Annotation of secoiridoids in bioactive extracts of Ferdinandusa hirsuta Standl. (Rubiaceae) using untargeted LC-MS/MS based molecular network

Iridoids are a class of secondary metabolites with pronounced biological activities. Among Rubiaceae plants, they are found mainly in the Ixoroideae subfamily, which includes the Ferdinandusa genus. Some of these species exhibit antimicrobial activity, but the compounds responsible for the reported activities remain unknown. Considering this gap, we investigated the chemical constituents of the leaves and branches extracts from Ferdinandusa hirsuta Standl. and the evaluation of antibacterial and cytotoxic potential. Initially, we performed a clean-up step using a solid-phase extraction cartridge C18 on methanolic extracts (MeOH extracts from leaves and branches) that were analyzed by liquid chromatography coupled to mass spectrometry (LC-MS/MS), with fragmentation spectra (MS2) converted to mzML format and submitted to the GNPS2 platform for molecular network analysis. The compounds annotated had their fragmentation patterns manually verified. The extracts were tested against clinically significant bacterial strains, non-cancerous cell lines (Vero cells and PBMC), and tumor cell lines: MDA-MB-231, CCRF-CEM, HL60, and K562. Among the metabolites annotated in the extracts, five secoiridoids were putatively identified: secologanoside 1 , secologanin 2 , sweroside 3 , epivogeloside 4 , swertiamarin 5 , and one phenolic compound: caffeic acid 6 . Secoiridoids were predominantly annotated in the MeOH (methanol) extract from leaves. The MeOH extract from leaves and the hexanic extracts from leaves and branches showed low inhibition against the bacteria tested. However, the MeOH extract from branches showed cytotoxic potential against the tumor cell lines, and no toxicity to healthy cells. The observed activities could be related to the presence of secoiridoids 3 and 5, which have been previously reported to exhibit antimicrobial and cytotoxic activity. Furthermore, molecular network analysis revealed the potential for the isolation of other secoiridoids. This study represents the first report of this metabolite class within the genus Ferdinandusa .