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

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 β- 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.