Mar. Drugs 2014, 12, 3060-3071; doi:10.3390/md12053060 OPEN ACCESS
marine drugs
ISSN 1660-3397 www.mdpi.com/journal/marinedrugsArticle
Klymollins T–X, Bioactive Eunicellin-Based
Diterpenoids from the Soft Coral Klyxum molle
Fang-Yu Chang 1, Fang-Jung Hsu 1, Chi-Jen Tai 1, Wen-Chi Wei 2, Ning-Sun Yang 2,3,4,* and Jyh-Horng Sheu 1,5,6,7,8,*
1 Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan; E-Mails: [email protected] (F.-Y.C.);
[email protected] (F.-J.H.); [email protected] (C.-J.T.)
2 Agricultural Biotechnology Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115, Taiwan; E-Mail: [email protected]
3 Institute of Biotechnology, National Taiwan University, Taipei 106, Taiwan 4 Department of Life Science, National Central University, Taoyuan 320, Taiwan 5 Division of Marine Biotechnology, Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 804, Taiwan
6 Doctoral Degree Program in Marine Biotechnology, National Sun Yat-sen University and Academia Sinica, Kaohsiung 804, Taiwan
7 Department of Medical Research, China Medical University Hospital, China Medical University, Taichung 404, Taiwan
8 Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
* Authors to whom correspondence should be addressed; E-Mails:
[email protected] (N.-S.Y.); [email protected] (J.-H.S.); Tel.: +886-2-2787-2067 S.Y.); +886-7-525-2000 ext 5030 (J.-H.S.); Fax: +886-2-2787-2066 (N.-S.Y.); +886-7-525-5020 (J.-H.S.).
Received: 4 January 2014; in revised form: 18 April 2014 / Accepted: 29 April 2014 / Published: 22 May 2014
Abstract: Five new eunicellin-based diterpenoids, klymollins T–X (1–5), along with two known compounds (6 and 7) have been isolated from the soft coral Klyxum molle. The structures of these new metabolites were elucidated by extensive spectroscopic analysis and by comparison with related known compounds. Compound 5 was found to exert
significant in vitro anti-inflammatory activity against LPS-stimulated RAW264.7 macrophage cells. Furthermore, compounds 4 and 7 were shown to exhibit cytotoxicity against a limited panel of human cancer cell lines. Mar. Drugs 2014, 12 3061
Keywords: soft coral; Klyxum molle; eunicellin-based diterpenoids; klymollins; cytotoxic activity; anti-inflammatory activity
1. Introduction
Soft corals are known to be a rich source of terpenoidal metabolites [1]. Many studies about the discovery of versatile molecular structures and bioactivities of eunicellin-type compounds from soft corals have been reported recently [2–18]. Our previous studies on the secondary metabolites of a Formosan soft coral Klyxum molle have resulted in the isolation of a series of new eunicellin-based diterpenoids, klymollins A–S [19,20]. In our continuing investigation effort to discover new metabolites from the soft coral K. molle, we have identified five new eunicellin-type metabolites, klymollins T–X (1–5) (Chart 1 and Supplementary Figures S1–S15), along with two known eunicellin-based
diterpenoids, sclerophytin A (6) and sclerophytin B (7) [21] (Chart 1). The molecular structures of these compounds, including their relative configurations, were established by detailed spectroscopic analysis and by comparison with related physical and spectral data of known compounds. The ability of compounds 1–7 to inhibit IL-6 (interlukin-6) and TNF-α (tumor necrosis factor α) expression in LPS (lipopolysaccharide)-stimulated murine RAW264.7 macrophage cells and the cytotoxicity of 3–7 against five human cancer cell lines, human T cell lymphoblast-like cell line (CCRF-CEM), human erythromyeloblastoid leukemia (K562), human acute lymphoblastic leukemia cell line (Molt 4), human ductal breast epithelial tumor cell line (T47D) and human colorectal adenocarcinoma cell line (DLD-1) were evaluated.
2. Results and Discussion
Klymollin T (1) was obtained as a colorless oil. The HRESIMS (m/z 545.2722 [M + Na] +) of 1 provided its molecular formula as C28H42O9, implying the presence of eight degrees of unsaturation. The IR spectrum of 1 revealed the presence of hydroxy and carbonyl groups from absorptions at 3481 and 1746 cm–1, respectively. The 13C NMR spectroscopic data of 1 exhibited 28 carbon signals (Table 1), which were assigned by the aid of DEPT spectrum to six methyls (including two acetate methyl at δC 21.2 and 20.8), seven methylenes (including one oxymethylene at δC 53.0), nine methines (including five oxymethines at δC 91.6, 80.6, 74.2, 73.0 and 72.9), and six quaternary carbons (including three sp2 oxygenated quaternary carbons at δC 172.0, 170.1 and 170.1, two sp3 oxygenated quaternary carbons at δC 84.9 and 55.7, and one sp2 quaternary carbon at δC 150.5). The NMR data of 1 in C6D6 (Table 1) showed the presence of one n-butyrate (δC 172.0, C; 37.8, CH2; 19.2, CH2; and 14.1, CH3; and δH 1.98, 2H, m; 1.53, 2H, m; and 0.83, 3H, t, J = 7.5 Hz), one 1,1-disubstituted double bond (δC 116.9, CH2 and 150.5, C; and δH 5.24, 1H, d, J = 2.0 Hz and 4.86, 1H, brs), one terminal epoxide (δC 53.0, CH2 and 55.7, C; δH 2.31, d and 1.99, d, each 1H, J = 5.0 Hz) and two acetate groups (δC 170.1, C; 170.1, C; 20.8, CH3 and 21.2, CH3; and δH 1.62, s, and 1.82, s, each 3H), respectively. Analysis of HMQC correlations showed that proton signals appearing at δH 2.33 (1H, m), 2.17 (1H, t, J = 8.5 Hz), 3.97 (1H, br s), and 5.00 (1H, d, J = 5.5 Hz) were correlated to two ring
juncture methine carbons at δC 42.4 and 43.5 and two oxymethine carbons at δC 91.6 and 80.6, respectively. Therefore, the remaining three degrees of unsaturation identified 1 as a tricyclic diterpenoid. In addition, the COSY correlations of 1 assigned three isolated consecutive proton spin systems (Figure 1). The molecular framework of 1 was further established by HMBC correlations (Figure 1). Furthermore, H-12 (δ 5.24) and an acetate methyl (δ 1.62) exhibited HMBC correlations to the acetate carbonyl carbon (δ 170.1), and H-13 exhibited HMBC correlation to the n-butyrate carbonyl carbon (δ 172.0), revealing the location of an acetate at C-12 and an n-butyrate at C-13. The location of an acetate group at C-3 was then deduced by the chemical shifts of C-3 (δ 84.9) and H3-15 (δ 1.75). From the above results, the structure of compound 1 was shown to be related to that of the known compound, klymollin C [19]. Comparison of the NMR data of them revealed that the replacement of the acetoxy group at C-13 in klymollin C by an n-butyryloxy group in 1.
Figure 1. Selected COSY (▬) and HMBC (→) correlations of 1, 3 and 4. Mar. Drugs 2014, 12 3063
The relative configuration of 1 was determined by comparison of the chemical shifts with klymollin C and was further confirmed by NOE correlations (Figure 2). The NOE
correlations between H-12 and H-13, and between H-13 with H-1, H-10 and H-12 suggested that H-12 and H-13 were β-oriented and the relative configuration of 1 was proposed as 1R*, 2R*, 3R*, 6S*, 9R*, 10S*, 11S*, 12S*, 13S* and 14R*.
Figure 2. Key NOESY Correlations for 1.
The HRESIMS of klymollin U (2) exhibited a [M + Na]+ peak at m/z 545.2723 established the same molecular formula as that of 1. The 1H and 13C NMR data of 2 (Table 1) were similar to those of 1, revealed the presence of two acetoxy groups (δC 170.0, C; 169.4, C; 22.5, CH3 and 21.1, CH3; and δH 2.00, s, 3H and 1.92, s, 3H), one n-butyryloxy group (δC 172.6, C; 36.5, CH2; 18.8, CH2; 13.5, CH3; and δH 2.38, m, 2H; 1.70, m, 2H; 1.00, t, 3H, J = 7.6 Hz), one 1,1-disubstituted double bond (δC 116.8, CH2 and 150.0, C; and δH 5.36, brs and 4.98, brs, each 1H), one terminal epoxide (δC 53.6, CH2 and 55.2, C; δH 2.87, d and 2.64, d, each 1H, J = 4.8 Hz). The positions of one n-butyrate group and one acetate group at C-12 and C-13, respectively, was confirmed by the HMBC correlations of H-12 and the oxymethylene protons (δH 2.38) to the n-butyryloxy carbonyl carbon (δ 172.6), and H-13 and an acetate methyl (δH 2.00) to the acetate carbonyl carbon (δ 170.0). Thus, the remaining one acetate group had to be positioned at C-3, an oxygen-bearing quaternary carbon resonating at δ 84.6 ppm. A more detailed analysis of the 1H and 13C NMR spectroscopic data and correlations in the 1H–1H COSY and HMBC spectra led to the establishment of the gross structure of 2 (Figure 1). The stereochemistry of 2 was finally confirmed by comparison of its NMR data and NOE correlations with 1. Mar. Drugs 2014, 12 3064
Table 1. 13C and 1H NMR data for compounds 1–3. 1 a 2 b 3 b δH δC δH δC δH δC 1 2.33 m 42.4 (CH) c 2.38 t (7.2) d 41.8 (CH) 2.20 m 46.0 (CH) 2 3.97 brs e 91.6 (CH) 3.79 brs 90.8 (CH) 3.58 brs 90.9 (CH) 3 84.9 (C) 84.6 (C) 86.7 (C) 4 1.49 m 2.35 m 28.5 (CH2) 1.53 m 2.26 m 27.8 (CH2) 2.10 m 1.80 t (10.8) 37.6 (CH2) 5 1.62 m 2.30 m 34.4 (CH2) 1.69 m 2.20 m 34.3 (CH2) 2.76 m 1.92 t (12.0) 32.8 (CH2) 6 4.24 dd (9.5, 4.0) d 73.0 (CH) 4.29 d (8.0) 72.5 (CH) 113.4 (C) 7 150.5 (C) 150.0 (C) 2.16 m 38.8 (CH) 8 2.57 d (13.5) 2.71 dd (13.5, 4.0) 41.4 (CH2) 2.48 d (13.6) 2.78 dd (13.6, 4.0) 40.7 (CH2) 2.41 ddd (16.0, 6.8, 3.2) 1.68 m 36.0 (CH2)
9 5.00 d (5.5) 80.6 (CH) 4.90 m 80.1 (CH) 4.05 dt (8.8, 3.2) 82.1 (CH) 10 2.17 t (8.5) 43.5 (CH) 2.26 t (10.4) 42.9 (CH) 3.92 t (8.0) 46.6 (CH) 11 55.7 (C) 55.2 (C) 148.1 (C) 12 5.24 d (2.0) 74.2 (CH) 4.92 brs 73.6 (CH) 2.02 m 2.20 m 31.2 (CH2) 13 5.11 dd (11.0, 2.0) 72.9 (CH) 4.91 d (10.4) 72.2 (CH) 0.99 m 1.70 m 24.9 (CH2) 14 2.11 m 41.8 (CH) 2.01 m 40.7 (CH) 1.26 m 43.2 (CH) 15 1.75 s 22.9 (CH3) 1.65 s 22.1 (CH3) 1.31 s 23.2 (CH3) 16 5.24 d (2.0) 4.86 brs 116.9 (CH2) 4.98 brs 5.36 brs 116.8 (CH2) 1.36 d (7.6) 19.1 (CH3) 17 1.99 d (5.0) 2.31 d (5.0) 53.0 (CH2) 2.64 d (4.8) 2.87 d (4.8) 53.6 (CH2) 4.77 brs 4.70 d (1.2) 109.8 (CH2) 18 2.06 m 28.3 (CH) 2.03 m 27.3 (CH) 1.70 m 29.1 (CH) 19 0.89 d (7.0) 16.3 (CH3) 0.84 d (7.2) 15.3 (CH3) 0.95 d (6.8) 21.9 (CH3) 20 1.12 d (7.0) 24.5 (CH3) 1.09 d (7.2) 24.0 (CH3) 0.76 d (6.8) 15.4 (CH3) 3-OAc 1.82 s 170.1 (C) 21.2 (CH3) 1.92 s 169.4 (C) 22.5 (CH3) 6-OMe 3.26 brs 48.5 (CH3) 12-OAc 1.62 s 170.1 (C) 20.8 (CH3) 12-OCOPr 2.38 m 1.70 m 1.00 t (7.6) 172.6 (C) 36.5 (CH2) 18.8 (CH2) 13.5 (CH3) 13-OAc 2.00 s 170.0 (C) 21.1 (CH3) 13-OCOPr 1.98 m 1.53 m 0.83 t (7.5) 172.0 (C) 37.8 (CH2) 19.2 (CH2) 14.1 (CH3)
