Glycosidation of 2,5-anhydro-3,4-di-O-benzyl-d-mannitol with different glucopyranosyl donors. A comparative study

2,5-Anhydro-3,4-di-O-benzyl-d-mannitol was glycosylated using different donors such as tetra-O-acetyl-α-d-glucopyranosyl bromide in the presence of Hg(CN)2, the corresponding β-thiophenylglycoside in the presence of NIS and TfOH as well as the α- and β-trichloroimidate with TMSOTf as promoter. The resulting mixtures were analyzed by HPLC and the following main components were isolated and characterized: 2,5-anhydro-3,4-di-O-benzyl-1-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-d-mannitol; 6-O-acetyl-2,5-anhydro-3,4-di-O-benzyl-1-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-d-mannitol; 2,5-anhydro-3,4-di-O-benzyl-1,6-bis-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-d-mannitol; 2,5-anhydro-3,4-di-O-benzyl-1-O-[-2-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-3,4,6-tri-O-acetyl-β-d-glucopyranosyl]-6-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-d-mannitol and 2,5-anhydro-3,4-di-O-benzyl-1,6-bis-O-(3,4,6-tri-O-acetyl-1,2-O-ethylidene-2′-yl-α-d-glucopyranosyl)-d-mannitol. The latter compound representing a bis-orthoester might be a common intermediate in all the investigated reactions, as its rearrangement and/or decomposition can yield all of the isolated compounds.