title: Sialylation reactions with 5-N,7-O-carbonyl-protected sialyl donors: unusual stereoselectivity with nitrile solvent assistance.
abstract: A 5-N,7-O-carbonyl-protected sialyl donor was synthesized, and, unexpectedly, this donor showed beta-selectivity (alpha/beta = 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 AgClO(4).H(2)O) was highly effective in activating the 5-N,7-O-carbonyl donor, providing moderate alpha-selectivity (alpha/beta = ~1.8/1).
authors.affiliation: Department of Chemistry, Faculty of Engineering, Gifu University, Gifu, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Tanaka
authors.forename: Hiromune
authors.initials: H
authors.lastname: Ando
authors.forename: Hideharu
authors.initials: H
authors.lastname: Ishihara
authors.forename: Mamoru
authors.initials: M
authors.lastname: Koketsu
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D006031:Glycosylation; D012794:Sialic Acids / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000097:Acetonitriles; D012794:Sialic Acids; C032159:acetonitrile