Simultaneous isolation of gallotannins and a related phenolic from Mangifera indica kernels and assessment of their anti-Trichomonas vaginalis activities

Therapeutic alternatives are being searched for trichomoniasis as a result of the increased prevalence of metronidazoleresistant infections. Mangifera indica L. (Anacardiaceae) is an important tree with a long history in medicine. Traditionally, it has been used as an anti-diarrheal and anti-diabetic, and recently, its gallotannin-rich leaves and stem bark extracts have shown antiparasitic activities against various parasites. Aiming at exploring the anti-Trichomonas vaginalis activity of mango's gallotannins, an aqueous ethanol extract of fresh kernels of M. indica was phytochemically investigated. Based on a simple gel chromatographic procedure, ethyl gallate (2), a group of five isomeric tetragalloyl-glucoses (3-7), and a pentagalloylglucose (8) were simultaneously isolated from a single fraction by a preparative Reversed-phase-high performance liquid chromatography. The isolates were identified based on spectroscopic analyses and comparison with reported data. They showed structural-dependent inhibitory effects on the growth of T. vaginalis trophozoites in an in vitro investigation. Ethyl gallate and 1,2,4,6-tetra-O-galloyl-ß-D-glucose (7) exhibited elevated anti-T. vaginalis activity (IC₅₀ = 1.3, 2.4 μg/ml, respectively). This is the first report exploring the potential of gallotannins as trichomonacidal agents.