Synthesis of three tetrasaccharides containing 3-O-methyl-D-mannose, as model compounds for xylose-containing carbohydrate chains from N-glycoproteins

Article abstract of DOI:10.1016/0008-6215(94)80060-X

The synthesis is reported of methyl 3,6-di-O-(3-O-methyl-α-D-mannopyranosyl)-2-O-β-D-xylopyranosyl-β-D-mannopyranoside (2), methyl 6-O-α-D-mannopyranosyl-3-O-(3-O-methyl-α-D-mannopyranosyl)-2-O-β-D-xylopyranosyl-β-D-mannopyranoside (3), and methyl 3-O-α-D-mannopyranosyl-6-O-(3-O-methyl-α-D-mannopyranosyl)-2-O-β-D-xylopyranosyl-β-D-mannopyranoside (4).The various methyl β-D-Man p acceptor derivatives were prepared from the corresponding methyl β-D-Glc p derivatives via oxidation-reduction.All glycosyl donors were coupled using the trichloroacetimidate method at -40 degC in dichloromethane with trimethylsilyl triflate as a catalyst.Methyl-3-O-benzyl-4,6-O-benzylidene-β-D-mannopyranoside (7) was condensed with 2,3,4-tri-O-acetyl-α-D-xylopyranosyl trichloroacetimidate (8).Regioselective reductive 4,6-O-benzylidene ring-opening on the resulting disaccharide derivative, followed by acetylation, and hydrogenation gave methyl 4-O-acetyl-2-O-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)-β-D-mannopyranoside (12).Coupling of 12 with 2,4,6-tri-O-acetyl-3-O-methyl-α-D-mannopyranosyl trichloroacetimidate (18) afforded tetrasaccharide derivative 19, and subsequent O-deacetylation gave 2.Methyl 3-O-benzyl-4,6-O-prop-2-enylidene-β-D-mannopyranoside (22) was condensed with 2,3,4-tri-O-acetyl-α-D-xylopyranosyl trichloroacetimidate (8).Regioselective reductive 4,6-O-prop-2-enylidene ring-opening on the resulting disaccharide derivative, followed by acetylation, and deallylation at O-6 gave methyl 4-O-acetyl-3-O-benzyl-2-O-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)-β-D-mannopyranoside (26-a), which was either condensed with 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl trichloroacetimidate (27) or 18, to give trisaccharide derivatives 28 or 31, respectively.Debenzylation of 28 followed by condensation with 18 gave, after O-deacetylation, 3, whereas debenzylation of 31 followed by condensation with 27 gave, after O-deacetylation, 4.