Synthesis of a 3,6-Orthogonally-Protected Mannopyranoside Building Block

Many medically relevant mannoconjugates were isolated as part of N-glycans, ¹ GPI anchors, ² fungal cell wall, ³ and ligands of plant or bacterial lectins. ⁴ Among these, oligomannosides, linear and branched, have been shown to exhibit a wide range of biological functions. Synthesis of such polysaccharides yield valuable tools for studies of biological recognition mechanisms. Polymannosides can be assembled via linking various mannose residues by stereoselective glycosylation. In this context, regioselective masking and unmasking of hydroxy groups is often required. ⁵ Among numerous mannose-containing oligosaccharides, 3,6-branched mannosides (i.e., Hex(1→3)[Hex(1→6)]Man) have been shown to exhibit important biological functions. ^1–4 Thus, preparation of a mannoside building block with orthogonal protecting groups at the O-3 and O-6 positions is of great interest. ⁶