272 4 Carbohydrates
(4.52)The reasons for the partial stability of such
Amadoricompounds in comparison with imines
can be explained by the cyclic molecular
structures.
The imine (Formula 4.52) formed by the reaction
of glucose with the amine is easily converted to
the cyclic hemiaminal,α-andβ-glucosylamine.
However, N-glycosides of this type are relatively
instable because they very easily mutarotate, i. e.,
they are easily hydrolyzed via the open-chain
imine or are converted to the respectiveα-and
β-anomer. However, theAmadorirearrangement
leads to furanose, which as a hemiacetal, has
a stability to mutarotation comparable with that
of carbohydrates.
TheAmadoricompounds can react further with
a second sugar molecule, resulting in glycosy-
lamine formation and subsequent conversion
to di-D-ketosylamino acids (“diketose amino
acids”) by anAmadorirearrangement:
(4.54)4.2.4.4.2 Formation of Deoxyosones
Amadoriproducts are only intermediates formed
in the course of theMaillardreaction. In spite of
their limited stability, these products can be used
under certain conditions asan analytical indicator
of the extent of the heat treatment of food. Unlike
the acidic (pH<3) and alkaline (pH>8) sugar
degradation reactions, theAmadoricompounds
are degraded to 1-, 3-, and 4-deoxydicarbonyl
compounds (deoxyosones) in the pH range 4–7.
As reactiveα-dicarbonyl compounds, they yield
many secondary products. Formulas 4.54–4.57
summarize the degradation reactions starting with
theAmadoricompound.
Analogous to fructose (cf. Formula 4.37), amino-
l-deoxyketose can be converted to 2,3-eneaminol
as well as 1,2-eneaminol (Formula 4.54) by
enolization. Analogous to the corresponding
1,2-enediol, water elimination and hydrolysis of
the imine cation gives 3-deoxy-1,2-diulose, also
called 3-deoxyosone (Formula 4.55).
Like the corresponding 2,3-enediol, the 2,3-
eneaminol has two different β-elimination
options. Formula 4.56 shows the elimination of
the amino acid by aretro-Michaelreaction with