AUFBAU VON OLIGOSACCHARIDEN MIT GLYCOSYLFLUORIDEN UNTER LEWISSAEURE-KATALYSE

Article abstract of DOI:10.1016/S0008-6215(00)90057-0

Glycosylation of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (6), as well as its 6-trimethylsilyl ether 7 with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl fluoride (5) was achieved stereospecifically in a mild and fast manner in the presence of Lewis acids like, e.g., titanium tetrafluoride, to give the β-(1<*>6)-linked disaccharide derivative 1.By use of 2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl fluoride (8) or its α anomer 10 and titanium tetrafluoride in acetonitrile with 6 or 7, a fast reaction proceeds preponderantly to yield 1,2:3,4-di-O-isopropylidene 6-O-(2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl)-α-D-galactopyranose (2).In ether, however, mainly the α-(1<*>6) anomer was formed.These model systems were used to elucidate the limiting conditions for this procedure, and mechanistic conceptions are discussed.By glycosylation at O-4 of 1,6:2,3-dianhydro-β-D-mannopyranose (11) with the perbenzylated α-fluoride 10 both the α- and the β-D-(1<*>4) disaccharide derivatives 12 and 14 were obtained, but 5 gave exclusively the β-D-(1<*>4) compound 16.Opening of the anhydro rings of 12 led to the synthesis of N-acetyl-maltosamine (22). 1,6-anhydro-2-azido-4-O-benzyl-2-deoxy-β-D-glucopyranose was glycosylated with methyl (2,3,4-tri-O-acetyl-β-D-galactopyranosyl fluoride)uronate under titanium tetrafluoride catalysis to give the β-D-(1<*>3)-linked disaccharide 26, subsequently transformed into 29.