Formation mechanism and characterization of dilysyl-dipyrrolones, the Maillard-type yellow pigments

Abstract

Our group has recently isolated and identified novel yellow compounds named dilysyl-dipyrrolones A (DPL A; 1) and B (DPL B; 2) in a heated aqueous solution containing xylose and lysine under weakly acidic conditions. In this study, we isolated and identified a novel DPL derivative (DPL C; 3), which has the same structure as DPL B, except for containing a hydroxymethyl group. To estimate the formation mechanism of DPL derivatives, ¹³C-labeled DPLs were prepared and analyzed with LC/MS and NMR. ¹³C-labeling experiments using [1-¹³C] ribose showed that the formation pathway of DPL C was different from those of DPLs A and B. In addition, ¹³C-labeling experiments using [U-¹³C₅] ribose and [1-¹³C] lysine showed that C-6 of a methine moiety in DPL C was derived from C-5 of ribose or acetic acid in buffer. Based on these results, we postulated the formation mechanism of DPLs. We then showed that DPLs A and B had potent antioxidant activities.