A facile and effective synthesis of α-(1→6)-linked mannose di-, tri-, tetra-, hexa-, octa-, and dodecasaccharides, and β-(1→6)-linked glucose di-, tri-, tetra-, hexa-, and octasaccharides using sugar trichloroacetimidates as the donors and unprotected or

Reaction of 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl trichloroimidate with allyl α-d-mannopyranoside in the presence of TMSOTf selectively gave allyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl-(1→6)-α-d-mannopyranoside through an orthoester intermediate. Benzoylation of 3, followed by deallylation, and then trichloroimidation afforded the disaccharide donor 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl trichloroimidate, while benzoylation of 3 followed by selective removal of acetyl groups yielded the disaccharide acceptor allyl α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranoside. Coupling of 5 with 6 gave the tetrasaccharide allyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranoside, which were converted into the tetrasaccharide donor 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl trichloroimdate and the tetrasaccharide acceptor allyl α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranoside, respectively, by the same strategies as used for conversion of 3 into 5 and 6. Condensation of 5 with 13 gave the hexasaccharide 14, while condensation of 12 with 13 gave the octasaccharide 17. Dodecasaccharide 21 was obtained by the coupling of 12 with the octasaccharide acceptor 20. Similar strategies were used for the syntheses of β-(1→6)-linked glucose di-, tri-, tetra-, hexa-, and octamers. Deprotection of the oligosaccharides in ammonia-saturated methanol yielded the free α-(1→6)-linked mannosyl and β-(1→6)-linked glucosyl oligomers.