Revealing inhibitory mechanism of thiamine on the formation of 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline based on quantum chemistry calculations and experimental verification

The effects of five water-soluble vitamins (thiamine, nicotinic acid, nicotinamide, pyridoxine, l-ascorbic acid) on the formation of MeIQx in a chemical model system containing glycine/glucose/creatinine were investigated. Thiamine was the most potential inhibitor among these five vitamins, which could reduce the formation of MeIQx by 33.9%–100.0%, depending on the concentration of thiamine. Furthermore, the inhibiting effect of thiamine was highly correlated (R2 = 0.887) with its trapping capabilities for methylglyoxal. The proposed inhibitory mechanism of thiamine on the formation of MeIQx was based on quantum chemistry calculations and structural elucidation of the 4-amino-5-hydroxymethyl-2-methylpyrimidine-methylglyoxal adduct. This study indicated that thiamine could act as an effective inhibitor on the formation of MeIQx, and trapping methylglyoxal may be its key inhibiting mechanism on MeIQx's formation. These findings provide a new idea for the study of the sustained-release effect of new inhibitors on heterocyclic aromatic amines in the future.