis of a vast variety of value-added products and can be electrochemically efficiently generated from H2O and O2 as demonstrated in conventional BES with three-electrodes. One of the first objectives of this project is to develop a fully controllable BES for in situ and on-demand synthesis of H2O2 based on a novel All-in-One (AiO) electrode developed recently by one of the project partners. To realize a controlled H2O2 generation in the AiO electrode with high energy efficiency, highly porous carbon foams coated with carbon nanotubes (CNTs) will be designed and tailored by a sophisticated novel CVD process, yielding low density (20 mg/cm3) and high conductive hierarchical porous structure. H2O2 generated in such a controlled way is instantly used by enzymatic oxyfunctionalization in multistep chemoenzymatic reaction cascades. The reaction systems aimed at will include a peroxidase catalyzed sequential hydroxylation towards the synthesis of hydroquinone in aqueous media as well as the simultaneous chemoenzymatic esterification and epoxidation towards epoxidized fatty acid esters in a solvent free organic environment (adapted Prilezhaev reaction). The mentioned reactions will be investigated using both free and immobilized enzymes on functionalized CNTs. This integrated approach is unique and promising in tackling one of the major issues in H2O2 -dependent enzymatic oxyfunctionalization, namely the lowered half-life time of enzyme activity in the presence of H2O2. By integrating the AiO-electrode in an organic reaction medium in situ H2O2 addition will be realized without the addition of water, omitting side reactions (e.g. in the Prilezhaev reaction). With a fine-tunable system in hand, the rates of electrochemical H2O2 synthesis and enzymatic H2O2 consumption can be tightly coupled, enabling a constantly low concentration of H2O2 during the whole cascade reaction. This will open up new possibilities to develop chemoenzymatic reaction cascades with improved enzyme stability and activity and a more stable entire process.
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