One-Step Syntheses of 1,2,3,5,6-Penta-O-Benzoyl-a,b-D-Galactofuranose and 1,2,3,5-Tetra-O-Benzoyl-a,b-D-Arabinofuranose

CARLA MARINO; LUCÍA GANDOLFI-DONADIO; CAROLA GALLO -RODRIGUEZ; YU BAI; ROSA M. DE LEDERKREMER

Carbohydrate Chemistry: Proven Methods

CRC Press

Año: 2010;

D-Arabinofuranose (Araf) and D-galactofuranose (Galf) are found in the arabinogalactan of the cell wall of mycobacteria.1,2 D-Galf is also present in glycoconjugates of infectious protozoa like Trypanosoma cruzi and Leishmania,3,4 and of fungi.5,6 The chemistry and biology of arabinofuranosyl and galactofuranosyl containing polysaccharides has been reviewed.7 The furanose form of arabinose and galactose is absent in mammals, hence the interest of several groups in the synthesis of the oligosaccharides containing these sugars for metabolic and immunological studies. Per-O-acylated monosaccharides are important synthons for the synthesis of glycosides, in particular oligosaccharides.8 We have used galactofuranose per-O-benzoate for the first synthesis of a-D-Galf phosphate9 and 1-thio-b-D-galactofuranosides.10 Also, Araf and Galf were introduced as the terminal quasi non-reducing (upstream) unit in oligosaccharides using the tin(IV) chloride promoted condensation.11,12 The perbenzoate 1 was also used as precursor of the trichloroacetimidate derivative employed in oligosaccharide syntheses.13,14 These per-O-benzoates are obtained as a crystalline, anomeric mixture of the a,b-furanoses, and it can be used, without separation, for the glycosylation reactions. The method is based on the tautomerization of the monosaccharide in hot pyridine that yields a considerable proportion of the furanosyl forms, which are then benzoylated. We have optimized the original method for the preparation of 1,2,3,5,6-penta-O-benzoyl-a,b-D-Galf,15 and extended the reaction to D-arabinose.