Isolation and characterization of antiplasmodial and antimicrobial compounds from Tetracera alnifolia using a bioassay-guided approach

Abstract

A preliminary biological screening demonstrated that leaf extracts from Tetracera alnifolia exhibit promising activity against Plasmodium falciparum and Candida albicans. To identify the constituents responsible for these effects, a bioassay-guided fractionation strategy was subsequently employed. Fractions were purified using flash chromatography, followed by semi-preparative HPLC-DAD-MS and LC-SPE-NMR. Structural elucidation of the isolated compounds was accomplished through comprehensive 1D and 2D NMR analyses in combination with HR-ESI-MS. The purified metabolites were subsequently evaluated for their bioactivity against Plasmodium falciparum and Candida albicans, and their cytotoxicity was assessed in MRC-5_SV2 human foetal lung fibroblast cells. In total, nineteen compounds (1–19) were isolated from T. alnifolia leaves. Among these, the strongest antiplasmodial activities were observed for pheophorbide-b methyl ester (1.0 ± 0.7 µM), (1,2)-bis-nor-phytone (2.0 µM), isophytol (4.0 µM), pheophorbide-a methyl ester (2.8 ± 1.2 µM), epicatechin-3-galloyl ester (5.5 ± 2.1 µM), and phytol (6.9 ± 2.4 µM). Other compounds, including myricetin-3-O-rhamnopyranoside, α-tocopherol and cycloart-24-en-3β-yl α-linolenate, exhibited lower activity, with IC₅₀ values ranging from 13.5 to 25 µM. None of the evaluated compounds showed antifungal activity against C. albicans. Notably, high cytotoxicity was observed for pheophorbide-b methyl ester, pheophorbide-a methyl ester, and phytol. These findings provide insight into the constituents that underlie the antiplasmodial activity of T. alnifolia leaf extracts.