Improved synthesis of an aldobiouronic acid related to hardwood xylans, and preparation of a derivative thereof suitable for linking to proteins

Treatment of 1,3,4-tri-O-acetyl-α-d-xylopyranose with methyl 2,3-di-O-benzyl-1-chloro-1-deoxy-4-O-methyl-α,β-d-glucopyranuronate in the presence of silver trifluoromethanesulfonate was highly stereoselective to give the α-linked aldobiouronic acid derivative (4) in 86% yield, after hydrogenolysis of the crude product of the coupling and chromatography. Compound 4 was acetylated and the fully protected substance was converted to the corresponding glycosyl chloride. Reaction of the latter with p-nitrophenol under phase-transfer catalysis afforded, after deacetylation, p-nitrophenyl 2-O-(methyl 4-O-methyl-α-d-glucopyranosyluronate)-β-d-xylopyranoside.