Concerted base-promoted elimination in the decomposition ofN-halo amino acids

Abstract

N-Chloroamino acids are unstable in aqueous solution and decompose through different pathways depending on the reaction conditions, yielding precursors of carcinogenic and/or mutagenic compounds. One of these pathways is a 1,2-elimination process, which has scarcely received any attention and for which no systematic analysis is available. The process is first order relative to the N-chloroamino acid and to that of hydroxide ion.The use of 2,2,2-trifluoroethanoI and 1,1,1,3,3,3-hexafluoropropan-2-ol buffer solutions established that the process is general-base catalysed. The reaction rate is affected by the presence of a methyl group on the nitrogen atom and the nature of the leaving group. The results show an important steric effect due to the alkyl substituents on the a-carbon. With bulky alkyl substituents on the a-carbon, and in particular in the case of N-

Intracellular Oxidation of Dipeptides. Base-Promoted Elimination from N-Halodipeptides to 2-[N-Alkyl-N-(2-N-alkylimino-2-alkylethanoyl)amino]-2,2-dialkylethanoic Acids

“…A similar value has been found for p ssy ′ in the base-promoted decomposition of (N-X)-amino acids. 29 Thus, the results obtained seem to indicate that the observed steric effect arises as a result of the interaction between the R 1 groups on C R and the nucleofuge, which supports the hypothesis of the elimination taking place in the anti, and not in the syn conformation.…”

“…Comparing the rates of elimination obtained for analogous (N-X)-amines [k OH -((N-Cl)-EtNH) ) 0.15 × 10 -3 M -1 ‚s -1 ] 37 and (N-X)-R-amino acids [k OH -((N-Cl)-Gly) ) 44 × 10 -3 M -1 ‚s -1 ] 29 with those obtained in this work for 1 [k OH -((N-Cl)-Gly‚Gly) )1.29 M -1 ‚s -1 ], it seems clear that the electron-withdrawing effect of the peptide group is responsible for the observed rate enhancement. From these values it also follows that 3 is more stable from compounds such as 1, 52 the activation energy for the process leading to 3 being lowered compared with reactions of (N-X)-amines and (N-X)-R-amino acids.…”

“…Such parameters quantitatively describe the effect of the substituents on the structure of the TS. 58 To take into account the steric effect, the following parameters have been defined: 29 The crossed-interaction coefficient p sxy ′ reflects the interaction between the substituents R 1 in 1 and the reacting base. We found p sxy ′ ) 0, in agreement with the lack of steric effect of R 1 discussed above.…”

“…While alkyl substituents on the N slow the reaction in the case of (N-X)-amines and (N-X)-amino acids, 37,38 a rate enhancement is observed for (N-X)-Pro, for which the steric hindrance is smaller. 29 Most likely, a similar effect is responsible of the effect observed for (N-X)-Pro‚Gly.…”

Chemical fate and mutagenic formation potentials of phenothiazine and related compounds during water chlorination

“…The N-chloro compounds formed by this reaction can be reconverted to the parent compound by reactions with strong nucleophiles, such as thiosulphate or bisulphite, which are used to dechlorinate wastewater prior to discharge. In the absence of Chemical fate and mutagenic formation potentials of phenothiazine and related compounds during water chlorination Taro Sekizawa and Sukeo Onodera (Antero et al, 1996;Armestro et al, 1996).…”