Mechanochemical generation of N,N-diglycated glycine and MS/MS characterization of its isomeric composition

The formation of Schiff bases and Amadori rearrangement products (ARP) during the Maillard reaction in solutions is well documented, but their studies in solid-state are limited. Here we report mass-spectrometric characterization of N,N-diglycated Schiff bases and Amadori products obtained during ball milling of amino acids and glucose. Signal intensities of the diglycated adducts in mass-spectra depended on type of the amino acid and the MS ionization mode. Glycine provided for the highest yields of N,N-diglycation, followed by lysine, when the reaction was analyzed under negative ionization mode. Using diagnostic MS/MS fragmentation, we were able to distinguish between Schiff-Schiff, Schiff-Amadori, or Amadori-Amadori isomers. Milling glucose/glycine model for 30 min at ambient temperature produced diglycated glycine as a mixture of the three possible isomers in approximately equal molar proportions. Milling of synthetic Schiff base or ARP of glycine with [U-¹³C]-glucose generated the same but partially labelled isomers, with respective predominance of N,N-diglucosyl-glycine or N,N-difructosyl-glycine.