Sialylation reactions with 5-N,7-O-carbonyl-protected sialyl donors: unusual stereoselectivity with nitrile solvent assistance

Article abstract of DOI:10.1016/j.carres.2008.05.005

A 5-N,7-O-carbonyl-protected sialyl donor was synthesized, and, unexpectedly, this donor showed β-selectivity (α/β = 1/2.4-1/20) on coupling with sugar acceptors in acetonitrile upon treatment with various promoter systems. For the coupling reaction in dichloromethane, a modified Ellervik's method (IBr and AgClO₄·H₂O) was highly effective in activating the 5-N,7-O-carbonyl donor, providing moderate α-selectivity (α/β = ～1.8/1).