Integrating Biology and Phytochemistry to Identify Antiparasitic Natural Products from Gardenia imperialis K. Schum (Rubiaceae)

Background Gardenia imperialis is used in Cameroonian traditional medicine to treat malaria and related symptoms. This study aimed to conduct a phytochemical investigation of G. imperialis extracts through bioassay-guided fractionation to identify anti-parasitic compounds. Methods Crude methanolic extracts from the leaves and stem bark were subjected to bioassay-guided fractionation using liquid chromatography–mass spectrometry (LC–MS) and preparative high-performance liquid chromatography (HPLC). The structures of isolated natural products were elucidated by spectroscopic analysis, including NMR and MS. All extracts, fractions, subfractions, and pure compounds were evaluated for cytotoxicity against Vero and Raw264.7 cell lines and for anti-parasitic activity against Plasmodium falciparum (Dd2 and 3D7 strains), Trypanosoma brucei brucei , and Leishmania donovani . Results The leaf methanolic extract (GIlMeOH) exhibited broad-spectrum anti-parasitic activity (IC₅₀ < 11 µg/mL) without cytotoxicity towards mammalian cell lines. Dereplication and isolation yielded fractions, subfractions, and compounds with improved activity (IC₅₀ values ranging from 0.67 to 37.2 µg/mL). Among the isolated compounds, gradenin A, salvigenin, hispidulin, and 5,7,3’-trihydroxy-6,4’,5’-trimethoxyflavone showed potent antitrypanosomal activity with IC₅₀ values of 2.8, 2.5, 16.6, and 9.7 µg/mL, respectively. The anti-parasitic activities of gradenin A, salvigenin, and 5,7,3’-trihydroxy-6,4’,5’-trimethoxyflavone are reported here for the first time. Conclusion The promising anti-parasitic profile of the G. imperialis leaf extract and its isolated constituents, particularly and 5,7,3’-trihydroxy-6,4’,5’-trimethoxyflavone, gradenin A, and salvigenin, supports further investigation into their potential as novel and selective agents against parasitic diseases.