Degradation of 1-Deoxy-D-erythro-hexo-2,3-diulose in the Presence of Lysine Leads to Formation of Carboxylic Acid Amides

A novel species of amides formed from degradation of one of the most important key intermediates in Maillard hexose chemistry-1-deoxyhexo-2,3-diulose-was investigated. In 1-deoxyhexo-2,3-diulose/N-alpha-t-BOC-lysine reaction mixtures four amides, N-epsilon-acetyl lysine, N-epsilon-formyl lysine, N-epsilon-lactoyl lysine and N-epsilon-glycerinyl lysine, were identified and their structures verified by authentic reference standards. Amides and corresponding carboxylic acids (acetic acid, formic acid, lactic acid and glyceric acid) accumulated over time. Both N-lysine amides and carboxylic acids were thus determined as stable Maillard end products. Results of model incubations suggested the synthesis of amides to be mechanistically closely related to the formation of their corresponding carboxylic acids by beta-dicarbonyl cleavage. Due to the different chemical properties of all the compounds monitored, various analytical strategies had to be carried out (LC-MS2, GC-MS, GC-FID, enzymatic determination).