Untargeted UHPLC–HRMS/MS Profiling of Secondary Metabolites in Roots and Aerial Parts of Plagiorhegma dubium

Plagiorhegma dubium is an underexplored member of Berberidaceae whose secondary metabolite composition and distribution between plant organs remain poorly characterized. Here, untargeted UHPLC-ESI-QTOF-HRMS/MS combined with feature-based molecular networking was applied to profile and obtain putative structural annotations of major metabolite families in the roots and aerial parts of P. dubium. The analysis revealed marked differences between root and aerial-part metabolite profiles and enabled annotation of 14 alkaloid-related features, 61 putative triterpenoid saponins, and 17 flavonoid, hydroxycinnamate, and related metabolites. Among the annotated alkaloids, magnoflorine strongly dominated the root profile, whereas jatrorrhizine/columbamine-type protoberberines were enriched in the aerial-part profile. LC–MS/MS data revealed an extensive family of structurally diverse triterpene saponins, a metabolite class not previously reported from P. dubium. The saponins comprised multiple aglycones, glycan, and non-carbohydrate substituent combinations, with C30H46O6-type aglycones enriched in roots and the more highly oxygenated C30H46O7 family predominant in aerial parts. Flavonoid glycosides and hydroxycinnamate derivatives were strongly enriched in the aerial parts. These findings substantially expand the known phytochemical diversity of P. dubium and identify it as a rich source of structurally unresolved metabolites requiring isolation and definitive structure elucidation.