Benzophenone C-glucosides and gallotannins from mango tree stem bark with broad-spectrum anti-viral activity

The high mutation rate of RNA viruses has resulted in limitation of vaccine effectiveness and increased emergence of drug-resistant viruses. New effective antivirals are therefore needed to control of the highly mutative RNA viruses. The n-butanol fraction of the stem bark of Mangifera indica exhibited inhibitory activity against influenza neuraminidase (NA) and coxsackie virus 3C protease. Bioassay guided phytochemical study of M. indica stem bark afforded two new compounds including one benzophenone C-glycoside (4) and one xanthone dimer (7), together with eleven known compounds. The structures of these isolated compounds were elucidated on the basis of spectroscopic evidences and correlated with known compounds. Anti-influenza and anti-coxsackie virus activities were evaluated by determining the inhibition of anti-influenza neuraminidase (NA) from pandemic A/RI/5+/1957 H2N2 influenza A virus and inhibition of coxsackie B3 virus 3C protease, respectively. The highest anti-influenza activity was observed for compounds 8 and 9 with IC50 values of 11.9 and 9.2 μM, respectively. Compounds 8 and 9 were even more potent against coxsackie B3 virus 3C protease, with IC50 values of 1.1 and 2.0 μM, respectively. Compounds 8 and 9 showed weak cytotoxic effect against human hepatocellular carcinoma and human epithelial carcinoma cell lines through MTT assay.