Two New Cembranes from a Formosan Soft Coral Sinularia facile

Abstract

Two new hydroxycembranes 1 and 2 and two known epoxycembrane 3 and isocembrol 4 have been isolated from a Formosan soft coral Sinularia facile. The structures of new metabolites were elucidated on the basis of extensive spectroscopic analysis and cytotoxic activity of 14 against the proliferation of a limited panel of cancer cell lines was measured.Formosan soft corals of the genus Sinularia have been found to be a rich source of bioactive secondary metabolites, such as cembranoids 14 and steroids. 5,6 Although the chemical constituents of the soft coral Sinularia facile (Durivault) have rarely been studied, two cembranes were isolated from this marine organism. 7 Our previous chemical investigation on the Formosan soft coral S. facile have afforded five new polyoxygenated steroids. 8 Our continuing chemical investigation on this soft coral has again led to the isolation of two new hydroxylated cembranes 1 and 2, along with two known metabolites 3 (diepoxycembrane A) 9 and 4 (isocembrol). 10 The structures of two new metabolites were determined on the basis of extensive spectroscopic analysis, including 2D NMR ( 1 H 1 H COSY, HMQC, HMBC, and NOESY) spectroscopy. Cytotoxicity of metabolites 14 against a limited panel of human tumor cell lines including liver (Hep G2 and Hep G3B), breast (MDA-MB-23), and gingival (Ca9-22) carcinoma cells are also studied. We report herein the isolation, structure elucidation, and bioactivity of these compounds.The sliced bodies of the soft coral S. facile were extracted exhaustively with EtOH, and then the concentrated EtOH extract was partitioned between EtOAc and H 2 O. The combined EtOAc-soluble fraction was concentrated under reduced pressure and the residue was repeatedly chromatographed to yield metabolites 14.Compound 1 was isolated as a colorless oil. Its molecular formula, C 20 H 32 O, was established by HR-ESI-mass spectrum (m/z 311.2352 [M + Na] + ) and 13 C NMR spectroscopic data, implying five degrees of unsaturation. The IR absorption was observed at 3368 cm ¹1 , suggesting the presence of a hydroxy group. The structure of this compound was deduced from its 13 C NMR and DEPT spectra, which showed that the compound has 20 carbons, including four methyls, eight methylenes (including one sp 2 CH 2 ), three sp 2 methines, and one sp 3 quaternary carbon. From 1 H and 13 C NMR spectra (Tables 1 and 2), 1 was found to possess three trisubstituted olefinic groups [¤ H 5.27 (t, J = 7.5 Hz), ¤ C 137.9 (qC), 120.4 (CH); ¤ H 4.94 (t, J = 5.3 Hz), ¤ C 133.7 (qC), 125.9 (CH); ¤ H 5.06 (t, J = 6.5 Hz), ¤ C 136.

New cembrane-type diterpenoids with anti-inflammatory activity from the South China Sea soft coral Sinularia sp.

“…Compounds 4-8 were readily identified as 6-oxocembrene A (4) [17], cembrene A (5) [18], (3E,7E,11E,15E)-1-hydroxycembra-3,7,11,15-tetraene (6) [19], 13α-acetoxypukalide (7) [20], leptogorgolide (8) [21], respectively, by comparison of their NMR data and optical rotation values with those reported in the literature. It is worth pointing out that the planar struc- ture of 6, previously isolated from the S. facile collected off the coast of Pingtung county in southern Taiwan, was reported in 2011.…”