General Fragmentations of Alkaloids in Electrospray Ionization Tandem Mass Spectrometry

Various types of alkaloids observed in several herbal medicines were analyzed by electrospray ionization tandemmass spectrometry in positive ion mode. In the present study, MS/MS spectralpatterns were investigated for eight-types of alkaloids(aporpine, protoberberine, tetrahydroprotoberberine, benzylisoquinoline, protopine, phthalide, morpine, and bisbenzylisoquinoline). For aporpine- and protoberberine-type alkaloids, main fragmentations occurred at substituted groups on rigid ringstructures, not showing ring fusion. Interesting fragmentations due to iminolization and retro-Diels-Alder (RDA) reaction wereobserved in MS/MS spectra of protopine- and tetrahydroprotobereberine-type alkaloids. Also, several types of fragmentationssuch as inductive cleavage and α-cleavage, or bond cleavage between two ring structures were observed depending on theirstructural characteristics. These fragmentation patterns are expected to allow instant classification of the specific alkaloid type invarious MS/MS spectra of alkaloids.