Structural elucidation of a novel lysine-lysine crosslink generated in a glycation reaction with L-threose

Abstract

A novel lysine-lysine crosslink was isolated from a reaction containing L-threose (a degradation product of ascorbic acid) and N-α acetyllysine. The compound, after chromatographic purification, had a relative molecular mass of 628 as determined by fast atom bombardment spectrometry. Structural analysis by NMR spectroscopy (1H,13C, COSY, HETCOR and DEPT) suggests that the compound is composed of 3 threose residues and 2 N-α-acetyllysines with an empirical formula of C28H45N4O12. The compound, referred to as threosidine (2,5-dihydroxy-5,6,7,8-tetrahydro 1,7-naphthyridinium as the core molecule) has an absorption maximum at 328 nm with an excitation and emission maxima at 328 nm and 402 nm respectively. Threosidine was stable upon acid hydrolysis, and it was not found in the reactions containing threose and amino acids other than N-α-acetyllysine. Threosidine was also not found in the reactions containing N-α-acetyllysine and sugars other than threose.