Spongian Diterpenes Including One with a Rearranged Skeleton from the Marine Sponge Spongia officinalis

Five new diterpenes, including an unprecedented 5,5,6,6,5-pentacyclic diterpene, sponalactone (1), two new spongian diterpenes, 17-O-acetylepispongiatriol (2) and 17-O-acetylspongiatriol (3), and two new spongian diterpene artifacts, 15α,16α-dimethoxy-15,16-dihydroepispongiatriol (4) and 15α-ethoxyepispongiatriol-16(15H)-one (5), were isolated from a South China Sea collection of the marine sponge Spongia officinalis, together with three known analogues (6–8). The structures of the new diterpenes were elucidated by extensive spectroscopic analysis. The absolute configurations were established on the basis of ECD data. Compounds 1–5 and 7 exhibited moderate inhibition against LPS-induced NO production in RAW264.7 macrophages with IC50 values of 12–32 μM.