Synthesis of a novel asparagine-linked heptasaccharide structure via p-methoxybenxyl-assisted #beta-mannosylation

摘要

Stbtgesus if a cire geotasaccgarude asoaragube B~4-{#alpha#-D-mannopyranosyl-(1->2)]-(#beta#-D-mannopyranosyl)-(1->4)-(2-acetamido-2-deoxy-#beta#-D-gluco-pyranosyl)-(1->4)-[(#alpha#-L-fucopyranosyl)-(1->6)]-2-acetamido-2-deoxy-#beta#-D-glucopyranosyl}-L-asparagine (1a)found from CHO glycosylation mutant cell LEC 14 is described.The structure of 1a is highly novel in terms of the presence of an extra GlcNAc residue linked to the 2-position of #beta#-linked mannose. The synthesis was performed using p-methoxybenzyl-assisted intramolecular aglycon delivery as the key transformation. 4,6-O-TIDPS-protected thiomannoside methyl 2-O-p-methoxybenzyl-4,6-O-(1,1,3,3-tetraisopropyl)disiloxanylidene-3-O-trimethylsilyl-1-thio-#alpha#-D-mannopyranoside was adopted for this particular purpose,which afforded #beta#-mannoside p-methoxyphenyl 2,3-O-(p-methoxybenzylidene)-4,6-O(1,1,3,3,-tetraisopropyl)disiloxanylidene-#beta#-D-mannopyranosyl-(1->4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-#beta#-D-glucopyranoside stereoselectively in 75% yield.