The collisionally activated mass spectral fragmentations of N-(2, 4-dinitrophenyl) alanine and phenylalanine [MH]− may be gas-phase analogs of the base-catalyzed cyclization of N- (2, 4-dinitrophenyl) amino acids in aqueous dioxane. This latter reaction is one source of the 2-substituted 5-nitro-1H-benzimidazole-3-oxides, which are antibacterial agents. The fragmentation of both compounds, established by tandem mass spectrometric ...