Novel biocatalytic routes for the synthesis of small cyclic molecules

Hegarty, Eimear (2020) Novel biocatalytic routes for the synthesis of small cyclic molecules. PhD thesis, University of Nottingham.

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Abstract

The catalytical asymmetric reduction of small cyclic prochiral ketones with the formation of optically pure alcohols and amines is a fundamentally important reaction in synthetic organic chemistry. However, achieving selectivity using traditional synthetic methodology is challenging, particularly when the prochiral ketone has minimal discrimination between the two side chains. In light of this, new biocatalytic strategies for the enantioselective preparation of small cyclic molecules starting from readily available and inexpensive prochiral ketones was explored.

To this aim, initial efforts focussed on the use of an established and highly efficient solid phase screening methodology for the screening of aminotransferase (ATs) variants. The screen was successfully applied to an AT from Halomonas elongata (HeWT), evolved through rounds of random mutagenesis towards a series of 4 small cyclic ketones, which lead to the identification of a variant with modest improvements in activity (ca. 2-fold) (Chapter 3). The substrate scope of a ketoreductase from Pichia glucozyma (KRED1-Pglu) and a structurally different AT from Pseudomonas fluorescens (PfTA) was subsequently probed using the same panel of small cyclic ketones. Under the reaction conditions tested, KRED1-Pglu failed to produce the target alcohols with a synthetically useful optical purity, while HeWT presented itself as a much more robust biocatalyst for the synthesis of the target amines, with respect to PfTA. To increase the complexity of the system, the development of a tandem enzymatic reaction, combing HeWT with a second biocatalyst, an acyltransferase from Mycobacterium smegmatis (MsAcT), for the synthesis of optically active amides was explored (Chapter 4). Finally, a multi-enzymatic cascade in continuous flow, featuring the immobilised HeWT and MsAcT is presented, demonstrating a fully intensified and industrially relevant biocatalytic process for the synthesis of small cyclic chiral molecules (Chapter 5).

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Paradisi, Francesca
Keywords: Green chemistry, Flow biocatalysis, Enzyme immobilisation
Subjects: Q Science > QD Chemistry > QD241 Organic chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 59887
Depositing User: Hegarty, Eimear
Date Deposited: 29 Jun 2020 15:32
Last Modified: 29 Jun 2020 15:32
URI: http://eprints.nottingham.ac.uk/id/eprint/59887

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