Discovery of Cyclic Diarylheptanoids as Inhibitors against Influenza A Virus from the Roots of Casuarina equisetifolia .

Four new cyclic diarylheptanoids, casuarinols A-C ( 1 - 3 ) and casuarinolide A ( 4 ), together with six known ones ( 5 - 10 ), were isolated from the roots of Casuarina equisetifolia . Structures were elucidated by extensive spectroscopic analysis, theoretical conformational, and electronic circular dichroism analyses. Casuarinol C ( 3 ) is a novel cyclic diarylheptanoid-aldehyde adduct. Casuarinolide A ( 4 ) represents the first structure of a seco -cyclic diarylheptanoid. Compounds 1 - 9 were evaluated for their anti-influenza A virus (IAV) activity against A/WSN/33 (H1N1). (-)-( M )-11-Oxo-3,12 R ,17-trihydroxy-9-ene-[7,0]-metacyclophane ( 5 ) displayed significant anti-IAV activity with an IC 50 value of 8.64 ± 2.49 μM and a CC 50 higher than 100 μM.