Experimental observations on the regioselectivity of glycosylation of a 4,6-diol system in the β-D-mannopyranosyl unit of a N-glycan pentasaccharide core structure.

The regioselectivity of glycosylation of a 4,6-diol system in the β-mannopyranosyl unit of a N-glycan pentasaccharide core structure is found to be strongly dependent on the structure of the glycosyl donor. While glycosylation with a 2-O-acetyl-D-mannopyranosyl trichloroacetimidate and with a d-mannopyranosyl (α1→3) 2-O-acetyl mannopyranosyl trichoroacetimidate regioselectively occurs at the primary OH-6 position, reaction with d-mannopyranosyl (α1→6) mannopyranosyl 2-O-benzoyl, 2-O-acetyl and 2-O-pivaloyl trichloroacetimidate results in approximately 1:1 mixture of regioisomers at primary OH-6 and secondary OH-4 positions.