1H- and 13C-N.M.R. assignments for structural elements of xylose-containing N-linked oligosaccharides, using 1D- and 2D-N.M.R. experiments

1H-N.m.r. and 13C-n.m.r. spectral assignments for synthetic β-D-Xyl-(1→2)-β-D-Man-OMe, β-D-Xyl-(1→2)-[α-D-Man-(1→3)]-β-D-Man-OMe, β-D-Xyl-(1→2)-[α-D-Man-(1→6)]-β-D-Man-OMe, and β-D-Xyl-(1→2)-[α-D-Man-(1→3)]-[α-D-Man-(1→6)]-β-D-Man-OMe, which are structural elements of xylose-containing carbohydrate chains from N-glycoproteins, have been made on the basis of 1D and 2D (DQF 1H-1H COSY, HOHAHA) 500-MHz 1H-n.m.r. spectroscopy and 1D 50-MHz 13C-n.m.r. spectroscopy, respectively

Synthesis of four structural elements of xylose-containing carbohydrate chains from N-glycoproteins

The synthesis of the oligosaccharides β-D-Xylp-(1->2)-β-D-Manp-OMe (12), β-D-Xylp-(1->2)-[α-D-Manp-(1->6)]-β-D-Manp-OMe (17), β-D-Xylp-(1->2)-[α-D-Manp-(1->3)]- β-D-Manp-OMe (21), and β-D-Xylp-(1->2)-[α-D-Manp-(1->3)][α-D-Manp-(1->6)]-β-D-Manp-OMe (25) is described. Methyl 3-O-benzyl-4,6-O-isopropylidene-β-D-mannopyranoside (6) was prepared from the corresponding gluco-epimer (4) by oxidation, followed by stereoselective reduction. Condensation of 6 with 2,3,4-tri-O-acetyl-α-D-xylopyranosyl bromide in the presence of mercuric cyanide gave a 1:9 mixture of methyl 3-O-benzyl-4,6-O-isopropylidene-2-O-(2,3,4-tri-O-acetyl-α- (7a) and -β-D-xylopyranosyl)-β-D-mannopyranoside (7), and then 7 was converted into the acetylated disaccharide-glycoside 11. Regioselective mannosylation, with 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide, at position 6 of deisopropylidenated 7 (8), using mercuric bromide as a promoter, afforded the trisaccharide-glycoside derivative 13, which was transformed into the acetylated trisaccharide-glycoside 16. The disaccharide derivative 10, obtained from 8, and the trisaccharide derivative 15, obtained from 13, were glycosylated at position 3 with O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)trichloroacetimidate (19), using trimethylsilyl triflate as a promoter, giving rise to acetylated tri- (20) and tetra-saccharide (24) derivatives, respectively. O-Deacetylation of 11, 16, 20, and 24 gave 12, 17, 21, and 25, respectively

Synthesis of fully and partially benzylated glycosyl azides via thioalkyl glycosides as precursors for the preparation of N-glycopeptides

Fully O-benzylated mono-, di- and trisaccharide glycosyl azides representing the reducing terminal of the core structure of N-glycans were synthesized. Totally and partially benzylated thioalkyl glucosamine glycosides were converted into the corresponding glycosyl azides with trimethylsilyl azide in the presence of methyl triflate. The beta-mannosidic linkage was created by C-2 epimerization of the initially introduced beta-D-gluco-unit via oxidation followed by stereoselective reduction with tetrabutylammonium borohydride

Synthesis of a selectively protected trisaccharide building block that is part of xylose-containing carbohydrate chains from N-glycoproteins

The synthesis is reported of ethyl 4-O-[3-O-allyl-4,6-O-isopropylidene-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 (16), a key intermediate in the synthesis of xylose-containing carbohydrate chains from N-glycoproteins. Condensation of ethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (5) with 2,4,6-tri-O-acetyl-3-O-allyl-alpha-D-glucopyranosyl bromide, using silver triflate as a promoter, gave the beta-linked disaccharide derivative 8 (84%). O-Deacetylation of 8 and then isopropylidenation afforded 10, which was converted via oxidation-reduction into ethyl 4-O-allyl-4,6-O-isopropylidene-beta-D-mannopyranosyl)-3, 6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (12). Silver triflate-promoted condensation of 12 with 2,3,4-tri-O-acetyl-alpha-D-xylopyranosyl bromide gave 16 (71%). The Xylp unit in 16 and in de-isopropylidenated 16 (17) existed in the 1C4(D) conformation, but that in O-deacetylated 17 (18) existed in the 4C1(D) conformatio