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Digital archive of theses discussed at the University of Pisa


Thesis etd-09122022-113932

Thesis type
Tesi di laurea magistrale LM5
Thesis title
Reiterative stereospecific synthesis of 1,4-oligosaccharides by glycal-derived vinyl epoxide assembly
Course of study
relatore Prof.ssa Di Bussolo, Valeria
relatore Dott. Di Pietro, Sebastiano
  • glycal
  • oligosaccharides
  • vinyl epoxide
Graduation session start date
Release date
Stereodefined carbohydrates, the most abundant class of biomolecules found in living organisms, are very interesting molecules due their various applications: many antibacterial, antiviral, anticancer, and even vaccination drugs today have oligosaccharides and/or glycoconjugates as their essential component.
However, despite the biological and medical relevance of carbohydrates, their structural complexity and heterogenicity has hampered their synthesis. Fortunately, scientific research invests enormous resources in the development of chemical and enzymatic methods for stereoselective synthesis of glycosides.
Recently, one of the most attractive strategy for oligo- and polysaccharides synthesis is the “one pot” procedure: the glycosyl donor reacts in a single batch with the glycosyl acceptor, and the obtained product acts as the glycosyl acceptor for the subsequent step. This method produces oligosaccharides quickly and without the need to manipulate protecting groups or perform intermediate purification. My thesis work is focused on the synthesis and study of stereodefined oligosaccharides obtained by glycal-derived vinyl epoxides assembly. Indeed, in recent years, our research group has identified the glycal derived vinyl epoxides 1α and 1β, as new building blocks for a stereospecific glycosylation process to synthesize 2,3 unsaturated glycosides. One of the most attractive application of this new glycosylation process is the possibility to reiterate the process to obtain stereodefined 1,4-oligosaccharides. The purpose of my thesis work was to develop a new reiterative approach for the construction of 2,3-unsaturated-1,4-oligosaccharides via conjugated addition to vinyl epoxide 1β or 1α . The optimized oligomerization procedure involves the addition of the glycosyl donor vinyl epoxide 1β (or 1α), generated in situ by cyclization under basic conditions (t-BuOK) of its stable precursor, the α or β-hydroxy mesylate, to a series of previously synthesized glycosyl acceptors 2 through a microwave activated process. This method is an example of “one pot glycosylation”. Once the synthetic protocol was established, my thesis work was focused on the synthesis of dihydroxylated oligomers. The resulting molecule was studied by one- and two-dimensional NMR experiments, which showed that the dihydroxylation process is still completely stereoselective and directed by the stereochemistry of the allylic substituents.
Moreover, my focus has been on the synthesis and characterization of oligomers derived from glycal vinyl epoxide 1α. The glycal-derived vinyl epoxides 1α and 1β represent efficient glycosyl donors even in this oligomerization process giving only conjugate addition, in an uncatalyzed substrate-dependent stereospecific process and oligomers with desired lengths are obtained.