Liquid secondary ionization mass spectrometry and collision-induced dissociation study of 2-chloro-N10-substituted...

Positive-ion liquid secondary ionization mass spectrometry in combination with 3-nitrobenzyl alcohol as the liquid matrix was used to investigate the mass spectral features of a set of 21 N10-substituted derivatives of 2-chlorophenoxazine. The N-10 substitution included propyl, butyl and acetyl groups containing various secondary amines (N,N-diethylamine, N,N-diethanolamine, morpholine, piperidine, pyrrolidone or beta-hydroxyethylpiperazine) or a chloro group. These compounds are potent multi-drug resistance modulators. The molecular ions are observed as M+ and [M + H]+ ions. In general, the fragmentation pathways of these molecules are similar and very straightforward. The phenoxazine ring system remains stable under the Cs+ ion beam bombardment conditions, while fragmentations are observed along the length of the alkyl and acetyl side-chains. The fragmentation reactions were corroborated by acquiring product ion and constant neutral loss tandem mass spectrometric scans of the pertinent ions.