Antiviral activities of purified compounds from Youngia japonica (L.) DC (Asteraceae, Compositae)

The ethanol extract of a biannual medicinal herb, Youngia japonica (commonly known as Oriental hawk's beard) was reported previously to have potent antiviral activity against respiratory syncytial virus (RSV) cultured in HEp-2 cells. Three anti-microbial agents, namely 3,4-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid, and luteolin-7-O-glucoside were subsequently purified and chemically characterized from the ethanol extract of Youngia japonica. The two dicaffeoylquinic acids exhibited prominent anti-RSV with 50% inhibitory concentration (IC50) of 0.5 μg/ml in vitro. Luteolin-7-O-glucoside together with the two dicaffeoylquinic acids were also manifested to have some antibacterial activity towards the causal agents of food-borne disease, namely Vibrio cholerae and Vibrio parahaemolyticus at the concentration of 2 mg/ml. Bacillus cereus was sensitive to 3,4-dicaffeoylquinic acid and 3,5-dicaffeoylquinic acid only, but not to luteolin-7-O-glucoside.