Bioactive diterpene derivatives from the marine sponge Spongionella sp.

Three new compounds of the rare classes trisnorditerpenes, bisnorditerpenes, and norditerpenes, gracilins J-L (1, 2, 6), and a new diterpene, 3'-norspongiolactone (8), were isolated from the extract of the marine sponge Spongionella sp. using NMR- and bioassay-guided fractionation, in addition to three known gracilins (3-5) as well as the known diterpenoid tetrahydroaplysulphurin-1 (7). The structures were elucidated using NMR spectroscopic techniques and mass spectrometric analysis. The structure of gracilin H (3) was confirmed by single-crystal X-ray analysis. All compounds were tested for their cytotoxicity and for their potential to inhibit EGF-R tyrosine kinase.