We have investigated the chemical constituents of the organic extracts of soft coral Lobophytum crassum, collected at Dongsha Atoll. This study has led to the isolation of eight new compounds, including six cembrane-type diterpenoids 1-6 and two a-tocopherol-type compounds 7 and 8 The chemical structures of compounds 1-8 were elucidated by extensive analysis of 1D, 2D NMR spectroscopic data (1H and 13C NMR¡B1H-1H COSY¡BHSQC¡BHMBC¡BNOESY), UV, IR, CD and MS. Compounds 1 and 6 possess unprecedented diterpenoid skeletons. The absolute configurations of compound 1 were determined using a modified Mosher¡¦s method. Compounds 1-8 were tested against A-549 (human lung epithelial carcinoma)¡BHT-29 (human colon adenocarcinoma)¡BP-388 (mouse lymphocytic leukemia) tumor cell lines. Compounds 1, 7, and 8 displayed modest cytotoxicity against P-388 cell line with ED50 values of 3.2, 3.2, and 2.7 £gg/mL, respectively. Compound 8 exhibited marginal cytotoxicity against H-29 cell line with an ED50 value of 3.9 £gg/mL.

Marine invertebrate have been found to be a rich source of bioactive secondary metabolites. During the course of our investigation on the bioactive chemical constituents from marine invertebrates, twenty-eight metabolites have been isolated from two soft coral Lobophytum crassum and Dendronephthya griffini. Investigation on L. crassum has led to the isolation of fourteen compounds, including seven new cembranoids, crassumolides A¡VG (1¡V7), and three new glycolipids (2R)-1-hydroxy -3-hexadecyloxy-propyl-£]-D-arabinopyranoside (8), (2R)-1-hydroxy-3- octadecyloxy-propyl-£]-D-arabinopyranoside (9), and (2R)-1-acetoxy-3- hexadecyloxy-propyl-£]-D-arabino-pyranoside (10), coupled with four known compounds, lobohedleolide (11), 17-dimethylaminolobohedleolide (12), sinulariol A (13), and denticulatolide (14). Ten new steroids, griffinisterones A¡VJ (15¡V24), were isolated from the soft coral D. griffini, while a known, 15-chlorogriffinsulfate (25), and three new polychlorinated acyclic compounds¡Agriffinsulfate (26), 15-chlorogriffinol (27), and griffinol (28), were also purified from the same organism. Structures of these metabolites were identified as new natural products by extensive spectroscopic methods. Except for the use of 2D NMR, the 24-epimers of 15 and 16 were identified by a single-crystal X-ray crystallography on 15. Lobohedleolide (11), obtained in large quantity in L. crassum, has also been modified to 29¡V34 by chemical conversion. Oxidation with meta-chloro-peroxybenzoic acid (MCPBA) afforded compounds 29 and 30, and with selenium dioxide led to the formation of 31. Compound 34 is the product of O-coupling reaction of 11 with 1-hydroxybenzotriazole (HOBt). Over 99¢Mdiastereoselectivity was observed in the process of Henbest hydroxyl-directed epoxidation on 11 to yield 32. EDC-coupling with an aid of HCl salt of DMAP afforded methylester 33 in high yield, and proved the absolute stereochemistry of 3. The cytotoxicity and anti-inflammatory activities of the natural and modified compounds were also discussed herein.