Chemical approach for the syntheses of GM4 isomers with sialic acid to non-natural linkage positions on galactose

• GM4 derivatives with unnatural linkages were synthesized.
• Benzyl ether protection of galactose acceptors was preferred in sialylations.
• 2-OH on galactose was sialylated efficiently like 6-OH.
• Sialylation to 4-OH on galactose was afforded only β-form.

Cell-surface glycans containing sialic acid are involved in various biological phenomena. However, the syntheses of GM4 derivatives with (2→2) and (2→4) linkages have not been investigated to date. In this study, sialylation of all of the hydroxyl groups on galactose were investigated for the syntheses of GM4 isomers. Regioselective sialylation was achieved via protection of galactosyl acceptors using electron-rich benzyl groups. These synthetic sialylated glycans will prove to be useful tools for studying unidentified carbohydrate-mediated biological roles.

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