Solid-Phase Supported Synthesis of the Branched Pentasaccharide Moiety That Occurs in Most Complex Type N-Glycan Chains.

Repetitive glycosylation on a sulfanylalkyl-functionalized Merrifield resin leads to the branched, complex pentasaccharide 1 in 20% overall yield in ten steps when appropriately protected O-glycosyl trichloroacetimidates are used as glycosyl donors. A decisive factor here was the tuning of the reaction conditions for the solid-phase glycosylation and the conditions for selective removal of the protecting groups and for cleavage of the samples from the resin for characterization. The subsequent cleavage of the product was achieved with a thiophilic reagent that does not attack the O-glycosidic linkages.