A mass spectrometric and molecular orbital study of H2O loss from protonated tryptophan and oxidized tryptophan derivatives

Abstract

Protonated N-acetyltryptophan, oxindolylalanine (a mono-oxidized derivative of tryptophan), and N-acetyloxindolylalanine, as well as several di- and tripeptide derivatives containing oxindolylalanine, undergo a range of fragmentation reactions in the gas phase, including the loss of water. In order to elucidate the sites of water loss within these ions, and to determine the mechanisms associated with these processes, we have conducted a series of experiments employing multistage tandem mass spectrometry (MS/MS and MS 3) in a quadrupole ion trap mass spectrometer, regiospecific structural labeling, and independent solution-phase syntheses of proposed product ion structures, coupled with the u..