A series of regioisomeric cyclic tertiary amines were prepared and evaluated in electron ionization mass aspectrometry (EI-MS) and MS/MS product ion experiments.
A number of synthetic cathinones (aminoketones, 'bath salts') are tertiary amines containing a cyclic amino group, most commonly pyrrolidine. These totally synthetic compounds can be prepared in a number of regioisomeric designer modifications and many of these can yield isomeric major fragment ions in electron ionization mass spectrometry (EI-MS). In the current study, the cyclic amines azetidine, pyrrolidine, piperidine and azepane were incorporated into a series of aminoketones related to the cathinone derivative drug of abuse known as MDPV. Deuterium labeling in both the cyclic amine and alkyl side chain allowed for the confirmation of the structure for the major product ions formed from the EI-MS iminium cation base peaks. These iminium cation base peaks show characteristic product ion spectra which allow differentiation of the ring and side-chain portions of the structure. The small alkyl side chains favor ring fragmentation in the formation of the major product ions. The higher side-chain homologues appear to promote product ion formation by side-chain fragmentation. Both side-chain and ring fragmentation yield a mixture of product ions in the piperidine and azepane series. The study concludes that product ion fragmentation provides useful data for differentiation of cyclic tertiary amine iminium cations from cathinone derivative drugs of abuse. Regioisomeric iminium cations of equal mass yield characteristic product ions for the alkyl side-chain homologues of azetidine, pyrrolidine, piperidine and azepane cyclic amines. (Publisher abstract modified)