Fragmentation carbohydrate chain

Figure 20.14 Periodate oxidation of HRP creates aldehyde groups on the carbohydrate chains of the enzyme. Reaction with a Fab fragment then may be done using reductive amination to produce a lower-molecular-weight complex than would be obtained using intact IgG antibodies.

Carbohydrate chains of teichuronic acids and neutral polysaccharides linked to the carbohydrate chains of peptidoglycans are fragments of macromolecules of Gram-positive cell-wall. Only two examples of the biosynthesis of these polymers have been studied in detail. Evidence for both block and monomeric mechanisms of the chain assembly was obtained. 

I n the previous two chapters, we described the catabolism of glucose to pyruvate by glycolysis and the further breakdown of pyruvate to C02 and H20 in the TCA cycle. These are oxidative processes. As the carbohydrate chain is chopped into progressively smaller fragments, electrons are... 

In carbohydrates, P-fragmentation of radicals adjacent to the glycosidic linkage [e.g reactions (14) and (15)] will also lead to chain scission. 

V. A. Derevitskaya, L. M. Likhosherstov, M. D. Martynova, and N. K. Kochetkov, Specific method for the fragmentation of the polypeptide chain of glycoproteins. Distribution of carbohydrate chains on the peptide core of blood-group-specific glycoprotein, Carbohydr. Res., 120 (1983) 85-94. 

There are several methods for the preparation of optically pure 3-carbon compounds from carbohydrates. These fall into 3 major categories namely the cleavage of carbohydrate chains to form the desired compounds directly, the transformation of a (larger) carbohydrate-derived fragment to a 3-carbon one and the use of carbohydrates as a chiral auxiliaiy to induce chirality into a pro-chiral 3-carbon fragment. We will review the first approach and discuss our efforts in the other two areas more fully. 

These data show that hemolytic activity depends upon both aglycon and carbohydrate chain structures. The presence of a linear tetrasaccharide fragment in carbohydrate chains is significant for the activity. Moreover, a sulfate group, attached to the C-4 of the... 

The linear tetrasaccharide fragment in carbohydrate chains is also very important. In fact, the branched tetraoside - bivittoside B (44) is less active than the linear tetraosides 30 and 31. Progenin 36, obtained from holotoxin Ai (33), has no antifungal activity at concentrations up to 100 ig/ml. 

The linear tetrasaccharide fragments are also important for the formation and maintenance of the channel. The holothurin A2 (57) carbohydrate chain is such tetrasaccharide fragment. As shown above, all the branched tetraosides, trioside, bioside and monooside derivatives have low activity. Hence, all monosaccharide units are connected with this block by arrows. To show the special significance of linear tetrasaccharide unit, the connecting arrow from the terminal S-O-methylglucose is indicated by a bold line. 

Fig. 6. Structure of the Fc fragment of human IgG. ( ), Alpha carbon positions (o), approximate centres of carbohydrate hexose units. Coordinates were obtained from the Brookhaven Data Bank (after Dei-senhofer [23]). The pairing of Cn3 domains and the position of carbohydrate between C 2 domains is clearly seen in this view. The contact between carbohydrate chains is much more extensive in rabbit Fc. Note that the heavy chains are described only from residue 238 residues 225-238 do not show well-defined electron density.

Figure 6.12 The Domon and Costello nomenclature system for fragmentations of carbohydrate chains. Reprinted from Ref [91] with kind permission from Springer.

FIGURE 103 Identification of a glycopeptide produced by peptic digestion of a monoclonal antibody using accurate mass measurements (the peptide mass matches two possible iso-baric fragments from the protein sequence, and application of CAD fails to provide useful sequence information due to the presence of a labile carbohydrate chain). The identity of this peptide is unequivocally established using accurate mass measurements with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS).TOFMS,time-of-flight mass spectrometry. 

A FruA-mediated stereoselective DHAP addition to a suitable aldehyde precursor 114 (Figure 5.51) served as the key step in the synthesis of the "non-carbohydrate , skipped polyol C9-C16 chain fragment 115 of the macrolide antibiotic pentamydn [238, 239]. Using the same enzyme, compound 117 has been stereoselectively prepared as a synthetic equivalent to the C3-C9 fragment of (+)-aspidllin, a lichen macrolactone (Figure 5.51) [240]. 

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