Discovery of Ircinianin Lactones B and C-Two New Cyclic Sesterterpenes from the Marine Sponge Ircinia wistarii .

Two new ircinianin-type sesterterpenoids, ircinianin lactone B and ircinianin lactone C ( 7 and 8 ), together with five known entities from the ircinianin compound family ( 1 , 3 - 6 ) were isolated from the marine sponge Ircinia wistarii . Ircinianin lactones B and C ( 7 and 8 ) represent new ircinianin terpenoids with a modified oxidation pattern. Despite their labile nature, the structures could be established using a combination of spectroscopic data, including HRESIMS and 1D/2D NMR techniques, as well as computational chemistry and quantum-mechanical calculations. In a broad screening approach for biological activity, the class-defining compound ircinianin ( 1 ) showed moderate antiprotozoal activity against Plasmodium falciparum (IC 50 25.4 μM) and Leishmania donovani (IC 50 16.6 μM).