Electrospray Tandem Mass Spectrometry for Structural Characterization of Aporphine-Benzylisoquinoline Alkaloids

Abstract

Electrospray mass spectrometry and tandem mass spectrometry techniques were utilized to elucidate the structures of ten aporphine-benzylisoquinoline alkaloids, consisting of a monoether link between aporphine and benzyltetrahydroisoquinoline units, which were isolated and identified previously from a variety of Thalictrum sp. (Ranunculaceae family) based mainly on the ultraviolet, infrared, circular dichroism, nuclear magnetic resonance, electron ionization mass spectrometry (EI-MS), chemical ionization mass spectrometry (CI-MS), derivatization and chemical degradation techniques. In this investigation, protonated molecules, [M + H]+ ions, for nine tertiary alkaloids, a molecular ion, [M+•] ion, for a quaternary alkaloid and very intense doubly-protonated molecules, [M + 2H]2+ ions (100% of relative abundance) in Q1 Scan MS spectra, and prominent, as well as diagnostic, product ions for structural information in the tandem mass spectra were observed for all investigated alkaloids each in nanogram quantities. More than 10 μg quantities of each investigated alkaloid or other isoquinoline and aporphine analogs were needed for the CI-MS, EI-MS and fast atom bombardment mass spectrometric analysis from the previous studies.