Agarans and carrageenans are abundant natural polysaccharides which are obtained in large scale by water extraction from a variety of red seaweeds. These galactans in addition of being valuable products for pharmaceutical and food industries are low cost starting material for the preparation of useful and rare carbohydrate-based building blocks whose access by total synthesis is difficult and expensive. The semisynthesis of two sets of C-glycosyl aldehydes with L- and D-configuration from agarose and kappa-carrageenan respectively is described. Succinctly, the partial acid-catalyzed mercaptolysis of the two galactans under mild conditions afforded agarobiose and carrabiose (β-D-Galp-(1-4)-3,6-anhydro-aldehydo-L- and D-galactose, respectively) derivatives. Complete depolymerization of agarose and kappa-carrageenan under harsher conditions produced 3,6-anhydro L- and D-galactose aldehyde derivatives. Chain shortening of these products via alditol formation and oxidative carbon-carbon bond cleavage furnished C-formyl alpha-L- and alpha-D-threofuranosides. The above C-glycosyl aldehydes were all prepared in meaningfully preparative scale starting from gram quantities of galactans. Finally, a new procedure for the preparation of the 2,3-O-benzyl L-threofuranose was established by Baeyer-Villiger oxidation of the benzylated C-formyl alpha-L-threofuranoside here prepared from agarose.

Production of Carbohydrate Building Blocks from Red Seaweed Polysaccharides. Efficient Conversion of Galactans into C-Glycosyl Aldehydes

MASSI, Alessandro;DONDONI, Alessandro;
2009

Abstract

Agarans and carrageenans are abundant natural polysaccharides which are obtained in large scale by water extraction from a variety of red seaweeds. These galactans in addition of being valuable products for pharmaceutical and food industries are low cost starting material for the preparation of useful and rare carbohydrate-based building blocks whose access by total synthesis is difficult and expensive. The semisynthesis of two sets of C-glycosyl aldehydes with L- and D-configuration from agarose and kappa-carrageenan respectively is described. Succinctly, the partial acid-catalyzed mercaptolysis of the two galactans under mild conditions afforded agarobiose and carrabiose (β-D-Galp-(1-4)-3,6-anhydro-aldehydo-L- and D-galactose, respectively) derivatives. Complete depolymerization of agarose and kappa-carrageenan under harsher conditions produced 3,6-anhydro L- and D-galactose aldehyde derivatives. Chain shortening of these products via alditol formation and oxidative carbon-carbon bond cleavage furnished C-formyl alpha-L- and alpha-D-threofuranosides. The above C-glycosyl aldehydes were all prepared in meaningfully preparative scale starting from gram quantities of galactans. Finally, a new procedure for the preparation of the 2,3-O-benzyl L-threofuranose was established by Baeyer-Villiger oxidation of the benzylated C-formyl alpha-L-threofuranoside here prepared from agarose.
2009
Massi, Alessandro; Dondoni, Alessandro; Ducatti, D.; Noseda, M.; Duarte, M.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/529934
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