Studies of Lewis acid promoted anomerisation reactions
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Date
2023-01-23Embargo Date
2025-01-20
Author
Meany, Fiach B.
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Abstract
The stereoselective synthesis of the glycosidic bond still remains a challenge for the synthetic
carbohydrate chemist. Lewis acid promoted anomerisation offers a useful means of generating
1,2-cis glycosides from their 1,2-trans counterparts. The main aim of this thesis is the study of
anomerisation reactions and the factors affecting them. Previously The Murphy group has
reported the anomerisation of a variety of glycosides, however it is hoped that a greater
understanding of factors affecting the anomerisation reaction may enhance its synthetic utility.
Chapter 2 involves the study of the role of the C-2 benzoate in the Lewis acid promoted
anomerisation of benzoylated glycosides. Previous studies showed rate enhancements when a
benzoate was present at the C-2 position and this was proposed to be due to resonance effects.
A variety of para substituted benzoates at the C-2 position were synthesized and their rates of
anomerisation determined. Hammett and Swain-Lupton plots were generated using the data
generated.
Chapter 3 details the study of the effect of conformation in the anomerisation reaction.
Previously, rate enhancements were observed in the anomerisation of butyl glucopyranosides
which were armed with bulky silyl groups. A series of galactopyranosides were synthesized to
investigate if the α-anomers could be obtained from their β counterparts and if arming these
with silyl groups resulted in enhanced reactivity. Efforts towards the synthesis of a reactant
with a carboxylate at the C-3 position are also described.
Chapter 4 describes the application of anomerisation in the synthesis of aromatic S-glycosides.
Both the α and β anomers of thioglycosides have previously shown to be galectin inhibitors
and anomerisation offers a means to generate the α-anomers. Glycosyl thiol anomerisation was
found to be an efficient means towards α-thiopyridyl linkages as well as in the synthesis of
other compounds.