Glycans, complex, glycoprotein-derived

Kitajima et al. [264] used the mixture of mercury salts and molecular sieves in 1,2-dichloromethane to condense (370) with the trisaccharide derivative (382) to give similar tetrasaccharides [on the primary hydroxyl group of (382)] with again equal amounts (30% each) of a- and (3-linked derivatives. With the allyl glycoside (383) under the same conditions 48 % of a- and 33 % of P-linked glycosides were obtained [265]. The a-isomer was used to prepare [265] the undecasaccharide characteristic of the complex type of glycan of glycoproteins. 

Fig. 17.4 Simplified structure of a complex N-linked glycan and the sites of action of B-hexosaminidase. Glycoproteins are degraded by specific enzymes from both directions. Lysosomal catabolism is terminated when an A-acetylglucosamine residue is encountered by the catalytically impaired enzyme B-hexosaminidase, and thus the glycoprotein-derived oligosaccharide in the box accumulates in Sandhoff patients.

In 1998, Morten Meldal and coworkers demonstrated the semisynthesis of Asn derivatives of complex-type bi- and triantennary asialo N-glycans [58], After isolation of these oligosaccharides from the glycoproteins fetuin and ribonuclease (RNase) B by hydrazinolysis, the glycans were converted to Fmoc-Asn(oligosaccharide)-OH derivatives with an acetylated sugar part. In 2003, the Yasuhiro Kajihara group... 

The biosynthesis and functions of the membrane glycoproteins of eukaryotic cells have been reviewed. The general features of the biosynthesis of these glycoproteins closely resemble those involved in the biosynthesis of complex bacterial glycans, especially the O-antigen of lipopolysaccharides. Syntheses of polyisoprenyl jS-o-mannopyranosyl phosphate and P -di-A-acetylchitobiosyl P -dolichyl pyrophosphate have been reported. A preparation from human-lymphocyte membranes was able to transfer D-mannose from GPD-o-mannose to the chitobiosyl derivative, whereas dolichyl D-mannosyl phosphate did not act as a D-mannosyl donor. It appears that D-mannosyl residues at various positions of the glycoprotein have different anomeric configurations, so that different D-mannosyl donors are required in their synthesis. 

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