This thesis describes the use of enzymes to partially deprotect or deprotect sugars. The advantages of this technique are that mild conditions may be used for the protections and that enzymatic catalysis may allow derivatives to be made which involve multi-step procedures or cannot be made using standard methods. These protected sugars can then be used to synthesise interesting derivatives. The particular aim of this project at the outset was to use biotransformations to make partially protected derivatives for the synthesis of a novel artificial sweetener, l',4,6'-trichloro-r,4,6'-trideoxy-ga/acto- sucrose, known as sucralose. The analysis of the products from a deacetylation reaction is a potential problem due to the number of possible products that may be formed. A new approach to this problem is discussed in Chapter Two. A combination of n.m.r. and mass spectrometry is used to analyse the products after they have first been perdeuterioacetylated by treatment with d6-acetic anhydride. The analysis is therefore carried out on one compound, the starting material, now containing deuteriated acetate groups in place of those that were hydrolysed during the reaction. The technique was used initially to analyse the deacetylation of sucrose octaacetate catalysed by yeast esterase. The selectivity of the enzyme for certain positions of the sugar may be determined in this way but little information can be found about the individual species that are formed. The technique can be considerably enhanced by the introduction of a chromatographic separation step. The separation of the deacetylation mixture into classes, according to the number of acetate groups, allows a much more detailed analysis of the individual components to be carried out. If the reaction shows a certain amount of selectivity then it is possible to determine the quantity of each of the individual species. This technique is used to analyse the deacetylation of glucose pentaacetate catalysed by Aspergillus niger lipase. The deacetylation of sucrose octaacetate catalysed by yeast esterase is also analysed in the same way. Chapter Three describes the conversion of N-acetyl- glucosamine to N-acetyl-galactosamine. This is of interest due to the importance of this sugar in biological systems and its high cost relative to the starting material. The synthesis involves the use of an enzyme catalysed deesterification to make a partially protected intermediate, demonstrating the practical application of biotransformations in the synthesis of sugar derivatives.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:304584 |
| Date | January 1991 |
| Creators | Chaplin, David Andrew |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/108830/ |
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