FULL PAPER Plakinamines C and D and Three Other New Steroidal Alkaloids from the Sponge Corticium sp. Simona De Marino, [a] Maria Iorizzi, [b] Franco Zollo,* [a] Christos Roussakis, [c] and Ce ´cile Debitus [d] Dedicated to the memory of Professor Luigi Minale, deceased May 11th, 1997 Keywords: Corticium sp. / Steroids / Alkaloids / Secondary metabolites / Cytotoxic activity Five new steroidal alkaloids, plakinamines C (1) and D (2), human bronchopulmonary non-small-cell lung carcinoma cells (NSCLC-N6) with IC 50 values of  3.3–5.7 μg/mL. When and the related compounds 3–5 have been isolated from the Vanuatu sponge Corticium sp. Their structures have been tested against T leukemia virus type one (HTLV-I), compounds 1, 4 and 5 were found to exhibit slight anti-HIV elucidated by a detailed spectroscopic analysis, including 2D-HMBC and ROESY correlation experiments. The new activity. compounds show significant in vitro cytotoxicity against respectively. These fractions were chromatographed and the Introduction components were purified to afford pure compounds 1-5. Steroidal alkaloids are well-known metabolites of certain Plakinamines C (1) and D (2), and the related alkalostero- terrestrial plants, [1] but only a few examples have been re- ids 3-5 bear a skeletal relationship to the previously de- ported from marine organisms. [2,3] scribed plakinamine A. [2] The steroidal nature of 1-5 was As part of a systematic screening of the bioactive com- suggested by comparison with literature data and by pounds from marine organisms, we have examined the mar- NMR experiments. ine sponge Corticium sp., collected off Porth Havannah, Vanuatu, South Pacific, the crude ethanolic extracts of which showed 100% cytotoxic activity towards KB cells at Plakinamine C (1) 10 μg/mL. The first paper on the sponge Corticium sp. dealt Compound 1 showed a molecular ion peak (HREIMS) with the isolation of lokysterolamines A and B, [3] and re- at m/z = 510.4229, corresponding to the molecular formula cently we have described new modified steroidal alkaloids C 33 H 54 N 2 O 2 (calcd. 510.4185). This was further supported with seven-membered B rings obtained from the same by 13 C-NMR data, which, in combination with the COSY sponge. [4] spectrum, clearly indicated the steroidal nature of 1. The 1 H-NMR spectrum in CD 3 OD exhibits two methyl group singlet signals at δ = 0.62 and δ = 0.74, and a methyl dou- Results and Discussion blet at δ = 0.98 (J = 6.8 Hz), which were correlated by HMQC to carbon atom signals at δ = 12.6, 15.3 and 19.6 In this paper we report the isolation and structure eluci- (C-18, C-19 and C-21, respectively). The 13 C-NMR spec- dation of five new steroidal alkaloids 1-5 following a bio- trum also features a signal at δ = 211.8 attributable to a assay-guided fractionation. The methanolic extract of the ketone function. The downfield shift of the C-19 signal is lyophilized sponge Corticium sp. was subjected to Kup- compatible with the ketone carbon atom C-4 of the steroid chan’s partitioning methodology. [5] In preliminary tests on nucleus, and this was corroborated by the chemical shift of the NSCLC-N6 cell line, the active CHCl 3 and nBuOH the 5α-H signal, which was found to be downfield shifted fractions showed IC 50 values < 1.1 μg/mL and < 3.3 μg/mL, at δ = 2.40 by analysis of the COSY spectrum. When the COSY experiment was performed in [D 5 ]pyridine, the 3-H [a] Dipartimento di Chimica delle Sostanze Naturali, Universita ` di Napoli “Federico II”, signal was observed as a doublet of doublets at δ = 3.14 via D. Montesano 49, I-80131 Napoli, Italy (J = 12.0, 5.8 Hz). The 1 H-NMR spectrum (CD 3 OD) also Fax: (internat.) + 39(0)81/748-6552 features a signal at δ = 2.37 (s), corresponding to 6 H, E-mail: fzollo@cds.unina.it [b] Dipartimento di Scienze e Tecnologie Agro-Alimentari, Am- typical for two N-methyl groups. The downfield shift of the bientali e Microbiologiche, Universita ` degli Studi del Molise, C-3 signal (δ = 72.0) suggests a β orientation of the dimeth- via De Sanctis, I-86100 Campobasso, Italy ylamino group; in the corresponding 3α-aminosteroids the [c] Institut des Substances et Organismes de la Mer (ISOMER), Faculte ´ de Pharmacie, 13 C-NMR chemical signal is found at much higher field. [6] 1, Rue Gaston Veil, F-44035 Nantes Cedex 01, France This observation is in agreement with data obtained from [d] ORSTOM, Centre de Noume ´a, B. P. A5, Noume ´a, New Caledonia ROESY experiments in [D 5 ]pyridine, which show a mutual Eur. J. Org. Chem. 1999, 697-701  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 1434-193X/99/0303-0697 $ 17.50+.50/0 697