ETD system

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Tesi etd-02122020-145558

Thesis type
Tesi di laurea magistrale LM5
New synthetic stereoselective approaches to oligosaccharides and glyco-based chiral lanthanide complexes
Corso di studi
relatore Prof.ssa Di Bussolo, Valeria
relatore Dott. Di Pietro, Sebastiano
Parole chiave
  • glyco-based chiral lanthanide complexes
  • oligosaccharides
  • stereoselective synthesis
Data inizio appello
Data di rilascio
Riassunto analitico
Oligosaccharides, which are fully oxygenated structural entities that are present in many natural and unnatural compounds, have been used as antibacterial, antifungal, antiviral, and antitumor agents. Furthermore, oligosaccharides are structural components of several glycoproteins and glycolipids and they are involved in a wide range of biological processes. The interest around these class of compounds has stimulated the development of several solution and solid-phase protocols for the synthesis of fully oxygenated natural oligosaccharides. In particular, the power of the reiterative strategy for oligosaccharide construction based on glycal acceptors and glycal-derived donors via epoxidation has found an important application in the synthesis of tumor antigens and the carbohydrate domains of the enediyne antibiotic calicheamicin.
In our laboratory, in the recent years, it has been established novel stereoselective method to synthesize 2,3-unsaturated glycosides using the glycal derived vinyl epoxide 1β as powerful glycosyl donor. 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 Pd0 catalyzed. The methyl glycoside 2 was selected as first glycosil acceptor: the process consisted in a stepwise addition of the in situ prepared vinyl epoxide donor to the relative acceptor without any isolation or purification.
The other main topic of my thesis concerned the synthesis of new chiral luminescent Ln(III) complexes. Lanthanide chelates are useful probes in analytical chemistry and imaging in biomedicine both as fluorescence and/or, for chiral complexes, as circularly polarized luminescence (CPL) emitters. The latter phenomenon has been recently used for metabolite anion binding studies in aqueous media, as test for the existence of chiral Ln(III) structures and as indicators of changes in chiral structure especially associated to chiral structures of metal-containing biological systems.
In this context, luminescent carbohydrate-based lanthanide probes have been much less explored and our main aim was to synthesize a new functionalized chiral DPA-based ligand: dipicolinic lanthanide complexes are widely known in literature as robust and performant lanthanide ligand/sensitizer. The idea was to bind a glucose unit on one carboxyl moiety via glycosidation reaction with a known glycosil donor as the trichloroacetimidate (TCA). We wanted to assess if the complexation capabilities and the photophysical properties of such chelates were retained after their tethering to the sugar moieties, and most importantly if the chiral complexes were able to produce CPL. The chiral ligands were obtained from the dipicolinic acid (DPA) and the glycosilated products complexed with Europium salts.