Synthesis of allyl 2-O-(α-l-arabinofuranosyl)-6-O-(α-d-mannopyranosyl)-β-d-mannopyranoside, a unique plant N-glycan motif containing arabinose

The synthesis of the trisaccharide allyl 2-O-(α-l-arabinofuranosyl)-6-O-(α-d-mannopyranosyl)-β-d-mannopyranoside is reported. Stereoselective glycosylation at C-6 of a non-protected allyl β-mannoside with the acetylated α-d-mannosyl bromide gave the α-(1→6)-disaccharide as the main product and the crystalline 3,6-branched trisaccharide as minor compound. Further glycosylation of the 2,3 diol (1→6) disaccharide with l-arabinofuranosyl bromide furnished a mixture of 3-O- and 2-O-α-l-Ara-trisaccharides from which the title compound was isolated.