New 3,4- seco -3,19-Dinor- and Spongian-Based Diterpenoid Lactones from the Marine Sponge Spongia sp.

Continuing chemical investigation of the Red Sea sponge Spongia sp. led to the isolation of four new 3,4- seco -3,19-dinorspongian diterpenoid lactones, secodinorspongins A-D ( 1 - 4 ), along with a classical spongian diterpenoid lactone, sponginolide ( 5 ). The chemical structures, including the absolute configurations of these compounds, were elucidated using the extensive spectroscopic study composed of 1D and 2D NMR data analyses, and a comparison between calculated-electronic-circular-dichroism (ECD) and experimental-circular-dichroism (CD) spectra. A plausible biosynthetic pathway of 1 - 4 was also proposed. Furthermore, the cytotoxicity, antibacterial and anti-inflammatory activities of 1 - 5 were evaluated. Compound 1 was found to exhibit inhibitory activity against the growth of Staphylococcus aureus ( S. aureus ), and 4 and 5 exhibited suppression of superoxide-anion generation and elastase release in fMLF/CB-induced human neutrophils.