Targeted discovery of diterpene compounds ostamycins with anti-influenza a viral activity from a deepsea-derived Streptomyces strain.

Heterologous expression of a nonconventional terpene biosynthetic gene cluster from the deepsea-derived Streptomyces amphotericinicus DS22-01 led to the production of a novel cyclic diterpene, ostamycin A (1). Anti-influenza A virus activity evaluation revealed that compound 1 showed significant activity with an IC50 value of 4.72 μM, which was much stronger than that of the positive control ribavirin (IC50 = 20.80 μM). Inspired by its intriguing activity, yield optimization was achieved through a combined approach involving promoter engineering and codon modification in a stepwise manner. This strategy led to a ∼ 13-fold increase in the production of ostamycin A (1), as well as the concurrent accumulation of another novel cyclic diterpene, ostamycin B (2), which also displayed anti-influenza A virus activity with an IC50 value of 195.59 μM. The planar structures and stereochemistry of compounds 1 and 2 were established through extensive MS and NMR spectroscopic analyses together with ECD calculations. Further investigations revealed that compound 1 inhibits the influenza A virus (A/Puerto Rico/8/34) replication by directly targeting the nucleoprotein (NP). These findings highlight compound 1 as a promising lead for the development of novel influenza virus inhibitors.