Fragmentation carbohydrates

Fig. 2 Inrnume complex binding enhancing activity of Carbohydrate fragments obtained by endo-polygalacturonase digestion...

Fig, 2 (a) Synthetic routes to carbohydrate fragments from AGPs... 

The tricarboxylic acid cycle was therefore validated, having been tested not only in pigeon-breast muscle but also with brain, testis, liver, and kidney. The nature of the carbohydrate fragment entering the cycle was still uncertain. The possibility that pyruvate and oxaloacetate condensed to give a 7C derivative which would be decarboxy-lated to citrate, was dismissed partly because the postulated compound was oxidized at a very low rate. Further, work on the oxidation of fatty acids (see Chapter 7) had already established that a 2C fragment like acetate was produced by fatty acid oxidation, en route for carbon dioxide and water. It therefore seemed likely that a similar 2C compound might arise by decarboxylation of pyruvate, and thus condense with oxaloacetate. For some considerable time articles and textbooks referred to this unknown 2C compound as active acetate. ... 

The naphtho[2,3-d]-l,3-dioxole was oxidized using recombinant E. coli whole cells overexpressing the gene for the naphthalene dioxygenase from Pseudomonas putida G7. The linear carbohydrate fragment was enzymatically formed after ozon-ization of the diol, by chain extension with a dihydroxyacetone fragment in an... 

Glycosylatioti of Inositol Synthesis of the Terminal Carbohydrate Fragment in GPI-Anchors [47]... 

Similar concerns regarding the stability of our activated lipid intermediate led us to reject a method that involves the in situ preparation of lipid-derived phosphoric anhydrides.22 The common theme for each of the methods illustrated above is that each involves activation of the lipid intermediate for the diphosphate coupling reaction. Given the expense of the undecaprenyl monophosphate precursor, we sought a method that would entail activation of the carbohydrate fragment for capture by an undecaprenyl monophosphate nucleophile. This, in principle, would also allow the opportunity for the coupling reaction to take place under basic reaction conditions and enable us to preserve the chemical integrity of our expensive lipid precursor. 

The 2-3-dihydro-(lH)-pyrrolizines have two responses to reaction temperature increasing with rising temperature or reaching a maxima at 152.5°C. These are compounds in which proline plays a structural as well as a catalytic role. The concentration of these compounds do not follow proline content as would be expected if the structural role of proline was determining. It appears that the concentration of carbohydrate fragments determines the pyrrolizine content. 

Figure 2 illustrates the formation of 5-acetyl-7-methyl-[iv], 5-acetyl-6-methyl-[v], 7-formyl-5-methyl-[vi] and [vii] 7-acetyl-5-methyl-2,3-dihydro-(lH)-pyrrolizines after Tressl et al. (5). The 2,3-dihydro-(lH)-pyrrolizines require both carbohydrate fragmentation products and proline for their formation. Both the 5-acetyl- pyrrolizines [iv] and [v] increased in quantity as the reaction temperature increased while [vi] and [vii] were found at maximum quantity at 152.5°C. The first pair are formed through an iminium carboxylate intermediate which is decarboxylated into an exocyclic iminium ion which then undergoes an aldol... 

The Model for 2-acetoxy-3-pentanone. This compound is formed by a condensation of acetic acid and 2-hydroxy-3-pentanone, common carbohydrate fragmentation products. As such it would be expected that C(r) would be important (from the carbohydrate source) and pH since its precursors are affected by both acid and base. The most significant model terms according to Prob > T were C(r) (0.0002)... 

Experiments with [13C6]-D-glucose showed that the sugar s carbon chain remains intact in the course of crosslink formation. Thus, the formation of bicyclic compounds from carbohydrate fragments is likely to be at most only a minor pathway.392... 

Ribonuclease from other mammalian sources may have several carbohydrate fragments in their structures. Thus, ribonuclease B from porcine pancreas contains at least three carbohydrate moieties, and these are attached9 at asparagine residues 21, 34, and 76. The carbohydrate moieties present at residues 21 and 76 are considerably more complex than that at residue 34, and their structures are under investigation in several laboratories. The carbohydrate portions of the isoenzymes of deoxyribonuclease are similar in structure to those from the ribonucleases.11 As ribonuclease and deoxyribonuclease originate in the same organ, it is possible that the same pathways and enzymes are utilized for the biosynthesis of the carbohydrate moieties of both enzymes. 

Domon, B. Costello, A. 1988. Systematic nomenclature for carbohydrate fragmentation in FAB-MS/MS spectra of glycoconjugates. Glycoconj. J. 5 397-409. 

---