In Vitro Antitrypanosomal Activity and Molecular Docking Studies of the Constituents of the Dichloromethane Fraction of Talbotiella Gentii Stem Bark

Abstract

Trypanosomiasis remains a major neglected tropical disease, with existing therapies limited by toxicity, drug resistance, and poor accessibility in endemic regions, emphasizing the need for safer chemotherapeutic agents from natural sources. This study investigated Talbotiella gentii Hutch. & Greenway (Fabaceae-Detarioideae), a critically endangered Ghanaian plant traditionally used to manage stomach disorders, to determine whether it contains phytoconstituents with antitrypanosomal potential. The research was guided by the hypothesis that some of its bioactive compounds possess antiparasitic properties capable of inhibiting key Trypanosoma brucei enzymes. The dichloromethane (DCM) stem bark extract was subjected to chromatographic separation and spectroscopic analysis, yielding three known compounds, friedelan-3-one (friedelin), lup-20(29)-en-3β-ol (lupeol), and a sterol mixture containing stigmast-5-en-3β-ol (β sitosterol) and (22E)-stigmasta-5,22-dien-3β-ol (stigmasterol), as well as a semi-synthetic derivative, lup-20(29)-en-3β-yl acetate (lupeol acetate). In vitro assays on the isolates against Trypanosoma brucei brucei using the Alamar Blue method revealed that lupeol acetate exhibited the highest potency (IC50 = 2.9 µg/mL), followed by lupeol (IC50 = 3.5 µg/mL), the sterol mixture (IC50 = 13.9 µg/mL), and friedelin (IC50 = 45.5 µg/mL), relative to diminazene aceturate (IC50 = 0.05 µg/mL). The docking results showed that all compounds demonstrated significant binding to TbDHFR, with binding energies ranging from -10.8 to -8.7 kcal/mol, surpassing those of reference inhibitors cycloguanil and pyrimethamine (-8.0 and -7.2 kcal/mol, respectively). Additionally, all compounds displayed strong binding affinities for TbPTR1, with binding scores ranging from 11.2 to -9.0 kcal/mol, which were superior to the standard inhibitor. These results suggest that the compounds may inhibit both enzymes, thereby contributing to their observed antitrypanosomal activity by potential mechanisms of action through DHFR and PTR1 inhibition. These findings provide a scientific basis for the traditional use of T. gentii and constitute the first report on its phytochemical and antitrypanosomal profile, highlighting lupeol and lupeol acetate as a promising lead scaffolds. The results enhance understanding of triterpenoid and sterol structure–activity relationships and underscore the potential of Fabaceae-derived metabolites as templates for developing safer and affordable antitrypanosomal drugs.