Oxidase-based biocatalytic processes

Biocatalytic processes are gaining significant focus in frontiers where they offer unique advantages(selectivity and mild operating conditions) over chemical catalysts. It is therefore not surprising that therehave been many industrial biocatalytic processes implemented.Despite past successes, the implementation of a new biocatalytic process still presents some challenges (demands placed on the biocatalyst) in terms of the requirements to make a viable industrial process.

Inorder for a biocatalytic process to be economically successful, it is necessary that certain a set of targetmetrics (product titre, biocatalyst yield or space time yield and reaction yield) are achieved. Hence, the biocatalyst must be able to work at high substrate and product concentrations. Such constraints that arisefrom the biocatalyst are classified as biocatalyst-related limitations.

In addition, other limitations can arisefrom the reaction species (substrate and product volatility for example) and the process (such as oxygen supply, ability to control pH) and are classified as reaction-related and process-related constraintsrespectively. Although the development of biocatalyst and process engineering tools offers a number ofsolutions to overcome the limitations, it is often complicated to identify the key limitation of the system that prevents economic scale-up.

Hence, development of a systematic method for identifying the limitations during early-stage development of a biocatalytic process and potentially the order in which theyneed to be tackled would offer a valuable tool for process development.Biocatalytic oxidationsare potentially of great value because of theselective chemistry that they offer,resulting in higher yieldscompared to thoseachievable through chemical catalysis.

Oxidases areparticularly interestingbiocatalystsbecause they use a mild oxidant (oxygen) as a substrateas opposed to their chemical counterparts which use strong oxidants such as permanganates. A class of oxidases calledmonoamine oxidases has been used as the central case study for the thesis. The rationale for choosing thissystemis that it has been shown to exhibit the potential for resolution of racemic amines, and is capable ofproducing industrially interesting imines which are rather difficult to synthesize by chemical routes.An important aspect for biocatalytic reactions would be the implementation of monitoring and control systems that allow for rapid data collection to gain process knowledge.

For oxidase-based biocatalysis,oxygen is consumed in stoichiometric amounts for the reaction. Therefore, oxygen sensors which canmeasure the oxygen concentration can be a valuable tool for monitoring of the process. The thesis exemplifies the use of novel solvent-resistant oxygen sensors as supporting technology for oxidase-basedreactions using a glucose oxidase reaction system as an example.iiImplementation of biocatalytic oxidation at scale still requires process knowledge which includes thelimitations of the system and the knowledge about the potential solutions available to alleviate theselimitations.

This thesis presents a methodology for development of oxidase-based biocatalytic processes. Aparticularly important aspect of the methodology includes the use ofin silicoanalysis where propertyprediction tools have been used to identify the potential limitations to the reaction system prior toexperimentation.

Such an analysis presents the opportunity to direct experimental work and therefore reduce the time and effort spent on process development, by eliminating unfeasible routes. The example chosen for the development of the methodology was a specific monoamine oxidase-based syntheses forthe production of a pharmaceutical intermediate.

This particular reaction system was chosen because ofthe potential use of the product of the biocatalytic reaction as a pharmaceutical intermediate. However,therewas little information on the reaction system in the literature for the use of this biocatalyst forsynthesis of chemicals. Therefore, early stage process understanding was required.

The chapters of thethesis identify the potential limitations for the reaction system by systematic evaluation of the reactionsystem through the use of property prediction tools as well as experiments. The results obtained from theexperiments are then used to identify the bottleneck for the implementation at scale.

Furthermore, adiscussion of the limitations and the order which they need to be tackled is presented