Pyridinium-carbaldehyde: active Maillard reaction product from the reaction of hexoses with lysine residues

Syntheses are described for the Maillard reaction product 14 - 13C 1 and the model compound 18 . Besides the formation of the aminotriazine N 6-[4-(3-amino-1,2,4-triazin-5-yl)-2,3-dihydroxybutyl]- l-lysine, the reaction of [1- 13C] d-glucose with lysine and aminoguanidine leads to the generation of 6-[2-({[amino(imino)methyl]hydrazono}methyl)pyridinium-1-yl]- l-norleucine ( 14 - 13C 1). The dideoxyosone N 6-(2,3-dihydroxy-5,6-dioxohexyl)- l-lysine was shown to be a precursor in the formation of 14 - 13C 1, which proceeds via the reactive carbonyl intermediate 6-(2-formylpyridinium-1-yl)- l-norleucine ( 13 - 13C 1). In order to study the reactivity of 13 - 13C 1, the model compound 1-butyl-2-formylpyridinium ( 18 ) was prepared in a two-step procedure starting from 2-pyridinemethanol. The reaction of the pyridinium-carbaldehyde 18 with l-lysine yielded the Strecker analogous degradation product 2-(aminomethyl)-1-butylpyridinium and another compound, which was shown to be as 1-butyl-2-[(2-oxopiperidin-3-ylidene)methyl]pyridinium. Reaction of 18 with the C–H acidic 4-hydroxy-5-methylfuran-3(2 H)-one leads to the formation of the condensation product 1-butyl-2-[hydroxy-(4-hydroxy-5-methyl-3-oxofuran-2(3 H)-ylidene)methyl]-pyridinium.