D-Fructose-amino acids

To model the moiety of glycoproteins which coimects the protein and carbohydrate parts of the molecule, amino acid - carbohydrate adducts (e.g. V-D-gluconylamino acids, thiazolidine-4-carboxylic acid derivatives of carbohydrates, " D-fructose amino acid derivates, etc.) have been synthetized. The protonation and metal ion (Cu2+, Ni2+, Co ", Zn2+ and Et2Sn2+) coordination equilibria of these model compounds have been studied by means of potentiometric equilibrium measurements. CD, EPR, NMR, EXAFS and MSssbauer investigations (the latter in frozen solutions) have been used to determine the structure and symmetry of the coordination sphere of the complexes. >6... 

The utility of liquid chromatography-mass spectrometry (LC/MS) for determination of food-related D-fructose-amino acids has been evaluated in several studies. 

A combination of capillary elecfrophoresis and tandem MS is considered as a eomplementary technique to LC/MS, with the potential for higher resolving power in some cases. It was successfully applied to model mixtures of D-fructose-amino acids, but its practical utiUty for determination of fructosamines in food/biosamples needs to be established. 

As already noted, the main interest of fructosamine derivatives in food and health sciences stems from their role as intermediates in tiie Maillard reaction in foods and in vivo. It is thought tiiat the vast majority of o-fructosamine transfoimation reactions, such as dehydration, oxidation, and fragmentation, are effected by acid/base and transition metal-ion catalysts. A relatively limited effort has been spent on proper documentation of proton- and metal-binding characteristics of D-fructosamine derivatives, however. Roper et a/. evaluated acidity constants for the P-pyranose tautomer of several D-fructose-amino acids using C-NMR. More precise p/iTa values were obtained from... 

In vivo, these compounds demonstrated the ability to markedly reduce metastasis of MDA-MB-435 xenografts in nude rnice. A different mechanism of antitumor activity has been proposed for D-fructose-L-histidine. FruHis stands out of other naturally occurring D-fructose-amino acids in respect of its exceptional metal-binding and antioxidant activities. Remarkably, FruHis completely protected DNA degradative oxidation by copper-promoted hydroxyl radicals in vitro, while none of other tested major antioxidants from tomato (ascorbic acid, quercetin, caffeic acid etc.) could match the protective potential of FruHis. Even more... 

The simplest member of the fructose-amino acid series is the glycine derivative, N-(l -carboxy)-methyl-l-amino-l-deoxy-D-fructose (7). Substances of this type are produced in the so-called chemical browning of foods and they have been isolated and characterized from hog liver. They may be obtained synthetically by heating the appropriate amino acid with a very large excess of D-glucose. Several workers have observed... 

Comparison of the complex-formation constants for bofli 1 1 (57 and 58) and 1 2 (such as 59) species ° with those obtained for the respective copper(II) complexes with parent amino acids revealed that the fructosyl moiety provides for an additional chelate effect in D-fructose-a-amino acids and as a consequence, a significant increase in the complex stability. In the absence of an anchoring chelating group, such as a-carboxylate, the D-finctosamine structure is not a good copper(II) chelator, and Cu(n) expectably does not form stable complexes with the carbohydrate in A -d-Iructose-L-lysine peptides. Although it would be expected that iron(III) complexes with D-finctose-amino acids in aqueous solutions, no related thermodynamic equilibrium studies have been done so far for this important redox-active metal. 

For clinical application as a protein-deglycating enzyme, however, the carbohydrate cleavage in A/ -D-fructose-L-lysine on glycated proteins is needed, and a search for enzymes eapable of such activity has been ongoing for the past two decades (Table V). Most of the characterized fungal fructose-amino acid oxidases carry a relatively high... 

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