Novel Yellow Compounds, Dilysyldipyrrolones A and B, Formed from Xylose and Lysine by the Maillard Reaction

When a solution containing xylose and L-lysine is heated under weakly acidic conditions, it turns brown by the Maillard reaction. We isolated here two novel yellow compounds from a heated solution containing xylose and lysine, and identified pyrrolyl-methylidene-pyrrolone derivatives named dilysyldipyrrolones A and B. Their chemical structures were elucidated by instrumental analyses as 6-[[1-[(S)-5-amino-1-carboxypentyl]-3-hydroxy-pyrrol-2-yl]-(E)-2-methylidene-5-methyl-1,2H-pyrrol-3-one-1-ly]-(S)-2-amino-hexanoic acid (dilysyldipyrrolone A) and 6-[[1-[(S)-5-amino-5-carboxypentyl]-3-hydroxy-pyrrol-2-yl]-(E)-2-methylidene-5-methyl-1,2H-pyrrol-3-one-1-yl]-(S)-2-amino-hexanoic acid (dilysyldipyrrolone B). These were the major pigments in the heated solution.