Syntheses of α(2,8) Sialosides Containing NeuAc and NeuGc by Using Double Carbonyl-Protected N-Acyl Sialyl Donors.

We report on the syntheses of NeuAc and NeuGc-containing glycosides via the use of double carbonyl-protected N-acetyl sialyl donors. The 7-O,9-O-carbonyl protection of an N-acyl-5-N,4-O-carbonyl-protected sialyl donor markedly increased the α-selectivity during glycosylation, particularly when glycosylating the C-8 hydroxyl group of sialic acids. The N-acyl carbamates were selectively opened with ethanethiol under basic conditions to provide N-acyl amines.

Chemical synthesis of α(2,8) octasialosides, the minimum structure of polysialic acids.

Chemical synthesis of an α(2,8) octasialic acid by using an N-acetyl-5-N,4-O:7-O,9-O-dicarbonyl protected sialyl donor is reported. The glycosyl donor underwent α-selective sialylation at the C8 hydroxyl group to give α(2,8) sialyl oligomers. The resulting oligosaccharides were then deprotected to give the fully deprotected α(2,8) octasialic acid without lacking the N-acetyl groups.