N-Substituted aldosylamine

The initial stage of the Maillard browning is a condensation reaction between the carbonyl group of an aldose and the free amino group of an amino acid, to give an N-substituted aldosylamine. This reaction, which is initiated by an attack of the nucleophilic amino compound on the carbonyl carbon, is reversible and requires an acidic catalyst. The Schiff base is in equilibrium with the cyclic aldosylamine structure as shown in Figure 11.9 [170]. 

The initiating reaction between aldoses and amines, or amino acids, appears to involve a reversible formation of an N-substituted aldosyl-amine (75) see Scheme 14. Without an acidic catalyst, hexoses form the aldosylamine condensation-product in 80-90% yield. An acidic catalyst raises the reaction rate and yet, too much acid rapidly promotes the formation of 1-amino-l-deoxy-2-ketoses. Amino acids act in an autocat-alytic manner, and the condensation proceeds even in the absence of additional acid. A considerable number of glycosylamines have been prepared by heating the saccharides and an amine in anhydrous ethanol in the presence of an acidic catalyst. N.m.r. spectroscopy has been used to show that primary amines condense with D-ribose to give D-ribopyrano-sylamines. ... 

A large number of iV-substituted aldosylamines have been synthesized by the above methods, but only a few A -substituted ketosylamines have yet been made. These have been found difficult to prepare, and the yields have been poor. Recently, however, Barry and Honeyman have described an improved method for preparing A -phenyl- and A -p-tolyl-n-fructosyl-amines, in which the amine and n-fructose are heated in anhydrous ethanol with a catalytic quantity of amine hydrochloride. Yields of up to 70% (based on the unrecovered sugar) result when the duration of reaction is short (seven minutes), and well characterized compounds have been obtained for the first time. In a similar manner, Helferich and Portz have isolated Y-p-hydroxyphenyl- and Y-p-methoxyphenyl-n-fructosylamine in yields of about 20%. 

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