Add time:08/24/2019         Source:sciencedirect.com

SummaryKetoses are known to react with amino compounds via ketimines to form the so-called Heyns compounds (2-aminoaldoses), which are assumed to undergo subsequent transformations parallel to those observed with the corresponding Amadori compounds. Until now, this assumption was not established by separate mechanistic studies. Therefore, we prepared [1-13C]-D-fructose from [1-13C]-D-glucose by enzymatic methods. In a series of model experiments [1-13C]-D-fructose was heated with 4-aminobutyric acid (Strecker inactive), L-isoleucine (Strecker active), and L-proline (secondary amine type), respectively. The labeled products were analyzed by capillary GC/MS and NMR spectroscopy and the labeling characteristics were examined from MS data. Compared to corresponding experiments with [1-13C]-D-glucose, the significant results are: (1) With 4-aminobutyric acid only trace amounts of 3-deoxyaldoketose products are formed in the D-fructose system, whereas 1-deoxydiketose products were generated in comparable amounts from D-glucose and D-fructose; and (2) With L-isoleucine both D-glucose and D-fructose form 3-deoxyaldoketose- and 1-deoxydiketose products in comparable amounts; but with D-fructose the most effective reaction is the formation of pyrazines initiated by a retro aldol cleavage into C3+C3 fragments. This cleavage is also responsible for the formation of mixtures of isotopomeric products in D-fructose systems.

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