Taurine–nitrite interaction as a precursor of alkylation mechanisms

Taurine (2-aminoethanesulphonic acid) is an amino acid-like-compound widely used as an ingredient in some nutraceuticals and energy drinks. Here the interaction of taurine (Tau) with nitrite was investigated. The reactions were carried out mimicking the conditions of the stomach lumen. The conclusions drawn are as follows: (i) Nitrite showed nitrosating capacity on Tau. The rate equation was ν N = k obs [ Tau ] o [ nitrite ] o 2 , this result suggesting that the yield of nitrosation products in the human stomach would increase sharply with higher nitrate/nitrite intakes; (ii) the experimental results suggest a mechanism for the nitrosation, whose rate-limiting step is bimolecular attack by N2O3; (iii) the nitrosation of taurine affords ethanesultone (ES), which displays alkylating capacity on the nucleophile 4-(p-nitrobenzyl)pyridine (NBP), a trap for alkylating agents with nucleophilic characteristics similar to those of DNA bases. Although the NBP alkylation rate for ethanesultone is much higher than those for carcinogenic four-membered ring lactones, resulting in the nitrosation of amino carboxylic acids, the fraction of ES-forming adduct with NBP is much smaller; (iv) in spite of the low risk to human health, since the stomach lumen conditions could be a favourable medium for Tau nitrosation, attention should be paid to potential situations of the concurrence of high contents of taurine and nitrite/nitrate in the diet.