Chinese Journal of Natural Medicines 2014, 12(9): 06970699

Chinese Journal of Natural Medicines

A new lignan glycoside from Forsythia suspensa LI Chang1, DAI Yi2, 3, DUAN Ying-Hui2, 3, LIU Ming-Li2, 3, YAO Xin-Sheng1, 2, 3* 1

College of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang 110016, China;

2

Institute of Traditional Chinese Medicine and Natural Products, College of Pharmacy, Jinan University, Guangzhou 510632,

China; 3

Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research, Jinan University,

Guangzhou 510632, China Available online September 2014

[ABSTRACT] Phytochemical investigation on Forsythia suspensa (Thunb.) Vahl afforded ten compounds, including five lignan glycosides and five phenylethanoid glycosides. The compounds were isolated by using HP-20 macroporous resin, silica gel, octadecyl silica gel (ODS), size exclusion chromatography resin HW-40 chromatography, and preparative HPLC. The structures were established through application of extensive spectroscopic methods, including ESI-MS, 1D- and 2D-NMR spectroscopy. They were identified as forsythialanside E (1), 8-hydroxypinoresinol-4-O-β-D-glucoside (2), 8-hydroxypinoresinol (3), lariciresinol-4-O-β- D-glucoside (4), lariciresinol-4-O-β-D-glucoside (5), forsythoside H (6), forsythoside I (7), forsythoside F (8), plantainoside B (9), and plantainoside A (10). Compound 1 was a new lignan glycoside. [KEY WORDS] Forsythia suspensa; Chemical constituents; Lignan glycosides

[CLC Number] R284.1

[Document code] A

[Article ID] 2095-6975(2014)09-0697-03

Introduction Forsythia suspensa (Thunb.) Vahl (Oleaceae) is widely distributed in China, Japan, Korea, and many European countries. The fruit of this plant, locally named ‘Lianqiao’, is a well-known Chinese plant medicine for the treatment of pyrexia and infections [1]. A number of compounds, including phenylethanoid glycosides, lignan glycosides, and quinoid glycosides have been isolated from the fruit of this plant [2-4]. Some of them possessed various bioactivities, including antiviral, antibacterial and anti-inflammatory activities [5-7]. The present investigations on the fruit of F. suspensa led to the isolation of ten compounds. Herein, the isolation and structural elucidation of those compounds are described.

Results and Discussion The dried fruit of F. suspensa was extracted with reflux[Received on] 07-Dec.-2013 [Corresponding author] YAO Xin-Sheng: Prof., Tel: 86-2085225849, Fax: 86-20-85221559, E-mail: [email protected] These authors have no conflict of interest to declare. Published by Elsevier B.V. All rights reserved

ing 60% EtOH, and then the extract was subjected to column chromatography to yield ten compounds, which were identified as forsythialanside E (1), 8-hydroxypinoresinol-4-O-β-D-glucoside (2) [8], 8-hydroxypinoresinol (3) [9], lariciresinol-4-O-βD-glucoside (4) [10], lariciresinol-4-O-β-D-glucoside (5) [10], forsythoside H (6) [3], forsythoside I (7) [3], forsythoside F (8) [11], plantainoside B (9) [12], and plantainoside A (10) [13]. Compound 1 was obtained as a yellow gum. [α] 26 D 24.9 (c 0.3, MeOH). UV (MeOH) λmax (log ε): 201 (4.54), 226 (4.21), 277 (3.79) nm. IR (KBr) νmax (cm–1): 3 405, 2 932, 2 868 cm−1. The molecular formula was deduced to be C26H32O12 by HR-ESI-MS {[M - H]− 535.183 6 (Calcd. for C26H31O12, 535.181 6)}. The 1H NMR spectrum (400 MHz, CD3OD) showed proton signals of two tri-substituted benzene rings [δ 7.04 (1H, d, J = 1.7 Hz), 6.78 (1H, d, J = 8.2 Hz) ,6.85 (1H, dd, J = 1.7, 8.2 Hz); 7.04 (1H,d, J = 1.4 Hz), 7.16 (1H, d, J = 8.4), 6.90 (1H, dd, J = 1.4, 8.4 Hz)]. In addition, the anomeric carbon signal at  4.90 showed the presence of a monosaccharide moiety. The 13C NMR (100 MHz, CD3OD) spectrum showed 26 carbon signals. The characteristic chemical shifts of 18 carbon signals at  150.7, 148.7, 147.6, 147.1, 134.6,

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129.0, 121.7, 119.3, 117.9, 115.7, 112.9, 111.3, 91.6, 90.8, 82.5, 76.9, 69.1, and 58.7 indicated that 1 was a furofuran lignan. The 13C NMR data of 1 were similar to the signals of 8-hydroxyepipinoresinol [9], except for an additional monosaccharide moiety, whose structure was further determined by key HMBC and 1H-1H COSY correlations (Fig. 1). Considering that the two tetrahydrofuran rings were fused in the cis-form for steric reasons [14], the relative configurations of H-7/H-8 were confirmed to be cis by the chemical shift of H-7 (δ 5.20) and the NOESY correlation between H-7/H-8. In addition, H-7/H-7 was deduced to be trans by the chemical shift of H-7 (δ 4.39) and the NOESY correlations of H-7/H-9a and H-7/H-9b. Thus, the structure of compound 1 was elucidated (Fig. 2). The acid hydrolysis and HPLC analysis were performed according to the method of Tanaka [15], which suggested that the monosaccharide was D-glucose. Moreover, the β configuration was prompted by the large coupling constant of the anomeric proton ( 4.90, d, J = 7.3 Hz). The CD spectrum of 1 showed a positive Cotton effect at 232 nm and a negative CotTable 1 No.

Fig. 1 Key HMBC (→) and 1H-1H COSY (▬) correlations of compound 1

Fig. 2 Chemical structure of compound 1

1

H NMR (400 MHz) and 13C NMR (100 MHz) data for compound 1 (in CD3OD) Compound 1 δH

1 2

ton effect at 276 nm, which indicated that the absolute configuration of 1 was 7R, 8R, 7R, 8S [9].

7.04 (1H, d, J = 1.4 Hz)

No.

δC 134.6 111.3

Compound 1 δH

δC

5

6.78 (1H, d, J = 8.2 Hz)

115.7

6

6.85 (1H, dd, J = 8.2, 1.7 Hz)

121.7

4.39 (1H, s)

3

150.7

7

4

147.1

8

90.8 91.6

4.21 (1H, d, J = 9.2 Hz) 3.62 (1H, m) 4.90 (1H, d, J = 7.3 Hz)

5

7.16 (1H, d, J = 8.4 Hz)

117.9

9

6

6.90 (1H, dd, J = 8.4, 1.4 Hz)

119.3

1

7

5.20 (1H, d, J = 5.9 Hz)

82.5

2

3.51 (1H, m)

74.9

8

3.14 (1H, m) 3.91 (1H, m) 3.17 (1H, m)

58.7

3

3.42 (1H, m)

78.2

69.1

4

3.41 (1H, m)

71.4

129.0

5

77.9

112.9

6

56.8

9

3

148.7

-OCH3

3.47 (1H, m) 3.70 (1H, dd, J = 12.1, 4.7 Hz) 3.63 (1H, m) 3.87 (3H, s)

4

147.6

-OCH3

3.88 (3H, s)

1 2

7.04 (1H, d, J = 1.7 Hz)

Materials and Methods General experimental procedures UV spectra were recorded on a JASCO V-550 UV/Vis spectrometer. IR spectra were recorded on a JASCO FT/IR480 plus spectrometer. CD spectrum was recorded on JASCO J-810 spectropolarimeter (JASCO, Tokyo, Japan). 1D and 2D NMR spectra were measured on a Bruker AV-300/400 spectrometer (Bruker, Fallanden, Switzerland). HRESI-MS data were determined by a Waters Synapt G2 MS mass spec- trometer (Waters, Milford, MA, USA). Open column chro- matography (CC) was performed using silica gel (200-300 mesh, Qingdao Haiyang Chemical Goup Corp., Qingdao, China), ODS (50 μm, YMC, Japan), HW-40 (Tosoh, Japan). Thin-

76.9 102.9

62.5 56.4

layer chromatography (TLC) was performed using pre- coated silica gel plates (silica gel GF254, 1 mm, Yantai). Plant material The plant material was provided by Heilongjiang Provincial Songhuajiang Pharmaceutical Co., Ltd., and identified as the fruit of Forsythia suspensa by Professor ZHOU Guang-Xiong (College of Pharmacy, Jinan University). A voucher specimen (No. 20090919FS) has been deposited at the Institute of Traditional Chinese Medicine and Natural Products, Jinan University, Guangzhou, China. Extraction and isolation The dried fruit of F. suspensa (2 kg) was refluxed twice with 60% (V/V) EtOH-H2O, for two hours each time, and then concentrated under reduced pressure to yield a brownish extract (540

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LI Chang, et al. / Chin J Nat Med, 2014, 12(9): 697699

g). The extract (500 g) was chroma- tographied over a Diaion HP-20 resin column eluted with an EtOH-H2O gradient. The 30% EtOH-H2O eluate (C, 50 g) was then subjected to a silica-gel column eluted with a CHCl3-MeOH gradient to give nine fractions

[2]

[3]

(C1-C9). The sub-fraction C6 (3.1g) was chromatographed over an ODS column eluted with a MeOH-H2O gradient to yield twelve fractions. The sub-fraction C6E (600.3 mg) was further subjected to HW-40 column with a MeOH-H2O gradient and purified by preparative HPLC with 20%-MeOH-H2O to give 1 (6.2 mg). Fraction C6H (45.3 mg) was purified by preparative HPLC eluting with 15%-MeOH-H2O to give 2 (5.4 mg) and 5 (12.0 mg). The sub-fraction C7 (15.6 g) was subjected to ODS column eluted with a MeOH-H2O gradi- ent to yield thirteen sub-fractions (C7AC7M). The frac- tions C7B (1.7 g) and C7C (607.8 mg) were then chroma- tographed over an ODS column, HW-40, and further purified by preparative HPLC to afford 4 (4.0 mg), 7 (442.1 mg), 9 (12.5 mg), and 10 (8.6 mg). Compounds 3 (7.0 mg), 6 (23.5 mg) and 8 (24.2 mg) were isolated from sub-fractions C2 (5.2 g) and C9 (3.5 g) by similar procedures, respec- tively. Acid hydrolysis of compound 1: The absolute configuration of the sugar unit was determined by the method of Tanaka et al [15]. Compound 1 (1.0 mg) was hydrolyzed with 2 mol·L−1 HCl for 2 h at 90 °C. The mixture was evaporated under vacuum, and then the residue was dissolved in H2O and extracted with CHCl3. The aqueous layer was collected. After drying in vacuo, the residue was dissolved in pyridine (1 mL) containing L-cysteine methyl ester (1 mg) (Sigma, St. Louis, MO, USA) and heated at 60 °C for 1 h. Then, o-tolyl isothiocyanate (5 µL) (Alfa Aesar, Ward Hill, MA, USA) was added to the mixture, which was heated at 60 °C for 1 h. The reaction mixture was directly analyzed by reversed-phase HPLC. Analytical HPLC was performed on a Cosmosil C18- MS-II column (250 mm × 4.6 mm i.d., 5 mm) at 35 °C with isocratic elution of 25% CH3CN containing 0.1% formic acid for 40 min at a flow rate 0.8 mL·min−1. Peaks were detected by a UV detector at 250 nm. One peak of the derivatives of 1 was observed at tR19.2 min (D-Glu).

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

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[4]

Cui Y, Wang Q, Shi X, et al. Simultaneous quantification of 14 bioactive constituents in Forsythia suspensa by liquid chromatography-electrospray ionization-mass spectrometry [J]. Phytochem Anal, 2010, 21 (3): 253-260.

[15]

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Cite this article as: LI Chang, DAI Yi, DUAN Ying-Hui, LIU Ming-Li, YAO Xin-Sheng. A new lignan glycoside from Forsythia suspensa [J]. Chinese Journal of Natural Medicines, 2014, 12(9): 697-699

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A new lignan glycoside from Forsythia suspensa.

Phytochemical investigation on Forsythia suspensa (Thunb.) Vahl afforded ten compounds, including five lignan glycosides and five phenylethanoid glyco...
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