• oligosaccharides
• solid-phase
• stereoselective synthesis
• trityl

Oligosaccharides have important functions in cells; they are often found in glycoconjugates, such as glycoproteins and glycolipids, whose represent mediators of complex cellular events. Moreover, oligosaccharides and glycoconjugates have important role in pathological processes; this is the reason why their synthesis is considered interesting for development of therapeutic agents and studies of recognition process.
The chemical synthesis of, linear or branched, oligosaccharides is fascinating but, even for simple linear chains, is often a discrete stepwise process, which still makes extensive use of orthogonal protection protocols, introduction of leaving groups and activators for a total control of the molecular outcome, in an extremely time-consuming fashion.
More recently, chemists have been concerned with the optimisation of the oligo- and polysaccharides synthesis by resins with appropriate linkers, based on Merrifield solid phase peptide synthesis, aimed at reducing synthesis time by avoiding intermediate purifications.
The project of this thesis is centred on an efficient method, developed in our laboratory, of stereospecific reiterative oligosaccharides assembly in solution, activated by microwave irradiation. In this process vinyl oxirane, derived from D-glucal, represents the efficient glycosyl donor, and allyl alcohol, embedded in a dihydropyran-like structure, represents the glycosyl acceptor. Anyway, this new and versatile procedure shows some limitations: a statistical mixture of oligosaccharides is obtained, and it is only possible to get linear oligosaccharides.
The aim of this work was to transfer the batch solution process applying a polystyrene resin functionalized with a trityl (triphenylmethane) chloride, used to support the first glycosyl acceptor allylic alcohol I that allows to realize the reiterative glycosylation process in the reaction with the classical vinyl epoxide II as glycosyl donor. This procedure aims to be a more discrete version of the batch solution process, allowing a controlled elongation of the oligosaccharide chain in a stepwise fashion, greatly narrowing the distribution of the species. This approach could make also possible the realization of branched oligosaccharides.
The close correspondence between the configuration of the oligosaccharide V and that of the starting epoxide II is rationalizable on the basis of the expected coordination between the O-nucleophile and the epoxide oxygen atom in the form of a hydrogen bond.
Efficiency of the resin functionalization with initiator glycoside I, that presents a chromophore group in anomeric position, was checked by means of a calibration plot established by HPLC/UV.