Chemistry Reference
In-Depth Information
Figure 7.5.
Steps in the Maillard reaction.
cases, has been isolated. Thus, N-substituted glycosylamines derived from
amino acids are inherently unstable and they are either hydrolysed to the
parent amino acid and reducing sugar or react via a spontaneous rearrange-
ment to form the corresponding keto-(
-1-amino-1-deoxy-2-ketose) or aldo-
(
-2-amino-2-deoxyaldose) derivative, depending on whether the parent
sugar is an aldose or a ketose, respectively. The rearrangements are similar
chemically to the LA transformation of sugars in heated alkaline solutions.
The aldo
!
keto transformation is referred to as the Amadori rearrangement
and the corresponding keto
!
aldo rearrangement as the Heyns rearrange-
ment. As in the case of LA transformations, such reactions are multistep; for
example, in the case of Amadori rearrangements, glycosylamines rearrange
first to 1,2-enaminols via a sigmatropic shift followed by ketonization to the
Amadori rearrangement product. It appears that the formation of the immi-
nium ion by dehydration during the Amadori rearrangement is rate limiting.
Acid catalyses this step, with a maximum rate reported to be between pH 2
and 5 (Yaylayan and Huyghues-Despointes, 1994). Thus, the chemistry of the
