The decomposition of N-chloro amino acids of essential branched-chain amino acids: kinetics and mechanism

Abstract The formation of N-chloro-amino acids is of outmost importance in water treatment technologies and also in vivo processes. These compounds are considered as secondary disinfectants and play important role in the defense mechanism against invading pathogens in biological systems. Adversary effects, such as apoptosis or necrosis are also associated with these compounds and the intermediates and final products formed during their decomposition. In the present study, the decomposition kinetics of the N-chloro derivatives of branched chain amino acids (BCAAs) – leucine, isoleucine, valine – were studied. On the basis of spectrophotometric measurements, it was confirmed that the decomposition proceeds via a spontaneous and an OH− assisted path in each case: kobs = k + kOH[OH−]. 1H, 13C NMR and MS experiments were also performed to identify the products and to monitor the progress of the reactions. It was established that the pH independent and the [OH−] dependent paths lead to the formation of the same aldehyde in each system (isovaleraldehyde, 2-methyl-butyraldehyde, and isobutyraldehyde) as a primary product. Under alkaline conditions, a portion of the aldehydes are converted into the corresponding Schiff-bases by the excess amino acid in a reversible process. A common mechanism was proposed for these reactions which postulates the formation of imines and hemiaminals as reactive intermediates.