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 β-d-glycero-d-mannoheptopyranoside unit, and of a 2,3-O-diphenylmethylene acetal to install the α-l-rhamnopyranosidic linkages. Comparison of the spectral data for the hexasaccharide with that of the natural confirms the structure of this very unusual and structurally challenging glycan.