Prearranged glycosides. Part 14: Intramolecular glycosylation of non-symmetrically tethered glycosides

Partially benzylated 1-thio-beta -D-glucopyranosides were tethered via posi tion 2 to position 3 of methyl alpha -D-glucopyranosyl and benzyl 2-phthali mido-2-deoxy-beta -D-glucopyranosyl derivatives, respectively, by non-symme trical o-, m-, and p-methylbenzoate linkers. Intramolecular glycosylation o f these prearranged glycosides lead to the corresponding non-symmetrically tethered alpha-(1-->4)-linked disaccharides as the exclusive or main produc ts. The tethers were regioselectively opened by transesterification affordi ng isomeric disaccharide accepters which are susceptible for further elonga tion of the sugar chain at positions 3 and 2', respectively. (C) 2001 Elsev ier Science Ltd. All rights reserved.