Antiviral flavans from the leaves of Pithecellobium clypearia.

Two new antiviral flavan derivatives were isolated from a methanol extract of leaves of Pithecellobium clypearia as guided by antiviral assays. The structures were characterized, by spectroscopic analyses, as 7-O-galloyltricetifavan (1) and 7,4'-di-O-galloyltricetifavan (2). Cytopathic effect (CPE) reduction assay showed that both compounds 1 and 2 possess antiviral activity against respiratory syncytial virus (RSV), with 50% inhibition concentration (IC(50)) values of 5 and 10 microg/mL, respectively; influenza A (H1N1) virus, with IC(50) values of 15.7 and 30 microg/mL; Coxsackie B3 (Cox B3) virus, with IC(50) values of 12.5 and 25 microg/mL, respectively; and Herpes simplex virus type 1 (HSV-1) with IC(50) values of 30 and 20 microg/mL, respectively. Cytotoxicity evaluation using the MTT assay showed that both compounds 1 and 2 were also moderately toxic to several cultured cell lines.