Taurine Bromamine: Reactivity of an Endogenous and Exogenous Anti-Inflammatory and Antimicrobial Amino Acid Derivative

Taurine bromamine (Tau-NHBr) is produced by the reaction between hypobromous acid (HOBr) and the amino acid taurine. There are increasing number of applications of Tau-NHBr as an anti-inflammatory and microbicidal drug for topical usage. Here, we performed a comprehensive study of the chemical reactivity of Tau-NHBr with endogenous and non-endogenous compounds. Tau-NHBr reactivity was compared with HOBr, hypochlorous acid (HOCl) and taurine chloramine (Tau-NHCl). The second-order rate constants (k(2)) for the reactions between Tau-NHBr and tryptophan (7.7 × 10(2) M(−1)s(−1)), melatonin (7.3 × 10(3) M(−1)s(−1)), serotonin (2.9 × 10(3) M(−1)s(−1)), dansylglycine (9.5 × 10(1) M(−1)s(−1)), tetramethylbenzidine (6.4 × 10(2) M(−1)s(−1)) and H(2)O(2) (3.9 × M(−1)s(−1)) were obtained. Tau-NHBr demonstrated the following selectivity regarding its reactivity with free amino acids: tryptophan > cysteine ~ methionine > tyrosine. The reactivity of Tau-NHBr was strongly affected by the pH of the medium (for instance with dansylglycine: pH 5.0, 1.1 × 10(4) M(−1)s(−1), pH 7.0, 9.5 × 10 M(−1)s(−1) and pH 9.0, 1.7 × 10 M(−1)s(−1)), a property that is related to the formation of the dibromamine form at acidic pH (Tau-NBr(2)). The formation of singlet oxygen was observed in the reaction between Tau-NHBr and H(2)O(2). Tau-NHBr was also able to react with linoleic acid, but with low efficiency compared with HOBr and HOCl. Compared with HOBr, Tau-NHBr was not able to react with nucleosides. In conclusion, the following reactivity sequence was established: HOBr > HOCl > Tau-NHBr > Tau-NHCl. These findings can be very helpful for researchers interested in biological applications of taurine haloamines.