Collisional activation spectra of bisbenzylisoquinoline alkaloids

Abstract

Collisional activation (CA) spectra of the molecular protonated ions generated under fast atom bombardment (FAB) and the molecular ions under electron ionization (EI) from 14 bisbenzylisoquinoline alkaloids have been compared. The FAB CA spectra show mainly elimination of MeOH from the MH⁺ ion and no characteristic fragmentation pattern. The EI spectra, on the other hand, show abundant structurally diagnostic ions free of doubly charged ions. The double benzylic cleavage results in bisisoquinoline ions giving rise to the most intense peak in the spectra of all the compounds. Loss of one of the isoquinoline moieties comprising rings C and D and elimination of both the benzyl groups (rings E and F) are characteristic of compounds containing no 1,4-dioxine bridge (1-5). These compounds are also characterized by more abundant (>50%) [M - Me]⁺ ions, while the compounds with a 1,4-dioxine bridge give [M - Me]⁺ ions with <50% abundance.