K. Cejpek et al., Reactions of allyl isothiocyanate with alanine, glycine, and several peptides in model systems, J AGR FOOD, 48(8), 2000, pp. 3560-3565
The nucleophilic addition reactions of allyl isothiocyanate (AITC) with ala
nine, glycine, and five alanine and/or glycine containing di- and tripeptid
es were investigated in model aqueous solutions of pH 6, 8, and 10 at 25 de
grees C for 2-4 weeks. The formation of primary adducts, i.e., N-allylthioc
arbamoyl amino acids (ATC-amino acids) or ATC-peptides, their transformatio
n products, i.e., 3-allyl-2-thiohydantoins originating by cyclization of AT
C-amino acids or by cleavage of ATC-peptides, and several other minor compo
nents were observed. The results revealed that both addition and cleavage r
ates rise proportionally to pH,whereas the formation of 2-thiohydantoins fr
om ATC-amino acids is controlled by H3O+ concentration. Depending on pH, di
fferences in reaction rates of the additions are determined by either pK(a)
(NH2) of amino compounds or electrical effects and steric hindrance of the
molecules. The latter factors are crucial also for differences in cleavage
rates of ATC-peptides. With regard to the pK(a) values and simultaneous AIT
C decomposition by aqueous nucleophiles, the reactions with amino acids and
oligopeptides are predominant reaction pathways of AITC in solutions of pH
10 and 8, respectively. Reaction mechanism of the cleavage of 2-thiohydant
oins from ATC-peptides in alkaline and mild acidic solutions is different f
rom the conventional Edman scheme used for anhydrous acid medium.