Spongiains A-C: Three new spongian diterpenes with ring A rearrangement from the marine sponge Spongia sp.

Spongiains A-C (1–3), the first examples of spongian diterpenes bearing a pentacyclic skeleton composed of a fused 5/5/6/6/5 ring system through ring A rearrangement, together with four new spongian diterpenes, spongiains D-G (4–7), were isolated from the marine sponge Spongia sp.. The structures with absolute configurations of these compounds were elucidated by the methods of NMR, X-ray diffraction and quantum chemical approaches. The hypothetical biogenetic pathways as well as cytotoxic activities of 1–7 were also discussed.     

New oxygenated diterpenes from an Australian nudibranch of the genus Chromodoris

Chemical analysis of a chromodorid nudibranch has provided two new diterpene metabolites 1 and 2 together with the known metabolites 3-6. In an NMR study, the dialdehyde metabolite 1 underwent facile conversion to cyclic hemiacetals 8-9 on exposure to methanol, a reaction that mimics chemical conversions that may occur during the isolation of some diterpenes from molluscs and sponges. Compounds 1, 2, 5 and 8 showed moderate cytotoxicity against P388 cells (IC₅₀=1.2-4.1 μg/mL).