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Title: Applications of enzymatic methods to the preparation of enantiomerically pure compounds
Author: Harvey, Ian
ISNI:       0000 0001 3542 2332
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1989
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This thesis describes investigations in the field of biotransformations, concentrating on the mode of action of esterases and lipases, and the application of these systems to the production of enantiomerically pure compounds. The behaviour of pig liver esterase (PLE) in the presence of some commonly use alcohol and ketone cosolvents was examined. Methanol, ethanol and 2-butanone were found to be potent inhibitors of PLE. At low concentrations, acetone accelerated the rata of PLE catalysed hydrolysis, but is also inhibitory at higher concentrations. The effects of alcohols as product inhibitors were examined. This, and other data obtained suggests that the complex kinetics of this enzyme could be explained using the 'Ligand Induced Slow Transition Model" (Ainslie et al., J. Biol. Cham., 1972, 247, 7088). Examination of PLE by gel filtration hplc suggested that the active form of this enzyme may not be trimeric as previously thought. Soma analogous studies were carried out with pig pancreatic lipase. The use of the isosyme-specific inhibitors, eserine and phenylmethylsulfonyl fluoride did not improve the enantiospecificity of the hydrolysis of trans-1,2-diacetoxy-cyclopentane catalysed by PLE. Dimethyl mono-3-cyclobutene-1,2-dicarboxylate was hydrolysed to the corresponding mono-ester by pig liver esterase with high optical purity (56% a.e.) and chemical yield. The mono-ester epimerised during derivatisation mediated by 1,1-carbonyldiimidazole, allowing the preparation of optically pure trans derivatives. Rapid derivatisation allowed the preparation of cis analogues. This was demonstrated by the preparation of both the optically pure cis and trans benzylamide derivatives. Mono-3-Cyclobutane-1.2-dimethanol diacetate was hydrolysed to the corresponding mono-acetate by Pseudomonas fluorescene lipase with high optical purity (>97% a.e. at 0.8 mol-equivalent) and chemical yield. The corresponding (4-phenyl)benzoyl, (4-toluene)sulphonyl and (4-phenylethene-9-yl) derivatives were prepared. The racemic allene diethyl penta-2,3-dismodicate was hydrolysed by pig liver esterase in buffer containing 232 (v/v) acetone. The product, (g)-(-)-ethyl penta-2,3-dismodicate, was produced with 30 – 33% a.e. at 0.3 mol-equivalents. As a demonstration of the development of a hydrolytic resolution procedure, such a method was devised for the preparation of an optically pure halogenated propan-l-el derivative. Pig pancreatic lipase was chosen as the model system. By manipulating the reaction conditions and the acid moiety, the enantiospecificity of the hydrolysis was improved by a minimum of 6.4 times, and possibly by greater than ten-fold.
Supervisor: Not available Sponsor: Science and Engineering Research Council ; Imperial Chemical Industries plc
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry