Syntheses of arabinogalactans consisting of β-(1 → 6)-linked d-galactopyranosyl backbone and α-(1 → 3)-linked l-arabinofuranosyl side chains Original Research Article

Two arabinogalactosyl nonasaccharides, β-d-Galp-(1 → 6)-[α-l-Araf-(1 → 3)]-β-d-Galp-(1 → 6)-β-d-Galp-(1 → 6)-β-d-Galp-(1 → 6)-[α-l-Araf-(1 → 5)-α-l-Araf-(1 → 3)]-β-d-Galp-(1 → 6)-β-d-Galp and β-d-Galp-(1 → 6)-[α-l-Araf-(1 → 5)-α-l-Araf-(1 → 3)]-β-d-Galp-(1 → 6)-β-d-Galp-(1 → 6)-β-d-Galp-(1 → 6)-[α-l-Araf-(1 → 3)]-β-d-Galp-(1 → 6)-β-d-Galp, were synthesized as their 4-methoxyphenyl glycosides with 2,3,4,6-tetra-O-benzoyl-α-d-galactopyranosyl trichloroacetimidate (1), 6-O-acetyl-2,3,4-tri-O-benzoyl-α-d-galactopyranosyl trichloroacetimidate (14), 4-methoxyphenyl 3-O-allyl-2,4-di-O-benzoyl-β-d-galactopyranoside (2), 4-methoxyphenyl 2,3,4-tri-O-benzoyl-β-d-galactopyranoside (5), 2,3,5-tri-O-benzoyl-α-l-arabinofuranosyl trichloroacetimidate (8), and 2,3,5-tri-O-benzoyl-α-l-arabinofuranosyl-(1 → 5)-2,3-di-O-benzoyl-α-l-arabinofuranosyl trichloroacetimidate (11), as the key synthons. The tetra- (10) and pentasaccharide donor (13), and the tetra- (20) and pentasaccharide acceptor (22) were synthesized based on these synthons through simple transformations. Coupling of 22 with 10, and coupling of 20 with 13 and subsequent deacylation gave nonasaccharides 24 and 26, respectively, consisting of β-(1 → 6)-linked glactopyranosyl backbone and α-(1 → 3)-linked arabinofuranosyl side chains of different size.