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Carbohydrates 383

SCHEME 5 Millard reaction scheme.

important of these structures are the acyclic Schiff bases
and the two pairs of anomeric cyclic forms (the two five-
and two six-membered rings). However, when crystal-
lized, one form of the hydrazone is usually isolated. For
example, the crystalline form of D-galactose phenylhydra-
zone was shown by the following sequence of reactions to
be the acyclic form (see Scheme 6).
Osazones and bis(hydrazones) are hydrazine deriva-
tives of aldosuloses and diuloses, respectively. If the two
hydrazone residues are attached to C-1 and C-2 of a sac-
charide, the derivative is referred to as an osazone and
is named by suffixing osazone to the name of the ketose
that possesses the same carbon chain and the same con-
figuration (irrespective of the sugar used in its prepara-
tion); for example, D-arabino-2-hexulose phenylosazone
is the name given to the osazone obtained from D-glucose,
D-mannose, and D-fructose. The stability of osazones is at-
tributed to their chelated rings (see Scheme 7).
SCHEME 6 Formation of the same galactose hydrazone pen-
Reducing sugars react with hydroxylamine to give taacetate from a pyranose, a furanose, and an acyclic sugar
oximes, which have been prepared for use in the Wohl acetate.