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

The synthesis is reported of methyl 2-acetamido-4-O-[2-acetamido-2-deoxy-4-O-(3,6-di-O-α-d- mannopyranosyl-2-O-β-d-xylopyranosyl-β-d-mannopyranosyl)-β-d-glucopyranosyl]-2-deoxy-β- d-glucopyranoside (4) and methyl 2-acetamido-4-O-[2-acetamido-2-deoxy-4-O-(3,6-di-O-α-d- mannopyranosyl-2-O-β-d-xylopyranosyl-β-d-mannopyranosyl)-β-d-glucopyranosyl]-2-deoxy-6- O-α-l-fucopyranosyl-β-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-β-d-xylo- pyranosyl)-β-d-mannopyranosyl]-3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyra- noside (9) was coupled with methyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside (11). Desilylation of the resulting tetrasaccharide derivative, followed by condensation with 2,3,4,6- tetra-O-acetyl-α-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-α-d-mannopyranosyl)-2-O-(2,3,4-tri-O-acetyl-β-d-xylo- pyranosyl)-β-d-mannopyranosyl]-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl}- 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-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-β-d-xylopyranosyl)-β-d-mannopyranosyl]-2- phthalimido-1-thio-β-d-glucopyranoside (17) was coupled with methyl 3-O-benzyl-2-deoxy-6-O- (4-methoxybenzyl)-2-phthalimido-β-d-glucopyranoside. Demethoxybenzylation of the tetrasac- charide derivative thus obtained, followed by fucosylation using ethyl 2,3,4-tri-O-benzyl-1-thio- evaporated from the residue, which was fractionated on Sephadex LH-20 (1:1 MeOH- CH2Cl2 to yield impure 5. This product was then subjected to purification by rp-HPLC on a Cp tm spher C18 column (250 × 4.6 mm. Chrompack) by elution with 95:5 water- MeOH for 5 min, followed by a linear gradient of 95:5→ 1:1 water-MeOH for 35 min, and detection at 205 nm. The fraction eluting at 14.3 min was collected and concentrated to yield 5, isolated as a white amorphous solid (13 mg, 83%); (α)d - 24° (c 0.1, H2O). For 1H NMR data, see Table 1.