Ceylonins AâF, Spongian Diterpene Derivatives That Inhibit RANKL

Article pubs.acs.org/jnp

Ceylonins A−F, Spongian Diterpene Derivatives That Inhibit RANKL-Induced Formation of Multinuclear Osteoclasts, from the Marine Sponge Spongia ceylonensis Ahmed H. El-Desoky,† Hikaru Kato,† Ippei Kagiyama,† Yuki Hitora,† Fitje Losung,‡ Remy E. P. Mangindaan,‡ Nicole J. de Voogd,§ and Sachiko Tsukamoto*,† †

Graduate School of Pharmaceutical Sciences, Kumamoto University, Oe-honmachi 5-1, Kumamoto 862-0973, Japan ‡ Faculty of Fisheries and Marine Science, Sam Ratulangi University, Kampus Bahu, Manado 95115, Indonesia § Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, The Netherlands S Supporting Information *

ABSTRACT: Six new spongian diterpene derivatives, ceylonins A−F (1−6), were isolated from the Indonesian marine sponge Spongia ceylonensis along with spongia13(16),14-dien-19-oic acid (7). They contained three additional carbons in ring D to supply an ether-bridged bicyclic ring system. Their structures were elucidated by analyzing NMR spectroscopic data and calculated ECD spectra in comparison to experimental ECD spectra. The bicyclic ring system may be derived from the major metabolite 7 and a C3 unit (an acrylic acid equivalent) through an intermolecular Diels−Alder reaction, which was experimentally supported by the formation of 1−6 from 7 and acrylic acid. The inhibitory effects of the isolated compounds on the RANKL-induced formation of multinuclear osteoclasts in RAW264 macrophages were examined.

■

S

RESULTS AND DISCUSSION In our screening of biologically active natural products, the EtOAc-soluble fraction prepared from S. ceylonensis potently inhibited the RANKL-induced formation of multinuclear osteoclasts in RAW264 cells. Purification of the fraction by SiO2 column chromatography and HPLC afforded six new spongian diterpene derivatives, ceylonins A−F (1−6), in addition to spongia-13(16),14-dien-19-oic acid (7). Ceylonin A (1) was obtained as a white, amorphous solid. HRESITOFMS established its molecular formula as C23H32O5. The 1H and 13C NMR spectra displayed characteristic signals reminiscent of spongian-type diterpenes including three methyl signals [δH 0.93 (s)/δC 20.5 (C-17); δH 1.10 (s)/δC 28.4 (C-18); δH 0.71 (s)/δC 13.9 (C-20)] and two olefinic carbons [δC 135.2 (C-13) and 151.9 (C-14)] (Tables 1 and 2). COSY correlations showed three spin systems, H2-1/H2-2/H2-3, H-5/ H-6/H-7, and H-9/H-11/H-12 (Figure 1). HMBC correlations from H2-11 (δH 1.15 and 1.58), H2-12 (δH 1.89 and 2.08), H3-17, H3-18, and H3-20 (Figure 1) clearly showed that the planar structure of the A/B/C ring system was identical to that of 7. The remaining formula C5H6O3 contained two oxygenated methines [δH 4.80 (d, J = 4.3 Hz)/δC 77.4 (C-15) and δH 4.73 (d, J = 4.9 Hz)/δC 80.6 (C-16)], a methylene [δH 1.85 (dd, J = 11.0, 3.8 Hz) and 1.55 (dd, J = 11.0, 3.2 Hz)/δC 30.4 (C-21)], a methine [δH 2.97 (m)/δC 43.6 (C-22)], and a

pongian diterpenes have mostly been isolated from marine sponges and nudibranches.1−5 These metabolites have attracted the attention of chemists and biologists due to their structural diversity as well as biological activities. Spongian diterpenes were previously reported to exhibit cytotoxic,6−8 antiviral,6 ichthyotoxic,9 antiprotozoal,10 androgen receptor inhibitory,11 phospholipase A2 inhibitory,4 and farnesyl transferase inhibitory12 activities. Spongian diterpenes have a tetracyclic skeleton composed of a fused 6/6/6/5 ring system with the five-membered ring existing as a furan (e.g., spongia13(16),14-dien-19-oic acid13), unsaturated γ-lactone (e.g., 15-oxospongi-13-en-19-oic acid14), or γ-hydroxybutenolide (e.g., spongiabutenolide A15). In addition, after the initial isolation of haumanamide,16 three studies on nitrogenous spongian diterpenes with a γ-lactam ring (e.g., spongolactam A 12 and oxeatamide A 17 ) including our study (ceylonamide A18) have since been published. In our continuing efforts to search for leads from natural sources to prevent or treat osteoporosis,18,19 we isolated six new spongian diterpene derivatives, ceylonins A−F (1−6), from the marine sponge Spongia ceylonensis, collected in Indonesia in 2006. Ceylonins may be derived by an intermolecular Diels−Alder reaction between the furan ring of spongia13(16),14-dien-19-oic acid13 (7), a main metabolite of this sponge, and a C3 unit (an acrylic acid equivalent). We herein describe the isolation, structure elucidation, and possible route of formation of ceylonins as well as their inhibition of the RANKL-induced formation of multinuclear osteoclasts in RAW264 cells. © 2016 American Chemical Society and American Society of Pharmacognosy

Received: August 5, 2016 Published: December 27, 2016 90

DOI: 10.1021/acs.jnatprod.6b00725 J. Nat. Prod. 2017, 80, 90−95

Journal of Natural Products

Article

The planar structures of ceylonins B−D (2−4) were identical to that of 1, which was established by HRESITOFMS and NMR experiments (Tables 1 and 2, Figure S37). The molecular formulas of ceylonins E (5) and F (6) established by HRESITOFMS were identical to those of 1−4. The 1H and 13C NMR spectra of 5 and 6 were almost superimposable on those of 1−4 (Tables 1 and 2). The HMBC correlations of 5, H-15/C-21, C-22, and C-23 and H-21β (δH 1.47)/C-23 (Figure 1), along with the NOE correlation H-12β (δH 2.06)/H-16 clearly indicated that 5 possessed an identical carbon skeleton to those of 1−4, except for the position of the carboxylic acid (C-23) on ring D. An analysis of the 2D NMR spectra of 6 showed the same planar structure as 5. The relative configurations in the A/B/C ring systems of 1−6 were found to be identical to that of 7 by a comparison of their 1H and 13C NMR spectra along with analyses of NOE spectra (Figure 2). The relative configurations of ring D in 1−6 were obtained by coupling constants and NOE spectra. The splitting patterns of H-16 for 1/2 appeared as doublets (J 4.9 Hz), whereas those of H-16 for 3/4 and H-15 for 5/6 were singlets. These results clearly showed that the bridging oxygen and carboxylic acid (C-23) possessed anti and syn configurations for 1/2 and 3−6, respectively. On the other hand, the observed NOE correlations H-17/H-21β and H-7α/ H-21α for 1/3 and 2/4, respectively, indicated the orientations of the bridging oxygens, i.e., α for 1/3 and β for 2/4. Similarly, the bridging oxygens of 5 and 6 were oriented as α and β, respectively, on the basis of NOE correlations H-17/H-22 and H-7α/H-22 (Figure 2), respectively. In order to confirm the absolute configurations of 1−6, we calcu-

carbonyl carbon [δC 172.7 (C-23)]. HMBC cross-peaks, H2-12/C-13 and C-16, H-15/C-13, and H-16/C-14 and C-15, showed that a 2,5-dihydrofuran moiety was fused to the C ring. The spin system H-15/H2-21/H-22/H-16 indicated by a COSY spectrum together with HMBC cross-peaks, H-21β (δH 1.55) and H-22/C-23, showed that the 2,5-dihydrofuran moiety was incorporated into an ether-bridged bicyclic ring with a carboxylic acid at C-22. Thus, the planar structure of 1 was established.

lated the theoretical ECD spectrum of 4S,5R,8R,9R,10R,15S,16R,22S-1

by a standard calculation procedure (Figure 3), although the

Table 1. 1H NMRa Data for 1−6 in DMSO-d6 no. 1α 1β 2α 2β 3α 3β 5 6α 6β 7α 7β 9 11α 11β 12α 12β 15 16 17 18 20 21α 21β 22 COOH a1

1 0.82, 1.70, 1.35, 1.79, 1.98, 0.94, 1.05, 1.74, 1.91, 1.26, 1.90, 0.93, 1.58, 1.15, 1.89, 2.08, 4.80, 4.73, 0.93, 1.10, 0.71, 1.85, 1.55, 2.97, 12.04,

td (13.0, 3.9) brd (13.0) brd (13.9) m brd (12.8) m dd (13.6, 3.2) m m td (13.2, 3.1) m m m dd (12.1, 5.5) m ddd (17.9, 10.9, 6.5) d (4.3) d (4.9) s s s dd (11.0, 3.8) dd (11.0, 3.2) m brs

2 0.71, 1.69, 1.33, 1.80, 1.99, 0.94, 0.98, 1.72, 1.94, 1.17, 1.70, 0.85, 1.60, 1.28, 1.73, 2.22, 4.87, 4.69, 1.06, 1.10, 0.72, 1.56, 1.88, 2.98, b

m m brd (13.7) dt (13.7, 3.5) brd (13.0) td (13.0, 3.9) d (12.9) m d (13.4) td (12.5, 2.8) m d (11.8) dd (12.1, 6.4) dd (12.1, 5.4) m dd (17.1, 5.0) d (4.1) d (4.9) s s s dd (10.8, 2.7) m m

3 0.83, 1.70, 1.35, 1.80, 1.97, 0.95, 1.05, 1.75, 1.91, 1.21, 1.89, 0.92, 1.64, 1.20, 1.99, 2.06, 4.81, 4.71, 0.88, 1.10, 0.71, 1.96, 1.50, 2.35, 12.09,

4

td (12.6, 3.6) brd (12.6) brd (13.9) dt (13.9, 3.6) m td (13.3, 4.0) m m m m brd (12.5) m brd (11.0) m m m d (4.2) s s s s m dd (11.0, 8.7) dd (8.4, 4.1) brs

0.81, 1.68, 1.33, 1.78, 1.98, 0.92, 1.01, 1.70, 1.92, 1.15, 1.67, 0.84, 1.64, 1.29, 1.85, 2.22, 4.86, 4.68, 1.03, 1.08, 0.72, 1.52, 1.93, 2.35, 11.94,

td (13.1, 3.7) m m m dt (13.3, 3.5) td (13.3, 4.1) m m m td (13.0, 2.6) brd (13.0) brd (11.3) m m m dd (17.2, 5.1) d (4.1) s s s s dd (11.4, 8.7) brd (11.4) dd (8.3, 3.9) brs

5 0.83, 1.70, 1.35, 1.80, 1.97, 0.93, 1.05, 1.77, 1.94, 1.24, 1.90, 0.91, 1.64, 1.20, 1.99, 2.06, 4.87, 4.63, 0.92, 1.10, 0.72, 1.93, 1.47, 2.37, 12.05,

6

td (13.0, 3.4) brd (13.0) brd (13.8) m m m brd (12.9) m m td (12.9, 2.9) m m dd (12.8, 6.1) m m dd (10.7, 6.6) s d (4.4) s s s m dd (11.0, 8.6) dd (8.6, 3.5) brs

0.82, 1.71, 1.35, 1.81, 1.99, 0.93, 1.06, 1.75, 1.96, 1.23, 1.72, 0.85, 1.66, 1.31, 1.83, 2.22, 4.95, 4.62, 1.05, 1.10, 0.73, 1.47, 1.93, 2.42, 12.09,

td (13.2, 3.8) m m m brd (13.0) m m m m t (13.0) brd (13.0) brd (12.4) dd (12.5, 6.3) td (12.5, 5.3) m dd (17.4, 5.3) s d (4.3) s s s dd (11.0, 8.7) dt (11.0, 4.1) dd (8.2, 3.3) brs

H NMR spectra were recorded at 600 MHz. bThe signal was not detected. 91



Article

Table 2. 13C NMRa Data of 1−6 in DMSO-d6 no.

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

39.7, 18.7, 37.7, 42.9, 56.4, 19.6, 38.4, 35.5, 55.0, 37.4, 17.6, 24.3, 135.2, 151.9, 77.4, 80.6, 20.5, 28.4, 178.4, 13.9, 30.4, 43.6, 172.7,

2 CH2 CH2 CH2 C CH CH2 CH2 C CH C CH2 CH2 C C CH CH CH3 CH3 C CH3 CH2 CH C

40.1, 18.8, 37.8, 43.0, 56.5, 19.4, 37.4, 34.9, 56.0, 36.7, 17.7, 25.3, 134.8, 152.3, 77.6, 80.8, 21.7, 28.5, 178.6, 13.9, 29.9, 43.8, 172.8,


39.4, 18.7, 37.7, 42.9, 56.3, 19.5, 38.2, 35.4, 54.9, 37.3, 17.7, 22.2, 137.7, 151.9, 76.5, 82.7, 20.1, 28.4, 178.4, 13.9, 32.3, 43.3, 174.8,


39.1, 18.7, 37.8, 42.9, 56.2, 19.4, 36.4, 34.7, 56.5, 36.4, 17.5, 23.3, 136.9, 152.0, 76.6, 83.0, 21.8, 28.4, 178.4, 13.9, 31.7, 43.5, 175.1,


40.0, 18.7, 37.7, 42.9, 56.3, 19.5, 38.3, 35.4, 55.1, 37.3, 17.7, 22.6, 140.0, 149.9, 79.7, 79.3, 20.5, 28.4, 178.4, 13.9, 29.5, 45.8, 174.6,


39.0, 18.7, 37.4, 42.9, 56.1, 19.4, 36.6, 34.7, 56.5, 37.8, 17.5, 23.5, 138.9, 150.1, 80.0, 79.6, 21.9, 28.4, 178.4, 13.9, 29.5, 45.4, 175.0,

CH2 CH2 CH2 C CH CH2 CH2 C CH C CH2 CH2 C C CH CH CH3 CH3 C CH3 CH2 CH C

a13

C NMR spectra were recorded at 150 MHz.

Figure 1. COSY (bold lines) and key HMBC (blue arrows) correlations of 1 and 5.

biogenetic relationship with 720 suggests that 1−6 have the 4S,5R,8R,9R,10R-configurations. The experimental and

Figure 3. Experimental ECD spectrum of 1 along with the calculated spectrum of 4S,5R,8R,9R,10R,15S,16R,22S-1.

Figure 2. Key NOE correlations (dashed red arrows) in energy-minimized conformations of 1−6, calculated using Spartan’14 (Wavefunction, Inc.). Dashed green lines: hydrogen bonds. 92



Article

Scheme 1. Plausible Route of Formation of 1−6a

a

The direction of the C3 unit toward 7 is opposite in pathways a and b.

calculated spectra matched well, and, thus, absolute configurations were established for all compounds. Ceylonins A−F (1−6) are the first spongian diterpene derivatives with an ether-bridged bicyclic ring as ring D. They may be derived from the major metabolite, spongia-13(16), 14-dien-19-oic acid (7), of this sponge and a C3 unit (an acrylic acid equivalent) by an intermolecular Diels−Alder reaction (Scheme 1). According to the direction of the C3 unit toward 7, two types of adducts, 1−4 (pathway a) and 5/6 (pathway b), may be produced. In pathway a, ceylonins A (1)/B (2) and C (3)/D (4) are endo- and exo-adducts, respectively, and the C3 unit approached 7 from the α- or β-face to afford 2/4 or 1/3, respectively. In pathway b, the endo products corresponding to 1 and 2 were not isolated in this experiment, but may have been produced in the sponge. Because the yields of 1−6 were nearly identical (1.2−3.6 mg), the intermolecular Diels−Alder reaction likely occurred in a nonenzymatic manner in the sponge. In order to examine if 7 can readily react with a C3 unit, we kept 7 and acrylic acid in DMSO-d6 at room temperature. After 12 days, the 1H NMR spectrum of the solution indicated the presence of 1−6 (Figure 4a). Then, the reaction mixture was analyzed by LC-MS, which clearly showed the formation of 1−6 from 7 and acrylic acid (Figure 4b). These experiments strongly support the nonenzymatic formation of 1−6 from 7 and a C3 unit in the sponge. Compounds 1−6 isolated in this study were tested for their potential to inhibit RANKL-induced osteoclastogenesis in RAW264 cells. After the treatment of RAW264 cells with RANKL and each compound (50 μM), the cells were fixed and stained to visualize TRAP-positive multinuclear osteoclasts (Figure 5a). Among the compounds tested, ceylonin A (1) significantly inhibited the formation of multinuclear osteoclasts by 70% in a dose-dependent manner without cytotoxicity, followed by ceylonins E (5) (47%), F (6) (31%), and D (4) (28%) (Figure 5b). The major compound 7 did not inhibit the formation of multinuclear osteoclasts at 50 μM. The inhibition

Figure 4. (a) 1H NMR spectra (DMSO-d6) of 7 (top) and the reaction mixture of 7 and acrylic acid (bottom), indicating the presence of 1−6. (b) LC-ESIMS chromatogram extracted at m/z 387 [M − H]− of the reaction mixture of 7 and acrylic acid (top) and 1−6.

of the formation of multinuclear osteoclasts by 1 is currently being investigated. 93



Article

Co., Ltd., 21.5 × 500 mm; MeOH) followed by C30 reversed-phase HPLC (Develosil C30-UG-5 column, Nomura Chemical Co., Ltd., 20 × 250 mm; 40% CH3CN−H2O) to yield 1 (3.0 mg), 2 (1.4 mg), 3 (1.2 mg), 4 (1.8 mg), 5 (2.0 mg), and 6 (3.6 mg). Ceylonin A (1): white, amorphous solid; [α]21D −28 (c 0.45, MeOH); UV (CH3CN) no absorption maximum above 195 nm; ECD (200 μM, MeOH) λmax (Δε) 221 (1.32) nm; IR (film) νmax 3400, 2957, 2922, 2848, 1699, 1577, and 1463 cm−1; 1H and 13C NMR data, Tables 1 and 2; HRESITOFMS m/z 411.2097 [M + Na]+ (calcd for C23H32O5Na, 411.2142). Ceylonin B (2): white, amorphous solid; [α]21D +14 (c 0.83, MeOH); UV (CH3CN) no absorption maximum above 195 nm; IR (film) νmax 3428, 2953, 2923, 2349, and 1579 cm−1; 1H and 13C NMR data, Tables 1 and 2; HRESITOFMS m/z 411.2126 [M + Na]+ (calcd for C23H32O5Na, 411.2142). Ceylonin C (3): white, amorphous solid; [α]21D −23 (c 0.60, MeOH); UV (CH3CN) no absorption maximum above 195 nm; IR (film) νmax 3427, 2950, 2924, 2853, 1703, 1577, and 1466 cm−1; 1 H and 13C NMR data, Tables 1 and 2; HRESITOFMS m/z 411.2126 [M + Na]+ (calcd for C23H32O5Na, 411.2142). Ceylonin D (4): white, amorphous solid; [α]21D +1.7 (c 1.0, MeOH); UV (CH3CN) no absorption maximum above 195 nm; IR (film) νmax 3378, 2950, 2921, 2851, 1704, 1577, and 1466 cm−1; 1 H and 13C NMR data, Tables 1 and 2; HRESITOFMS m/z 411.2130 [M + Na]+ (calcd for C23H32O5Na, 411.2142). Ceylonin E (5): white, amorphous solid; [α]21D −26 (c 0.50, MeOH); UV (CH3CN) no absorption maximum above 195 nm; IR (film) νmax 3426, 2950, 2924, 2853, 1703, and 1460 cm−1; 1H and 13C NMR data, Tables 1 and 2; HRESITOFMS m/z 411.2177 [M + Na]+ (calcd for C23H32O5Na, 411.2142). Ceylonin F (6): white, amorphous solid; [α]21D −5.2 (c 1.9, MeOH); UV (CH3CN) no absorption maximum above 195 nm; IR (film) νmax 3412, 2950, 2924, 2853, 1705, and 1460 cm−1; 1H and 13C NMR data, Tables 1 and 2; HRESITOFMS m/z 411.2109 [M + Na]+ (calcd for C23H32O5Na, 411.2142). Spongia-13(16),14-dien-19-oic acid (7): [α]21D +22 (c 0.50, CHCl3) (lit.13 +15; lit.12 +10 (c 0.50, CHCl3)). LC-MS Analyses of the Reaction Mixture of 7 and Acrylic Acid along with 1−6. To a solution of 7 (3.7 mg, 12 μmol) in DMSO-d6 (50 μL) was added acrylic acid (1 μL, 15 μmol), and the mixture was left at room temperature for 12 days. The reaction mixture was diluted with 350 μL of DMSO-d6 to measure the 1H NMR spectrum. Then, the solution was dried by freeze-dryer, and the residue was analyzed by LC-MS on a Cosmosil 2.5C18-MS-II column (4.6 mm × 150 mm) at 40 °C eluted with a gradient of two solvents, 0.1% acetic acid in H2O (solvent A) and 0.1% acetic acid in CH3CN (solvent B), at 0.32 mL/min. The gradient program was conducted as follows: 2−35% B from 0 to 5 min, 35−50% B from 5 to 20 min, and 50−100% B from 20 to 25 min. Mass spectra were detected in negative ion mode, and the data were analyzed using Hystar data analysis software. Conformational Analysis and ECD Calculation for 1. These experiments were performed as previously described.21 Formation of Multinuclear Osteoclasts in RAW264 cells. This experiment was performed as previously described.18,19

Figure 5. Inhibitory effects of 1−6 on the formation of multinuclear osteoclasts in RAW264 cells. RAW264 cells were treated with RANKL (50 ng/mL) in the presence or absence of 1−6 (50 μM) and allowed to differentiate for 4 days. (a) Cells were stained with TRAP-staining solution. (b) TRAP-positive multinuclear osteoclasts (nuclei ≥3) that stained red were counted. Experiments were performed in triplicate, and the error bars represent the standard deviation. Asterisks show significant differences at *P < 0.05 and **P < 0.001. The Student’s t-test was used for the statistical analysis. Quercetin (25 μg/mL (83 μM)) was used as a positive control.

■

EXPERIMENTAL SECTION

General Experimental Procedures. Optical rotations were measured on a JASCO DIP-1000 polarimeter in MeOH. UV spectra were measured on a JASCO V-550 spectrophotometer in CH3CN. Electronic circular dichroism spectrum was measured on a JASCO J-820 spectropolarimeter in MeOH. IR spectra were recorded on a JEOL JIR-6500W spectrophotometer. 1H and 13C NMR spectra were recorded on a Bruker Avance III 500 or Bruker Avance III 600 NMR spectrometer. Chemical shifts were referenced to the residual solvent peaks (δH 2.49 and δC 39.5 for DMSO-d6). ESIMS spectra were measured on a Bruker BioTOFQ mass spectrometer. LC-MS experiments were performed on a Shimadzu LC-20AD solvent delivery system and interfaced to a Bruker amaZon Speed mass spectrometer. A preparative HPLC system was composed of a Waters 515 HPLC pump, Waters 2489 UV/visible detector, and Pantos Unicorder U-228. Animal Material, Extraction, and Isolation. The sponge, Spongia ceylonensis, was collected by scuba at a depth of 10 m in Tiwoho, North Sulawesi, Indonesia, in 2006 and immediately soaked in EtOH. A voucher specimen (RMNH POR 10006) of the sponge has been deposited in the Naturalis Biodiversity Center. The sponge (400 g, wet weight) was extracted with EtOH. After evaporation, the residual aqueous solution was extracted with EtOAc. The EtOAc fraction (3.5 g) was subjected to SiO2 column chromatography with a stepwise gradient elution using n-hexane, n-hexane/EtOAc, EtOAc, and MeOH to yield 13 fractions (Frs. 1−13). Fr. 2, which eluted with n-hexane/EtOAc (90:10), afforded spongia-13(16),14-dien-19-oic acid (7) (2.0 g). Fr. 12 (340 mg), which eluted with MeOH, was subjected to ODS column chromatography with MeOH/H2O. The fraction (130 mg) that eluted with 75% MeOH/H2O was purified by gel filtration HPLC (Asahipack GS-310P column, Asahi Chemical Industry

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.6b00725. 1D and 2D NMR spectra of 1−6; COSY and key HMBC correlations of 2−4 and 6 (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Sachiko Tsukamoto: 0000-0002-7993-381X 94



Article

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank Dr. H. Kobayashi of the University of Tokyo and Dr. H. Rotinsulu of Universitas Pembangunan for collecting the sponges. This work was supported by Grants-in-Aid for Scientific Research (Nos. 18406002, 25293025, and 26305005 to S.T.) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan.

■

REFERENCES

(1) Cambie, R. C.; Craw, P. A.; Stone, M. J.; Bergquist, P. R. J. Nat. Prod. 1988, 51, 293−297. (2) Kernan, M. R.; Cambie, R. C.; Bergquist, P. R. J. Nat. Prod. 1990, 53, 724−727. (3) McPhail, K.; Davies-Coleman, M. T. Tetrahedron 1997, 53, 4655−4660. (4) Potts, B. C. M.; Faulkner, D. J.; Jacobs, R. S. J. Nat. Prod. 1992, 55, 1701−1717. (5) Somerville, M. J.; Mollo, E.; Cimino, G.; Rungprom, W.; Garson, M. J. J. Nat. Prod. 2006, 69, 1086−1088. (6) Betancur-Galvis, L.; Zuluaga, C.; Arnó, M.; González, M. A.; Zaragozá, R. J. J. Nat. Prod. 2002, 65, 189−192. (7) Miyamoto, T.; Sakamoto, K.; Arao, K.; Komori, T.; Higuchi, R.; Sasaki, T. Tetrahedron 1996, 52, 8187−8198. (8) Agena, M.; Tanaka, C.; Hanif, N.; Yasumoto-Hirose, M.; Tanaka, J. Tetrahedron 2009, 65, 1495−1499. (9) Gavagnin, M.; Vardaro, R. R.; Avila, C.; Cimino, G.; Ortea, J. J. Nat. Prod. 1992, 55, 368−371. (10) Orhan, I.; Şener, B.; Kaiser, M.; Brun, R.; Tasdemir, D. Mar. Drugs 2010, 8, 47−58. (11) Yang, Y. C.; Meimetis, L. G.; Tien, A. H.; Mawji, N. R.; Carr, G.; Wang, J.; Andersen, R. J.; Sadar, M. D. Mol. Cancer Ther. 2013, 12, 621−631. (12) Mori, D.; Kimura, Y.; Kitamura, S.; Sakagami, Y.; Yoshioka, Y.; Shintani, T.; Okamoto, T.; Ojika, M. J. Org. Chem. 2007, 72, 7190− 7198. (13) Capelle, N.; Braekman, J. C.; Daloze, D.; Tursch, B. Bull. Soc. Chim. Belg. 1980, 89, 399−404. (14) Li, C. J.; Schmitz, F. J.; Kelly-Borges, M. J. Nat. Prod. 1999, 62, 287−290. (15) Mitchell, S. S.; Harper, M. K.; Faulkner, D. J. Tetrahedron 1999, 55, 10887−10892. (16) Pham, A. T.; Carney, J. R.; Yoshida, W. Y.; Scheuer, P. J. Tetrahedron Lett. 1992, 33, 1147−1148. (17) Wojnar, J. M.; Dowle, K. O.; Northcote, P. T. J. Nat. Prod. 2014, 77, 2288−2295. (18) El-Desoky, A. H.; Kato, H.; Angkouw, E. D.; Mangindaan, R. E. P.; de Voogd, N. J.; Tsukamoto, S. J. Nat. Prod. 2016, 79, 1922−1928. (19) Tsukamoto, S.; Takeuchi, T.; Kawabata, T.; Kato, H.; Yamakuma, M.; Matsuo, K.; El-Desoky, A. H.; Losung, F.; Mangindaan, R. E. P.; de Voogd, N. J.; Arata, Y.; Yokosawa, H. Bioorg. Med. Chem. Lett. 2014, 24, 5315−5317. (20) The specific rotation of 7 isolated in this study was +22 (c 0.50, CHCl3), and its absolute configuration was obtained by a comparison of the data reported (lit.13 +15; lit.12 +10 (c 0.50, CHCl3)). (21) Kagiyama, I.; Kato, H.; Nehira, T.; Frisvad, J. C.; Sherman, D. H.; Williams, R. M.; Tsukamoto, S. Angew. Chem., Int. Ed. 2016, 55, 1128−1132.

95


Ceylonins AâF, Spongian Diterpene Derivatives That Inhibit RANKL

Recommend Documents

Ceylonins AâF, Spongian Diterpene Derivatives That Inhibit RANKL