Isolation and Structural Elucidation of Bioactive Compounds from the Stem Bark of Vitex doniana Used in Traditional Medicine in North Central Nigeria

Vitex doniana, known locally as black plum, is extensively used by traditional medicine practitioners in North Central Nigeria for the management of malaria, diarrhoea, hypertension, and skin diseases, yet the chemical basis for these therapeutic claims has been inadequately investigated through phytochemical isolation and structure elucidation studies. This study undertook systematic isolation and structural elucidation of bioactive compounds from the methanol extract of stem bark of Vitex doniana collected from Kogi State. Extraction was performed by cold maceration, and the extract was fractionated by vacuum liquid chromatography followed by preparative column chromatography using gradient elution. Isolated compounds were characterised by one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy, mass spectrometry, infrared spectroscopy, and ultraviolet spectroscopy, with data compared against published spectral databases. Seven compounds were isolated and fully characterised, including three iridoid glycosides, two flavonoid aglycones, one oleanolic acid triterpenoid, and one stigmasterol derivative. The iridoid agnuside was identified for the first time in a Nigerian specimen of Vitex doniana. Antiplasmodial activity was screened in vitro against Plasmodium falciparum chloroquine-sensitive strain, and two iridoid glycosides showed IC50 values of 3.8 and 6.2 micromolar respectively. These results provide the first systematic chemical characterisation of bioactive constituents from North Central Nigerian Vitex doniana bark, validate its traditional antiplasmodial use at the molecular level, and lay the foundation for future in vivo pharmacological studies and potential drug development efforts.

Keywords: Vitex doniana, bioactive compounds, iridoid glycosides, structural elucidation, antiplasmodial activity