title: Deprotonated N-(2,4-Dinitrophenyl)amino Acids Undergo Cyclization in Solution and the Gas Phase.
abstract: The collisionally activated mass spectral fragmentations of N-(2,4-dinitrophenyl)alanine and phenylalanine [M - H](-) 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 experiments and supported by molecular modeling using DFT methods, indicate that the [M - H](-) ions dissociate via sequential eliminations of CO(2) and H(2)O to produce deprotonated benzimidazole-N-oxide derivatives. The gas-phase cyclization reactions are analogous to the base-catalyzed cyclization in solution, except that in the latter case, the reactant must be a dianion for the reaction to occur on a reasonable time scale. The cyclization of N-(2-nitrophenyl)phenylalanine, which has one less nitro group, requires a stronger base for the cyclization than the compound with a second nitro group at the 4-position. Following losses of CO(2) and H(2)O are expulsions of both neutral molecules and free radicals, the latter being examples of violations of the even-electron ion rule.
authors.affiliation: Department of Chemistry, Sacred Heart College, Thevara, Cochin, Kerala, India-682013.
authors.forename: M
authors.initials: M
authors.lastname: George
authors.forename: V
authors.initials: V
authors.lastname: Ramesh
authors.forename: R
authors.initials: R
authors.lastname: Srinivas
authors.forename: Daryl
authors.initials: D
authors.lastname: Giblin
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gross