Sugars, amino ketose, oxidation

Several 4-deoxy-4-nitro ketose derivatives have been synthesized. Three crystalline 2,7-anhydro-4-deoxy-4-nitro-/3-D-heptulopyranoses arose by nitromethane cyclization92 of the dialdehyde (74) produced by periodate oxidation of sedoheptulosan (73), and were assigned93 the D-alio (75), D-gulo (76), and D-altro (77) configurations by nuclear magnetic resonance spectroscopy of the corresponding, peracetylated amino sugars. When the cyclization of 74 was performed in methan-olic medium, a solid mixture of stereoisomeric nitronates was obtained in almost quantitative yield, and it could be partially separated into the individual nitronates, which furnished 75 and 76. The isomer 77... 

Extension and elaboration of the original nitromethane work continued to occupy the attention of Sowden and his collaborators until his death. A convenient synthesis of 2-deoxy-D-er2/f/tro-pentose was a particularly noteworthy achievement, and the substitution of 2-nitroethanol for nitromethane opened the door to the ketoses. The addition of sodium meth-oxide or ammonia to C-nitro-olefins also provided convenient means for preparing 2-0-methyl derivatives and 2-amino sugars, respectively. 

The Maillard reaction is best known as the phenomenon responsible for the browning of untreated foodstuffs, by non-enzymic oxidation. It involves the condensation of amino acids on sugars, both aldoses (glucose) and ketoses (fructose) (Figure 8.27). When aldoses are involved, the primary condensation products are aldimines (Rj = H) (or Schiff base), while ketoses produce ketimine (Ri H). Due to their enoliz-able character, these imines develop according to two tautomeric equilibriums into enaminol and... 

Amadori compounds, N-substituted 1-amino-l-deoxy-2-ketoses e.g. (1) in Scheme 1, formed by reaction of free sugars with the primary amino-groups in free amino acids, peptides or proteins can be determined by g.c. analysis of the A-(carboxymethyl)-amino acid derivatives e.g. (2) released by a protocol involving periodate oxidation of the sugar residue. ... 

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