title: Side reaction of S-to-N acetamidomethyl shift during disulfide bond formation by iodine oxidation of S-acetamidomethyl-cysteine in a glutamine-containing peptide.
abstract: During the time course of disulfide bond formation by iodine oxidation (in a methanolic and hydrochloric acid solution) of a cysteinyl(S-acetamidomethyl)-glutaminyl tridecapeptide, we observed by ESI, FAB mass spectrometry (pseudo-molecular ion and ion-fragments) and 1H-NMR a side reaction due to a shift of the Acm leaving group from cysteine to the carboxamide side chain of glutamine. This type of Acm-shift at low level was described previously by L.W. Mendelson et al. (Int. J. Pept. Protein Res. 35:249-257) for an aspariginyl-cysteinyl(S-acetamidomethyl) peptide in an anhydrous hydrochloric solution. We report here the efficiency of glutamine as a scavenger to suppress the S-->N shift of the acetamidomethyl group during S-acetamidomethyl cleavage and sulfhydryl oxidation with iodine, as the folded tridecapeptide was obtained with the expected molecular weight.
authors.affiliation: CEA/Saclay, Gif sur Yvette, France.
authors.forename: H
authors.initials: H
authors.lastname: Lamthanh
authors.forename: H
authors.initials: H
authors.lastname: Virelizier
authors.forename: D
authors.initials: D
authors.lastname: Frayssinhes
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000737:chemistry; D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000737:chemistry*; D005973:Glutamine / Q000737:chemistry*; D007455:Iodine / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry*
chemical_list: D004220:Disulfides; D010455:Peptides; D005973:Glutamine; C079740:(S-acetamidomethyl)cysteine; D007455:Iodine; D000111:Acetylcysteine