Intrinsic Issues in the Assembly of 1,2-Linked Oligosaccharides

This review aims to highlight common issues involved in the assembly of 1,2-linked oligosaccharides. There is extensive literature on the subject, but most of the publications only address general oligosaccharides. Construction of 1,2-glycosidic linkage has an additional and intrinsic complexity due to its glycosylated O-2 position. Elongation of the fragment from reducing end curtails the possibility of using O-2 participating groups in the donor. The 2-O-glycosylated donors used in this context or in a convergent approach lead to the principal stereocontrol loss when 1,2-trans gluco type or manno type linkage are targets. Only non-reducing end elongation strategy can ensure 1,2-trans linkage, but following a more expensive and cumbersome route. Archetypical cases where the convergent approach drove to a stereocontrol loss are presented. The perspective of this analysis attempts to complement Paulsen, Boons and Demchenko's masterworks about strategies in oligosaccharides synthesis.