A. I. Kalinovskii, and V. A. StonikThe chemical composition of the EtOH extract of the nudibranch mollusk Phyllidiella pustulosa was studied. Six sesquiterpenoids including the novel secondary metabolite (+)-10(R)-isothiocyanoalloaromodendrane were isolated. The steroid composition of the extract was studied. The structures of three previously known ketosteroids and six sterols were identified.Nudibranch mollusks of the family Phyllidiidae are commonly known to be sources of various toxic sesquiterpenoids containing cyanate, isocyanate, thiocyanate, and isothiocyanate groups [1]. Secondary metabolites from populations of these animals collected along the shores of China [2], Fiji [3], the Philippines [4], Japan [5-9], and Australia [10] have been previously studied. These soft mollusks lack shells and feed on sponges. They use certain compounds ingested with their food for chemical protection against predators. Several compounds isolated from them exhibit various types of biological activity in addition to a deterrant action. These include antimicrobial [11], antifouling [9], antifungal [5], and antimalarial [3]. The qualitative and quantitative contents of secondary metabolites in extracts of nudibranch mollusks are known to depend on the time, site, and food source of the animals [1,12].Seven sesquiterpenoids including the new isothiocyanate 1 were isolated by chromatographic methods from the extract of Phyllidiella pustulosa collected during cruise O34 of RS Akademik Oparin off the shores of Vietnam.The structure and stereochemistry of 1 were determined by PMR and 13 C NMR spectroscopy (including NOESY, HMBC, and HMQC experiments), mass spectrometry, and comparision of the results with the literature. NMR spectra of 1 were identical to those of the previously known semisynthetic (-)-1S,4R,5R,6S,7R,10S-isothiocyanoalloaromadendrane [13]. However, its optical rotation [D] D 20 +6.0° (c 0.15, CHCl 3 ) turned out to be close but opposite in sign to that of (-)-alloaromadendrane {[D] D 20 -5.9° (c 2.10, CHCl 3 )}. Therefore, 1 had the absolute configuration 1R,4S,5S,6R,7S,10R and was an enantiomer of the synthetic product.In addition to 1, we isolated and identified the structures of previously known sesquiterpenoids. The major metabolite was the isocyanate 2; a minor one, isothiocyanate 3, which is related to it. Both metabolites were found earlier in the sponge Acanthella acuta [14]. The inseparable mixture of 4a-4b (1:1) obtained by us turned out to be identical to a mixture of these Pacific Institute of Bioorganic Chemistry, Far-East Branch, Russian Academy of Sciences, 690022, Vladivostok, Russia, fax 7(4232) 31 40 50,
