New prenylated C6–C3 compounds from the roots of Illicium henryi

Phytochemistry Letters 6 (2013) 444–448

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New prenylated C6–C3 compounds from the roots of Illicium henryi Peng-Yu Zhuang 1, Shuang-Gang Ma 1, Gui-Jie Zhang, Xiao-Jing Wang, Yan Zhang, Shi-Shan Yu *, Yun-Bao Liu, Jing Qu, Yong Li, Qi Hou State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People’s Republic of China

A R T I C L E I N F O

A B S T R A C T

Article history: Received 21 January 2013 Received in revised form 4 May 2013 Accepted 8 May 2013 Available online 4 June 2013

One new dimeric prenylated C6–C3 compound, namely, illihendione A (1), two prenylated C6–C3 compounds, illihenryifunone C (2) and illihenryipyranone A (3), and one known dimeric prenylated C6– C3 compound, illicidione A (4), were isolated from the roots of Illicium henryi. The structures and absolute configurations of these compounds were determined by extensive spectroscopic and chemical analyses, including nuclear magnetic resonance (NMR), circular dichroism (CD) and a modified Mosher method. Compound 1 exhibited a weak inhibitory ratio for b-glucuronidase release induced by plateletactivating factor (PAF) in rat polymorphonuclear leukocytes (PMNS) in vitro. Crown Copyright ß 2013 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.

Keywords: Illicium henryi Dimeric prenylated C6–C3 compound Illihendione A Roots Modified Mosher method

1. Introduction Prenylated C6–C3 compounds, also named phytoquinoids, are characteristic constituents of the genus Illicium. Some prenylated C6–C3 compounds were found to exhibit increased choline acetyltransferase inhibition and cytotoxic activities (Yakushijin et al., 1984; Fukuyama et al., 1994a,b; Fukuyama et al., 1995; Itoigawa et al., 2004). In our previous studies, a large number of prenylated C6–C3 compounds from I. oligandrum and I. simonsii with cytotoxic and anti-inflammatory activities were reported (Tang et al., 2009; Ma et al., 2011; Wu et al., 2009). I. henryi, a toxic shrub, is mainly distributed in southern China and is used for the treatment of rheumatism (Liu and Zhou, 1988). Several sesquiterpene lactones, lignans and flavonoids from this plant were reported (Liu et al., 2010a,b, 2011; Song et al., 2009; Xiang et al., 2010; Xie et al., 1990). In our studies, new prenylated C6–C3 compounds with antioxidant activities were isolated from the roots of this plant (Zhuang et al., 2013). As a result of our continued search for new constituents of this plant, one new dimeric prenylated C6–C3 compound, namely, illihendione A (1), two new prenylated C6–C3 compounds, illihenryifunone C (2) and illihenryipyranone A (3), and one known dimeric prenylated C6–C3 compound, illicidione A (4) (Tang et al., 2011), (Fig. 1) were isolated

* Corresponding author. Tel.: +86 10 63165326; fax: +86 10 63017757. E-mail address: [email protected] (S.-S. Yu). 1 These authors contributed equally to this work.

from the EtOAc soluble fraction of the EtOH extract. Herein, we report the isolation and structural elucidation of compounds 1–4. 2. Results and discussion Illihendione A (1) was obtained as a white, amorphous powder. Its molecular formula, C28H36O8, was established by HRESIMS (m/ z 501.2492 [M+H]+) and NMR data. IR absorptions revealed the presence of hydroxyl (3434 cm1), unconjugated carbonyl (1724 cm1), a,b-conjugated carbonyl (1647 cm1). The 13C NMR spectrum showed 28 carbon resonances. The 1H NMR, 13C NMR, 1H–1H COSY, and HMBC spectra indicated the presence of four methyl groups, two allyl groups and two partial structural fragments with ABX spin patterns [CH2(10)–CH(11) and CH2(100 )–CH(110 )]. These characteristic NMR data indicated that compound 1 was a prenylated C6–C3 dimer comprising moieties A and B (Fig. 2). The NMR characteristics of moiety A were similar to those of moiety A of illicidione A (Tang et al., 2011). Compared with C-12 (d 70.5) in moiety A of illicidione A, C-12 for moiety A of 1 was shifted downfield by Dd 14.2 ppm, and the downfield shift suggested that C-12 was attached to C-5 via an oxygen atom to form a tetrahydropyran ring in moiety A of 1. The 13C NMR data (Table 1) of moiety B of 1 were similar to those of illicidione A; this similar data indicated that moiety B of 1 and illicidione A possessed the same planar structure. The linkages between moieties A and B from C-3 to C-30 and C-4 to C-60 were verified by the HMBC correlations (Fig. 3) of H-3/C-20 , 30 , 40 , H-30 /C-2, 3, 4 and H-60 /C-3, 4, 5, 10 and by the strong vicinal coupling 1H–1H COSY

1874-3900/$ – see front matter . Crown Copyright ß 2013 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.phytol.2013.05.009

P.-Y. Zhuang et al. / Phytochemistry Letters 6 (2013) 444–448

445

Table 1 NMR data of compound 1.

Fig. 1. Structures of compounds 1–4.

correlation of H-3/H-30 . The stereochemistry of 1 was elucidated by NOE correlations, CD data, and a modified Mosher method. The relative configuration of 1 was determined based on a NOESY experiment (Fig. 3). NOE correlations were observed between H-3 and both H2-10 and H2-7, between H-30 and H-3, and between H11 and H-60 ; the correlations established the relative configurations, as shown in Fig. 3. The absolute configuration was determined by CD analysis. As in bicyclo[2,2,2]oct-5-en-2-one, the orientation of the b,g-unsaturated carbonyl moiety determines the sign of the Cotton effect (Kirk, 1986). The CD spectrum of 1 showed a negative Cotton effect at 312 nm for the n ! p* transition of the b,g-unsaturated carbonyl moiety; this spectrum is identical to that of bacchopetiolone (Zdero et al., 1991). Therefore, C-20 possesses the R absolute configuration. Additionally, the positive Cotton effect at 245 nm for the p ! p* transition of the a,b-unsaturated carbonyl moiety confirmed the 4R absolute configuration (Djerassi et al., 1962). The absolute configuration of C-11 and C-110 were determined by a modified Mosher method (Ohtani et al., 1991). Two equal portions of 1 were derivatized with (R)- and (S)-MTPA chlorides at C-11 and C-110 to yield (S)- and (R)-MTPA esters (1b and 1a), respectively, and this assignment was further confirmed by the downfield shift by Dd1b S 1 1.91 and Dd1a S 1 1.33 ppm for H-11 and Dd1b S 1 2.01 and Dd1a S 1 1.98 ppm for H-110 . Interpretation of the 1H NMR chemical shift differences (DdS S R) (Fig. 4) between the (S)- and

dH(J in Hz)a

Position

dC a

1 2 3 4 5 6 7 8 9 10 11 12 13 14 10 20 30 40 50 60 70 80 90 100 110 120 130 140

199.8 76.8 48.5 48.9 171.4 110.8 49.9 133.2 118.6 38.1 68.2 84.7 27.5 20.3 208.2 75.1 44.5 107.5 146.0 60.8 41.7 134.2 118.9 30.4 69.5 79.1 26.3 20.5

2.75(d, 2.4)

5.50(s) 2.42(d, 7.0, 2H) 5.69(m) Ha 5.02 (overlap) Hb 5.00 (overlap) Ha 2.21 (dd, 14.0, 4.7) Hb 2.02 (overlap) 4.02(m) 1.46(3H) 1.25(3H)

3.12(d, 2.4)

3.19(s) Ha 2.54 (dd, 14.6, 5.3) Hb 2.27 (dd, 14.6, 8.5) 5.98(m) Ha 5.13 (overlap) Hb 5.10 (overlap) Ha 2.08 (dd, 1.67, 7.5) Hb 1.88 (overlap) 3.37(m) 1.13(s,3H) 1.05(s,3H)

a Data were recorded in acetone-d6 at 500 MHz for proton and at 125 MHz for carbon.

(R)-MTPA esters assigned the R configuration to both C-11 and C110 . Combined with the relative configuration, the absolute configurations of C-2, C-3, C-4, C-11, C-20 , C-30 , C-60 and C-110 were assigned to be R, R, R, R, R, R, S and R, respectively. Therefore, the structure of 1 was elucidated as shown in Fig. 1 and named illihendione A (1). The molecular formula for illihenryifunone C (2), C15H20O4, was derived from NMR data and HRESIMS (m/z 269.1386 [M+H]+). The

HO

O

H O HO

H H H

OH O H

Fig. 3. HMBC correlations (

O

O OH

OH A

OH B

Fig. 2. Structures of moieties A and B in 1.

O H H OH

H H

O H

) and NOE correlations (

O H+0.14 H

+0.05

OH

H

O

OH ) of 1.

-0.11 -0.08

H

O

H

O HO

OH

APTMO O

HO

O

O HO

O

H H

OH H

O H +0.23 H

-0.17 -0.06

OMTPA

+0.07

Fig. 4. 1H NMR chemical shift differences of the MTPA ester derivatives of 1.

P.-Y. Zhuang et al. / Phytochemistry Letters 6 (2013) 444–448

446 Table 2 NMR data of compound 2 and 3. Position

1 2 3 4 5 6 7 8 9 10 11 12 13 14 a

2

Position

dC a

dH (J in Hz)a

199.1 78.3 72.6 43.3 181.4 96.4 41.8 133.9 118.1 25.1 93.3 72.3 26.9 26.2

4.11 (d, 3.2) 3.67 (m) 5.27 (s) Ha 2.39 (overlap) Hb 2.29 (overlap) 5.86 (m) Ha 5.05 (br d, 4.1) Hb 5.02 (br s) Ha 2.39 (overlap) Hb 2.29 (overlap) 4.53 (dd, 9.4, 1.4) 1.23 (s, 3H) 1.29 (s, 3H)

3

dH (J in Hz)a

dC a 1 2 3 4 5 6 7 8 9 10 11 12 13 14

199.6 79.1 74.7 32.8 175.3 105.1 41.3 133.8 118.2 28.5 69.4 83.1 24.9 26.8

3.86(d, 2.8) 3.26 (m) 5.31 (s) Ha 2.37 (dd, 14.2, 8.0) Hb 2.29 (dd, 14.2, 6.2) 5.85 (m) Ha 5.07 (br d, 17.2) Hb 5.02 (br d, 10.2) Ha 2.47 (m) Hb 1.80 (m) 3.85 (overlap) 1.39 (s, 3H) 1.26 (s, 3H)

Data were recorded in acetone-d6 at 500 MHz for proton and at 125 MHz for carbon.

IR spectrum indicated the presence of an a,b-conjugated carbonyl (1621 cm1). The 1H NMR spectrum of 2 showed signals from two methyl groups and a deshielded, trisubstituted olefin proton at dH 5.27. Additionally, the NMR data (Table 2) revealed the presence of one allyl group [dH 5.86 (1H, m), 5.04 (2H, m), 2.39 (overlapped), 2.29 (overlapped); dC 133.9, 118.1, 41.8] and one dimethylcarbinol group [dH 1.28 (3H, s), 1.23 (3H, s); dC 26.9, 26.2, 72.3]. A combination of 2D HSQC and HMBC correlations was used to elucidate the planar structure of 2. In the HMBC spectrum, correlations from H-3 to C-1 (C5 5O), C-2, C-4, and C-5 and from H-6 to C-1 (C5 5O), C-4, and C-5 indicated the presence of a cyclohexenone ring (the C6 unit). Correlations from H2-10 to C4, C-5 and C-11, and from H-11 to C-4 and C-5, in combination with the degrees of unsaturation, allowed for the assignment of a tetrahydrofuran ring. Additional HMBC correlations from H2-7 to C-1 (C5 5O), C-2 and C-3 permitted the attachment of the allyl group to C-2. Finally, HMBC correlations from CH3-13 and CH3-14 to C-11 permitted connections between the dimethylcarbinol group and C11, thus completing the planar structure of 2. The stereochemistry of 2 was determined by NOE difference experiments and analysis of the CD. In the NOE difference spectrum, the irradiation of H-4 enhanced H-3, H3-13 and H3-14. The CD spectrum showed a positive Cotton effect at 301 nm for the n ! p* transition of the a,b-unsaturated carbonyl moiety, and the effect indicated that the configuration of C-2 was R (Djerassi et al., 1962). The absolute configuration of the 2, 3-diol unit in 2 was established using the in situ dimolybdenum CD method (Tang et al., 2009). The negative Cotton effect at 314 nm observed in the Mo2(OAc)4-induced CD (DMSO) spectrum permitted the assignment of the 3R configuration for 2 (Tang et al., 2009). Per the above relative configuration, the absolute configurations for C-4 and C-11 were both determined to be S. Therefore, the structure of 2 was elucidated as shown in Fig. 1 and named illihenryifunone C (2). Compound 3 was obtained as a colorless oil with an identical molecular formula to 2. The NMR spectra of 3 were similar to 2. Compared with C-12 (d 72.3) of 2, C-12 of 3 was shifted downfield by Dd 9.8; the downfield shift suggested that C-12 was attached to C-5 via an oxygen atom to form a tetrahydropyran ring in compound 3. In the NOE difference spectrum, the irradiation of H-4 enhanced H-10a and H-3, and the irradiation of H-10a enhanced H-11. In the CD spectrum, 3 showed opposite Cotton effects to 2; the opposite effects indicated that the configuration of C-2 was S (Djerassi et al., 1962). The positive Cotton effect at 305 nm observed in the Mo2(OAc)4-induced CD (DMSO) spectrum permitted the assignment of the 3S configuration for 3 (Tang et al., 2009). Per the above relative configuration, the absolute configurations for C-4 and C-11 were both determined to be R. Therefore, the

structure of 3 was elucidated as shown in Fig. 1 and named illihenryipyranone A (3). The anti-inflammatory effects of 1–4 were determined. Compounds 1–4 were assessed by measuring the inhibitory ratios for b-glucuronidase release induced by platelet-activating factor (PAF) in rat polymorphonuclear leukocytes (PMNS) in vitro (Kang et al., 2006). The inhibitory ratio of 1 was 24.3% at a concentration of 10 mM. Ginkgolide B, with an inhibitory ratio of 79.5% at 10 mM, was used as a positive control (Table 3) In the previous investigations, a number of prenylated C6–C3 compounds have been isolated from the Illicium plants (Yakushijin et al., 1984; Fukuyama et al., 1992, 1994a,b,1995,1997; Wu et al., 2009; Tang et al., 2009; Ma et al., 2011). From a chemical viewpoint, these compounds belong to cyclic prenylated tetrahydrofurano-type and non-cyclic prenylated C6–C3 compounds as reported (Fukuyama et al., 1994a). Compounds 2 and 3 are new prenylated C6–C3 compounds, which are classified as cyclic prenylated tetrahydrofurano-type and cyclic prenylated tetrahydropyrano-type C6–C3 compounds, respectively and compound 1 is a new dimeric prenylated C6–C3 compound. Three newly identified prenylated C6–C3 compounds contributed to the structural diversity of natural products seen in this species. 3. Experimental 3.1. General experimental procedures Optical rotations were measured with a Perkin-Elmer 241 automatic digital polarimeter. CD spectra were measured on a JASCO J-810 spectropolarimeter with a 0.1 cm cell at room temperature under the following conditions: speed, 200 nm/ min; time constant, 1 s; and bandwidth, 2.0 nm. IR spectra were recorded on a Nicolet 5700 FT-IR spectrometer with a microscope transmission method. NMR spectra were obtained on an INOVA500 spectrometer. ESIMS were measured on an Agilent 1100 Series LC/MSD Trap mass spectrometer. HRESIMS data were recorded Table 3 Inhibition effect of compounds 1–4 on PAF-induced release of b-glucuronidase from rat PMNs (in vitro). Compound

Concentration (mM)

Inhibition rate (%)

1 2 3 4 Ginkgolide Ba

10 10 10 10 10

24.3 0.3 5.5 8.0 79.5

a

Positive control.

P.-Y. Zhuang et al. / Phytochemistry Letters 6 (2013) 444–448

using a micromass Autospec-Ultima ETOF spectrometer. Preparative HPLC was performed on a Shimadzu LC-6AD instrument with an SPD-10A detector using a YMC-Pack ODS-A column (250 mm  20 mm, 5 mm). Silica gel (160–200, 200–300 mesh, Qingdao Marine Chemical Factory, China) and ODS (50 mm, Merck) were used for column chromatography (CC). TLC was performed with precoated Si gel GF254 glass plates. Spots were visualized under UV light or by spraying with 10% H2SO4 in EtOH-H2O (95:5, v/v) followed by heating. GC was performed on a 7890A (Agilent) instrument. 3.2. Plant material Roots of I. henryi were collected in Guangxi Province, China, in August 2009 and identified by Prof. Song-ji Wei from Guangxi Traditional Medical College. A voucher specimen (ID-21974) was deposited in the Herbarium of the Department of Medicinal Plants, Institute of Materia Medica, Chinese Academy of Medical Sciences. 3.3. Extraction and Isolation Roots of I. henryi (10 kg) were air-dried, ground, and extracted (2 h each) with EtOH-H2O (3  30 L, 95:5, v/v) by refluxing (90– 95 8C). The combined EtOH extracts were evaporated to near dryness under vacuum. The resulting residue (800 g) was absorbed on kieselguhr (1600 g) and then successively extracted with petroleum ether, EtOAc, and MeOH. The EtOAc extract (80 g) was subjected to a silica gel column (80 cm  8 cm, 200–300 mesh) eluted with a CH2Cl2/MeOH (50:1 ! 1:1, v/v) gradient system to yield four fractions, A1–A4. Fraction A1 (2 g) was chromatographed on a silica gel column and eluted with petroleum ether/EtOAc (5:1) to yield fraction A1B1–A2B3. Fraction A2B2 (200 mg) was purified using a semi-preparative HPLC [MeCN–H2O (40:60)] to yield compounds 1 (15 mg, tR = 18 min) and 4(100 mg, tR = 23 min). Fraction A2B3 (35 mg) was purified by semi-preparative HPLC [MeOH–H2O (70:30)] to yield compounds 2 (10 mg, tR = 36 min) and 3 (7 mg, tR = 39 min).

447

3.7. Esterification of 1 A 8 mL portion of (S)-MTPACl was added to a solution of 1 (2 mg) in pyridine-d5 (0.5 mL), and the mixture was kept at room temperature for 10 h to afford the (R)-MTPA ester 1a. In the same manner, compound 1 (2 mg) was treated with (R)-MTPACl to give the (S)-MTPA ester 1b. (R)-MTPA ester (1a): 1H NMR (500 MHz, pyridine-d5) d 7.49– 7.35 (10H, m, aromatic), 6.22 (1H, m, H-80 ), 6.05 (1H, m, H-8), 6.08 (1H, s, H-6), 5.94 (1H, dd, J = 11.8, 4.7 Hz, H-11), 5.35 (1H, t, J = 5.2 Hz, H-110 ), 5.06 (1H, d, J = 5.9 Hz, H-90 a), 4.86 (1H, d, J = 17.1 Hz, H-90 b), 5.07 (2H, m, H2-9), 3.49 (3H, s, OCH3 of MTPA), 3.58 (3H, s, OCH3 of MTPA), 3.83 (1H, d, J = 2.5 Hz, H-30 ), 3.69 (1H, d, J = 2.5 Hz, H-3), 3.43 (1H, s, H-60 ), 2.93 (1H, dd, J = 17.4, 5.0 Hz, H100 a), 2.18 (1H, dd, J = 17.4, 5.0 Hz, H-100 b), 3.20 (1H, dd, J = 13.4, 4.6 Hz, H-10a), 2.45 (1H, br d, J = 13.4, H-10b), 2.99 (1H, dd, J = 14.8, 5.6 Hz, H-70 a), 2.40 (1H, dd, J = 14.8, 8.9 Hz, H-70 b), 2.70 (1H, dd, J = 14.0, 7.1 Hz, H-7a), 2.63 (1H, dd, J = 14.0, 7.1 Hz, H-7b), 1.31 (3H, s, CH3-13), 1.24 (3H, s, CH3-14), 1.48 (3H, s, CH3-130 ), 1.36 (3H, s, CH3-140 ); ESIMS (positive) m/z 933 [M+H]+, 955 [M+Na]+. 13 C NMR, 1H–1H COSY, HMQC and HMBC see supporting information. (S)-MTPA ester (1b): 1H NMR (500 MHz, pyridine-d5) d 8.08 (10H, m, aromatic), 6.35 (1H, m, H-80 ), 6.08 (1H, m, H-8), 6.08 (1H, s, H-6), 5.93 (1H, dd, J = 11.9, 4.7 Hz, H-11), 5.38 (1H, t, J = 5.5 Hz, H110 ), 5.25 (1H, d, J = 17.1 Hz, H-90 a), 5.21 (1H, d, J = 10.1 Hz, H-90 b), 5.12 (2H, m, H2-9), 3.45 (3H, s, OCH3 of MTPA), 3.52 (3H, s, OCH3 of MTPA), 3.92 (1H, d, J = 2.5 Hz, H-30 ), 3.54 (1H, d, J = 2.5 Hz, H-3), 3.69 (1H, s, H-60 ), 3.00 (1H, dd, J = 17.2, 5.0 Hz, H-100 a), 2.41 (1H, dd, J = 17.2, 5.0 Hz, H-100 b), 3.25 (1H, dd, J = 13.4, 4.7 Hz, H-10a), 2.68 (1H, br d, J = 13.4, H-10b), 3.11 (1H, dd, J = 14.8, 5.8 Hz, H-70 a), 2.57 (1H, dd, J = 14.8, 8.4 Hz, H-70 b), 2.78 (1H, dd, J = 13.8, 7.2 Hz, H-7a), 2.71 (1H, dd, J = 13.8, 7.2 Hz, H-7b), 1.23 (3H, s, CH3-13), 1.13 (3H, s, CH3-14), 1.31 (3H, s, CH3-130 ), 1.30 (3H, s, CH3-140 ); ESIMS (positive) m/z 933 [M+H]+, 955 [M+Na]+. 13C NMR, 1H–1H COSY, HMQC and HMBC see supporting information. 3.8. Anti-inflammatory activity assay

3.4. Illihendione A (1) White amorphous powder, [a]20D + 50.6 (c 0.50 MeOH); CD (MeOH) d e245 + 2.84, d e312  10.82; UV (MeOH) lmax (loge): 260 (3.42); IRnmax 3434, 3077, 2978, 2936, 1724, 1647, 1621, 1433, 1370, 1200, 1175, 1120, 1078, 948, 923 cm1; For 13C and 1H NMR spectroscopic data, see Table 1; ESIMS m/z 501 [M+H]+, 523 [M+Na]+; HRESIMS m/z 501.2492 [M+H]+ (calcd for C28H37O8, 501.2483). 3.5. Illihenryifunone C (2) Colorless oil, [a]20D  30.0 (c 0.5 MeOH); CD (MeOH) d e268  5.98, d e301 + 2.99; Mo2(OAc)4-induced CD (DMSO) d e314  4.23; UV (MeOH) lmax (loge): 261 (2.01); IRnmax 3409, 2977, 2938, 1621, 1469, 1389, 1267, 1188, 1150, 957, 938 cm1; For 13C and 1H NMR spectroscopic data, see Table 2; ESIMS m/z 269 [M+H]+, 291 [M+Na]+; HRESIMS m/z 269.1386 [M+H]+ (calcd for C14H21O5, 269.1384). 3.6. Illihenryipyranone A (3) 20

Colorless oil, [a] D + 18.6 (c 0.5 MeOH); CD (MeOH) d e261 + 0.40, de214  0.42; Mo2(OAc)4-induced CD (DMSO) d e305 + 6.36; UV (MeOH) lmax (loge): 261 (2.01); IRnmax 3405, 2978, 2937, 1639, 1598, 1383, 1203, 1122, 1075, 1001, 863 cm1; For 13C and 1H NMR spectroscopic data, see Table 2; ESIMS m/z 269 [M+H]+, 291 [M+Na]+; HRESIMS m/z 269.1384 [M+H]+ (calcd for C14H21O5, 269.1384).

On the basis of reported procedures (Kang et al., 2006), the antiinflammatory activities of compounds 1–4 were assayed by measuring the inhibition of the platelet-activating factor induced release of b-glucuronidase from rat polymorphonuclear leukocytes in vitro. Acknowledgment This project was supported by the Natural Science Foundation of China (No. 201072234; 21132009) and the National Science and Technology Project of China (No. 2012ZX09301002-002). We are grateful to the Department of Instrumental Analysis, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College for measuring the IR, UV, NMR, and MS spectra. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.phytol.2013.05.009. References Djerassi, C., Records, R., Bunnenberg, E., Mislow, K., Moscowitz, A., 1962. Inherently dissymetric chromophores. Optical rotatory dispersion of a,b-unsaturated ketones and conformational analysis of cyclohexenones. J. Am. Chem. Soc. 84, 870–872.

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