The Oligosaccharides

We shall choose only a few substances as examples for discussion here, because, in most instances, the constitution has not been completely determined. 

Lanatosides.— Lanatoside A (3) can be written with a great degree of certainty as (78), but this structure is not yet completely confirmed. The tetrasaccharide of (78) is not known in the free form. Lanatoside B, (3 28.80.31 D 280 nd contain the same tetraose but different aglycons. This tetraose occurs in unacetylated form in purpurea glycosides A and 

2-deoxy sugars occur in the Strophanthus species (and in many other plants) in similarly constituted glycosides of di- and tri-saccharides. 

Gitoxin cellobioside (88) contains the largest oligosaccharide of any glycoside yet isolated from the digitalis extract. It is a pentaose which has not yet been isolated as such. 

Gentiobiose and cellobiose are the only oligosaccharides (occurring in the cardiac glycosides) which have been synthesized. 

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The first member of the oligosaccharide antibiotics to have its complete chemical stmcture elucidated was everninomicin D (5). The stmcture of everninomicin D then represented a template for the assignment of the stmctures of flambamycin (23), avdamycias (14), curamycias (19), and, more recendy, everninomicin 13-384 Components 1 and 5 (13). 

Fig. 1. Proposed ortho-ester configuration for ring C of the oligosaccharide antibiotics.

FIGURE 9.29 Some of the oligosaccharides found in N-llnked glycoproteins. 

As impressive as the oligosaccharide domain is, calicheamici-none, the aglycon sector 7 (see Scheme 3) is the most striking substructure of calicheamicin y. The rigid bicyclic framework of 7 accommodates an unusual allylic methyl trisulfide and a novel pattern of unsaturation that had not been encountered in natural products before. 

The important advantage of the immunosorbents based on WPG-PA is the fast rate of biospecific interaction between the oligosaccharides and antibodies. For B-trisaccharide-WPG-PA the average sorption time of monoclonal B8 antibodies was 20 times shorter than with B-trisaccharide-Sepharose 4B. The role of the flexible polymeric spacer, therefore, is in this case very pronounced. 

To allow all culture productiou to be coutrolled, a method for rapid analysis is required. Prior to development of an LC-MS method, the analysis was both complex and time-consuming, involving the purification of a relatively large amount of the antibody using affinity chromatography, enzymatic release, and subsequent derivatizafion of the oligosaccharides and their analysis by using capillary electrophoresis. 

Transformation of the raw spectrum from the heavy-chain component shows the presence of three species with molecular weights of 50517.2, 50676.8 and 50 840.2 Da, which were rationalized in terms of the oligosaccharide structures shown in Figure 5.9 - the differences of 162 Da corresponding to a dehydrated galactose residue (CeH Oe - H2O). 

Metastasis Abnormalities in the oligosaccharide chains of membrane glycoproteins and glycolipids are thought to be of importance... 

The process of N-glycosylation can be broken down into two stages (1) assembly of Dol-P-P-oligosaccha-ride and transfer of the oligosaccharide and (2) processing of the oligosaccharide chain. 

The oligosaccharide GICjMangCGIcNAcjj is transferred from dolichol-P-P-oligosaccharide in a reaction catalyzed by oligosaccharide protein transferase, which is inhibited by tunicamycin. 

Isoelectric focusing of transferrin is a useful biochemical test for assisting in the diagnosis of these conditions truncation of the oligosaccharide chains of this protein alters its isolectric focusing pattern... 

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