Differentiation of the Aziridine Functionality from Related Functional Groups in Protonated Analytes by Using Selective Ion-Molecule Reactions Followed by Collision-Activated Dissociation in a Linear Quadrupole Ion Trap Mass Spectrometer

Aziridinesare commonly used as reagents for the synthesisof drugsubstances although they are potentially mutagenic and genotoxic.Therefore, their unambiguous detection is critically important. Unfortunately,tandem mass spectrometry (MS2) based on collision-activateddissociation (CAD), a powerful method used for the identificationof many unknown compounds in complex mixtures, does not provide diagnosticfragmentation patterns for ionized aziridines. Therefore, a differentmass spectrometry approach based on MS3 experiments ispresented here for the identification of the aziridine functionalities.This approach is based on selective gas-phase ion-molecule reactionsof protonated analytes with tris(dimethylamino)borane (TDMAB) followedby diagnostic CAD reactions in a modified linear quadrupole ion trap(LQIT) mass spectrometer. TDMAB reacts with protonated aziridinesby forming adduct ions that have lost a dimethylamine (DMA) molecule([M + H + TDMAB - HN(CH3)(2)](+)). CAD on these product ions generated diagnostic fragment ions with m/z-values 25- and 43-units lower than those of the ion-moleculereaction product ions. None of the ion-molecule reaction product ionsformed from other, structurally related, protonated analytes producedrelated fragment ions. Quantum chemical calculations were employedto explore the mechanisms of the observed reactions.

Automated summary

Aziridines are commonly used in drug synthesis but their detection is important due to their potential mutagenicity and genotoxicity. Tandem mass spectrometry (MS2) based on collision-activated dissociation (CAD) does not provide diagnostic fragmentation patterns for ionized aziridines. Therefore, a different mass spectrometry approach based on MS3 experiments using protonated analytes with tris(dimethylamino)borane (TDMAB) is presented for aziridine identification. Gas-phase ion-molecule reactions and CAD reactions in a modified linear quadrupole ion trap (LQIT) mass spectrometer were used.