β-selective glycosylations with masked D-mycosamine precursors

[GRAPHICS] Both an intramolecular aglycon delivery (IAD) method and an intermolecular S(N)2 displacement method were examined for beta -selective glycosylations of cholesterol with D-mycosamine. An anomeric sulfoxide, sulfide, selenide, and fluoride were all successfully used as glycosyl donors in IAD reactions. The alpha -bromo ketone 19 was synthesized from protected mycosamine and employed in an intermolecular S(N)2 glycosylation reaction, Both routes were successful for the model alcohol, cholesterol.