MINOR BISNORDITERPENES FROM THE MARINE SPONGE SPONGIONELLA-GRACILIS AND REVISION OF THE DELTA-6 CONFIGURATION OF GRACILIN-B

Two new representatives of the rare class of bisnorditerpenes, gracilin C (I) and D II were isolated as minor metabolites from S. gracilis, a Mediterranean sponge. The structure of these compds., both related to that of gracilin B (III), the major metabolite of S. gracilis, were solved by spectral analyses, including 2-dimensional NMR spectroscopy, and chem. interconversions. The structure of III was revised on the basis of addnl. NOE difference expts. and 13C NMR data