A Facile Access to Trisaccharides with Central β‐D‐Mannose, α‐D‐Glucosamine, and β‐D‐Mannosamine Units

Abstract

Abstract An expedient synthesis of the trisaccharides β‐D‐Gal p ‐(1→4)‐β‐D‐Man p ‐(1→6)‐D‐Gal ( 8 ), β‐D‐Gal p ‐(1→4)‐β‐D‐Man p NAc‐(1→6)‐D‐Gal ( 11 ), and β‐D‐Gal p ‐(1→4)‐α‐D‐Glc p ‐NAc‐(1→6)‐D‐Gal ( 12 ) is achieved utilizing the readily accessible lactose‐derived building blocks hexa‐ O ‐benzoyl‐α‐D‐lactosulosyl bromide ( 4 ) and its 2‐(benzoyloxy)imino analogue 5 as glycosyl donors and 1,2:3,4‐di‐ O ‐isopropylidene‐D‐galactose ( 6 ) as the acceptor. Stereocontrolled α‐ (silver triflate) and β‐glycosidations (silver carbonate) were as smoothly effected as the subsequent, essentially stereospecific reductions of oxo (NaBH 4 ) and (benzoyloxy)‐imino functions (diborane). The overall yields of 55– 60% attainable for 4 → 8 and 5 → 11/12 render this disaccharide‐derived building block approach highly effective for the construction of oligosaccharides with interior β‐D‐Man, β‐D‐ManNAc, and α‐D‐GlcNAc units.