ABSTRACT
Three novel norsesquiterpenoids, (2R,4S,8aR)-8,8a,1,2,3,4-hexahydro-2-hydroxy-4,8a-dimethyl-2(2H)-naphthalenone (1), (1S,3S,4S,4aS,8aR)-4,8a-dimethyloctahydronaphthalene-1,3,4a(3H)-triol(2), (4S,4aS,8aS)-octahydro-4a-hydroxy-4, 8a-dimethyl-1(2H)-naphthalenone (3), as well as six other known analogues (4-9), were isolated from the culture broth of Streptomyces sp. XM17, an actinobacterial strain inhabiting the fresh feces of the giant panda Ailuropoda melanoleuca. The chemical structures of 1-3 were elucidated comprehensively by NMR spectroscopic and MS analyses, furthermore, the stereochemical configurations were resolved by NOESY experiments, along with ECD spectral and single-crystal X-ray crystallographic analyses. These compounds were then tested for their antiviral activities using the "pretreatment of virus" approach, which showed that most of these compounds were potent in inhibiting the entry of influenza A virus, with IC50 values ranging from 5 to 49 nM and selectivity indices all above 500.