Amadori rearrangement product Amino acids

Knowledge about the chemical structure of the antioxidative MRP is very limited. Only a few attempts have been made to characterize them. Evans, et al. (12) demonstrated that pure reductones produced by the reaction between hexoses and secondary amines were effective in inhibiting oxidation of vegetable oils. The importance of reductones formed from amino acids and reducing sugars is, however, still obscure. Eichner (6) suggested that reductone-like compounds, 1,2-enaminols, formed from Amadori rearrangement products could be responsible for the antioxidative effect of MRP. The mechanism was claimed to involve inactivation of lipid hydroperoxides. 

When the structure of a compound is known, the current British-Ameri-can practice42 will be followed. No specific recommendation was made for naming Amadori rearrangement products, but, under Rule 8, the systematic name for the Amadori product of JV-i>-glucosyl-DL-leucine could be 1-(dl-l-carboxy-3-methylbutyl)amino-l-deoxy-D-fructose (I or II), and this name conflicts with the requirement that the carboxyl function takes precedence and that the name should end in acid. Consequently, this compound should be named as N- (n-ara zno-tetrahydroxy-2-oxohexyl)-DL-leucine. A shorter and equally unambiguous name would be l-(DL-leucino)-l-deoxy-D-fructose. (This is sometimes shortened to DL-leucino-deoxyfructose. Such compounds have also been called fructose-leucine, but this is not recommended since it may be confused with such expressions as the fructose-leucine system.11)... 

The formation of the pyridinol is prevented if, in the step 19 to 20, no anion can be eliminated from C-3 this is the case with 5-amino-3,5-dideoxy-l,2-0-isopropylidene-a-D-er /thro-pentofuranose, which, on acid hydrolysis, afFords only the Amadori rearrangement product and no pyridine derivative. The reaction then proceeds, according to the above mechanism, in only one direction from 19. The 3-deoxypentose is prepared, in a manner analogous to the formation of 15, from 3-deoxy-l,2-0-isopropylidene-a-D-riho-hexofuranose through catalytic reduction of the phenylhydrazone of its periodate-oxidation product. ... 

Cold barium hydroxide quantitatively removes the sulfite group from 25 and 26. The 5-amino-5-deoxy-D-xylose so liberated exists mainly in the form 17. Only in alkaline solution is it relatively stable toward acids it is extremely sensitive. Compound 17 accordingly behaves fundamentally differently from all other monosaccharides. In neutral solution (obtained by neutralization of its solution in barium hydroxide with carbon dioxide), the Amadori rearrangement product (22) is formed on standing at room temperature. With hydrochloric acid, 22 is likewise formed as the major product, together with 3-pyridinol (21). Free 17 cannot be isolated in pure form the product obtained contains 16 and 22 in proportions that vary with the pH of the evaporated solution. The impurities are lowest at pH 9.6. It is reported that, from the evaporated solution of 17, a 96 % yield of 25 can be recovered, but it should be mentioned that 16 and 22 also react with sulfurous acid to form 25 and 29. Thin-layer chromatograms (silica gel with p-dioxane—water) always show, besides 17, spots for the secondarily formed 16 and 22. 

Another equilibrium partner of the form 102a is the cyclic Schiff base 101a, formed by dehydration. The C=N chromophore in 101a exhibits a weakly positive Cotton effect at 250 nm, by which the proportion of 101a present can be demonstrated. The Cotton effect disappears at pH values below 6. By comparison with 5-amino-5-deoxy-D-xylopyranose (17), 102a is definitely the more stable toward acids. Neither an Amadori rearrangement product, nor aromatization to a p)nTole derivative, is observed down to pH 1.0. 

The chemistry of the browning reaction has been reviewed periodically (1-7). The carbohydrate-amino acid browning reaction produces literally hundreds of reaction products. Despite the fact that the Maillard reaction has been investigated for many years, we cannot as yet identify all the reactant compounds. The first steps are, however, clearly established. The aldose or ketose reacts with amine to produce N-substituted glycosyl amine (Fig. 1). This rearranges, as illustrated, to produce a 1-amino-desoxy-2-ketosyl amine. If it is blocked, the overall reaction is blocked. This key compound or compounds can then continue to react (Fig. 2). The desoxy-ketose or amadori rearrangement product can dehydrate to produce furfural-like compounds or, through the loss of water, produce reductones. All of these compounds can react with one another or with other amine compounds to produce a wide variety of reaction products. 

D. R. Cremer, M. Vollenbroeker, and K. Eichner, Investigation of the formation of Strecker aldehydes from the reaction of Amadori rearrangement products with a-amino acids in low moisture model systems, Eur. Food Res. Technol, 211 (2000) 400-403. 

From Aldosuloses - Reductive amination of the 1-aldehydo-derivative produced by oxidation of 2,3 4,5-di-0-isopropylidene-P-D-fructopyranose, with a variety of amino acids, followed by deprotection, gave Amadori rearrangement products such as 32. The 3,4-ditosylate 33 was obtained similarly by reductive amination with propylamine, selective hydrolysis of the 3,4-( -isopropylidene group, tosylation and acid hydrolysis. In aqueous buffer at pH 7.4, it gave the... 

Radical reaction mechanisms during the early Maillard reaction were first detected by Namiki et al. (7, 2). He identified iV.A -dialkylpyrazine-cation radicals that originated from the primary Schiff base formed by reaction between glucose and amino acids. The glycolaldehyde alkylimine formed by a reverse aldol reaction of the Schiff base leads to a dialkylpyrazinium radical cation after self-condensation. The formation of dialkylpyrazinium radical cations, which could be detected by EPR spectrometry, represents an alternative pathway of the Maillard reaction it starts at the very beginning of die reaction, well before the formation of Amadori rearrangement products and depends on the pH value it starts around pH 7 and increases up to pH 11. 

Several mass spectra could not be assigned to peptides. Mass differences of 162 and 324 between the parent and the daughter ions did not correspond to a protein derived amino acid but indicated the presence of a glycoconjugate between an amino acid and a mono- or disaccharide [32]. The compounds were identified as Amadori rearrangement products on the basis of the comparison of the retention times, MS/MS, and MS spectra with those of reference compounds. Table 1 lists the glycoconjugates... 

The initial Schiff base is digestible but after the Amadori rearrangement, the products are not metabolically available. Since lysine is the amino acid most likely to be involved and is an essential amino acid, Maillard browning reduces the biological value of proteins. Interaction of lysine with lactose renders the adjacent peptide bond resistant to hydrolysis by trypsin, thereby reducing the digestibility of the protein. 

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