Syntheses of Acetylated Tetrasaccharides, Manα1→2Manα1→3Manβ1→4GlcNAc and Manα1→3Manα1→6Manβ1→4GlcNAc

As a preliminary experiment aimed ultimately at the total syntheses of high mannose-type oligosaccharides in glycoproteins, two fully acetylated tetrasaccharides, Manα1→2Manα1→3Manβ1→4GlcNAc (32) and Manα1→3Manα1→6Manβ1→4GlcNAc (35), were synthesized by block condensation of acetylated dimannopyranosyl bromides with suitably protected Manβ1→4GlcNAc derivatives by modified Koenigs-Knorr reactions, followed by acetylation of the deprotected tetrasaccharides. Proton and carbon-13 nuclear magnetic resonance spectral data for 32, 35, and synthetic intermediates are also presented. The present work confirms that 1, 6-anhydro-β-derivatives of GlcNAc and oligosaccharides are versatile starting materials or key intermediates for syntheses of complex oligosaccharides.