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, 15 alpha,16 alpha-dimethoxy-15,16-dihydroepispongiatriol (4) and 15 alpha-ethoxyepispongiatrio1-16(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 mu M.