The occurrence of retrosynthetic processes, usually observed in electron ionization conditions, can be considered of interest, giving information of on possible new synthetic routes. Generally retrosynthesis is typical of odd electron ion species, but in the present case it has been observed for electrospray (ESI) generated [MH]⁺ species of 2-pyridinecarboxamides. In fact either in the ESI spectrum or in the MS/MS spectrum of [MH]⁺ species a primary water loss is observed, giving rise to the molecular ion of the corresponding imidazolines, employed as synthons for the title compounds. The breakdown curves related to this water loss has been determined, indicating that this process is more favoured for the bromine-containing molecules.

Keywords: retrosynthesis, electrospray, collisionally-activated decompositions, breakdown curves