Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
N-Iodosuccinimide activation of prearranged glycosides constructed out of phenyl 2,3,4-tri-O-benzyl-1-thio-α-L- and -D-mannopyranosides which are linked by a succinyl spacer via position 6 to position 3 of the benzyl 2-O-benzoyl-6-O-benzyl-α-L- and -D-glucopyranosides (6,3-prearranged L-Man/L-Glc, D-Man/D-Glc, L-Man/D-Glc, and D-Man/L-Glc) affords α/β-mixtures of the corresponding 3,6′-succinyl bridged disaccharides Man-(1→4)-Glc in 70-78% yield. The diastereoselectivity of the intramolecular glycosylation is independent of the topographic properties of the prearranged glycosides (the α-anomers predominate for L-Man/L-Glc and D-Man/D-Glc) but depends on the geometric properties (the β-anomers predominate for L-Man/D-Glc and D-Man/L-Glc). Thus, a double asymmetric induction is operative during intramolecular glycosylation of prearranged glycosides. Furthermore, the diastereoselectivity strongly depends on the topological properties and on the donor moiety of the prearranged glycosides, since 2,3-prearranged L-Man/D-Glc affords solely the disaccharide α-L-Man-(1→4)-D-Glc whereas the corresponding L-Rha/D-Glc was previously shown to give predominantly the disaccharide β-L-Rha-(1→4)-D-Glc.
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