Carbohydrates fragmentation, types

FIGURE 7.7 Types of carbohydrate fragmentation. (Adapted from Domon, B. and Costello, C. E. Glycoconjugate J, 5, 397, 1988. With permission.)... 

Synthetic work has been reported on compound 9 which is a hydrolytically stable analogue of GM3 ganglioside lactone. Compound 10, which contains a trisaccharide having a hydrojgrlamine linking unit, and which is a derivative of the carbohydrate domain of calicheamicin, has been reported, and carbohydrate fragments of esperamicin Aj which also contain this type of bonding, have likewise been described. ... 

Three types of photochemical reaction of carbohydrate acetals have been investigated. Early studies centered on the photochemical fragmentation of phenyl glycosides, and the photolysis of o-nitrobenzyli-dene acetals. (The latter reactions will be discussed with the photolysis of other nitro compounds see Sect. VII,1.) Later experiments were concerned with hydrogen-abstraction reactions from acetal carbon atoms by excited carbonyl compounds. 

CBH I 497 core-BA aa sequence in part from protein and in full from gene (cbhl), number and location of SS bridges, region of O-glycosylation, types of carbohydrate, papain cleavage site, hydrophobic cluster analysis, computer model of active site, 2D-NMR on a synthetic tail fragment, SAXS on whole CBH I, head domain and xylan/CBH I complex... 

Fragmentation and recombination reactions predominate in nearneutral, alkaline solutions. Fragments from the cleavage of the carbohydrate, and from its dehydration products, undergo further dehydration, condensation, and intermolecular, Cannizarro-type reactions. The benzilic acid rearrangement, an intramolecular Cannizarro reaction, seems to be inoperative. 

Mass spectra have been measured for ketose acetates only,16 and the most characteristic feature of these mass spectra is the formation of a new series of fragments having no analogy in the mass spectra of other types of carbohydrate derivatives. 

Peptides formed enzymically or by mineral acid hydrolysis or thermal degradation of higher molecular veight protein can also serve as flavor precursors in thermally induced reactions. The reactivity of peptides is evidenced by their behavior during pyrolysis/GC (9), heating in air (10), reactions vith mono- (11), and dicarbonyl (12, 13) compounds and reactions in hot acetic acid (1A). The types of reactions observed for peptides include side-chain thermolysis, fragmentation into amino acids, DKP formation and Halliard reaction vith ambient carbohydrates. 

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