Sinulodurins A and B, Antiproliferative and Anti-invasive Diterpenes from the Soft Coral Sinularia dura Mohamed M. Radwan, † Susan P. Manly, † Khalid A. El Sayed, § Vikram B. Wali, § Paul W. Sylvester, § Bhushan Awate, § Girish Shah, § and Samir A. Ross* ,†,‡ National Center for Natural Products Research and Department of Pharmacognosy, School of Pharmacy, UniVersity of Mississippi, UniVersity, Mississippi 38677-1848, and Department of Basic Pharmaceutical Sciences, College of Pharmacy, UniVersity of Louisiana at Monroe, 700 UniVersity AVenue, Monroe, Louisiana ReceiVed April 1, 2008 Two new diterpenes, sinulodurin A (1) and sinulodurin B (2), along with two known sterols, 24S-methyl cholesterol and 24-methylene cholesterol, were isolated from the Palau soft coral Sinularia dura. The structures of the new metabolites were determined on the basis of spectroscopic methods and by comparison of NMR data with those of related metabolites. Sinulodurin A (1) and sinulodurin B (2) showed antiproliferative activity against highly malignant +SA mammary epithelial cells with an IC 50 range of 20-30 µM. They also displayed anti-invasive activity against human highly metastatic prostate cancer PC-3M-CT+ cells in the spheroid disaggregation assay. Furthermore, the antimicrobial activities of the isolates were tested. Soft coral of the genus Sinularia has been found to be a rich source of diterpenes belonging to cembranoide, 1–5 norcembranoid, 6,7 and amphilectane skeletal classes. 8 Many of these compounds were reported to possess cytotoxic, 3,5,8 anti-inflammatory, 4,9,10 and antimicrobial 11 activities. The chemistry and the bioactivity of the genus Sinularia have been reviewed by Kamel et al. 12 Previous work on Sinularia dura resulted in the isolation of the known cembranoid epoxypukalide and sindurol, a hydroquinone deriva- tive. 1 In the course of our study of biologically active secondary metabolites from marine organisms, 13 we have undertaken the chemical examination of the soft coral Sinularia dura. In this paper the details of isolation and structure elucidation of two new diterpenes, sinulodurin A (1) and sinulodurin B (2), as well as two known sterols, 24S-methyl cholesterol and 24-methylene cholesterol, are discussed together with their biological properties. Sinulodurin A(1) and sinulodurin B (2) showed antiproliferative and anti- invasive activities. Sinulodurin A (1) was obtained as a colorless oil, [R] D +91.3 (c 0.25, CHCl 3 ), and showed a pseudomolecular ion peak at m/z 425.2326 [M + Na] + in the HRESIMS, indicating the molecular formula C 24 H 34 O 5 and eight degrees of unsaturation. The IR spectrum displayed a characteristic absorbance for an R,-unsatur- ated ketone (1640 cm -1 ), which was confirmed by a UV absorbance band at λ max 239 nm (calcd 239 nm). 14 The IR spectrum also showed an ester carbonyl absorbance at ν max 1736 cm -1 . The 1 H NMR spectrum (Table 1) showed the presence of two olefinic protons (δ H 6.03 and 6.08, 1H each, s), an exocyclic methylene (δ H 4.73, 2H, brs), two vinyl methyls (δ H 1.94, 2.18, 3H each, s), two secondary methyls [δ H 0.99 (3H, d, J ) 7.0 Hz), 1.03 (3H, d, J ) 7.0 Hz)], two oxymethines [δ H 4.81 (1H, brs), 5.19 (1H, td, J ) 4.0, 12.8 Hz)], and two acetoxy methyl singlets resonating at δ H 2.05 and 2.14. The 13 C, DEPT-135, and HMQC NMR data (Table 1) displayed 24 resonances assigned to six methyl, four methylene, eight methine, and six quaternary carbons, of which three resonances are assigned to an R,-unsaturated (δ C 197.2 ppm) and two ester carbonyls (δ C 170.6, 170.4, 22.0, 21.1 ppm). Taking into account the eight degrees of unsaturation inferred from the molecular formula and the six degrees of unsaturation corresponding to three olefinic bonds and three carbonyl groups, sinulodurin A had to have a bicyclic structure. From the 2D COSY and HMBC spectra (Figure 1) as well as comparison of the NMR data of 1 (Table 1) with those reported for compounds 3 and 4, the related diterpenes previously isolated from Pseudopterogorgia elisabethae, 15,16 the structure of sinulodurin A (1) should be similar to 3 except for the absence of a hydroxyl group at C-7, the presence of a R,- unsaturated ketone at C-13, and two acetoxy groups at C-2 and C-12. The configurations at C-1, C-4, and C-9 were determined by comparing their 13 C NMR and proton-proton coupling constants with 3 and 4 (Table 1) and confirmed by ROESY correlations. 15,16 The S configuration of C-9 was based on matching its 13 C NMR chemical shift data (δ C 36.8) with C-9 of 3 (δ C 38.7), unlike the C-9R in 4 (δ C 49.9). 15,16 The -oriented proton H-9 (δ H 2.43) showed ROESY correlations with H-4 (δ H 2.58) and H 3 -20 (δ H 0.99), suggesting similar stereo-orientation. Similarly, protons H-1 and H-2 were found to be R-oriented. Despite the -substitution upfield shifting effect of the C-12 acetoxy, the downfield shifting of C-11 (δ C 50.7) in 1 compared to those of 3 (δ C 32.4) and 4 (δ C 35.5) (Table 1) suggested opposite configurations. Therefore, C-11 in 1 was proved to be in the S configuration. The 13 C NMR data similarity of 1 with those reported for sinulobatin A (an amphi- lectane-type diterpene previously isolated from Sinularia nanolo- bat), 8 support the assumption that 1 could be a biosynthetic intermediate for the amphelectane sinulobatin A. 16 The configu- ration at C-12 was not determined due to insufficiency of the compound (0.8 mg) left after running the bioactivity assay. Sinulodurin B (2) was isolated as a colorless oil, [R] D +110.7 (c 0.25, CHCl 3 ). Its molecular formula C 22 H 32 O 3 was determined * To whom correspondence should be addressed. Tel: +1-662-915-1031. Fax: +1-662-915-7989. E-mail: sross@olemiss.edu. † National Center for Natural Products Research. ‡ Department of Pharmacognosy, University of Mississippi. § University of Louisiana at Monroe. J. Nat. Prod. 2008, 71, 1468–1471 1468 10.1021/np800208k CCC: $40.75  2008 American Chemical Society and American Society of Pharmacognosy Published on Web 07/17/2008