STRUCTURAL ELUCIDATION OF A NOVEL LYSINE-LYSINE CROSS-LINK GENERATED IN A GLYCATION REACTION WITH L-THREOSE

A novel lysine-lysine crosslink was isolated from a reaction containin g L-threose (a degradation product of ascorbic acid) and N-alpha-acety llysine. The compound, after chromatographic purification, had a relat ive molecular mass of 628 as determined by fast atom bombardment spect rometry. Structural analysis by NMR spectroscopy (H-1, C-13, COSY, HET COR and DEFT) suggests that the compound is composed of 3 threose resi dues and 2 N-alpha-acetyllysines with an empirical formula of C28H45N4 O12. The compound, referred to as threosidine 5-dihydroxy-5,6,7,8-tetr ahydro-1,7-naphthyridinium as the core molecule) has an absorption max imum at 328 nm with an excitation and emission maxima at 328 nm and 40 2 nm respectively. Threosidine was stable upon acid hydrolysis, and it was not found in the reactions containing threose and amino acids oth er than N-alpha-acetyllysine. Threosidine was also not found in the re actions containing N-alpha-acetyllysine and sugars other than threose.