Collision Induced Dissociation of Deprotonated Isoxazole and 3-Methyl Isoxazole via Direct Chemical Dynamics Simulations

Abstract

Isoxazoles are an important class of organic compounds widely employed in synthesis and drug design. Fragmentation chemistry of the parent isoxazole molecule and its substituents has been the subject of several experimental and theoretical investigations. Collision induced dissociation (CID) of isoxazole and its substituents has been studied experimentally under negative ion conditions. Based on the observed reaction products, dissociation patterns were proposed. In the present work, we studied the dissociation chemistry of deprotonated isoxazole and 3-methyl isoxazole using electronic structure theory calculations and direct chemical dynamics simulations. Various deprotonated isomers of these molecules were activated by collision with an Ar atom, and the ensuing fractionation patterns were studied using on-the-fly classical trajectory simulations at the density functional B3LYP/6-31+G* level of electronic structure theory. A variety of reaction products and pathways were observed, and it was found that a nonstatistical shattering mechanism dominates the CID dynamics of these molecules. Simulation results are compared with experiments, and detailed atomic level dissociation mechanisms are presented.

Intramolecular interactions and the neutral loss of ammonia from collisionally activated, protonated ω-aminoalkyl-3-hydroxyfurazans

“…The rings in the structures of biologically active heterocycles, such as pharmaceuticals, 1 – 3 antifungal agents, 4 , 5 and herbicides, 6 provide both a rigid scaffold and hydrogen bonding sites. 7 – 10 When analyzed by tandem mass spectrometry (MS/MS), heterocyclic ions often fragment by a prominent and characteristic ring cleavage 11 – 18 or by cleavage of a bond to the ring. 19 In other instances, the ring participates in proton transfer prior to the dissociative step and is located intact in the neutral product or the product ion.…”

Two-body dissociation of isoxazole following double photoionization – an experimental PEPIPICO and theoretical DFT and MP2 study

“…The N(2)QC(3) bond length is shorter than the C(4)QC( 5) one (see Table 2), further strengthening the N(2)QC(3) side of the isoxazole structures. As a result, NO and C 3 H 3 fragments were not identified in isoxazole's photodissociation, 26,[28][29][30]33 collision-induced fragmentation 36,60,63 or under pyrolytic conditions. [64][65][66] m/z = 29 + 41 and 30 + 40 dissociation channels.…”

Molecular modeling, synthesis, and antiproliferative evaluation of new isoxazole ring linked by Schiff bases and azo bond

“…Isoxazole moieties have recently received more attention due to their increasing importance in medicinal chemistry. [ 5 ]…”