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New Synthetic Applications of Galactose Oxidase and Candida Antarctica Lipase B

Yuan, Bo

[Thesis]. Manchester, UK: The University of Manchester; 2011.

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Abstract

Increasing demand for chiral technology in industry has led to the rapid development of catalysts for enantioselective processes. In this respect biocatalysts are of particular interest due to their excellent regio- and stereo- selectivity and their ability to work under mild conditions.The development of catalysts for the selective oxidation of alcohols to aldehydes and ketones represents a major challenge in organic synthesis. Previous work showed that a variant of the enzyme galactose oxidase (GOase) was capable of oxidising a wide range of chiral secondary alcohols with high enantioselectivity.1 The aim of this work is to develop new applications for this variant.Two new stereoselective processes have been developed employing this variant:1. Enzymatic desymmetrisation of proatropisomeric diaryl ethers and biaryls. Atropisomers are stereoisomers resulting from restricted rotation about an axis, where the rotational barrier is high enough for isolation of the conformers. Desymmetrisation by GOase has allowed the production of atropisomers with enantiomeric excess (ee) up to 99% in good yields. An alternative approach based upon asymmetric reduction of the corresponding dialdehyde using ketoreductases (KREDs) has also been explored.2. Deracemisation of racemic secondary alcohols by a combination of enzyme and transition metal catalysts. Deracemisation is a method for the production of enantiopure compounds starting from racemic substrates. Combination of the enzyme GOase and a transition metal catalyst has allowed the production of a single enantiomer of a number of secondary alcohols from the corresponding racemic mixture (ee > 99%, yield > 98%).Primary amides are widely applied in the polymer industry. They are produced in large quantities each year. An efficient solvent-free process (yield > 90%) for the production of erucamide has been developed employing immobilised Candida antarctica Lipase B (CALB, Novozym® 435 ) under mild conditions (solid ammonia source, 90 °C).