Strophioblachins A–K, Structurally Intriguing Diterpenoids from Strophioblachia fimbricalyxwith Potential Anticardiac Hypertrophic Inhibitory Activity

Three new rearranged diterpenoids, strophioblachins A–C (1–3), eight new diterpenoids, strophioblachins D–K (4–11), and seven previously described diterpenoids (12–18) were purified from the aerial parts of Strophioblachia fimbricalyx.Compounds 1and 2contain a rare 6/6/5/6 ring system, while 3has an uncommon tricyclo[4.4.0.08,9]tridecane-bridged unit, and their diterpenoid skeletons are being reported for the first time. Utilizing spectroscopic and HRESIMS data analysis, the structures of the new compounds (1–11) were established, and ECD and 13C NMR calculations were used to confirm the relative and absolute configurations of 11and 9. The absolute configurations of compounds 1, 3, and 10were established using single-crystal X-ray diffraction. The results of testing for anticardiac hypertrophic activity demonstrated that compounds 10and 15dose-dependently lowered the mRNA expression of Nppaand Nppb. Protein levels were confirmed by Western blotting, which also demonstrated that compounds 10and 15lowered the expression of the hypertrophic marker ANP. The cytotoxic activity against neonatal rat cardiomyocytes was assayed in vitro by the CCK-8 and ELISA methods, and the results showed that compounds 10and 15were only very weakly active in the range.