Pentasaccharide core

An intramolecular acetal has also been introduced by the treatment of a mixture of a 1-thio-mannoside, having a methoxybenzyl protecting group at C-2 and an alcohol with DDQ [71] (Scheme 4.4c). Activation of the thioglycoside with methyl triflate gave a P-mannoside as the only anomer. This approach was employed for the synthesis of the core pentasaccharide of N-linked glycoproteins. 

For this purpose, Ag zeolite and Ag, developed by Garegg25 and Paulsen,26 respectively, have been widely employed (Scheme 7.6). Reactions using these activators have found practical use in synthetic studies on glycoprotein glycans and glycolipids. For instance, Paulsen reported the chemical synthesis of the core pentasaccharide structure 6 common to all types of Asn-linked glycans, using the Ag... 

Scheme 13.16 Synthesis of an Asn-Core pentasaccharide bidding block.

Dan, A. Ito, Y. Ogawa, T., A Convergent and Stereocontrolled Synthetic Route to the Core Pentasaccharide Structure of Asparagine-Linked Glycoproteins. J. Org. 

This is the most widely studied structural form of glycosylation and has the greatest effect on overall protein structure and function (Kornfeld and Kornfeld, 1985 Spellman, 1990). The glycan consists of a core pentasaccharide (Man3GlcNAc2) attached via an N-glycosidic bond to an Asn residue of a consensus amino acid sequence (sequon) Asn-X-Ser/Thr, where X can be any amino acid except pro line (Figure 6.1). 

Core N-glycan structure. This consists of a core pentasaccharide composed of a trimannosyl group attached to two Glc-NAc residues. The structure is attached to an asparagine (Asn) residue in a sequon which is an amino acid motif of three amino acids. X is any amino acid (except Pro) that is positioned between Asn and either serine or threonine. 

For the spectral interpretation, 52 is conceived of as an extension of 42 with a Fuc group a-(l— 3)-linked to GlcNAc-5. The spectral parameters of the structural-reporter groups of the fucosylated core pentasaccharide of 42 are found unaltered in 52 the same holds for those of the sialylated, upper branch. It may be mentioned that the apparent heterogeneity of the peptide moiety of 52 (and 42) clearly affects the... 

In the second family ofN-glycosylically linked carbohydrate chains, the core pentasaccharide aMan(l—>3)[aMan(l- 6)]/3Man(l—>4)-/3GlcNAc(l— 4)/3GlcNAc(l— N)Asn is substituted by mannose residues.1... 

From the spectrum of this complex mixture of glycopeptides, it may be inferred that all of the constituents have, in common, Man residues 3, 4, 4, A, and B, and the N,N -diacetylchitobiose unit. [The smallest component of this mixture differs from 63 (ov), obtained from ovalbumin, only in the peptide part.] The N-acetyl signals of GlcNAc-1 and -2 are both split into two singlets this reflects the heterogeneity of the peptide moiety. Nevertheless, the chemical shift of the N-acetyl signal of GlcNAc-2 (8 —2.055) is typical for extension of the core pentasaccharide with Man residues only [compare 61, 62, 63 (ov), and 67 see Tables XXIV and XXV],... 

Concerning structures of the oligomannoside type, the influences of substitution of the Man-4 and Man-4 residues of the core pentasaccharide by Man-A, -B, and -C, and, in turn, those of substitution of the latter by terminating Man-D residues, have been summarized in Table XXVII. Also, the characteristics of the H-l and H-2 signals of terminal a-(l- 2)-, a-(l—>3)-, or a-(l—>6)-linked Man residues have been given. 

Ratner DM, Swanson ER, Seeberger PH. Automated synthesis of a protected A-linked glycoprotein core pentasaccharide. Org. Lett., 2003 5 4717-4720. 

Solid-phase oligosaccharide synthesis olfers good opportunities for automahon, and using a modihed pephde synthesizer automated oligosaccharide synthesis has been described [114]. As an example of automated ohgosaccharide synthesis, the preparation of the core pentasaccharide of A-hnked glycoproteins (223) is shown in Scheme 5.38 and Scheme 5.39 [115]. 

SCHEME 5.38 Building blocks for the solid-phase synthesis of the core pentasaccharide of A -linked... 

Guo, Z-W, Nakahara, Y, Nakahara, Y, Ogawa, T, Solid-phase synthesis of the CD52 glycopeptide carrying an N-linked core pentasaccharide structure, Angew. Chem. Int Ed., 36, 1464-1466, 1997. 

The attachment of carbohydrate to nitrogen is invariably by A -acetyl-D-glucosamine and the attachment to oxygen is invariably by A/ -acetyl-D-galactosamine. A -linked carbohydrates are invariably composed of a core pentasaccharide [142] of the following structure ... 

The A/ -linked glycosides can be classified into three families that result from the further attachment of monosaccharides to the two branched D-mannopyranose residues at the nonreducing-end of the core pentasaccharide. These additional residues make up the variable regions of the oligosaccharides. The first family is the high mannose family that has additional... 

The second family of A-linked oligosaccharides are called the lactosamine family in which the D-mannose residues of the core pentasaccharide are substituted 1 2 by lactosamine, which is a lactose analogue with A-acetyl-D-glucosamine substituted for D-glucopyranose at the reducing-end of lactose. The lactosamine is frequently substituted by A-acetyl-D-neu-raminic acid (for the structure of A-acetyl-D-neuraminic acid, see the monomer residue in colominic acid,0 Sect. 8.2 andO Fig. 7) linked 2 3 or 2 6 [142,143]. The third family has a mixed structure of the high mannose and lactosamine families [144,145,146,147]. 

Core pentasaccharide Man(a1-6)[Man(a1-3)]Man()J1-4)GlcNAc(/S1-4)GlcNAc of JV-glycoproteins attached to the consensus sequence Asn-Xaa-Ser/Thr. Solid arrows indicate the points of attachment of the outer ami saccharides forming carbohydrate chains, caiied antennae, in addition, the inner-core may be substituted by several monosaccharides dashed arrows)... 

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