Syntheses of β-d-Galf-(1→6)-β-d-Galf-(1→5)-d-Galf and β-d-Galf-(1→5)-β-d-Galf-(1→6)-d-Galf, Trisaccharide Units in the Galactan of Mycobacterium tuberculosis

The galactofuran is a crucial constituent of the cell wall of mycobacteria. An efficient synthesis of the two trisaccharide units of the galactan is described. The strategy relies on the use of substituted d-galactono-1,4-lactones as precursors for the internal and the reducing galactofuranoses. Dec-9-enyl beta-d-Galf-(1-->6)-beta-d-Galf-(1-->5)-beta-d-Galf (2) and dec-9-enyl beta-d-Galf-(1-->5)-beta-d-Galf-(1-->6)-beta-d-Galf (9) so far reported as convenient substrates for the galactofuranosyl transferase, and possibly useful for immunological studies, were obtained by the trichloroacetimidate method of glycosylation.