Elimination of Isocyanate and Isothiocyanate Molecules at the Electrospray Ionization Ion Trap, Electrospray Ionization Quadrupole Time-of-Flight and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Tandem Mass Spectrometry Fragmentation of Sodium Cationized Brassitin, Brassinin and Their Glycosides

Abstract

Fragmentation mechanisms of phytoalexin analogs, including brassitin and brassinin and their glucosylated analogs, have been studied by electrospray (ESI) ion trap (IT) multistage (MS(n), n = 1-4) mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight (MALDI ToF/ToF) and ESI-Q/ToF tandem mass spectrometry techniques. At the fragmentation of sodium adducts a hitherto not described process has been elucidated The proposed mechanism of this process includes cyclization of the brassitin and brassinin cationized adducts through a six-membered cycle of the molecules and the elimination of isocyanate or isothiocyanate from the thio- or dithiocarbamate moiety, giving rise to [M + Na - 43](+) or [M + Na - 59](+) adducts. The elimination of NH=C=O or NH=C=S molecules has been confirmed by the high resolution measurement of the elemental composition of the ions produced and quantum-chemical calculations of the six-membered transition state. Other fragmentation routes include cleavage of an alkane linker, while numerous characteristic hexopyranose pathways are taking place in the glucosylated compounds. The presented theoretical data on the ESI and MALDI behavior of the saccharidic, as well as of the indole aglycon parts, can facilitate structural elucidation of the analogous compounds.

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2007–2008

“…Low energy spectra were obtained by ESI on a Q-TOF instrument and by MALDI on a QIT instrument and were virtually identical whereas high-energy spectra were recorded with a MALDI-R-TOF instrument (March et al, 2007). High-energy fragmentation of glucosylated phytoalexins (27) from Chinese cabbage have also been reported (Bekesová et al, 2007) with a combination of MALDI-TOF and ESI-ion trap mass spectrometers. Much fragmentation involved cross-ring cleavages of the glucose molecule.…”