Chemical constituents and anti-influenza viral activity of the leaves of vietnamese plant Elaeocarpus tonkinensis

Various Elaeocarpus species including Elaeocarpus tonkinensis have been important medicinal plants that used in traditional medication system and mainly used to cure nervous system-related disorders. However, their antiviral potential has not been reported yet. During the screening of medicinal plant extracts with the antiviral activity against influenza viruses, we found that E. tonkinensis extract has strong antiviral activity. Through organic solvent partition and repeated column chromatography using SiO₂, C-18 and Sephadex LH-20, a total of nine compounds were purified from the methanol extract of E. tonkinensis. Their chemical structures were determined by NMR and MS spectral data to be trolliamide (1), gallic acid (2), urolithin M-5 (3), hydroquinone (4), 2,4-dihydroxybenzoic acid (5), 3,5-dihydroxy-4-methoxybenzoic acid (6), corilagin (7), chebulagic acid (8), and shikimic acid (9). Their antiviral activity against influenza virus strains A/Puerto Rico/8/34 (H1N1; PR8), A/Hong Kong/8/68 (H3N2; HK) and B/Lee/40 (Lee) was examined on the basis of cytopathic effect (CPE) assay. Among them, compounds 2, 3, 4, 7, and 8 significantly inhibited viral replication in a dose-dependent manner with EC₅₀ values ranging from 7.8 to 59.6 μg/mL against influenza A and/or B viruses with selectivity indices above 5.0. This study suggests that the botanical materials of E. tonkinensis could be promising inhibitors of influenza A and B viruses and applied to the development of a novel herbal medicine.