Facile synthesis of alfa-D-Araf-(1-5)-D-Galf, the linker unit of the arabinan to the galactan in Mycobacterium tuberculosis

LUCÍA GANDOLFI DONADÍO; CAROLA GALLO-RODRIGUEZ; ROSA M. DE LEDERKREMER

CANADIAN JOURNAL OF CHEMISTRY

NRC Canada

Año: 2006 vol. 84 p. 486 - 491

0008-4042

Abstract The arabinogalactan is a crucial constituent of the cell wall of mycobacteria. Both monosaccharides, arabinose and galactose, are found in the furanose configuration, absent in mammals. An efficient synthesis of a-D-Araf(1-5)-D-Galf, the linker unit of the arabinan to the galactan is described. The strategy relies on the use of a conveniently substituted D-galactono-1,4-lactone as precursor of the reducing furanose ring. The glycosylation step was performed by the tin (IV) chloride promoted method using 1,2,3,5-tetra-O-benzoyl-a,b-D-arabinofuranose. The arabinose donor was obtained crystalline in one step by benzoylation of arabinose in hot pyridine. Selective glycosylation of the exocyclic OH-5 was obtained in 75 % yield to give 2,3,5-tri-O-benzoyl-a-D-arabinofuranosyl-(1-5)-2,6-di-O-pivaloyl-D-galactono-1,4-lactone. Reduction with disiamylborane gave the disaccharide synthon, useful for further glycosylations. Dec-9-enyl a-D-Araf(1-5)-b-D-Galf, a convenient substrate for arabinofuranosyl transferases studies was obtained by the trichloroacetimidate method of glycosylation.