Ent-atisane diterpenoids from Euphorbia wallichii and their anti-influenza A virus activity

The study entailed the investigation of the roots of Euphorbia wallichii, which resulted in the isolation of 29 ent-atisane diterpenoids (1-29), 14 of which were previously unknown. These previously undescribed ones were named euphorwanoids A-N (3-5, 7, 9, and 10-18). Various techniques, including comprehensive spectroscopic methods and calculated electronic circular dichroism, were employed to determine their molecular structures. Additionally, the absolute configurations of ten ent-atisane diterpenoids (1, 2, 5, 6, 8, 9, 11, 12, 14 and 16) were established through X-ray crystallographic analyses. All isolated compounds' potential to inhibit the influenza A virus in vitro were evaluated. Compounds 18, 20, and 24 exhibited notable antiviral activity against the A/Puerto Rico/8/1934 strain. Their effective concentrations for reducing viral activity (EC₅₀ values) were found to be 8.56, 1.22, and 4.97 μM, respectively. An intriguing aspect of this research is that it marks the first instance of ent-atisane diterpenes displaying anti-H1N1 activity. Empirical NMR rules were established with Δδ to distinguish the R/S configurations of C-13 and C-16 in ent-atisanes.