Next Article in Journal
Coral Carbonic Anhydrases: Regulation by Ocean Acidification
Next Article in Special Issue
Absorption and Transport of Sea Cucumber Saponins from Apostichopus japonicus
Previous Article in Journal
Identification of Angiotensin I-Converting Enzyme Inhibitory Peptides Derived from Enzymatic Hydrolysates of Razor Clam Sinonovacula constricta
Previous Article in Special Issue
Marine Invertebrate Metabolites with Anticancer Activities: Solutions to the “Supply Problem”
Article Menu

Export Article

Mar. Drugs 2016, 14(6), 111; doi:10.3390/md14060111

Article
Cembranoids from a Chinese Collection of the Soft Coral Lobophytum crassum
Min Zhao 1,, Shimiao Cheng 2,, Weiping Yuan 1, Yiyuan Xi 1, Xiubao Li 3, Jianyong Dong 1, Kexin Huang 1, Kirk R. Gustafson 4,* and Pengcheng Yan 1,4,*
1
School of Pharmaceutical Sciences, Wenzhou Medical University, Wenzhou 325035, China
2
The Fifth Affiliated Hospital, Wenzhou Medical University, Lishui 323000, China
3
Key Laboratory of Marine Bio-Resources Sustainable Utilization, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
4
Molecular Targets Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702-1201, USA
*
Correspondence: Tel.: +1-301-846-5197 (K.R.G.); +86-577-8669-9229 (P.Y.); Fax: +1-301-846-6851 (K.R.G.); +86-577-8668-9983 (P.Y.)
These authors contributed equally to this work.
Academic Editor: Kirsten Benkendorff
Received: 25 April 2016 / Accepted: 23 May 2016 / Published: 3 June 2016

Abstract

:
Ten new cembrane-based diterpenes, locrassumins A–G (17), (–)-laevigatol B (8), (–)-isosarcophine (9), and (–)-7R,8S-dihydroxydeepoxysarcophytoxide (10), were isolated from a South China Sea collection of the soft coral Lobophytum crassum, together with eight known analogues (1118). The structures of the new compounds were determined by extensive spectroscopic analysis and by comparison with previously reported data. Locrassumin C (3) possesses an unprecedented tetradecahydrobenzo[3,4]cyclobuta[1,2][8]annulene ring system. Compounds 1, 7, 12, 13, and 17 exhibited moderate inhibition against lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC50 values of 8–24 μM.
Keywords:
soft coral; Lobophytum crassum; cembrane-based diterpenes; NO inhibition

1. Introduction

Soft corals of the genus Lobophytum (family Alcyoniidae) have proven to be a rich source of structurally diverse diterpenes, especially macrocyclic cembranoids characterized by their 14-membered carbocyclic skeleton. To date, numerous marine cembranoids and novel derivatives (mainly formed by dimerization, cyclic addition, or ring rearrangement) have been isolated from Lobophytum species and other genera including Sinularia and Sarcophyton [1]. Some of these metabolites merit further study because of their significant ecological and pharmacological bioactivities, such as antifouling, antifeeding, cytotoxic, antibacterial, antiviral, and anti-inflammatory properties [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. Species L. crassum is widely distributed in the tropical waters of the world and is well known to produce a variety of oxygenated cembranoids, the structural variety of which is often correlated with geographic variation and environmental conditions [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. However, the soft coral L. crassum in the South China Sea has been rarely examined chemically [22,23,24]. In the course of our investigation of bioactive substances produced by marine invertebrates from the South China Sea [25,26,27], a specimen of L. crassum was collected. Chemical examination of this specimen led to the isolation of 18 cembrane-based diterpenes, including nine new cembranoids (1, 2, and 410), an unprecedented diterpene possessing a tetradecahydrobenzo[3,4]cyclobuta[1,2][8]annulene ring system (3), and eight known analogues (1118) (Figure 1). All compounds were tested for their inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in mouse peritoneal macrophages (PEMФ). This paper reports details of the isolation, structure elucidation, and biological evaluation of these compounds.

2. Results and Discussion

Locrassumin A (1) was assigned a molecular formula of C22H32O5 according to its HRESIMS (m/z 399.2134 [M + Na]+, calcd for C22H32O5Na, 399.2147) and NMR data (Figures S1–S7). The 1H NMR spectrum showed signals for three olefinic protons (δH 7.70 d, J = 12.0 Hz, H-3; 6.80 t, J = 7.2 Hz, H-11; 6.24 d, J = 12.0 Hz, H-2), two methoxy groups (δH 3.77 s, H3-21; 3.75 s, H3-22), and three additional methyls (δH 1.18 s, H3-19; 1.00 d, J = 6.6 Hz, H3-16; 0.95 d, J = 6.6 Hz, H3-17), while the 13C NMR spectrum exhibited 22 carbon signals including two ester carbonyls, six olefinic carbons, and two carbons indicative of an epoxide (Table 1 and Table 2). These NMR data were very similar to those of the known cembranoids sarcrassin A [28] and sarcophytonolides B [29] and O (13) [30]. Detailed analysis of COSY and HMBC correlations (Figure 2) confirmed that 1 shared the same planar structure with those three analogues. The NOE correlations of H-3/H-15 (δH 3.20 m), H-2/H-5b (δH 2.55 m), H-2/H-14a (δH 2.42 m), and H3-19/H-6b (δH 1.57 m) (Figure 3) revealed that the geometries of the C-1/C-2 and C-3/C-4 double bonds and configurations of the 7,8-epoxy ring in 1 were identical to those in sarcrassin A [28]. In addition, the NOE correlation of H-10b (δH 2.15 m)/H-13a (δH 2.63 m) and the lack of an NOE correlation between H-11 and H2-13 revealed E geometry for the C-11/C-12 double bond. Thus, 1 was established as the 11E isomer of sarcrassin A [28].
Locrassumin B (2) was also isomeric with sarcrassin A [28] and sarcophytonolides B [29] and O (13) [30] based on the compatible HRESIMS (m/z 399.2135 [M + Na]+, calcd for C22H32O5Na, 399.2147) and 1D and 2D NMR data (Figures S8–S14). The NOE correlations of H-2 (δH 6.23 d, J = 12.0 Hz)/H-15 (δH 2.17 m), H-3 (δH 7.62 d, J = 12.0 Hz)/H-5a (δH 2.66 m), H-3/H-14a (δH 2.83 m), and H3-19 (δH 1.12 s)/H-6b (δH 1.71 m) were indicative of 1E, 3Z, 7R*, and 8R* configurations (Figure 3), consistent with those of sarcophytonolide O (13) [30], while the NOE correlation of H-10a (δH 2.12 m)/H-13a (δH 2.69 m) and the lack of NOE correlation between H-11 and H2-13 allowed for the assignment of 11E, instead of 11Z as in 13. Thus, 2 was elucidated as the 11E isomer of sarcophytonolide O (13) [30].
Locrassumin C (3) had a molecular formula of C22H34O6 as determined by HRESIMS (m/z 417.2251 [M + Na]+, calcd for C22H34O6Na, 417.2253) and NMR data, requiring six degrees of unsaturation (Figures S15–S21). The IR absorptions at 3450 and 1726 cm−1 indicated the presence of hydroxy and carbonyl functionalities. The 13C NMR spectrum showed 22 carbon signals including two ester carbonyls (δC 177.4 and 176.7) and two olefinic carbons (δC 148.3, C; 113.8, CH) (Table 2), which accounted for three of the six degrees of unsaturation. Thus, 3 had to be tricyclic. COSY correlations established the subunits from C-2 to C-3, C-5 to C-7, C-9 to C-11, and C-13 to C-14, while their connectivities were completed by detailed analysis of HMBC correlations (Figure 2). The HMBC correlations from the olefinic proton H-2 (δH 5.31 d, J = 3.0 Hz), the aliphatic methine proton H-3 (δH 3.17 d, J = 3.0 Hz), and H2-13 (δH 2.08 m; 1.78 m) to the non-protonated carbon C-12 (δC 45.2), from H-3 and H2-13 to the non-protonated olefinic carbon C-1 (δC 148.3), and from H-2 to C-14 (δC 23.2, CH2) led to the establishment of a cyclohexene ring. The HMBC correlations from H3-19 (δH 1.14 s) to C-9 (δC 39.3, CH2) and two oxygenated carbons C-7 (δC 73.7, CH) and C-8 (δC 74.9, C) and from the aliphatic methine proton H-11 (δH 3.24 dd, J = 7.2, 5.4 Hz) and H2-6 (δH 1.74 m; 1.57 m) to another non-protonated carbon C-4 (δC 50.0) constructed a cyclooctane ring and revealed that C-7 and C-8 were hydroxylated and C-8 was also substituted by a methyl group. In addition, the HMBC correlations from H-3 to C-4 and from H-11 to C-12 finally connected the cyclohexene and cyclooctane rings to form an 8,4,6-tricarbocyclic nucleus. Further HMBC correlations from H-3 and H-11 to the two ester carbonyl carbons C-18 (δC 177.4) and C-20 (δC 176.7), from the methoxy protons H3-21 (δH 3.76 s) and H3-22 (δH 3.68 s) to C-18 and C-20, respectively, and from H2-13 to C-20 disclosed that C-4 and C-12 were substituted by methyl esters. Direct linkage of an isopropyl group to C-1 was inferred by the HMBC correlations from H3-16 (δH 1.00 d, J = 6.6 Hz) and H3-17 (δH 1.01 d, J = 6.6 Hz) to the non-protonated olefinic carbon C-1. Thus, the planar structure of 3 was established as depicted in Figure 1.
The relative configuration of 3 was determined on the basis of coupling constant and NOESY analysis (Figure 3). The NOE correlations of H-2/H-5a (δH 1.92 m), H-3/H-13b (δH 1.78 m), H-3/H-10a (δH 1.87 m), and H-11/H-5b (δH 1.75 m) suggested the trans fusions of the ring system and the opposite orientation of H-3 and H-11. In addition, the coupling pattern of H-7 (δH 3.58 d, J = 10.8 Hz) indicated its axial orientation (one large coupling due to dihedral angles of approximately 180° and 90° with the H2-6 protons), while the NOE correlations of H-7/H3-19, H-7/H-10a, and H3-19/H-10a suggested the same orientation of H-7, H3-19, and H-10a. Furthermore, the absolute configuration of the 7,8-diol was determined by an in situ dimolybdenum CD method [31,32], based on which the sign of the induced CD (ICD) bands at 310, 350, and 400 nm reflected the O-C-C-O torsion angle. After addition of dimolybdenum tetraacteate [Mo2(OAc)4] into a DMSO solution of 3, a metal complex was generated immediately and the ICD spectrum was acquired. The positive CD effects observed at 318 and 357 nm (Figure 4) allowed for the assignment of the 7R and 8S configurations. Accordingly, the configurations of the remaining chiral centers of 3 were assigned as 3R, 4R, 11R, and 12R.
It is interesting to note that 3 represents an unprecedented diterpenoid with a tetradecahydrobenzo[3,4]cyclobuta[1,2][8]annulene ring system, which could be derived from the coisolated cembranoids locrassumins A (1), B (2), or sarcophytonolide O (13) [30] via a series of isomerization, intramolecuar [2 + 2] cycloaddition between C-3/C-4 and C-11/C-12 double bonds [2], and hydrolysis reactions.
The molecular formula of locrassumin D (4) was determined to be C20H30O3 on the basis of HRESIMS (m/z 341.2094 [M + Na]+, calcd for C20H30O3Na, 341.2093) and NMR data, implying six degrees of unsaturation (Figures S22–S28). The IR absorption at 1707 cm−1 indicated the presence of a carbonyl functionality. A carbonyl carbon (δC 177.8) and six olefinic carbons were evident by 13C NMR data (Table 2), requiring a bicyclic structure for the remaining two degrees of unsaturation. A conjugated diene was easily recognized by a COSY correlation between the two olefinic protons H-2 (δH 6.02 dd, J = 11.4, 1.8 Hz) and H-3 (δH 5.87 d, J = 11.4 Hz) as well as the HMBC correlations from H3-18 (δH 1.79 s) to two olefinic carbons C-3 (δC 121.7, CH) and C-4 (δC 138.2, C) and from H-3 to C-1 (δC 133.7, C). Further COSY correlations established the other four subunits from C-5 to C-7, C-9 to C-11, C-13 to C-14, and C-15 to C-16, while HMBC correlations from H3-18 to a methylene carbon C-5 (δC 40.4, CH2), from H3-19 (δH 1.30 s) to two olefinic carbons C-7 (δC 125.0, CH) and C-8 (δC 136.3, C) and a methylene carbon C-9 (δC 35.5, CH2), from H3-20 (δH 1.28 s) to two oxygenated carbons C-11 (δC 67.9, CH) and C-12 (δC 87.0, C) and a methylene carbon C-13 (δC 32.9, CH2), from H3-16 (δH 1.47 d, J = 7.2 Hz) to the ester carbonyl C-17 (δC 177.8) and C-1, and from H-2 to a methylene carbon C-14 (δC 22.1, CH2) (Figure 2) finally connected the subunits to form a cembrane skeleton, in which C-1/C-2, C-3/C-4, and C-7/C-8 formed double bonds and C-11 was hydroxylated. In addition, an ester linkage between C-12 and C-17 could be inferred by the chemical shifts of C-12 and C-17 and the remaining one degree of unsaturation in the molecule. The geometries of 3E and 7E were indicated by the diagnostic chemical shifts of C-18 and C-19 (<20 ppm) [33,34] and confirmed by the NOE correlations of H-3/H-5b (δH 1.98 m) and H-7 (δH 5.11 dd, J = 10.2, 5.4 Hz)/H-9a (δH 2.25 m), respectively. The coupling constant value of JH-2/H-3 (11.4 Hz) and NOE correlations of H-2/H3-18 and H-3/H-14a (δH 2.98 m) suggested the trans-axial orientation of H-2 and H-3, and 1E geometry. An NOE correlation of H-2/H-15 (δH 3.43 q, J = 7.2 Hz) established that these two protons were on the same face of the molecule and thus H-15 had an α-orientation (Figure 3). Furthermore, the significant NOE correlations of H-11 (δH 3.79 br d, J = 10.8 Hz)/H-3 and H-11/H-14a, and the lack of an NOE correlation between H-11 and H3-20 were in agreement with the 11R* and 12S* configurations. Thus, 4 was elucidated as (11R*,12S*,15R*,1E,3E,7E)-11-hydroxycembra-1,3,7-trien-17,12-olide.
Locrassumin E (5) had a molecular formula of C20H32O3 as determined by HRESIMS (m/z 343.2247 [M + Na]+, calcd for C20H32O3Na, 343.2249) and NMR data, indicating five degrees of unsaturation (Figures S29–S35). The preliminary analysis of 1D NMR data revealed that compound 5 had a structure closely related to that of 4. The only difference was loss of signals for a methyl doublet, an ester carbonyl, and an aliphatic methine and the appearance of signals for an additional methyl singlet (δH 1.49 s, H3-16) and two additional oxygenated sp3 carbons (δC 77.6, C, C-15; 73.6, CH2, C-17). Thus, 5 should be a 17-deoxo-15-hydroxy derivative of 4. This assumption was supported by the HMBC correlations from the methyl singlet H3-16 to an olefinic carbon C-1 (δC 140.9, C) and the two oxygenated carbons C-15 and C-17 (Figure 2). The ether linkage between C-12 and C-17 was confirmed by HMBC correlations from the oxymethylene protons H2-17 (δH 3.82 d, J = 12.6 Hz; 3.44 d, J = 12.6 Hz) to the oxygenated carbon C-12 (δC 80.2, C). The geometries of C-3/C-4 and C-7/C-8 double bonds and relative configurations at C-11 and C-12 were consistent with those in 4 as indicated by the similar chemical shifts of C-18 and C-19 and compatible NOE relationships [H-3 (δH 5.96 d, J = 11.4 Hz)/H-5b (δH 2.01 m), H-7 (δH 5.09dd, J = 10.2, 4.8 Hz)/H-9a (δH 2.20 m), and H-11 (δH 3.44 br d, J = 10.8 Hz)/H-3], as well as the lack of NOE correlation between H3-20 and H-11 (Figure 3). In addition, the coupling constant value of JH-2/H-3 (11.4 Hz) and the NOE correlations of H-3/H-14a (δH 2.84 ddd, J = 15.0, 11.4, 6.0 Hz), H-2 (δH 6.06 dd, J = 11.4, 1.8 Hz)/H3-18 (δH 1.79 s), and H-2/H3-16 allowed the assignment of 1E and α-orientation of H3-16. Thus, 5 was determined as (11R*,12S*,15R*,1E,3E,7E)-12,17-epoxycembra-1,3,7-trien-11,15-diol.
The molecular formula of locrassumin F (6) was determined to be C20H28O4 by its HRESIMS (m/z 355.1883 [M + Na]+, calcd for C20H28O4Na, 355.1885) and NMR data, requiring seven degrees of unsaturation (Figures S36–S42). The NMR data of 6 (Table 1 and Table 2) were found to be very similar to those of the co-occurring analogue ent-sarcophine (12) [35]. The only difference was attributed to the absence of a tetrasubstituted double bond, while presenting an additional tetrasubstituted epoxy (δC 71.7, C, C-1; 60.7, C, C-15), indicating that 6 was probably a C-1/C-15 epoxylation derivative of 12. The presence of an α,β-epoxy-γ-lactone was further supported by the HMBC correlations from H3-17 (δH 1.55 s) to the carbonyl carbon C-16 (δC 172.8) and two oxygenated carbons C-1 and C-15 and from the oxymethine proton H-2 (δH 5.29 d, J = 10.8 Hz) to C-16, while the substructure from C-3 to C-13 was established as identical to that in 12 based on the HMBC and COSY correlations as depicted in Figure 2. The relative configurations at C-1, C-7, and C-8, as well as the geometries of the two double bonds were assigned similarly to those in 12 by the compatible NMR data including the NOE relationships of H-2/H3-18 (δH 1.88 s), H-3 (δH 5.19 d, J = 10.8 Hz)/H-5b (δH 2.37 m), H-3/H-7 (δH 2.64 br t, J = 3.6 Hz), H-7/H-9b (δH 0.95 t, J = 13.2 Hz), H-11 (δH 5.12 dd, J = 9.0, 6.6 Hz)/H-13b (δH 1.99 m), and the lack of NOE correlations of H-7/H3-19 and H-11/H3-20. In addition, the NOE correlations of H-3/H-14a (δH 1.91 m) and the lack of an NOE correlation between H-2 and H2-14 suggested the α-orientation of C-1/C-15 epoxy ring. Thus, 6 was elucidated as (1R*,2R*,7R*,8R*,15R*,3E,11E)-7,8:1,15-diepoxycembra-3,11-dien-16,2-olide.
Locrassumin G (7) was assigned a molecular formula of C21H34O4 on the basis of HRESIMS (m/z 373.2351 [M + Na]+, calcd for C21H34O4Na, 373.2355) and NMR data, implying five degrees of unsaturation (Figures S43–S49). The 13C NMR spectrum showed six olefinic carbon signals (Table 2), requiring 7 to be a bicyclic molecule according to the remaining two degrees of unsaturation. A methyl-bearing dihydrofuranring was indicated by the 13C NMR signals at δC 132.4 (C, C-1), 127.9 (C, C-15), 84.0 (CH, C-2), 78.5 (CH2, C-16), 10.1 (CH3, C-17) and 1H NMR signals at δH 5.44 (br d, J = 9.6 Hz, H-2), 4.51 (d, J = 11.4 Hz, H-16a), 4.46 (d, J = 11.4 Hz, H-16b), 1.65 (s, H3-17), and further confirmed by the HMBC correlations from H3-17 to C-1, C-15, and C-16 and from the oxymethylene protons H2-16 to C-2 (Figure 2). The COSY correlation between H-2 and an olefinic proton H-3 (δH 5.08 d, J = 9.6 Hz) revealed that C-3/C-4 was located by a double bond. The other two olefinic carbons at δC 138.9 (CH, C-11) and 124.4 (CH, C-10) and two olefinic proton signals at δH 5.53 (m, H-10) and 5.52 (d, J = 18.6 Hz, H-11) were attributed to a 1,2-disubstituted double bond. These NMR data were similar to those of the known cembranoid (2S*,7S*,8S*,12R*,1Z,3E,10E)-7,8:2,16-diepoxycembra-1(15),3,10-trien-12-ol [27]. The difference arose from the absence of a trisubstituted epoxy in 7. The HMBC correlations from H3-19 (δH 1.15 s) to two oxygenated carbons C-7 (δC 71.2, CH) and C-8 (δC 78.4, C) and a methylene carbon C-9 (δC 36.7, CH2) and from the methoxy protons (δH 3.23 s, H3-21) to C-8 disclosed that C-7 and C-8 were substituted by a hydroxy and a methoxy group, respectively. Further HMBC correlations from H3-20 (δH 1.33 s) to an olefinic carbon C-11, an oxygenated carbon C-12 (δC 73.0, C), and a methylene carbon C-13 (δC 41.3, CH2) confirmed the location of a double bond at C-10/C-11 and C-12 was hydroxylated. The coupling constant value of JH-2/H-3 (9.6 Hz) and the NOE correlations of H-2/H3-18 (δH 1.74 s) and H-3/H-5a (δH 2.32 m) suggested the trans-axial orientation of H-2 and H-3 and 3E, which was also implied by the chemical shifts of C-18 (<20 ppm) [23,24], while the coupling constant value of JH-10/H-11 (18.6 Hz) indicated the 10E geometry. In addition, NOE correlations of H-3/H-14b (δH 1.69 m), H-7 (δH 3.34 d, J = 10.8 Hz)/H-14b, H-7/H-10, and H3-19/H-10, H3-20/H-10, and H3-20/H-14a (δH 2.14 m) were in agreement with the relative configurations of 7R*, 8S*, and 12S* (Figure 3). Thus, 7 was defined as (2R*,7R*,8S*,12S*,1Z,3E,10E)-8-methoxy-2,16-epoxycembra-1(15),3,10-trien-7,12-diol.
The spectroscopic data analysis and comparison of NMR and HRESIMS data revealed that the structures of compounds 810 were identical to the known cembranoids laevigatol B [36], (+)-isosarcophine [37], and (+)-7S,8R-dihydroxydeepoxysarcophytoxide [38], respectively. However, the antipodal specific rotations of 810 ( [ α ] D 25 −17 (c 0.10, CHCl3); −263 (c 0.10, CHCl3); −99 (c 0.10, CHCl3), respectively) in comparison with those of the three known analogues ( [ α ] D 25 +7.7 (c 1.00, CH2Cl2); +235.3 (c 0.14, CHCl3); +140.0 (c 0.48, CHCl3), respectively) suggested 810 to be enantiomers of the previously reported analogues, and named (–)-laevigatol B, (–)-isosarcophine, and (–)-7R,8S-dihydroxydeepoxysarcophytoxide, respectively.
Eight known compounds were also isolated from the L. crassum extract and identified as (–)-sarcophytoxide (11) [39], ent-sarcophine (12) [35], sarcophytonolide O (13) [30], sartrolide G (14) [40], emblide (15) [41], sarcrassin D (16) [28], ketoemblide (17) [42], and methyl sarcotroate B (18) [2], by comparison of their 1H and 13C NMR, MS spectroscopic data (Figures S50–S68), and specific rotations, with those reported in the literature.
All compounds were tested for their in vitro anti-inflammatory activities [43]. Nitric oxide (NO) is an important signaling molecule that is involved in the regulation of diverse physiological and pathological processes. Overproduction of NO is associated with various human diseases, particularly acute and chronic inflammation, while the level of NO can reflect the degree of inflammation. In the primary assay, compounds 1, 7, 12, 13, and 17 showed moderate inhibition against lipopolysaccharide-induced NO production in mouse peritoneal macrophages with IC50 values of 8–24 μM, whereas no inhibitory effect was observed for the other compounds (IC50 > 30 μM) (Table 3).

3. Materials and Methods

3.1. General Experimental Procedures

1H and 13C NMR spectra were acquired with a Bruker Avance-600FT NMR spectrometer (Bruker, Munich, Germany) using TMS as an internal standard. HRESIMS data were recorded using a Thermo Scientific Q Exactive hybrid quadrupole-Orbitrap mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). UV spectra were measured with a TU 1901 spectrometer (Puxi Ltd., Beijing, China). IR spectra were obtained using a Bruker Equinox 55 spectrometer (Bruker, Munich, Germany). Optical rotations were measured with a PoLAAR 3005 digital polarimeter (Optical Activity Ltd., Cambridgeshire, UK). Silica gel (200–300 mesh, Qingdao Marine Chemistry Co. Ltd., Qingdao, China), Sephadex LH-20 (GE Healthcare Bio-sciences AB, Uppsala, Sweden), and ODS (50 μm, YMC, Tokyo, Japan) were used for column chromatography. TLC analysis was carried out using silica gel GF254 (Qingdao Marine Chemistry Co. Ltd., Qingdao, China). Semipreparative HPLC was performed using an Agilent 1100 series instrument equipped with a VWD G1314A detector (Agilent, Palo Auto, Santa Clara, CA, USA) and a YMC-Pack C18 column (10 μm, 250 × 10 mm, YMC, Tokyo, Japan).

3.2. Animal Material

Specimens of the soft coral Lobophytum crassum von Marenzeller, 1886 were collected from the inner coral reef of Meishan, Hainan Province, China, in April 2014, at a depth of 6 m and frozen immediately after collection. The identification was carried out by one of the authors (X.L.). A voucher specimen (HS201404) was deposited at the Laboratory of Marine Natural Products Chemistry, Wenzhou Medical University, China.

3.3. Extraction and Isolation

The frozen soft coral Lobophytum crassum (wet weight: 1.06 kg) was homogenized and extracted with 95% EtOH at room temperature (r.t.). The concentrated extract was partitioned between EtOAc and H2O. Evaporation of EtOAc in vacuo afforded a dark residue of 30.0 g. The EtOAc fraction (15.0 g) was subjected to silica gel vacuum column chromatography, eluting with a gradient of EtOAc/petroleum ether (1:30, 1:10, 1:5, 1:3, and 1:2), to yield seven fractions (A1–A7). Fraction A3 (300.5 mg) was further fractionated on a silica gel column, eluting with a gradient of acetone/petroleum ether (1:15 and 1:10), to afford three fractions (A3a–A3c). Fraction A3b (30.5 mg) was purified by semipreparative HPLC, using MeOH/H2O (75:25) as eluent, to afford 9 (2.2 mg). Fraction A3c (62.1 mg) was purified by HPLC, eluting with MeOH/H2O (70:30), to yield 11 (15.8 mg). Fraction A4 (2.1 g) was chromatographed on a Sephadex LH-20 column, using CH2Cl2/MeOH (1:1) as a mobile phase, to obtain three fractions (A4a–A4c). Fraction A4b (1.1 g) was further subjected to an ODS column, eluting with a gradient of MeOH/H2O (70:30, 75:25, 80:20, 85:15, and 90:10), to afford six fractions (A4b1–A4b6). Fraction A4b1 (100.3 mg) was purified by HPLC (MeOH/H2O, 65:35) to obtain 6 (5.6 mg) and 12 (17.4 mg). In the same manner, fractionsA4b2 (120.0 mg) and A4b3 (98.2 mg) were eluted with MeOH/H2O (70:30) to yield 14 (6.0 mg), 17 (18.7 mg), 15 (9.1 mg), 4 (3.8 mg), and 16 (6.7 mg), while fraction A4b4 (103.5 mg) was purified with MeOH/H2O (75:25) to afford 1 (7.0 mg), 2 (8.0 mg), and 13 (28.7 mg). Fraction A5 (620.7 mg) was separated on a Sephadex LH-20 column (CH2Cl2/MeOH, 1:1) to yield three fractions (A5a–A5c). Fraction A5b (271.4 mg) was further fractionated on an ODS column, eluting with MeOH/H2O (70:30 and 75:25), to afford three fractions (A5b1–A5b3). Fraction A5b1 (58.9 mg) was purified by HPLC (MeOH/H2O, 65:35) to obtain 8 (3.3 mg) and 18 (9.6 mg). In the same manner, fraction A5b3 (16.8 mg) was eluted with MeOH/H2O (60:40) to afford 5 (3.2 mg). Fraction A6 (421.5 mg) was fractionated on a Sephadex LH-20 column (CH2Cl2/MeOH, 1:1) to yield four fractions (A6a–A6d). Fraction A6b (37.2 mg) was purified by HPLC (MeOH/H2O, 70:30) to afford 7 (3.5 mg) and 3 (3.8 mg). Following the same protocol as for fraction A6b, 10 (5.6 mg) was separated from fraction A6c (26.1 mg).
Locrassumin A (1): colorless oil; [ α ] D 25 +9 (c 0.10, CHCl3); UV (MeOH) λmax (log ε) 212 (4.08), 284 (4.25); IR (KBr) νmax 2967, 2870, 1708, 1624, 1436, 1384, 1263, 1198, 1109, 1067, 866, 762 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 399.2134 [M + Na]+ (calcd. for C22H32O5Na, 399.2147).
Locrassumin B (2): colorless oil; [ α ] D 25 +385 (c 0.10, CHCl3); UV (MeOH) λmax (log ε) 214 (4.05), 284 (4.22); IR (KBr) νmax 2955, 2872, 1708, 1631, 1435, 1384, 1264, 1191, 1121, 1070 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 399.2135 [M + Na]+ (calcd. for C22H32O5Na, 399.2147).
Locrassumin C (3): colorless oil; [ α ] D 25 +44 (c 0.10, CHCl3); IR (KBr) νmax 3450, 2966, 2871, 1726, 1459, 1379, 1222 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 417.2251 [M + Na]+ (calcd. for C22H34O6Na, 417.2253).
Locrassumin D (4): colorless oil; [ α ] D 25 −50 (c 0.06, CHCl3); UV (MeOH) λmax (log ε) 204 (3.55), 243 (3.21); IR (KBr) νmax 3442, 2930, 1707, 1646, 1460, 1383, 1081 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 341.2094 [M + Na]+ (calcd. for C20H30O3Na, 341.2093).
Locrassumin E (5): colorless oil; [ α ] D 25 +127 (c 0.06, CHCl3); UV (MeOH) λmax (log ε) 203 (3.96), 251 (4.13); IR (KBr) νmax 3449, 2924, 2858, 1742, 1446, 1378, 1271, 1085, 917, 873 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 343.2247 [M + Na]+ (calcd. for C20H32O3Na, 343.2249).
Locrassumin F (6): colorless oil; [ α ] D 25 −16 (c 0.10, CHCl3); IR (KBr) νmax 2930, 1777, 1451, 1383, 1320, 1243, 1104, 975 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 355.1883 [M + Na]+ (calcd. for C20H28O4Na, 355.1885).
Locrassumin G (7): colorless oil; [ α ] D 25 −48 (c 0.07, CHCl3); IR (KBr) νmax 3446, 2931, 2860, 1452, 1377, 1272, 1090, 979 cm−1; 1H and 13C NMR data, Table 1 and Table 2; HRESIMS m/z 373.2351 [M + Na]+ (calcd. for C21H34O4Na, 373.2355).
()-Laevigatol B (8): colorless oil; [ α ] D 25 −17 (c 0.10, CHCl3); IR (KBr) νmax 3435, 2928, 2858, 1662, 1450, 1384, 1031 cm−1; 1H NMR (600 MHz, CDCl3) δ 5.23 (1H, t, J = 1.8 Hz, H-17a), 5.16 (1H, d, J = 10.2 Hz, H-3), 5.10 (1H, t, J = 1.8 Hz, H-17b), 5.06 (1H, t, J = 7.8 Hz, H-11), 4.78 (1H, d, J = 10.2 Hz, H-2), 4.64 (1H, dt, J = 13.2, 1.8 Hz, H-16a), 4.45 (1H, dt, J = 13.2, 1.8 Hz, H-16b), 2.69 (1H, t, J = 4.2 Hz, H-7), 2.32 (1H, m, H-13a), 2.30 (2H, m, H2-5), 2.27 (1H, m, H-10a), 2.17 (1H, m, H-14a), 2.12 (1H, ddd, J = 12.6, 4.2, 3.0 Hz, H-9a), 1.94 (1H, m, H-10b), 1.83 (1H, m, H-6a), 1.83 (3H, s, H3-18), 1.81 (1H, m, H-13b), 1.65 (1H, m, H-6b), 1.60 (3H, s, H3-20), 1.26 (1H, m, H-14b), 1.26 (3H, s, H3-19), 0.96 (1H, td, J = 13.2, 3.0 Hz, H-9b); 13C NMR (150 MHz, CDCl3) δ 152.5 (C, C-15), 139.4 (C, C-4), 136.2 (C, C-12), 123.4 (CH, C-11), 121.6 (CH, C-3), 106.2 (CH2, C-17), 84.5 (CH, C-2), 81.2 (C, C-1), 69.0 (CH2, C-16), 62.1 (CH, C-7), 59.8 (C, C-8), 40.0 (CH2, C-9), 37.6 (CH2, C-5), 34.4 (CH2, C-13), 32.7 (CH2, C-14), 25.5 (CH2, C-6), 23.7 (CH2, C-10), 16.6 (CH3, C-19), 16.3 (CH3, C-18), 15.2 (CH3, C-20); HRESIMS m/z 341.2090 [M + Na]+ (calcd. for C20H30O3Na, 341.2093).
()-Isosarcophine (9): colorless oil; [ α ] D 25 −263 (c 0.10, CHCl3); UV (MeOH) λmax (log ε) 204 (4.24); IR (KBr) νmax 2924, 2854, 1754, 1676, 1446, 1384, 1287, 1089, 998 cm−1; 1H NMR (600 MHz, CDCl3) δ 5.45 (1H, d, J = 9.6 Hz, H-2), 4.98 (1H, d, J = 9.0 Hz, H-7), 4.85 (1H, d, J = 9.6 Hz, H-3), 2.54 (1H, dd, J = 10.2, 2.4 Hz, H-11), 2.54 (1H, m, H-14a), 2.46 (1H, m, H-6a), 2.37 (1H, m, H-5a), 2.32 (1H, m, H-9a), 2.22 (1H, m, H-5b), 2.13 (1H, m, H-6b), 2.10 (1H, m, H-10a), 2.10 (1H, m, H-14b), 2.00 (1H, m, H-13a), 1.99 (1H, m, H-9b), 1.85 (3H, s, H3-17), 1.68 (3H, s, H3-18), 1.68 (3H, s, H3-19), 1.32 (3H, s, H3-20), 1.26 (1H, m, H-10b), 1.05 (1H, m, H-13b); 13C NMR (150 MHz, CDCl3) δ 174.6 (C, C-16), 161.1 (C, C-1), 144.9 (C, C-4), 133.7 (C, C-8), 125.2 (CH, C-7), 123.4 (C, C-15), 120.6 (CH, C-3), 78.4 (CH, C-2), 62.0 (CH, C-11), 60.8 (C, C-12), 38.7 (CH2, C-5), 37.1 (CH2, C-13), 36.7 (CH2, C-9), 24.2 (CH2, C-10), 23.9 (CH2, C-6), 23.6 (CH2, C-14), 15.9 (CH3, C-20), 15.1 (CH3, C-18), 14.8 (CH3, C-19), 8.8 (CH3, C-17); HRESIMS m/z 339.1931 [M + Na]+ (calcd. for C20H28O3Na, 339.1936).
()-7R,8S-Dihydroxydeepoxysarcophytoxide (10): colorless oil; [ α ] D 25 −99 (c 0.10, CHCl3); IR (KBr) νmax 3443, 2925, 2857, 1446, 1379, 1000, 945 cm−1; 1H NMR (600 MHz, CDCl3) δ 5.54 (1H, m, H-2), 5.14 (1H, d, J = 10.2 Hz, H-3), 4.92 (1H, dd, J = 9.6, 3.6 Hz, H-11), 4.50 (2H, s, H2-16), 3.57 (1H, d, J = 10.8 Hz, H-7), 2.53 (1H, ddd, J = 13.8, 10.8, 8.4 Hz, H-14a),2.39 (H, td, J = 12.6, 2.4 Hz, H-5a), 2.23 (1H, m, H-10a), 2.18 (1H, m, H-5b), 2.11 (1H, m, H-10b), 1.93 (2H, m, H2-13),1.87 (1H, m, H-6a), 1.85 (3H, s, H3-18), 1.81 (1H, m, H-9a), 1.70 (1H, m, H-9b), 1.68 (1H, m, H-14b), 1.64 (3H, s, H3-17), 1.63 (3H, s, H3-20), 1.51 (1H, m, H-6b), 1.19 (3H, s, H3-19); 13C NMR (150 MHz, CDCl3) δ 139.1 (C, C-4), 135.9 (C, C-12), 133.3 (C, C-1), 127.9 (C, C-15), 126.8 (CH, C-3), 124.2 (CH, C-11), 84.0 (CH, C-2), 78.5 (CH2, C-16), 75.5 (C, C-8), 72.9 (CH, C-7), 37.0 (CH2, C-9), 36.7 (CH2, C-13), 35.7 (CH2, C-5), 26.7 (CH2, C-6), 25.3 (CH2, C-14), 24.3 (CH3, C-19), 23.7 (CH2, C-10), 16.0 (CH3, C-18), 15.4 (CH3, C-20), 10.2 (CH3, C-17); HRESIMS m/z 343.2240 [M + Na]+ (calcd. for C20H32O3Na, 343.2249).

3.4. Assay for Inhibition of Nitric Oxide Production

A previously established protocol [43] was followed except that 30 mM dexamethasone in DMSO was used as the positive control and each test compound (30 mM in DMSO) was diluted to 1–30 μM at r.t. before the experiment.

4. Conclusions

This is a further chemical examination on the soft coral Lobophytum crassum from the South China Sea, which presents ten new cembrane-based diterpenes (110) to enrich the chemical diversity of secondary metabolites from Lobophytum species. Compound 3 possesses an unprecedented tetradecahydrobenzo[3,4]cyclobuta[1,2][8]annulene skeleton which could be derived from 1, 2, or 13. Compounds 1, 7, 12, 13, and 17 exhibited moderate inhibition against lipopolysaccharide-induced NO production in mouse peritoneal macrophages with IC50 values of 8–24 μM. These results add to a growing class of diverse cembranoid structures that are known to inhibit NO production.

Supplementary Materials

The following are available online at www.mdpi.com/1660-3397/14/6/111/s1, Figures S1–S68: 1H,13C NMR and MS spectroscopic data of compounds 110.

Acknowledgments

This work was supported by grants from NSFC (No. 21202123), ZJNSF (No. LQ12B02002), CSC (No. 201408330121), and Start-Up Funding from Wenzhou Medical University (No. QTJ10018). This research was also supported in part by the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research.

Author Contributions

Min Zhao and Shimiao Cheng contributed to extraction and isolation of compounds. Weiping Yuan and Yiyuan Xi performed UV, IR, MS and optical rotation measurements. Xiubao Li carried out taxonomic identification of the soft coral specimen. Jianyong Dong and Kexin Huang contributed to biological evaluation and NMR measurement, respectively. Kirk R. Gustafson and Pengcheng Yan were the project leaders and made contribution to the structure elucidation and manuscript writing.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Marinlit Database; Department of Chemistry, University of Canterbury. Available online: http://www.chem.canterbury.ac.nz/marinlit/marinlit.shtml (accessed on 3 April 2016).
  2. Liang, L.-F.; Kurtán, T.; Mándi, A.; Yao, L.-G.; Li, J.; Zhang, W.; Guo, Y.-W. Unprecedented diterpenoids as a PTP1B from the Hainan soft coral Sarcophyton trocheliophorum. Org. Lett. 2013, 15, 274–277. [Google Scholar] [CrossRef] [PubMed]
  3. Thao, N.P.; Luyen, B.T.T.; Lee, S.H.; Jang, H.D.; Kiem, P.V.; Minh, C.V.; Kim, Y.H. Antiosteoporotic and antioxidant activities of diterpenoids from the Vietnamese soft corals Sinularia maxiama and Lobophytum crassum. Med. Chem. Res. 2015, 24, 3551–3560. [Google Scholar] [CrossRef]
  4. Cheng, S.-Y.; Wang, S.-K.; Duh, C.-Y. Secocrassumol, a seco-cembranoid from the Dongsha Atoll soft coral Lobophytum crassum. Mar. Drugs 2014, 12, 6028–6037. [Google Scholar] [CrossRef] [PubMed]
  5. Thao, N.P.; Luyen, B.T.T.; Ngan, N.T.T.; Song, S.B.; Nguyen, X.C.; Nam, N.H.; Kiem, P.V.; Kim, Y.H.; Minh, C.V. New anti-inflammatory cembranoid diterpenoids from the Vietnamese soft coral Lobophytum crassum. Bioorg. Med. Chem. Lett. 2014, 24, 228–232. [Google Scholar] [CrossRef] [PubMed]
  6. Lee, C.-H.; Kao, C.-Y.; Kao, S.-Y.; Chang, C.-H.; Su, J.-H.; Hwang, T.-L.; Kuo, Y.-H.; Wen, Z.-H.; Sung, P.-J. Terpenoids from the Octocorals Menella sp. (Plexauridae) and Lobophytum crassum (Alcyonacea). Mar. Drugs 2012, 10, 427–438. [Google Scholar] [CrossRef] [PubMed]
  7. Lin, S.-T.; Wang, S.-K.; Duh, C.-Y. Cembranoids from the Dongsha Atoll soft coral Lobophytum crassum. Mar. Drugs 2011, 9, 2705–2716. [Google Scholar] [CrossRef] [PubMed]
  8. Lee, N.-L.; Su, J.-H. Tetrahydrofuran cembranoids from the cultured soft coral Lobophytum crassum. Mar. Drugs 2011, 9, 2526–2536. [Google Scholar] [CrossRef] [PubMed]
  9. Duh, C.-Y.; Wang, S.-K.; Huang, B.-T.; Dai, C.F. Cytotoxic cembrenolide diterpenes from the Formosan soft coral Lobophytum crassum. J. Nat. Prod. 2000, 63, 884–885. [Google Scholar] [CrossRef] [PubMed]
  10. Chao, C.-H.; Wen, Z.-H.; Wu, Y.-C.; Yeh, H.-C.; Sheu, J.H. Cytotoxic and anti-inflammatory cembranoids from the soft coral Lobophytum crassum. J. Nat. Prod. 2008, 71, 1819–1824. [Google Scholar] [CrossRef] [PubMed]
  11. Tseng, Y.-J.; Wen, Z.-H.; Hsu, C.-H.; Dai, C.-F.; Sheu, J.H. Bioactive cembranoids from the Dongsha Atoll soft coral Lobophytum crassum. Bull. Chem. Soc. Jpn. 2011, 84, 1102–1106. [Google Scholar] [CrossRef]
  12. Kao, C.-Y.; Su, J.-H.; Lu, M.-C.; Hwang, T.-L.; Wang, W.-H.; Chen, J.-J.; Sheu, J.-H.; Kuo, Y.-H.; Weng, C.-F.; Fang, L.-S.; et al. Lobocrassins A–E, new cembrane-type diterpenoids from the soft coral Lobophytum crassum. Mar. Drugs 2011, 9, 1319–1331. [Google Scholar] [CrossRef] [PubMed]
  13. Liao, Z.-J.; Su, H.-J.; Shyue, Y.-C.; Wen, Z.-H.; Sheu, J.H.; Su, J.H. Two new cembranoids from the soft coral Lobophytum crassum. Bull. Chem. Soc. Jpn. 2011, 84, 653–655. [Google Scholar] [CrossRef]
  14. Wanzola, M.; Furuta, T.; Kohno, Y.; Fukumitsu, S.; Yasukochi, S.; Watari, K.; Tanaka, C.; Higuchi, R.; Miyamoto, T. Four new cembrane diterpenes isolated from an Okinawan soft coral Lobophytum crassum with inhibitory effects on nitric oxide production. Chem. Pharm. Bull. 2010, 58, 1203–1209. [Google Scholar] [CrossRef] [PubMed]
  15. Lin, S.-T.; Wang, S.-K.; Cheng, S.-Y.; Duh, C.-Y. Lobocrasol, a new diterpenoid from the soft coral Lobophytum crassum. Org. Lett. 2009, 11, 3012–3014. [Google Scholar] [CrossRef] [PubMed]
  16. Matthée, G.F.; König, G.M.; Wright, A.D. Three new diterpenes from the marine soft coral Lobophytum crassum. J. Nat. Prod. 1998, 61, 237–240. [Google Scholar] [CrossRef] [PubMed]
  17. Kinamoni, Z.; Groweiss, A.; Carmely, S.; Kashman, Y.; Loya, Y. Several new cembranoid diterpenes from three soft corals of the Red Sea. Tetrahedron 1983, 39, 1643–1648. [Google Scholar] [CrossRef]
  18. Kashman, Y.; Carmely, S.; Groweiss, A. Further cembranoid derivatives from Red Sea soft corals Alcyonium flaccidum and Lobophytum crassum. J. Org. Chem. 1981, 46, 3592–3596. [Google Scholar] [CrossRef]
  19. Tursch, B.; Braekman, J.C.; Daloze, D.; Dedeurwaerder, H.; Karlsson, R. Chemical studies of marine invertebrates. XXXI. Crassolide, a highly oxygenated diterpene from the soft coral Lobophytum crassum (Coelenterata, Octocorallia, Alcyonacea). Bull. Soc. Chim. Belg. 1978, 87, 75–81. [Google Scholar] [CrossRef]
  20. Bowden, B.F.; Brittle, J.A.; Coll, J.C.; Liyanage, N.; Mitchell, S.J.; Stokie, G.J. Studies of Australian soft corals. VI. A new cembranolide diterpene from the soft coral Lobophytum crassum (Coelenterata, Anthozoa, Octocorallia, Alcyonacea). Tetrahedron Lett. 1977, 18, 3661–3662. [Google Scholar] [CrossRef]
  21. Cuong, N.X.; Thao, N.P.; Luyen, B.T.T.; Ngan, N.T.T.; Thuy, D.T.T.; Song, S.B.; Nam, N.H.; Kiem, P.V.; Kim, Y.H.; Minh, C.V. Cembranoid diterpenes from the soft coral Lobophytum crassum and their anti-inflammatory activities. Chem. Pharm. Bull. 2014, 62, 203–208. [Google Scholar] [CrossRef] [PubMed]
  22. Zhang, W.; Krohn, K.; Ding, J.; Miao, Z.-H.; Zhou, X.-H.; Chen, S.-H.; Pescitelli, G.; Salvadori, P.; Kurtan, T.; Guo, Y.-W. Structural and stereochemical studies of α-methylene-γ-lactone-bearing cembrane diterpenoids from a South China Sea soft coral Lobophytum crassum. J. Nat. Prod. 2008, 71, 961–966. [Google Scholar] [CrossRef] [PubMed]
  23. Yin, S.W.; Shi, Y.P.; Li, X.M.; Wang, B.G. A new cembranoid diterpene and other related metabolites from the South-China-Sea soft coral Lobophytum crassum. Helv. Chim. Acta 2006, 89, 567–572. [Google Scholar] [CrossRef]
  24. Yin, S.W.; Shi, Y.P.; Li, X.M.; Wang, B.G. A novel hydroperoxyl-substituted cembranolide diterpene from marine soft coral Lobophytum crassum. Chin. Chem. Lett. 2005, 16, 1489–1491. [Google Scholar]
  25. Zhao, M.; Yin, J.; Jiang, W.; Ma, M.; Lei, X.; Xiang, Z.; Dong, J.; Huang, K.; Yan, P. Cytotoxic and antibacterial cembranoids from a South China Sea soft coral, Lobophytum sp. Mar. Drugs 2013, 11, 1162–1172. [Google Scholar] [CrossRef] [PubMed]
  26. Yin, J.; Zhao, M.; Ma, M.; Xu, Y.; Xiang, Z.; Cai, Y.; Dong, J.; Lei, X.; Huang, K.; Yan, P. New casbane diterpenoids from a South China Sea soft coral, Sinularia sp. Mar. Drugs 2013, 11, 455–465. [Google Scholar] [CrossRef] [PubMed]
  27. Zhao, M.; Li, X.; Zhao, F.; Cheng, S.; Xiang, Z.; Dong, J.; Huang, K.; Yan, P. Four new 7,8-epoxycembranoids from a Chinese soft coral Lobophytum sp. Chem. Pharm. Bull. 2013, 61, 1323–1328. [Google Scholar] [CrossRef] [PubMed]
  28. Zhang, C.; Li, J.; Su, J.; Liang, Y.; Yang, X.; Zheng, K.; Zeng, L. Cytotoxic diterpenoids from the soft coral Sarcophyton crassocaule. J. Nat. Prod. 2006, 69, 1476–1480. [Google Scholar] [CrossRef] [PubMed]
  29. Jia, R.; Guo, Y.-W.; Mollo, E.; Cimino, G. Sarcophytonolides A–D, four new cembranolides from the Hainan soft coral Sarcophyton sp. Helv. Chim. Acta 2005, 88, 1028–1033. [Google Scholar] [CrossRef]
  30. Liang, L.-F.; Gao, L.-X.; Li, J.; Taglialatela-Scafati, O.; Guo, Y.-W. Cembrane diterpenoids from the soft coral Sarcophyton trocheliophorum Marenzeller as a new class of PTP1B inhibitors. Bioorg. Med. Chem. 2013, 21, 5076–5080. [Google Scholar] [CrossRef] [PubMed]
  31. Frelek, J.; Klimek, A.; Ruskowska, P. Dinuclear transition metal complexes as auxiliary chromophores in chiroptical studies on bioactive compounds. Curr. Org. Chem. 2003, 7, 1081–1104. [Google Scholar] [CrossRef]
  32. Chen, D.; Chen, W.; Liu, D.; van Ofwegen, L.; Proksch, P.; Lin, W. Asteriscane-type sesquiterpenoids from the soft coral Sinularia capillosa. J. Nat. Prod. 2013, 76, 1753–1763. [Google Scholar] [CrossRef] [PubMed]
  33. Coates, R.M.; Ley, D.A.; Cavender, P.L. Synthesis and carbon-13 nuclear magnetic resonance spectra of all-trans-geranylgeraniol and its nor analogs. J. Org. Chem. 1978, 43, 4915–4922. [Google Scholar] [CrossRef]
  34. Couperus, P.A.; Clague, A.D.; van Dongen, J.P. 13C chemical shifts of some model olefins. Org. Magn. Chem. 1976, 8, 426–431. [Google Scholar] [CrossRef]
  35. Bowden, B.F.; Coll, J.C.; Mitchell, S.J. Studies of Australian soft corals. XVIII. Further cembranoid diterpenes from soft corals of the genus Sarcophyton. Aust. J. Chem. 1980, 33, 879–884. [Google Scholar] [CrossRef]
  36. Quang, T.H.; Ha, T.T.; Minh, C.V.; Kiem, P.V.; Huong, H.T.; Ngan, N.T.T.; Nhiem, N.X.; Tung, N.H.; Tai, B.H.; Thuy, D.T.T.; et al. Cytotoxic and anti-inflammatory cembranoids from the Vietnamese soft coral Lobophytum laevigatum. Bioorg. Med. Chem. 2011, 19, 2625–2632. [Google Scholar] [CrossRef] [PubMed]
  37. Kusumi, T.; Yamada, K.; Ishitsuka, M.O.; Fujita, Y.; Kakisawa, H. New cembranoids from the Okinawan soft coral Sinularia mayi. Chem. Lett. 1990, 19, 1315–1318. [Google Scholar] [CrossRef]
  38. Kobayashi, M.; Hirase, T. Marine terpenes and terpenoids. XI. Structures of new dihydrofuranocembranoids isolated from a Sarcophyton sp. soft coral of Okinawa. Chem. Pharm. Bull. 1990, 38, 2442–2445. [Google Scholar] [CrossRef]
  39. Bowden, B.F.; Coll, J.C.; Heaton, A.; König, G.; Bruck, M.A.; Cramer, R.E.; Klein, D.M.; Scheuer, P.J. The structures of four isomeric dihydrofuran-containing cembranoid diterpenes from several species of soft coral. J. Nat. Prod. 1987, 50, 650–659. [Google Scholar] [CrossRef]
  40. Liang, L.-F.; Lan, L.-F.; Taglialatela-Scafati, O.; Guo, Y.-W. Sartrolides A–G and bissartrolide, new cembranolides from the South China Sea soft coral Sarcophyton trocheliophorum Marenzeller. Tetrahedron 2013, 69, 7381–7386. [Google Scholar] [CrossRef]
  41. Toth, J.A.; Burreson, B.J.; Scheuer, P.J.; Finer-Moore, J.; Clardy, J. Emblide, a new polyfunctional cembranolide from the soft coral Sarcophyton glaucum. Tetrahedron 1980, 36, 1307–1309. [Google Scholar] [CrossRef]
  42. Uchio, Y.; Nitta, M.; Nakayama, M.; Iwagawa, T.; Hase, T. Ketoemblide and sarcophytolide, two new cembranolides with ε-lactone function from the soft coral Sarcophyta elegans. Chem. Lett. 1983, 12, 613–616. [Google Scholar] [CrossRef]
  43. Yan, P.; Deng, Z.; van Ofwegen, L.; Proksch, P.; Lin, W. Lobophytones O–T, new biscembranoids and cembranoid from soft coral Lobophytum pauciflorum. Mar. Drugs 2010, 8, 2837–2848. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Structures of compounds 118.
Figure 1. Structures of compounds 118.
Marinedrugs 14 00111 g001 1024
Figure 2. Key COSY and HMBC correlations for 1 and 37.
Figure 2. Key COSY and HMBC correlations for 1 and 37.
Marinedrugs 14 00111 g002 1024
Figure 3. Key NOE correlations and computer-generated models using MM2 force field calculations for 17.
Figure 3. Key NOE correlations and computer-generated models using MM2 force field calculations for 17.
Marinedrugs 14 00111 g003a 1024Marinedrugs 14 00111 g003b 1024
Figure 4. ICD curve of 3 induced by Mo2(OAc)4 in DMSO.
Figure 4. ICD curve of 3 induced by Mo2(OAc)4 in DMSO.
Marinedrugs 14 00111 g004 1024
Table 1. 1H NMR data for 17 (CDCl3, 600 MHz) a.
Table 1. 1H NMR data for 17 (CDCl3, 600 MHz) a.
No.1234567
26.24, d (12.0)6.23, d (12.0)5.31, d (3.0)6.02, dd (11.4, 1.8)6.06, dd (11.4, 1.8)5.29, d (10.8)5.44, br d (9.6)
37.70, d (12.0)7.62, d (12.0)3.17, d (3.0)5.87, d (11.4)5.96, d (11.4)5.19, d (10.8)5.08, d (9.6)
52.63, m2.66, m1.92, m2.28, m2.26, m2.40, m2.32, m
2.55, m2.63, m1.75, m1.98, m2.01, m2.37, m2.15, m
62.07, m1.91, m1.74, m2.27, m2.28, m1.95, m1.86, td (13.8, 3.0)
1.57, m1.71, m1.57, m2.04, m2.03, m1.92, m
1.35, m
72.87, dd (9.6, 3.0)2.64, m3.58, d (10.8)5.11, dd (10.2, 5.4)5.09, dd (10.2, 4.8)2.64, br t (3.6)3.34, d (10.8)
91.82, m2.05, m1.97, m2.25, m2.20, m2.15, m2.31, m
1.49, m1.19, m1.66, m2.15, m2.10, m0.95, t (13.2)
102.18, m2.12, m1.87, m1.82, m1.82, m2.28, m5.53, m
2.15, m2.00, m1.69, m1.35, m1.20, m1.90, m
116.80, t (7.2)6.60, dd (7.2, 4.2)3.24, dd (7.2, 5.4)3.79, br d (10.8)3.44, br d (10.8)5.12, dd (9.0, 6.6)5.52, d (18.6)
132.63, m2.69, m2.08, m2.26, m2.08, m2.29, m1.67, m
2.42, m2.43, m1.78, m1.94, m1.95, ddd (15.0, 6.0, 2.4)1.99, m1.53, m
142.42, m2.83, m1.94, m2.98, m2.84, ddd (15.0, 11.4, 6.0)1.91, m2.14, m
2.28, m2.37, m1.72, m2.17, m1.71, m1.69, m
2.26, m
153.20, m2.17, m2.22, m3.43, q (7.2)
161.00, d (6.6)1.00, d (6.6)1.00, d (6.6)1.47,d (7.2)1.49, s 4.51, d (11.4)
4.46, d (11.4)
170.95, d (6.6)1.08, d (6.6)1.01, d (6.6) 3.82, d (12.6)1.55, s1.65, s
3.44, d (12.6)
18 1.79, s1.79, s1.88, s1.74, s
191.18, s1.12, s1.14, s1.30, s1.34, s1.28, s1.15, s
20 1.28, s0.99, s1.58, s1.33, s
213.77, s3.77, s3.76, s 3.23, s
223.75, s3.76, s3.68, s
a The coupling constants (J) are in parentheses and reported in Hz; chemical shifts are given in ppm.
Table 2. 13C NMR data for 17 (CDCl3, 150 MHz) a.
Table 2. 13C NMR data for 17 (CDCl3, 150 MHz) a.
No.1234567
1158.8, C158.7, C148.3, C133.7, C140.9, C71.7, C132.4, C
2120.4, CH118.8, CH113.8, CH125.7, CH120.4, CH78.0, CH84.0, CH
3134.3, CH136.6, CH42.0, CH121.7, CH122.8, CH119.8, CH126.8, CH
4127.9, C127.7, C50.0, C138.2, C137.3, C144.4, C139.6, C
523.2, CH223.6, CH224.4, CH240.4, CH240.5, CH237.7, CH235.6, CH2
627.2, CH226.8, CH229.9, CH226.4, CH226.3, CH225.3, CH226.2, CH2
760.7, CH62.7, CH73.7, CH125.0, CH124.9, CH61.7, CH71.2, CH
860.9, C61.1, C74.9, C136.3, C136.5, C59.7, C78.4, C
936.2, CH236.3, CH239.3, CH235.5, CH236.3, CH240.0, CH236.7, CH2
1024.3, CH224.0, CH220.4, CH226.3, CH227.0, CH223.7, CH2124.4, CH
11142.5, CH144.4, CH43.5, CH67.9, CH70.8, CH124.5, CH138.9, CH
12132.4, C130.1, C45.2, C87.0, C80.2, C135.2, C73.0, C
1327.7, CH227.0, CH225.3, CH232.9, CH230.9, CH234.8, CH241.3, CH2
1430.0, CH228.9, CH223.2, CH222.1, CH222.6, CH227.0, CH221.8, CH2
1529.8, CH36.8, CH35.6, CH51.0, CH77.6, C60.7, C127.9, C
1621.2, CH322.3, CH321.4, CH316.3, CH328.0, CH3172.8, C78.5, CH2
1720.4, CH320.8, CH320.7, CH3177.8, C73.6, CH29.9, CH310.1, CH3
18168.8, C168.5, C177.4, C16.5, CH316.3, CH316.2, CH315.5, CH3
1917.9, CH316.9, CH321.1, CH314.8, CH314.9, CH316.7, CH317.8, CH3
20168.0, C167.8, C176.7, C23.1, CH319.0, CH314.8, CH326.9, CH3
2151.8, CH351.7, CH352.1, CH3 49.2, CH3
2251.8, CH351.8, CH352.0, CH3
a The assignments were based on HMQC, HMBC, and COSY spectra.
Table 3. Inhibitory Activity against LPS-Induced NO Production a.
Table 3. Inhibitory Activity against LPS-Induced NO Production a.
CompoundIC50 (μM)CC50 b (μM)
117 ± 3>60.0
713 ± 2>60.0
1224 ± 2>60.0
138 ± 1>60.0
1712 ± 2>60.0
a The other compounds were inactive at 30 μM; b CC50: cytotoxicity against mouse peritoneal macrophages.
Mar. Drugs EISSN 1660-3397 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top