Identification of Nyasol and structurally related compounds as the active principles from Anemarrhena asphodeloides against respiratory syncytial virus (RSV)

Three known phenolic compounds, (-)-(R)-nyasol (=4,4′-(1Z,3R)-Penta-1,4-diene-1,3-diyldiphenol; 1), its derivative 2, and broussonin A (3) - isolated from the rhizomes of Anemarrhena asphodeloides - were for the first time identified as the active principles capable of efficient respiratory-syncytial-virus (RSV) inhibition. The IC₅₀ values of 1-3 against the RSV-A2 strain, propagated in HEp-2 cells, were determined, their activities being higher than that of the standard antiviral drug ribavirin (IC₅₀ = 1.15 μm). In addition, the known, but inactive, compound 'trans-N-(para-coumaroyl)tyramine' (=(2E)-3-(4-hydroxyphenyl)-N-[2-(4-hydroxyphenyl)ethyl]prop-2-enamide; 4) was isolated from this plant for the first time.