Propargyl mediated intramolecular aglycon delivery (IAD):: applications to the synthesis of core N-glycan oligosaccharides

The use of propargyl mediated intramolecular aglycon delivery (IAD) for the synthesis of the key Man beta(1 -> 4)GlcNAc linkage of N-glycan oligosaccharides, including the core N-glycan pentasaccharide, is investigated. Isomerisation of a 2-O-progargyl group of manno thioglycoside donors to an allene is followed by iodonium ion mediated mixed acetal formation with the 4-OH of protected GlcNAc acceptors, and subsequent intramolecular glycosylation occurs with complete control of anomeric stereochemistry to form the Man beta(1 -> 4)GlcNAc linkage. A variety of linear and convergent approaches (1+2, 3+1, 3+2) to the core pentasacch and e are investigated as means of probing the generality and limitations of this type of intramolecular aglycon delivery for the formation of beta-mannoside linkages in complex oligosaccharides. (c) 2007 Elsevier Ltd. All rights reserved.