Gas Phase Reactions of Cysteine with Charged Electrophiles: Regioselectivities of the Dimethylchlorinium Ion and the Methoxymethyl Cation

Abstract

The gas phase reactions of cysteine with the dimethylchlorinium ion, (CH3)2Cl+, and the methoxymethyl cation, CH3OCH2+, have been studied by using chemical ionization tandem mass spectrometry (CI/MS/MS). The structures of the [M + CH]+ and [M + CH3]+ ions in the CH3Cl CI plasma and the [M + CH]+, [M + CH3]+, and [M + CH3OCH2]+ ions formed in the (CH3)20 CI plasmas have been probed by using MS/MS techniques. Where possible, these MS/MS spectra were compared to those generated for ions of known structure (i.e., the [M + H]+ ions of N-methylcysteine, S-methylcysteine, cysteine methyl ester, and (R)-thiozolidine-4-carboxylic acid, which were produced under isobutane CI conditions). Structure ass..