The synthesis of oligosaccharide-asparagine compounds. V. O- -D-mannopyranosyl-(1 leads to 6)-O-(2-acetamido-2-deoxy- -D-glucopyranosyl)-(1 leads to 4)-2-acetamido-N-(L-aspart-4-oyl)-2-deoxy- -D-glucopyranosylamine

Synthesis of glycopeptides and neoglycoproteins containing the fucosylated linkage region of N-glycoproteins

N-Glycoproteins fucosylated in the core region occur in tumor membranes and virus envelopes. Partial structures of such N-glycoproteins containing fucosylated chitobiosyl asparagine conjugates were synthesized using the allyloxycarbonyl (Aloc) and the tert-butyl ester protecting groups in the peptide portion. As the alpha-fucosidic bond of the conjugates revealed to be very sensitive to acids when carrying ether-type protecting groups, a method for exchanging the protecting groups of the fucose portion of saccharides was developed. Conjugates containing O-acetyl protected fucose proved to be stable against acids used in glycopeptide syntheses. These methods were applied in the synthesis of a fucosyl chitobiose hexapeptide with the partial sequence of a leukemia virus envelope glycoprotein. The glycopeptide was coupled to bovine serum albumin yielding a neoglycoprotein which contains a glycoconjugate of exactly specified structure.

High-pressure glycosylations of unreactive alcohols and the formation of N-glycosyl collidinium salts

The yields of disaccharide glycosylation products in tetramethylammonium bromide or silver triflate-collidine activated reactions between hindered alcohols and glycosyl halides were not greatly ++affected when a pressure of 15 kbar was applied. The formation of orthoester products was greatly increased under pressure. When orthoester formation was not possible both disaccharides and the related N-glycosyl collidinium salts were found.

The synthesis of 2-acetamido-2-deoxy-4-O-beta-D-mannopyranosyl-D-glucose

Condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-alpha-D-mannopyranosyl bromide with 2-amino-2-N,3-O-carbonyl-5.6-O-isopropylidene-D-glucose diethyl acetal gave, unexpectedly, 2-amino-2-N,3-O-carbonyl-2-deoxy-4-O-(4,6-di-O-acetyl-2,3-O-carbonyl-alpha-D-mannopyranosyl)-5,6-O-isopropylidene-D-glucose diethyl acetal, futher transformed, by de-esterification followed by acetylation, into the previously known 2-amino-2-N,3-O-carbonyl-2-deoxy-5,6-O-isopropylidene-4-O-alpha-D-mannopyranosyl-D-glucose diethyl acetal and its tetra-O-acetyl derivative. Benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside was condensed with 2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-glucopyranosyl bromide to give benzyl 2-acetamido-4-O-(2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-glucopyranosyl)-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside. Removal of the 2-O-acetyl group, followed by oxidation with acetic anhydridedimethyl sulfoxide, gave a beta-D-arabino-hexosid-2-ulose (25). After reduction with sodium borohydride, removal of the benzyl groups gave crystalline 2-acetamido-2-deoxy-4-O-beta-D-mannopyranosyl-D-glucose (27). The anomeric configuration of the glycosidic linkage was ascertained by comparison with the alpha-D-linked disaccharide.

The synthesis of glycopeptide fragments of human plasma alpha1-acid glycoproteins by sequential elongation at the terminal-amino group

Glycopeptides corresponding to sequences 27--28, 48--49, and 58--59 of human plasma alpha1-acid glycoproteins have been synthesized by sequential elongation of the peptide chain at the terminal amino group. 2-Acetamido-3,4,6-tri-O-acetyl-1-N-(L-aspart-4-oyl)-2-deoxy-beta-D-glucopyranosylamine was condensed with the p-nitrophenyl esters of protected amino acids to give the corresponding protected glycodipeptides having the sequences Gly-(GlcNAc-4-)Asn, Pro-(GlcNAc-4-)Asn, Val-(GlcNAc-4-)Asn, Leu-(GlcNAc-4-)Asn, Glu-(GlcNAc-4-)Asn, Tyr-(GlcNAc-4-)Asn, Ser-(GlcNAc-4-)Asn, and Cys-(GlcNAc-4-)Asn. Deprotection of the carbohydrate and of the peptide residues of these compounds was achieved, except for those having N-tert-butyloxycarbonyl protective groups, to give the corresponding free glycopeptides. The glycotripeptide 2-acetamido-1-N-(2-N-[N-(tert-butyloxycarbonyl)-L-glutam-1-oyl-L-tyrosyl]-L-aspart-4-oxy)-2-deoxy-beta-D-glucopyranosylamine, having the amino acid sequence 10--12 of human plasma alpha1-acid glycoprotein, was prepared by condensation of 2-acetamido 3,4,6-tri-O-acetyl-2-deoxy-1-N-[2-N-(L-tyrosyl)-L-aspart-4-oyl[-beta-D-glucopyranosylamine with 5-benzyl 1-p-nitrophenyl N-(tert-butyloxycarbonyl)-L-glutamate, followed by removal of the ester groups.