Two new benzofuran lignan glycosides from Gelsemium elegans

Wei Hua a,b, Qing Chun Zhao b, Jia Yang a, Guo Bing Shi b, Li Jun Wu a, Tao Guo b,*a School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang 110016, China

b Department of Pharmacy, Shenyang Northern Hospital, Shenyang 110016, China

Received 19 May 2008

Abstract

Two new benzofuran lignan glycosides, gelsemiunoside A and B, were isolated from the whole plant of Gelsemium elegans

Benth. Their structures were elucidated on the basis of spectroscopic evidence. Furthermore, gelsemiunoside A and B were shown a

potent cytotoxic activity by suppressing the proliferation of A375-S2 cells.

# 2008 Tao Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: Gelsemium elegans; Benzofuran lignan glycoside; Gelsemiunoside A; Gelsemiunoside B

Gelsemium elegans Benth. belongs to Gelsemium (Loganiaceae), the Chinese name of which is Hu man teng, Kou

wen, etc. It has been well known for its potent toxicity and has been used as one of the Chinese folk medicines. The

plant is mainly distributed in Fujian, Guangxi and Yunnan provinces of China. Previous investigations reported that the

whole plant of G. elegans was used for treatment of neuralgia, migraine, and certain shin ulcers [1]. As a kind of

traditional Chinese medicine, it has also been used for clinical anticancer therapy [2]. Until now, there are at least 40

alkaloids suggested as the constituents of G. elegans [3,4]. In this paper, we disclosed two new benzofuran lignan

glycosides isolated from G. elegans and determined their structures as well.

Dried whole plant (9.0 kg) was crushed and extracted with water (100 8C) for 2 h, three times. The extract was

concentrated in vacuo, and then the concentrated solution was submitted to macroporous resin (HP800) by eluting with

H2O, 30%, 50% and 75% ethanol, successively. The 30% fraction was partitioned between H2O and n-BuOH. The n-

BuOH fraction (30 g) was submitted to repeated column chromatography on silica gel and Sephadex LH-20, and was

finally purified on preparative HPLC by eluting with 45% MeOH to afford compounds 1 (35 mg) and 2 (15 mg).

Compound 1 was obtained as pale yellow amorphous powder, with mp 150–152 8C, ½a�22D �108.3 (c 0.33, MeOH), and

UV (MeOH) lmax (log e) 322 (3.89), 222 (4.01) nm. The IR spectrum showed an a,b-unsaturated carboxyl (3417 and

1684 cm�1) and aromatic ring (1614 and 1500 cm�1) functional group. The negative ESI-MS of 1 gave a quasi-

molecular ion peak at m/z 517 [M�H]�, and the molecular formula was determined as C26H30O11 by HRFABMS at m/z

517.1836 [M�H]�. The presence of trans-olefinic group was based on the 1H signals at dH 7.52 (d, 1H, J = 15.9 Hz), 6.40

(d, 1H, J = 15.9 Hz) and 13C signals at dC 144.5, 116.3. In the 1H and 13C NMR spectrum of 1, characteristic signals at dH

3.84 (s, 3H), 3.77 (s, 3H) and dC 55.9 and 55.8, indicated the presences of two methoxy moieties in 1. In addition, 1H NMR

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Chinese Chemical Letters 19 (2008) 1327–1329

* Corresponding author.

E-mail address: sy_guotao@263.net (T. Guo).

1001-8417/$ – see front matter # 2008 Tao Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

doi:10.1016/j.cclet.2008.09.012

data (Table 1) showed three aromatic protons, at dH 7.06 (dd, 1H, J = 8.4, 1.4 Hz), 7.01 (d, 1H, J = 1.4 Hz), 6.87 (dd, 1H,

J = 8.4, 1.4 Hz), forming ABX system and two aromatic protons, at dH 7.24 (s, 1H), 7.23 (s, 1H), forming AB system. The

sugar moiety was determined as L-rhamnose by acid hydrolysis and high-performance TLC (HPTLC) comparison with

authentic L-rhamnose in the same Rf value. According to the 1H and 13C NMR spectra data shown in Ref. [5], the anomeric

configuration was determined as a-L-rhamnose.

Based on the 2D NMR spectroscopic analysis, the structure of 1 was finally established (Fig. 1). The correlations

between H-7 and H-8, H-8 and H-9 revealed the connection between the oxygenated methine (C-7), methine (C-8) and

oxygenated methylene (C-9) in the 1H–1H COSY spectrum. The key HMBC correlations from H-7 to C-1, C-2, C-6,

W. Hua et al. / Chinese Chemical Letters 19 (2008) 1327–13291328

Table 11H (600 MHz) and 13C (125 MHz) chemical shifts and assignment for 1 and 2 in DMSO-d6

Position 1 2

dH (J in Hz) dC dH (J in Hz) dC

1 135.9 136.0

2 7.01 (d, 1H, 1.4) 110.7 7.02 (s, 1H) 110.6

3 150.1 150.0

4 145.0 144.9

5 7.06 (d, 1H, 8.4) 117.9 7.07 (d, 1H, 8.4) 117.8

6 6.87 (dd, 1H, 8.4, 1.4) 118.2 6.88 (d, 1H, 8.4) 118.1

7 5.60 (d, 1H, 6.0) 87.5 5.59 (d, 1H, 6.0) 87.4

8 3.51 (d, 1H, 6.0) 52.9 3.53 (m, 1H) 52.7

9 3.79 (m, 1H), 3.66(m,1H) 62.9 3.74 (m, 2H) 62.9

3-OCH3 3.77 (s, 3H) 55.8 3.76 (s, 3H) 55.8

10 128.0 117.7

20 7.24 (s, 1H) 112.4 7.48 (s, 1H) 113.7

30 144.0 142.9

40 149.7 150.3

50 129.7 128.7

60 7.23 (s, 1H) 117.9 7.53 (s, 1H) 119.2

70 7.52 (d, 1H, 15.9) 144.5 172.8

80 6.40 (d, 1H, 15.9) 116.3

90 167.9

30-OCH3 3.84 (s, 3H) 55.9 3.85 (s, 3H) 55.6

100 5.25 (br s, 1H) 99.7 5.25 (s, 1H) 99.5

200 3.84 (m, 1H) 70.3 3.87 (m, 1H) 70.2

300 3.63 (m, 1H) 70.4 3.64 (m, 1H) 70.4

400 3.27 (t, 1H, 9.0) 71.9 3.28 (m, 1H) 71.7

500 3.57 (m, 1H) 69.7 3.58 (m, 1H) 69.5

600 1.09 (d, 3H, 6.0) 17.9 1.10 (d, 3H, 6.0) 17.8

Fig. 1. The key HMBC (H! C) correlations of compound 1 and 2.

C-8 and C-40, from H-8 to C-7, C-9 and C-50, indicated the presence of benzofuran moiety [6]. Furthermore, the

HMBC correlation from the anomeric proton H-100 to C-4 connected the a-L-rhamnose with the benzofuran unit. In

NOESY experiment, cross-signals between H-8 and H-2, H-7 and one of H-9 provided the relative configuration, and

cross-signals between H-2 and 3-OCH3, H-20 and 30-OCH3 confirmed the positions of methoxyl groups. The

stereochemistry of compound 1 was confirmed by comparison of the chemical shifts and coupling constants with those

of the literature report. The trans-vicinal coupling of 7-aryl and 8-hydroxymethyl was proved according to the

coupling constant between H-7 and H-8 (J = 6.0 Hz) [6]. In the literature report [7], the chemical shifts of C-7 and C-8

at dC 86.5–87.5 and 55.0–56.5, respectively, indicated a 7S, 8R-configuration; whereas 7R, 8S-configuration was

shown the chemical shifts of C-7 and C-8 at dC 88.5–89.5 and 52.5–53.5, respectively. Moreover, 7S, 8R- and 7R, 8S-

configuration were shown contrary optical rotation values, plus in 7S, 8R- and minus in 7R, 8S-configuration [7,8].

Thus, compound 1 was finally confirmed as a 7R, 8S-configuration based on C-7 at dC 87.5, C-8 at dC 52.9, and ½a�22D

�108.3.

According to the spectral evidences, the chemical structure of compound 1 was elucidated as (7R,8S)-7,8-dihydro-

7-(4-hydroxy-3-methoxyphenyl)-8-hydroxymethyl-7-methoxybenzofuran propenoic acid 4-O-a-L-rhamnoside,

named gelsemiunoside A.

Compound 2 was obtained as pale yellow amorphous powder, with mp 138–140 8C, ½a�22D �32.8 (c 0.14, MeOH),

and UV (MeOH) lmax (log e) 324 (3.64), 223 (4.13) nm. The IR spectrum showed a carboxyl (3430 and 1686 cm�1)

functional group. The ESI-MS of 2 gave a quasi-molecular ion peak at m/z 491 [M�H]�, and the molecular formula

was deduced as C24H28O11 from HRFABMS at m/z 491.1498. The 1H NMR spectral data of 2 was very similar to those

of 1 (Table 1), except for the disappearances of the signals attributed to H-70and H-80 in 1. This evidence was further

proved by the disappearances of the carbon signals dC 144.5 and 116.3 in 1 and the loss of 26 units in the MS spectrum

of 2. Compared the NMR data (Table 1) with 1 and HRTLC with authentic rhamnose, the sugar moiety of 2 was

indicated as a-L-rhamnose. The key HMBC correlation (Fig. 1) from the anomeric proton H-100 to C-4 showed the

sugar moiety connected with the glycoside at C-4 position. In addition, the HMBC correlations from H-20 and H-60 toC-70 of the propenoic acid moiety in 1 were replaced by H-20 and H-60 to C-70 of the carboxyl moiety in 2. In NOESY

experiment, cross-signals presented between H-8 and H-2, H-7 and one of H-9, and cross-signals between H-2 and 3-

OCH3, H-20 and 30-OCH3 confirmed the positions of methoxyl groups. Compound 2 showed no changes of 7R, 8S-

configuration compared with those of 1 in NMR spectral data and optical rotation values [8,9]. Consequently, the

structure of 2 was confirmed as (7R,8S)-7,8-dihydro-7-(4-hydroxy-3-methoxyphenyl)-8-hydroxymethyl-7-methox-

ybenzofuran carboxylic acid-4-O-a-L-rhamnoside, named gelsemiunoside B.

Compounds 1 and 2 were both detected for their cytotoxicity against human A375-S2 cell line by MTT assay, and

were both shown certain inhibitory effects on cell growth. The IC50 values of 1 and 2 were 193.4 and 69.4 mmol/L,

respectively.

Acknowledgments

We wish to thank Professor Qi Shi Sun of Shenyang Pharmaceutical University, for identification of the plant

materials. The Project was sponsored by the Scientific Research Foundation for the doctoral Scholars (Q.C. Zhao, No.

20031040), Liaoning, China.

References

[1] M. Kitajima, T. Nakamura, N. Kogure, et al. J. Nat. Prod. 69 (2006) 715.

[2] K.Z. Yang, J. Huang, et al. Guangxi Yixueyuan Xuebao (J. Guangxi Med. Univ.) 3 (1981) 66 (in Chinese).

[3] C. Rujjanawate, D. Kanjanapothi, A. Panthong, et al. J. Ethnopharmacol. 89 (2003) 91.

[4] M. Kitajima, J. Nat. Med. 61 (2007) 14.

[5] M. Yoshiharu, N. Tomohiro, S. Akiyoshi, et al. Agric. Biol. Chem. 54 (1990) 557.

[6] J.C. Ho, C.M. Chen, L.C. Row, J. Chin. Chem. Soc. 50 (2003) 1271.

[7] X.K. Zheng, K.K. Li, Y.Z. Wang, et al. Chin. Chem. Lett. 19 (2008) 19.

[8] M.S.M. Yuen, F. Xue, T.C.W. Mak, et al. Tetrahedron 54 (1998) 12429.

[9] N. Hirai, M. Okamoto, H. Udagawa, et al. Biosci. Biotech. Biochem. 58 (1994) 1679.

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