Electrophilic properties of patulin.: N-acetylcysteine and glutathione adducts

In our studies on the electrophilic properties of the mycotoxin patulin (PAT), we have now investigated the nonenzymatic reaction of PAT with the thiol-containing tripeptide glutathione and its metabolic degradation product N-acetyl-L-cysteine (NAC). Adduct formation in aqueous phosphate buffer (pH 7.4) was studied by analytical HPLC/DAD, and most of the products were isolated by preparative HPLC. Structure elucidation was carried out mainly by means of high-resolution NMR experiments and comparison of the data with those previously obtained for PAT adducts formed with simple model nucleophiles such as 4-bromothiophenol and 2-mercaptoethanol [Fliege, R., and Metzler, M. (2000) Chem. Res. Toxicol. 13, 363-372]. The assigned structures were confirmed by UV spectroscopy, formation of daughter products from isolated adducts, and partly FAB-MS. The reaction pathways of PAT with NAC were qualitatively the same as those previously observed for the aliphatic thiol model compound 2-mercaptoethanol. Due to the chiral nature of NAC and the new chiral center generated during the reaction with PAT, two diastereomers of each adduct were formed and observed in HPLC analysis. The major products formed in the reaction of PAT with GSH were of the same structural type as obtained with NAG. In addition, three cyclic adducts were formed with GSH, arising from the nucleophilic activity of the alpha-amino groups of the glutamic acid and the cysteine residue. In contrast, free cysteine yielded a markedly different adduct pattern, possibly due to the preferred formation of mixed thiol/amine-type adducts involving the alpha-amino group.