•The first synthesis of β-D-fructopyranosyl hexamer.•N-phenyltrifluoroacetimidate glycosylation was vital for oligomer synthesis.•Provided an interesting method for selective glycosylation of ketose.•Fructopyranosyl oligomer provide new backbone, with promising applications.The hexa-fructopyranoside was synthesized with N-phenyltrifluoroacetimidate glycosylation. The synthesis was achieved by regioselective glycosylation on the 1-OH of fructopyranosyl acceptor. Fructosyl oligosaccharides were elongated with β-(2 → 1)-difructopyranosyl unit in every two steps, without any further protection/deprotection step. This work proved N-phenyltrifluoroacetimidate glycosylation a practical method for oligo-fructopyranoside synthesis.Download high-res image (132KB)Download full-size image

Glycosylation of 2-O-acyl fructopyranosides was investigated, which were shown to be effective glycosyl donors for d-fructopyranoside synthesis with good β-selectivity and yields. For bulky acceptor 4e, α-anomer 5e was obtained with α/β = 65:23. Unexpected ring-opening was observed during acetylation of 9, indicating the sensitivity of the fructopyranosyl ring.

The anti-thromboembolic pentasaccharide Fondaparinux was synthesized in 36 steps for the longest linear route, with 0.017% overall yield from d-glucose. Only three kinds of protecting groups were used for hydroxyl protection, Bn, Ac, and Bz, to accomplish this complex synthesis without decreasing the synthetic efficiency. Three l-idopyranosyl donors were investigated. Thioethyl glycoside is an efficient donor for l-idopyranosyl glycosylation with full α-selectivity, while l-idopyranosyl trichloroacetimidate resulted in poor α/β selectivity. A practical synthesis of key intermediate 1,6-anhydro-l-idopyranose 17 by H+/β-CD catalyst was developed.