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GLUCOLD – a new bis(lysyl)imidazolium cross-link derived from glucose

The Maillard reaction is a complex series of reaction between reducing sugars and other sugar derivates which leads to the formation of the Amadori product in the early stage of the reaction. A major consequence of the Maillard reaction is the formation of covalently cross-linked proteins. Formation of the majority of cross-links involves α -oxoaldehydes generated by the Amadori compound degradation. Bis(lysyl)imidazolium derivates represent one group of cross-links formed via α -dicarbonyls such as glyoxal, methylglyoxal and 3-deoxyglucosone also known as GOLD, MOLD and DOLD, respectively. Here we describe a new imidazolium cross-link formed from the Amadori product showing the possibility of direct involvement of the Amadori compound into cross-link formation without additional rearrangement into more reactive dicarbonyl compounds. The new imidazolium derivative was isolated from a model reaction incubation mixture containing the Nε -(1-deoxy-D-fructos-1-yl)-aminocaproic acid and ε -aminocaproic acid (a lysine analogue) by preparative RP HPLC. The NMR data of the isolated compound showed two proton signals at 8.64 (H-2) and 7.39 (H-5) ppm bound at two C-atoms at 136 and 122 ppm, respectively. Additional signal in the 13C NMR spectrum at 135 ppm and a coupling constant between H-2 and H-5 of 1.6 Hz confirm an imidazolium ring in the structure [1]. A molecular ion of the product at m/z 417 and the presence of a side chain containing three CH carbon atoms and one CH2 between 62 and 72 ppm in the 13C NMR spectrum and four proton signals between 3.4 and 3.8 ppm plus one at 5 ppm in the 1H NMR spectrum confirm a new imidazolium cross-link called GLUCOLD (glucose derived lysine dimer) (Fig. 1). Hydrogen/carbon assignments were confirmed by 1H, 13C, COSY, 13C-DEPT, HSQC and HMBC NMR experiments.

GLUCOGOLD; cross-link; glycation; Maillard

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