1. G. Cimino, S. De Stefano andL. Minale, Tetrahedron, in press.
2. The sponges, collected in the Bay of Naples, were obtained from the supply department of the Zoological Station (Naples).
3. The value of the chemical shift (δ 2.16) for Me on C-3 (formula5) established the stereochemistry of the 2, 3 double bond. SeeS. Bory, M. Fétizon andP. Laszlo, Bull. chem. Soc. Fr.1963, 2310 and references therein.
4. IR-spectra were determined with a Perkin-Elmer 257 Infracord spectrophotometer; NMR-spectra were recorded in CCl4 solutions (unless otherwise indicated) on a Varian HA-100 apparatus operating at 100 MHz with TMS as internal standard. Mass spectra were recorded on an A.E.I. MS-9 spectrometer. We are grateful to Mc.C. Di Pinto of our laboratory for NMR-measurements.
5. A. Caliezi andH. Schinz, Helv. chim. Acta33, 1129 (1950). —C. Collin-Asselineau, E. Lederer andJ. Polonsky, Bull. Soc. chim.17, 715 (1950).