An efficient and concise synthesis of a β-(1→6)-linked d-galactofuranosyl hexasaccharide

A β-(1→6)-linked d-galactofuranosyl hexasaccharide was synthesized efficiently in a block construction manner by the well-known Schmidt glycosylation method using 6-O-acetyl-2,3,5-tri-O-benzoyl-β-d-galactofuranosyl trichloroacetimidate (1) and allyl 2,3,5-tri-O-benzoyl-β-d-galactofuranoside (3) as the key synthons. Coupling of 3 with 1 gave β-(1→6)-linked disaccharide 4. Subsequent selective deacetylation of 4 afforded the disaccharide acceptor 5, while deallylation of 4 followed by trichloroacetimidate formation produced the disaccharide donor 6. Condensation of 5 with 6 gave the tetrasaccharide 7, and subsequent deacetylation afforded the tetrasaccharide acceptor 8. Finally, coupling of 8 with 6 followed by deacylation yielded the target β-(1→6)-linked galactofuranose hexasaccharide 10. All of the reactions in the synthesis were carried out smoothly and in high yield.