Mass spectrometric analysis of pentafluorobenzyl oxime derivatives of reactive biological aldehydes

We recently demonstrated that a battery of reactive aldehydes can be genera ted by human neutrophils through the action of myeloperoxidase on alpha-ami no acids. To determine the aldehydes, we formed the pentafluorobenzyloxime (PFBO) derivatives by reacting them with pentafluorobenzylhydroxylamine (PF BHA) and submitting the derivatives to gas chromatography electron-capture mass spectrometry (GC/EC/MS). Two geometric isomers are formed for each of the aldehydes, and they are separable by gas chromatography (GC) and exhibi t distinguishable electron-capture (EC) mass spectra. Major fragment ions i nclude [M - HF](radical anion), which probably has a six-membered ring form ed via HF loss from the molecular radical anion. Subsequent decomposition o f this intermediate yields other characteristic ions (e.g. those formed by elimination of NO and the anion of mit 178). We proposed fragmentation path ways and mechanisms that are consistent with the data derived from collisio nally-activated dissociations (CAD) coupled with tandem mass spectrometry, exact-mass measurements, studies of deuterium-labeled analogs, and calculat ions by PM3 semiemperical and ab initio methods. The generality of the stru cturally informative fragmentation pattern together with GC separation is t he basis of a powerful means for the identification of reactive aldehydes i n biological processes and the pathogenesis of disease. (Int J Mass Spectro m 185/186/187 (1999) 795-812) (C) 1999 Elsevier Science B.V.