Block Synthesis of Tetra- and Hexasaccharides (β-d-Glycero-d-manno-Hepp-(1→4)-[α-l-Rhap-(1→3)-β-d-glycero-d-manno-Hepp-(1→4)]n-α-l-Rhap-OMe (n = 1 and 2)) Corresponding to Multiple Repeat Units of the Glycan from the Surface-Layer Glycoprotein from Bacillus thermoaerophilus
摘要:
A fully stereocontrolled block synthesis of the title tetra- and hexasaccharides has been achieved taking advantage of the ability of the 4,6-O-benzylidene acetal to control the stereochemistry of the beta-D-glycero-D-mannoheptopyranoside unit and of a 2,3-O-diphenylmethylene acetal to install the alpha-L-rhamnopyranosidic linkages. Comparison of the spectral data for the hexasaccharide with that of the natural isolate confirms the structure of this very unusual and structurally challenging glycan.