Modularization and optimization of enzymatic reactions applying whole cell biocatalysis in micro-aqueous solvent systems

Growing understanding of enzymatic reactions and their utilization for synthetic purposes has led to a rising interest in development of artificial, biocatalytic multi-step reactions. These synthetic enzyme cascades selectively convert inexpensive substrates into valuable compounds of varying applications. Despite their many advantages, the productivity of biocatalytic cascade reactions is oftentimes considered unsatisfactory for implementation into industrial scale processes. To overcome this limitation and facilitate investigation, application, optimization, and scale-up of biocatalytic cascade reactions was the objective of this thesis. Representing a valuable chiral building block for pharmaceutical synthesis, 1-phenylpropane-1,2-diol was chosen as a model product, accessed by subsequent carboligation and oxidoreduction.In order to increase the economic and ecologic relevance of the model process and of synthetic enzyme cascades in general, lyophilized whole cell catalyst was used in a micro-aqueous solvent system. In doing so, a cheap and stable catalyst formulation was employed, independent of costly external cofactor addition. The cofactor, supplied by the whole cell catalyst itself, was recycled by substrate-coupled regeneration. Furthermore, the reaction in organic solvent enabled outstandingly high substrate and product titers together with facilitated downstream processing by straightforward solvent evaporation.To enable an easy cascade investigation and setup, the compartmentalized entrapment or encapsulation of whole cell catalyst was envisaged, allowing to serve as a catalytic module. Therefore, whole cell catalyst was retained in a polymeric membrane, resulting in a catalytic teabag. The catalytic teabag was proven a useful modularization tool, enabling (i) simplified and flexible handling and combination of biocatalysts, (ii) straightforward catalyst recovery and recycling, (iii) facilitated cascade optimization and set-up, as well as (iv) small scale preparative production of chiral compounds. In a second project part, the teabag approach was demonstrated scalable up to 150 mL, facilitating the gram-scale manufacturing of (1R,2R)-1-phenylpropane-1,2-diol in a 1-pot 2-step cascade. As suitable reaction vessel, not only novel reactor concepts such as the SpinChem reactor (Nordic Chemquest AB) were proven useful, but also ubiquitously available lab equipment. In a third project part, the investigated concepts were demonstrated transferable to two more catalysts, now granting stereoselective access to all four diastereoisomers of 1-phenylpropane-1,2-diol at industrially relevant product concentrations. To achieve this goal, a combination of reaction engineering and solvent engineering was applied. By the implementation of “smart” diol co-substrates up to 90 mol% of co-substrate could be saved during oxidoreduction in two of the final cascades. At the same time, product yield and space-time-yields obtained met industrial benchmarks while outstandingly small amounts of waste were generated.In summary, the investigation of synthetic enzyme cascades was strongly facilitated by the teabag approach. The developed module is quickly manufactured and easily manageable, also by users unexperienced in handling of biological systems and can even be used for the preparative production of chiral compounds. The combination of solvent and reaction engineering allowed exceeding industrial threshold and thus illustrated the potential of synthetic enzyme cascades even beyond the investigatory scale

Stereoselective Two-Step Biocatalysis in Organic Solvent: Toward All Stereoisomers of a 1,2-Diol at High Product Concentrations

Biotransformations on larger scale are mostly limited to cases in which alternative chemical routes lack sufficient chemo-, regio-, or stereoselectivity. Here, we expand the applicability of biocatalysis by combining cheap whole cell catalysts with a microaqueous solvent system. Compared to aqueous systems, this permits manifoldly higher concentrations of hydrophobic substrates while maintaining stereoselectivity. We apply these methods to four different two-step reactions of carboligation and oxidoreduction to obtain 1-phenylpropane-1,2-diol (PPD), a versatile building block for pharmaceuticals, starting from inexpensive aldehyde substrates. By a modular combination of two carboligases and two alcohol dehydrogenases, all four stereoisomers of PPD can be produced in a flexible way. After thorough optimization of each two-step reaction, the resulting processes enabled up to 63 g L–1 product concentration (98% yield), space-time-yields up to 144 g L–1 d–1, and a target isomer content of at least 95%. Despite the use of whole cell catalysts, we did not observe any side product formation of note. In addition, we prove that, by using 1,5-pentandiol as a smart cosubstrate, a very advantageous cofactor regeneration system could be applied