THE SYNTHESIS OF BETA-MANNOPYRANOSIDES BY INTRAMOLECULAR AGLYCON DELIVERY - SCOPE AND LIMITATIONS OF THE EXISTING METHODOLOGY

The synthesis of beta-mannopyranosides by intramolecular aglycon deliv ery is shown to proceed with complete stereoselectivity in six separat e cases. This strategy has been successfully applied to the synthesis of several disaccharides, including octyl syl)-2-deoxy-2-phthalimido-b eta-D-glucopyranoside, a precursor of the naturally occurring beta-D-M an-(1-->4)-beta-D-GlcNAc linkage, present in all N-linked glycoprotein s. Exclusive formation of the beta-mannosidic linkage has been confirm ed in all six cases, since independently synthesized alpha-linked mann opyranoside standards were shown to be absent from the reaction produc ts. The intramolecular stereocontrolled reaction proceeds even in the presence of competing methanol. The extension of this strategy to the synthesis of the core pentasaccharide of N-linked glycoproteins has re vealed limitations to the methodology, especially when a block synthes is approach is investigated.