Cembrane diterpenoids from the whole plant of Tournefortia sibirica

Journal Pre-proofs Cembrane diterpenoids from the whole plant of Tournefortia sibirica Shengbao Diao, Mei Jin, Jinfeng Sun, Chunshi Jin, Rongshen Wang, Wei Zhou, Gao Li PII: DOI: Reference:

S0040-4039(19)31204-3 https://doi.org/10.1016/j.tetlet.2019.151413 TETL 151413

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Tetrahedron Letters

Received Date: Revised Date: Accepted Date:

24 October 2019 15 November 2019 17 November 2019

Please cite this article as: Diao, S., Jin, M., Sun, J., Jin, C., Wang, R., Zhou, W., Li, G., Cembrane diterpenoids from the whole plant of Tournefortia sibirica, Tetrahedron Letters (2019), doi: https://doi.org/10.1016/j.tetlet. 2019.151413

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Cembrane diterpenoids from the whole plant of Tournefortia sibirica Shengbao Diaoa,1, Mei Jina,b,1, Jinfeng Suna, Chunshi Jina, Rongshen Wanga, Wei Zhoua,*, Gao Lia,* a

Key Laboratory of Natural Resources of Changbai Mountain and Functional

Molecules, Ministry of Education, Yanbian University College of Pharmacy, Yanji 133002, China b

Department of Pharmacy, Yanbian University Hospital, Yanji 133000, China

*Corresponding authors Tel: 86-433-2436001, Fax: 86-433-2435026, E-mail: [email protected] (G. Li); Tel: 86-433-2436007, Fax: 86-433-2435026, E-mail: [email protected] (W. Zhou) 1

Contributed equally to this work.

1

ABSTRACT Four new cembrane diterpenoids (1–4), along with four known compounds (5–8), were isolated from the whole plant of Tournefortia sibirica L. Their structures of these new compounds were elucidated mainly using NMR, HRESIMS and a modified version of Mosher’s method. The anti-inflammatory effects of the isolated compounds (1–8) were evaluated in terms of inhibition of production of nitric oxide, tumor necrosis factor-α and interleukin-6 in lipopolysaccharide-stimulated RAW264.7 cells.

Keywords

Tournefortia

sibirica;

Boraginaceae;

anti-inflammatory activity

2

Cembrane

diterpenoids;

The genus Tournefortia contains ~150 species, which are distributed widely in tropical and subtropical regions [1]. Tournefortia sibirica L. (Boraginaceae) is a salt-secreting halophyte found mainly in the Northeastern regions of China, Mongolia, Korea and Japan [2]. T. sibirica has value in medical, food and landscaping industries, and can be used for environmental protection, such as sand stabilization, soil improvement, and phytoremediation [3]. Phytochemical studies have revealed that T. sibirica contains essential oils [4,5], alkaloids [6], polysaccharides [7], lignans [8,9], flavonoids, steroids and triterpenoids [9,10]. Here, we describe the isolation of four new cembrane diterpenoids (1–4) and four known compounds (5–8) from the whole plant of T. sibirica (Fig. 1). Their structural identification was based on spectroscopy studies, a modified version of Mosher’s method, and literature comparisons. The known compounds were identified as corchoionol C (5) [11], corchoionoside C (6) [12],

amarantholidoside

V

(7)

9(S),12(S),13(S)-trihydroxyoctadeca-10(E),15(Z)-dienoic

[13] acid

(8)

and [14]

by

spectroscopy and by comparing the NMR data with that reported in the literature. Compounds 1–8 were evaluated for their inhibitory effects on the production of nitric oxide

(NO),

tumor

necrosis

factor

(TNF)-α

and

interleukin

(IL)-6

in

lipopolysaccharide (LPS)-induced RAW 264.7 cells. Compound 1 was obtained as a white powder with the molecular formula C20H34O4 based on the observed peak at m/z 361.2352 [M + Na]+ (calcd for 361.2355) in HRESIMS. The IR spectrum indicated a hydroxyl group (3444 cm−1) and double bond (1645 cm−1). The 1H NMR spectrum of 1 (Table 1) showed three olefinic protons at δH 5.42 (1H, d, J = 9.5 Hz, H-3), 5.02 (1H, d, J = 7.8 Hz, H-7) and 4.76 (1H, t, J = 7.8 Hz, H-11), three oxygenated methine protons at δH 4.63 (1H, t, J = 9.5 Hz, H-2), 4.11

3

(1H, dd, J = 10.8, 4.3 Hz, H-5) and 3.85 (1H, dd, J =10.5, 4.8 Hz, H-9), one methine proton at δH 1.56 (1H, dt, J = 9.5, 4.5 Hz, H-1), five methyl signals at δH 1.71 (3H, d, J = 1.2 Hz, H-18), 1.64 (3H, s, H-20), 1.60 (3H, s, H-19), 1.34 (3H, s, H-17) and 1.28 (3H, s, H-16).

13

C NMR and DEPT-135 spectra (Table 1) exhibited three

carbon–carbon double-bond signals at δC 140.4 (C-4), 138.2 (C-12), 138.0 (C-8), 132.6 (C-3), 123.8 (C-7) and 120.8 (C-11), four oxygenated carbon signals at δC 79.4 (C-9), 79.1 (C-5), 75.5 (C-15) and 70.6 (C-2), five methyl carbons at δC 29.9 (C-16), 26.0 (C-17), 16.0 (C-20), 10.5 (C-18) and 10.5 (C-19). The 1H–1H COSY spectrum showed connectivity between H-13/H-14/H-1/H-2/H-3, between H-5/H-6/H-7, and between H-9/H-10/H-11 (Fig. 2). In the HMBC spectrum, the locations of the five methyl groups were determined by the correlations between H-18 and C-3, C-4 and C-5, between H-19 and C-7, C-8 and C-9, between H-20 and C-11, C-12 and C-13, between H-16 and C-1 and C-15, and between H-17 and C-1 and C-15 (Fig. 2). The absolute configuration of compound 1 was determined by NOESY correlations (Fig. 3) and a modified version of Mosher’s method. To determine the absolute configuration of the hydroxyl groups of C-2, C-5 and C-9 positions, Mosher’s ester derivatives (1S, 1R) were prepared [15]. 1H NMR data were assigned based on the 1

H-1H COSY spectra of 1S and 1R. The negative values of δH (δS-δR) at H-3, H-7,

H-18 and H-19 and positive values of δH (δS-δR) at H-6, H-10, H-13, H-14 and H-20 suggested 2S, 5R and 9R configurations (Fig. 4). The NOESY spectrum of 1 showed correlations between H-3 and H-5, and between H-2 and H-18, which suggested an E-configuration of the C-3/C-4 double bond, and this configuration was also

4

supported by the higher field chemical shift of C-18 (δC 10.52) [16,17]. An E-configuration for the C-7/C-8 double bond was assigned from the NOE correlations between H-7 and H-9, and H-6 and H-19, and the chemical shift of C-19 (δC 10.54) [16,17]. NOE correlations between H-11 and H-13, and H-10 and H-20, and the chemical shift of C-20 (δC 15.99) also supported the E-configuration [18]. The absolute configuration at C-1 was confirmed as S by the NOE correlations between H-1 and H-3, H-3 and H-5, and between H-2 and H-17. Therefore, compound 1 was identified to be (1S,2S,3E,5R,7E,9R,11E)-3,7,11-cembradiene-2,5,9-triol. Compound 2 was obtained as a white powder with a molecular formula of C20H34O3 based on the observed peak at m/z 345.2401 [M + Na]+ (calcd for 345.2406) in HRESIMS. The UV, IR, 1H and 13C NMR data (Table 1) of 2 indicated a structure similar to that of 1 except for the hydroxyl group at the C-2 position, which was replaced by a hydrogen atom in 2; these data were supported by 1H–1H COSY and HMBC correlations (Fig. 2). The absolute configuration of the hydroxyl groups of C-5 and C-9 positions was also determined by analyses of Mosher’s ester derivatives (2S, 2R). The negative values of δH (δS-δR) at H-3, H-7, H-18 and H-19 and positive values of δH (δS-δR) at H-6, H-10 and H-20 suggested 5R and 9R configurations (Fig. 4). In the NOESY spectrum of 2, we noted the NOE correlations between H-3 and H-5, between H-7 and H-9, and H-6 and H-19, between H-11 and H-13, and H-10 and H-20. These data indicated the E-configurations of double bonds at C-3/C-4, C-7/C-8 and C-11/C-12, and this result was also supported by the higher-field chemical shifts of C-18 (δC 9.8), C-19 (δC 10.1) and C-20 (δC 15.0) [16,17]. The absolute

5

configuration at C-1 was confirmed as S by the NOE correlations between H-1 and H-3, and H-18, and H-3 and H-5, and H-5 and H-18 (Fig. 3). Thus, the structure of compound

2

was

determined

to

be

(1S,3E,5R,7E,9R,11E)-3,7,11-cembradiene-5,9-diol. The molecular formula of compound 3 was determined to be C26H44O9 based on the observed peak at m/z 523.2878 for [M + Na]+ (calcd for 523.2884) by HRESIMS. Compound 3 was hydrolyzed to afford D-glucose and the aglycone (1). The anomeric proton signal of 3 at δH 4.30 (1H, d, J = 7.7 Hz) indicated a β-configuration of the glucosyl moiety. The connectivity of the β-glucose moiety at C-9 was confirmed by the HMBC cross peak of H-1′ (δH 4.30) to C-9 (δc 88.5) (Fig. 2). The absolute configuration of 3 was deduced by comparing the 1H and

13

C NMR data and

optical-rotation value with those of 1, as well as NOESY correlations (Fig. S1). Thus, the

structure

of

compound

3

was

elucidated

to

be

(1S,2S,3E,5R,7E,9R,11E)-9-O-β-D-glucopyanosyl-3,7,11-cembradiene-2,5-diol. Compound 4 was obtained as a white powder, and its molecular formula was determined to be C26H44O8 by HRESIMS, m/z 467.2992 for [M – H2O + H]+ (calcd for 467.3003). Enzymatic hydrolysis of 4 gave D-glucose and the aglycone (2). The 1

H NMR spectrum of 4 showed the anomeric proton of glucose at δH 4.90 (1H, d, J =

7.7 Hz), which indicated a β-configuration for the glucosyl moiety. The position of the β-glucose unit was determined by the HMBC correlation between the anomeric proton H-1′ (δH 4.90) and C-9 (δc 87.6) of the aglycone (Fig. 2). The absolute configuration of 4 was assigned the same as 2 based on the similar optical rotation

6

value and NOESY correlations (Fig. S1). Therefore, the structure of compound 4 was determined

to

be

(1S,3E,5R,7E,

9R,11E)-9-O-β-D-glucopyanosyl-3,7,11-cembradiene-5-ol. Compounds 1–8 were assayed for their inhibitory effects on the production of NO, TNF-α and IL-6 in LPS-induced RAW 264.7 cells. Cell viability was determined by the MTT assay, which showed that compounds 1–8 did not have significant toxicity towards RAW 264.7 cells at 100 µM (data not shown). Then, compounds 1–8 were tested for inhibition of NO, TNF-α and IL-6 production using the Griess and ELISA method. Compounds 5–7 could inhibit NO production with Half-maximal inhibitory concentration (IC50) values of 33.17–49.84 µM. Compounds 1, 2, and 5 exhibited inhibitory activity against IL-6 production with IC50 values of 35.73–43.28 µM. Compounds 1, 2 and 5–7 inhibited the secretion of TNF-α with IC50 values of 52.42–69.97 µM (Table S1). In this study, four new cembrane diterpenoids (1–4), two ionones (5, 6), one sesquiterpene glucoside (7) and one fatty acid (8) were isolated from the whole plant of T. sibirica. Cembrane diterpenoids are a large and structurally varied group of natural products isolated from both terrestrial and marine organisms, especially in soft corals [19]. Cembrane diterpenoids (1–4) were isolated from family Boraginaceae for the first time, might be of systematic importance to this family. Cembrane diterpenoids have been previously acquired from Sapium discolor [20], Euphorbiae pekinensis [21] of family Euphorbiaceae. Plectranthus scutellarioides [22] and Anisomeles indica [23] of family Labiatae, Boswellia sacra [24] of family

7

Burseraceae

and Echinodorus macrophyllus of family Alismataceae [25], which

indicate the close relationship among these families. Compounds 1, 2, and 5–7 exhibited moderate anti-inflammatory activity, and compound 5 was found to possess better inhibitory activity than the other compounds tested. Our results provide a scientific basis to assist in completing characterization of the chemical components isolated from T. sibirica. Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 81760627, 81660699 and 81660579). We thank Arshad Makhdum, from Liwen Bianji, Edanz Group China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript. References [1] J.S. Miller, A new species of Tournefortia (Boraginaceae) from La Planada, Colombia. Novon 5 (1995) 188-189. [2] Y.M. Zhu, Nei Monggol Medicinal Flora. Vol. 2. Hohhot: Inner Mongolian People’s Publishing House, 1989, p. 425–426. [3] X.Y. Tian, C.S. Zhang, Front Microbiol. 8 (2017) 2288–2297. [4] K. Morteza-Semnani, M. Saeedi, M. Akbarzadeh, J. Essent. Oil Res. 20 (2008) 207–208. [5] C. Gao, H.B. Zhang, F.R. Yan, L.Y. Xu, Tech. Econ. Guide 15 (2015) 152–153. [6] M. Hikichi, Y. Asada, T. Furuya, Planta Med. 40(1980) 1–4. [7] X. Zhang, Z. Baim, C. Ding, Feed Ind. 36 (2015) 29–32. [8] Z.Z. Song, Z.M. Liu, Z.J. Jia, Q.X. Zhu, Chinese Chem. Lett. 3 (1992) 975–976. [9] Z.Z. Song, B.G. Wang, Z.J. Jia, Indian J. Chem. B 9 (1996) 955–959. 8

[10] S. Diao, M. Jin, C. Jin, C. Wei, J. Sun, W. Zhou, G. Li, Nat. Prod. Res. 33 (2018) 3021–3024. [11] Y. Zhang, Y.B. Liu, Y. Li, L. Li, S.G. Ma, J. Qu, J.D. Jiang, X.G. Chen, D. Zhang, S.S. Yu, J. Asian Nat. Prod. Res. 17 (2015) 1025–1038. [12] P.V. Kiem, C.V. Minh, X.N. Nguyen, B.H. Tai, T.H. Quang, H.L.T. Anh, X.C. Nguyen, T.N. Hai, S.H. Kim, J.K. Kim, H.D. Jang, Y.H. Kim, B. Korean Chem. Soc. 33 (2012) 3461–3464. [13] A. Fiorentino, M. Dellagreca, B. D'Abrosca, A. Golino, S. Pacifico, A. Izzo, P. Monaco, Tetrahedron 62 (2006) 8952–8958. [14] YK Qiu, YY Zhao, DQ Dou, BX Xu, K. Liu, Arch. Pharm. Res. 30 (2007) 665–669. [15] G. Li, M. Xu, H. Choi, S. Lee, Y. Jahng, C. Lee, D. Moon, M. Woo, J. Son, Chem. Pharm. Bull. 51 (2003) 262264. [16] G.A. Zou, G. Ding, Z.H. Su, J.S. Yang, H.W. Zhang, C.Z. Peng, H.A. Aisa, Z.M. Zou, J. Nat. Prod. 73 (2010) 792–795. [17] W.Y. Qi, Y. Shen, Y. Wu, Y. Leng, K. Gao, J.M. Yue, Phytochemistry 136 (2017) 101–107. [18] X.F. He, X.D.Hou, X. Ren, K. Guo, X.Z. Li, Z.Q. Yan, Y.M. Du, X.F. Zhang, B. Qin, Phytochem. Lett. 15 (2016) 238–244. [19] B. Yang, X. Zhou, X. Lin, J. Liu, Y. Peng, X. Yang, Y. Liu, Curr. Org. Chem. 16 (2012) 1512–1539. [20] B. Liu, H. Zhang, J. Yu, J. Yue, J. Asian Nat. Prod. Res. 17 (2016) 1117–1128. [21] Y. Zhang, Z. Liu, R. Zhang, P. Hou, K. Bi, X. Chen, J. Pharm. Biomed. Anal. 119 (2016) 159–165. [22] S. Cretton, N. Saraux, A. Monteillier, D. Righi, L. Marcourt, G. Genta-Jouve, J.L. 9

Wolfender, M. Cuendet, P. Christen, Phytochemistry 154 (2018) 39–46. [23] Y.L. Chen, Y.H. Lan, P.W. Hsieh, C.C. Wu, S.L. Chen, C.T. Yen, F.R. Chang, W.C. Hung, Y.C. Wu, J. Nat. Prod. 71 (2008) 1207–1212. [24] J.Q. Yu, Y.L. Geng, D.J. Wang, H.W. Zhao, L.P. Guo, X. Wang, Phytochem. Lett. 28 (2018) 59–63. [25] H. Shigemori, S. Shimamoto, M. Sekiguchi, A. Ohsaki, J. Kobayashi, J. Nat. Prod. 65 (2002) 82–84.

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Fig. 1. Structures of compounds 18 from Tournefortia sibirica L.

Fig. 2. Selected 1H-1H COSY (bold bonds) and HMBC (plain arrows) correlations of compounds 14

11

Fig. 3. Key NOESY correlations of compounds 1 and 2

Fig. 4. δH (δS-δR) values (in ppm) for the MTPA esters (1R and 1S, 2R and 2S)

12

Table 1 1H NMR (500 MHz) and 13C NMR (125 MHz) spectral data of 1 and 2 No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1a δH, mult, (J in Hz) 1.56, dt (9.5, 4.5) 4.63, t (9.5) 5.42, d (9.5) 4.11, dd (10.8, 4.3) 2.60, dt (14.5, 10.8) 2.28, dt (14.5, 7.8) 5.02, d (7.8) 3.85, dd (10.5, 4.8) 2.32, dt (15.6, 4.8) 2.15, dt (15.6, 7.8) 4.76, t (7.8) 1.98, m 1.90, m 1.48, m 1.31, m

15 16 1.28, s 17 1.34, s 18 1.71, d (1.2) 19 1.60, s 20 1.64, s a Measured in CD3OD b Measured in DMSO-d5

2b δH, mult, (J in Hz) 1.16, m 1.92, m 5.28, t (6.8)

δC 53.9 70.6 132.6 140.4 79.1 33.9

3.92, d (10.0) 2.31, m 2.23, m 4.86, d (9.5)

123.8 138.0 79.4 32.7

3.62, d (10.2) 2.09, m 1.91, m 4.63, m

120.8 138.2 38.9

1.93, m

28.8

1.48, m 1.16, m

75.5 29.9 26.0 10.52 10.54 16.0

1.05, s 1.07, s 1.45, s 1.50, s 1.50, s

13

δC 47.2 26.8 128.5 134.7 77.1 32.7 122.8 134.9 77.3 32.6 121.2 136.0 36.5 27.8 71.6 27.1 28.1 9.8 10.1 15.0

Table 2 1H NMR (500 MHz) and 13C NMR (125 MHz) spectral data of 3 and 4 No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Glc 1′ 2′ 3′ 4′ 5′ 6′

3a δH, mult, (J in Hz) 1.57, dd (9.6, 2.6) 4.64, t (9.6)

4b δH, mult, (J in Hz) 1.55, m 2.28, m 2.20, m 5.68, d (7.7)

δC 53.7 70.5

5.41, d (9.6)

132.6 140.3 4.12, dd (11.1, 3.8) 79.1 2.63, dd (14.5, 11.1) 34.0 2.26, d (14.5) 5.05, d (10.6) 125.1 136.9 3.86, dd (11.1, 4.2) 88.5 2.52, m 30.3 2.18, dt (12.5, 7.6) 4.74, t (7.6) 120.3 138.5 1.95, dd (11.2, 5.2) 38.5 1.90, d (11.2) 1.52, m 28.6 1.32, br s 75.5 1.28, s 29.9 1.34, s 26.0 1.70, s 10.5 1.67, s 11.3 1.61, s 16.0

4.30, d (7.7) 3.20, d (7.7) 3.37, d (9.7) 3.31, m 3.19, d (8.0) 3.81, d (11.8) 3.67, dd (11.8, 5.3) a Measured in CD3OD b Measured in pyridine-d5

4.40, d (11.0) 2.85, m 2.57, m 5.17, d (9.9) 4.23, t (7.0) 2.82, m 2.38, t (9.5) 4.92, m 2.24, m 2.14, m 1.74, m 1.40, m 1.37, s 1.38, s 1.81, s 1.82, s 1.59, s

103.2 75.3 78.3 71.6 77.8 62.7

4.90, d (7.7) 4.01, t (7.7) 4.24, m 4.21, m 3.81, m 4.40, d (11.0) 4.27, dd (11.0, 5.0)

14

δC 48.7 28.1 129.8 136.3 78.7 34.0 126.0 135.4 87.6 31.0 121.5 136.7 37.6 28.9 72.8 28.1 28.8 10.7 11.7 15.6 103.5 75.8 78.4 72.0 79.0 63.1

15

Highlights 

Four new cembrane diterpenoids 1–4 and four known compounds 5–8 were isolated.



The structures of 1–4 were characterized by NMR, HR-ESI-MS and a Mosher’s method.



This is the first report of 1–8 from the Boraginaceae family.



1, 2, and 5–7 exhibited moderate anti-inflammatory activity.

16