| Summary: | 碩士 === 國立臺灣大學 === 生化科學研究所 === 92 === Abstract
Glycals are unsaturated sugars containing the olefin in the anomeric position. endo- or exo-Glycals designate the double bond located inside or outside the sugar ring, respectively. endo-Glycals have been extensively studied to synthesize various biologically significant carbohydrates, including Lewis and blood group determinants, gangliosides and tumor-associated antigens. Consequently it is reasonable to consider analogous exo-glycals as useful and versatile synthons. However, the studies of exo-glycals were not available until recently. Our laboratory developed an expeditious method in the past to prepare exo-glycals that are reactive with various alcohols to proceed glycosyl additions. The reactions were carried out with high yield and exclusive stereoselectivity, to afford a number of disaccaarides, glycopeptides and glycolipid. All of the products had a β-vinyl group resulting from allylic rearrangement, reminiscent of the Ferrier reaction in the glycosylation of endo-glycals.
This thesis aims to investigate in detail the Ferrier rearrangement of exo-glycals in order to broaden the synthetic usage for the preparation of various important glycoconjugates. Special emphasis was laid on the inter- and intra-molecular glycosylation. In the study of the former reaction, t-butyl carbonate (t-Boc) is attached to the exo-glycosyl double bond and considered to provide an extra driving force at elevated temperature in the glycosylation. Several factors, including temperature, Lewis acid and solvent were studied to acquire the optimal condition that was further applied for the glycosylation of exo-glycals with a number of monosaccharides, amino acids and alcohols.
The latter investigation intended to understand if the Ferrier-type rearrangement is applicable to intramolecular glycosylation. Several exo-glycosyl carbonates were prepared to contain different substituents including n-butanol, benzyl alcohol and protected monosaccharide. The glycosylation was carried out in the existence of Lewis acid (BF3.OEt2 or TMSOTf) or at elevated temperature. So far only moderate yields were obtained.
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