Sites of protonation in phenothiazines: Methane and ammonia chemical ionization mass spectra

Fragmentation pathways of metopimazine and its metabolite using ESI-MS(n), HR-MS and H/D exchange

Metopimazine (MPZ) is a phenothiazine derivative used to prevent emesis during chemotherapy where few structural analysis of the aforementioned compound have been described in the literature. Thus, this work reports, for the first time, the detailed study of fragmentation pathways of MPZ and its metabolite (AMPZ) using electrospray ionization (EI) with multistage mass spectrometry (ESI-MS(n)) in positive-ion mode. The structures of 21 product ions were identified and their accurate masses were determined using high resolution mass spectrometry (HRMS) experiments. Characteristic product ions of these two phenothiazine derivatives are more particularly displayed along with differences between their relative abundances and their structures checked by H/D exchange experiments.

Mass spectral fragmentation reactions of a therapeutic 4-azasteroid and related compounds

Mass spectra were acquired for a therapeutic 4-azasteroid (dutasteride), and some related compounds, using various ionization conditions (EI, CI, APCI and ESI) in both positive and negative ion modes. The ionization and fragmentation behavior of the compound dutasteride, its precursors and several analogs is reported. Positive atmospheric pressure chemical ionization (APCI+) and positive electrospray ionization (ESI+) produced distinctive collision-induced dissociation (CID) spectra for the respective [MH]+ ions of dutasteride. The spectral differences are attributed to ion populations having either different structures or different internal energy distributions (as a consequence of the method of ionization). Irrespective of their origin, the protonated molecules undergo interesting fragmentation reactions when collisionally activated. The identity of the major fragmentation products was confirmed by accurate mass measurement. The negative APCI mass spectrum of dutasteride displays extensive dehydrohalogenation, apparently due to the thermal component of the APCI process. Some of the resulting radical anions display remarkable stability toward collisional decomposition. Details of the fragmentation behavior for the negative ion species and their relationship to the positive ion results are discussed.

Evaluation of automatically generated substructure identification rules from tandem mass spectra

Substructure identification rules for phenothiazine and barbiturate substructures were generated by using a new version of the Method for Analyzing Patterns in Spectra (MAPS) software. This software uses tandem mass spectra and known substructure content of reference compounds to provide "feature-combination" rules. A feature-combination is a series of tandem mass spectral features which are completely unique to compounds containing a specified substructure. The current reference databases contain over 11,000 daughter spectra of 100 compounds acquired at two different collision gas pressures (i.e., single- and multiple-collision conditions). The results of rule evaluation procedures are presented and include a comparison of the spectral features developed in rule generation to those identified in documented fragmentation pathways of the indicated substructure. Two potential sources of error due to spectral feature and substructure "cross-correlation" were identified. If errors occur, they can be detected by calculating cross-correlation coefficients and edited from the rules. A beneficial cross-correlation involving feature-combinations was also discovered. The rules obtained by using single- and multiple-collision data were further evaluated by applying them to tandem mass spectra of 20 test compounds (compounds not in the reference database). The results of these evaluations give a good indication of the utility of the rules for use in an automated structure elucidation system for tandem mass spectrometry data.