Convergent Preparation of DimLex Hexasaccharide Analogues

We report the convergent preparation of four hexasaccharides to be used towards the synthesis of a safe anticancer vaccine based on the tumor‐associated carbohydrate antigen dimLe x . A common trisaccharide intermediate was first synthesized as a precursor to the tetrasaccharide backbones. These tetrasaccharides were then converted into diol acceptors and fucosylated at O‐3 of both glucosamine residues. The conditions required to promote fucosylation at O‐3 of the reducing end glucosamine units led to some loss of the fucosyl units already introduced at O‐3 of the nonreducing end glucosamine residues. Despite this hurdle, optimization of the glycosylation conditions provided the desired hexasaccharides in sufficient quantities to prepare the final analogues. Propyl glycosides and cysteamine adducts were prepared easily in two steps from the protected allyl glycoside hexasaccharides, and a one‐step deprotection under metal‐dissolving conditions was key to our deprotection strategy.