Biflavonoids such as amentoflavone (1), agathisflavone (2), robustaflavone (3), hinokiflavone (4), volkensiflavone (5), rhusflavanone (7), succedaneflavanone (9), all isolated from Rhus succedanea and Garcinia multiflora, as well as their methyl ethers and acetates, volkensiflavone hexamethyl ether (6), rhusflavanone hexaacetate (8), and succedaneflavanone hexaacetate (10) were evaluated for their antiviral activities. The inhibitory activities against a number of viruses including respiratory viruses (influenza A, influenza B, respiratory syncytial, parainfluenza type 3, adenovirus type 5, and measles) and herpes viruses (HSV-1, HSV-2, HCMV, and VZV) were investigated. The results indicated that robustaflavone exhibited strong inhibitory effects against influenza A and influenza B viruses with EC50 values of 2.0 micrograms/ml and 0.2 microgram/ml, respectively, and selectivity index values (SI) of 16 and 454, respectively. Amentoflavone and agathisflavone also demonstrated significant activity against influenza A and B viruses. Amentoflavone and robustaflavone exhibited moderate anti-HSV-1 anti-HSV-2 activities with EC50 values of 17.9 micrograms/ml (HSV-1) and 48.0 micrograms/ml (HSV-2) and SI values of > 5.6 (HSV-1) and > 2.1 (HSV-2) for amentoflavone; EC50 values of 8.6 micrograms/ml (HSV-1) and 8.5 micrograms/ml (HSV-2), and SI values of > 11.6 (HSV-1) and > 11.8 (HSV-2) for robustaflavone. Rhusflavanone demonstrated inhibitory activities against influenza B, measles, and HSV-2 viruses with SI values of 9.3, 8 and > 6.4, respectively. Succedaneaflavanone exhibited inhibitory activities against influenza B virus and VZV with SI values of 15 and < 3.0, respectively.
