LAUSR

Previous chemical investigations of the genus Menella (Plexauridae) of gorgonian corals have shown that the main chemical components of the genus are sesquiterpenoids and steroids [1, 2], and some of these compounds were shown to possess antitumor and anti-inflammatory properties. However, there are only a few reports on the bioactive secondary metabolites obtained from Menella kanisa, which belongs to the genus Menella [3, 4]. In our continuing investigations of bioactive compounds from M. kanisa, we have reported on some diketopiperazines and highly oxygenated guaiane lactones [5, 6]. Further search for bioactive secondary metabolites from this specimen have led to the isolation of a new antifouling secondary metabolite, kanaphthalene (1). Herein, we describe the isolation, structure elucidation, and antifouling activity of the new isolate. The M. kanisa was collected from Xieyang Island of Beibu Gulf, P. R. China, in Octorber, 2010. The specimen was identified by Dr. Xiubao Li. A voucher specimen (No. 20100401) was deposited in the Guangxi Key Laboratory of Marine Environmental Science, Guangxi Academy of Sciences, China. The M. kanisa (3 kg, wet, wt) was extracted with ethanol (95%). Ethanol was evaporated in vacuo to afford a syrupy residue, which was suspended in distilled water and fractionated successively with petroleum ether, ethylacetate, and n-butanol. The ethyl acetate fraction was subjected to column chromatography with silica gel, Sephadex LH-20, and HPLC to yield a new naphthalene derivative, kanaphthaleneA (1). Compound 1, a yellowish powder, was established as C20H32N2O4 (six units of unsaturation) based on the HR-ESI-MS ([M + H]+ at m/z 365.1956, calcd for C20H33N2O4, 365.1959; [M + Na]+ at m/z 387.1782, calcd for C20H32N2NaO4, 387.1778). The 13C NMR data for 1 confirmed the presence of 20 carbon signals, characterized by DEPT as one methyl, eight sp3 methylenes, one sp2 methylene, two sp3 methines, three sp2 methines, two sp3 quaternary carbons, and three sp2 quaternary carbons. The above information, in combination with the molecular formula, indicated a dicyclic molecule. From the 1H–1H COSY spectrum of 1, it was possible to differentiate between the separate spin systems of H2-1/H2-2/H-3/H-4/H-5/H2-6/H2-7, H-3 /H2-4 , and H2-7 /H-8 /H2-9 . These data, together with the key HMBC correlations between H3-11/C-1, C-9; H2-5/C-3 and C-9; H2-12/C-9; H-1 /C-9 and C-3 ; H-3 /C-9 and C-5 ; and H2-7 /C-5 , permitted the elucidation of the carbon skeleton of 1. The configuration of C-5, C-9, and C-10 in compound 1 was determined by the optical rotation, CD, and NOESY spectrum. In the NOESY spectrum, H3-11 exhibited a correlation with H-1 but not with H-5, which indicated that H3-11 and H-1 were situated on the same face and assigned as protons.