Synthesis of a fucosylated and a non-fucosylated core structure of xylose-containing carbohydrate chains from N-glycoproteins

Abstract

The synthesis is reported of methyl 2-acetamido-4-O-[2-acetamido-2-deoxy-O-(3,6-di-O-alpha-D- mannopyranosyl-2-O-beta-D-xylopyranosyl-beta-D-mannopyranosyl)-beta-D- glucopyranosyl]-2-deoxy-beta-D-glucopyranoside (4) and methyl 2-acetamido-4-O-[2-acetamido-2-deoxy-4-O- (3,6-di-O-alpha-D- mannopyranosyl-2-O-beta-D-xylopyranosyl-beta-D-mannopyranosyl)-beta-D- glucopyranosyl]-2-deoxy-6- O-alpha-L-fucopyranosyl-beta-D-glucopyranoside (5), which represent the invariant hexasaccharide core structure of the xylose-containing glycans of N-glycoproteins and its 6-O- fucosylated derivative. Ethyl 4-O-[3-O-allyl-4-O-benzoyl-6-O-tert-butyldimethylsilyl-2-O- (2,3,4-tri-O-acetyl-beta-D-xylopyranosyl)- beta-D-mannopyranosyl]-3,6-di-O-benzyl-2-deoxy-2-phthalimido-1- thio-beta-D-glucopyranoside (9) was coupled with methyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D- glucopyranoside (11). Desilylation of the resulting tetrasaccharide derivative, followed by condensation with 2,3,4,6- tetra-O-acetyl-alpha-D-mannopyranosyl trichloroacetimidate (7), gave methyl 4-O-(4-O-[3-O-allyl-4- O-benzoyl-6-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)-2-O-(2,3,4 -tri-O- acetyl-beta-D-xylopyranosyl)- beta-D-mannopyranosyl]-3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D- glucopyranosyl)- 3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside (14). Deallylation of 14, followed by condensation with 7 and deprotection, gave hexasaccharide 4. Ethyl 3,6-di-O- benzyl-2-deoxy-4-O- [4,6-di-O-acetyl-3-O-allyl-2-O-(2,3,4-tri-O-acetyl-beta-D-xylopyranosyl) - beta-D-mannopyranosyl]-2- phthalimido-1-thio-beta-D-glucopyranoside (17) was coupled with methyl 3-O- benzyl-2-deoxy-6-O- (4-methoxybenzyl)-2-phthalimido-beta-D-glucopyranoside. Demethoxybenzylation of the tetrasaccharide derivative thus obtained, followed by fucosylation using ethyl 2,3,4-tri-O- benzyl-1-thio- beta-L-fucopyranoside, gave methyl 3-O-benzyl-2-deoxy-4-O-[3,6-di-O-benzyl-2- deoxy-4-O-[4,6- di-O-acetyl-3-O-allyl-2-O-(2,3,4-tri-O-acetyl-beta-D-xylopyranosyl)-beta -D- mannopyranosyl]-2-phthalimido- beta-D-glucopyranosyl)-2-phthalimido-6-O-(2,3,4-tri-O-benzyl-alpha-L- fucopyranosyl)-beta-D-glucopyranoside (23). O-Deacetylation followed by tert-butyldimethylsilylation, benzoylation, and desilylation gave methyl 4-O-(4-O-[3-O-allyl-4-O-benzoyl-2-O-(2,3,4-tri-O-benzoyl-beta-D- xylopyranosyl)- beta-D-mannopyranosyl]-3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta- D-glucopyranosyl)-3- O-benzyl-2-deoxy-2-phthalimido-6-O-(2,3,4-tri-O-benzyl-alpha-L-fucopy ran osyl)- beta-D-glucopyranoside (24). Mannosylation of 24 using 7, followed by deallylation, further mannosylation with 7, and deprotection, gave the heptasaccharide 5.