Amadori rearrangement derivatives

Another possible mechanism7 for the transformation of sugars with amino acids into colored products is through the Amadori rearrangement,44 which is the isomerization of an aldosylamine to a ketose derivative, for example, of a D-glucosylamine derivative to a derivative of 1-amino-l-deoxy-D-fruc-tose. Such a conversion has been shown to occur when an amino acid reacts... 

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. ... 

Like the 5-amino aldopentoses, the 5-amino aldohexoses have a pronounced tendency to form the pyranose ring in alkaline solution. In acid solution, three molecules of water are eliminated per molecule, to give the corresponding derivative of 3-pyridinol. 5-Amino-5-deoxyaldohexopyranoses are, however, distinctly more stable, as the Amadori rearrangement and pyridine formation occur at pH 5.7—6.2. With the pentose analogs, these reactions begin at pH 7—8. Because of the reactive a-amino alcohol arrangement at C-1, the 5-amino-5-... 

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. 

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