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DOI: 10.1055/s-0031-1280088
© Georg Thieme Verlag KG Stuttgart · New York
The First Bis-Retrochalcone from Fissistigma latifolium
Dr. Yu-Hsuan Lan
School of Pharmacy
China Medical University
No. 91 Hsueh-Shih Road
Taichung 40402
Taiwan
Phone: +886 4 22 05 33 66 ext. 51 38
Fax: +886 4 22 06 02 48
Email: lanyh@mail.cmu.edu.tw
Publication History
received May 15, 2011
revised June 21, 2011
accepted June 24, 2011
Publication Date:
17 August 2011 (online)
Abstract
Two novel chalconoids, [3–3′′]bi-2-hydroxy-4,5,6-trimethoxydihydrochalcone (1) and 4,6-dimethoxy-2,5-quinodihydrochalcone (2), and twelve known compounds were isolated from the methanolic extract of Fissistigma latifolium (Dun.) Merr. The structures of all compounds were determined by spectroscopic methods. Of these, compounds 1, 2, and 2-hydroxy-4,5,6-trimethoxydihydrochalcone (10) belong to an uncommon group of chalconoids, the retrochalcones. Compound 1 is the first bis-retrochalcone to be reported, and compound 2 is a quinoretrochalcone. Furthermore, 2 showed activity against the MDA-MB-231 human breast cancer cell line with an IC50 value of 7.1 µM.
#Introduction
The genus Fissistigma (Annonaceae), which consists of about 90 species, has been shown to be a rich source of bioactive components. For example, the aristolactams from F. balance and F. oldhamii display antiplatelet aggregation activity [1], kuafumine, fissistin, and isofissistin from F. glaucescens and F. lanuginosum, respectively, show potent cytotoxicity against KB cell in vitro [2], [3]. Additionally, in previous phytochemical studies carried out on this genus by our group, alkaloids, furano-fissohamione, cyclopentenones, and flavonoids have been found [2], [4], [5], [6], [7], [8]. In an attempt to find new cytotoxic natural products from the Fissistigma species, we examined the methanolic extract of F. latifolium (Dun.) Merr, which showed cytotoxicity against several cancer cell lines with IC50 values below 20 µg/mL. F. latifolium is a climbing shrub that grows in lowland forests in Malaysia, India, Singapore, Vietnam, and the Philippines. A previous phytochemical study of this plant reported the characterization of several aristolactams [9]. In this report, the isolation and structural elucidation of two novel compounds, [3–3′]bi-2-hydroxy-4,5,6-trimethoxydihydrochalcone (1) and 4,6-dimethoxy-2,5-quinodihydrochalcone (2) ([Fig. 1]), along with twelve known compounds, aristolactam III a (3) [10], 5,6,7-trimethoxyflavone (4) [11], liriodenine (5), oxocrebanine (6) [4], vanillic acid (7) [12], piperlactam A (8) [13], goniothalactam (9) [1], 2-hydroxy-4,5,6-trimethoxydihydrochalcone (10) [14], benzaldehyde (11) [15], 5-hydroxy-6,7,8-trimethoxyflavone (alnetin) (12) [16], lysicamine (13) [17], and artherospermidine (14) [18], are discussed. The chemical structures of the known compounds were established by comparison with data reported in the literature. Retrochalcone compounds 1, 2, and 10 were tested for their cytotoxic activity against several cancer cell lines.
Fig. 1 Structures of compounds 1 and 2.
Materials and Methods
#General experimental procedures
IR spectra were measured on an IRprestige-21 spectrophotometer. 1H NMR (400 MHz, using CDCl3 as the solvent for measurement), 13C NMR (100 MHz), HMQC, HMBC, 1H-1H COSY, DEPT, and NOESY spectra were recorded with Bruker Avance-400 NMR spectrometers. LREIMS were collected on a JEOL JMS-SX/SX 102A mass spectrometer. HREIMS were collected on a MAT-95XL mass spectrometer. Silica gel 60 (Merck; 70–230, 230–400 mesh) and Sephadex LH-20 (GE Healthcare) were used for column chromatography. TLC analysis was carried out on Si gel GF254 precoated plates with detection using 50 % H2SO4 followed by heating on a hot plate. HPLC was performed on a Shimadzu LC-6AD delivery system coupled to a PDA SPD-M20A detector. SUPLECO Ascientis C18 5 µm (250 × 4.6 mm i. d.) and SUPLECO Ascientis C18 5 µm (250 × 21.2 mm i. d.) columns were used for analytical and preparative purposes.
#Plant material
The plants of F. latifolium (Annonaceae) were collected from Phong Nha-Ke Bang National Park, Vietnam, in May 2008, and the plant materials were identified and authenticated by Dr. Tran Huy Thai (Institute of Ecology and Biological Resources, Vietnamese Academy of Science and Technology). A voucher specimen (20080515VN-TW) was deposited in the Herbarium of the Vinh University, Vietnam.
#Extraction and isolation
F. latifolium plants (8.5 kg) were extracted repeatedly with MeOH (15 L × 3) at room temperature. The combined MeOH extracts were evaporated under reduced pressure to give a syrup. The MeOH extracts (186.6 g) of F. latifolium were partitioned between EtOAc and H2O (1 : 1, v/v) to give an EtOAc fraction (121.9 g), which was then purified by column chromatography (10 × 25 cm, Celite 545) using n-hexane (5 L), followed by CHCl3 (5 L), EtOAc (5 L), and MeOH (10 L) as elution solvents. This yielded 4 fractions n-hexane (EH, 70.8 g), CHCl3 (EC, 39.7 g), EtOAc (EE, 2.5 g), and MeOH (EM, 8.9 g). The EtOAc fraction (EE, 2.5 g) was further purified by chromatography on a silica gel column (4 × 14 cm, CHCl3:MeOH = 40 : 1-MeOH, gradient), yielding 10 fractions. Fraction 3 (17.2 mg) was separated using a silica gel column and purified by preparative HPLC C18 column (250 × 21.2 mm; H2O/MeOH: 50/50; flow rate: 3 mL/min) to yield aristolactam AIIIa (3; 2.6 mg; t R 19.4 min). The CHCl3 fraction (EC, 39.8 g) was separated on a silica gel column (8 × 16 cm, CHCl3-MeOH, gradient) to give 12 fractions. Fraction 4 (2.1 g) was further purified by chromatography on a silica gel column (4 × 16 cm, CHCl3) to afford 6 fractions. Subfraction 4-2 (330.2 mg) was separated on a silica column (2 × 25 cm) using n-hexane : EtOAc (2 : 1) to afford 9 fractions. Subfractions 4-2-4 and 4-2-5 (91.3 mg) were purified on a reversed-phase HPLC column (250 × 21.2 mm, H2O/MeOH: 20/80, flow rate: 3.0 mL/min) to afford 5,6,7-trimethoxyflavone (4; 3.5 mg; t R 35.0 min). Subfraction 4-2-7 (32.0 mg) was further purified by chromatography on a silica gel column followed by reversed-phase HPLC (250 × 21.2 mm, H2O/MeOH: 20/80, flow rate: 3.0 mL/min), which resulted in the isolation of liriodenine (5; 2.7 mg, t R 30.0 min). Fraction 4-4 (356.5 mg) was purified on a silica gel column, followed by preparative thin-layer chromatography and reversed-phase HPLC (250 × 21.2 mm, H2O/MeCN: 25/75, flow rate 3.0 mL/min) to afford oxocrebanine (6; 2.8 mg; t R 26.3 min). Fr. 4-5 (612.4 mg) was purified on a silica gel column (2.5 × 18 cm, CHCl3) to provide 13 fractions. Subfraction 4-5-1 (91.3 mg) was purified (2 × 17 cm, Sephadex LH-20, MeOH eluent) to afford 5 fractions, and the resulting fraction 4-5-1-3 (21.8 mg) was further purified by preparative thin-layer chromatography (n-hexane : EtOAc, 4 : 1) to give vanillic acid (7; 7.1 mg, Rf 0.10). Subfraction 4-5-13 (119.0 mg) was purified on a Sephadex LH-20 column (2 × 17 cm, Sephadex LH-20, MeOH eluent) followed by preparative thin-layer chromatography (n-hexane : EtOAc, 4 : 1) to yield piperlactam A (8; 3.0 mg; Rf 0.15) and goniothalactam (9; 5.1 mg; Rf 0.10). Fraction 5 (8.1 g) was purified on a silica gel column to afford 10 fractions. Subfraction 5-4 (2.7 g) was separated by silica gel column chromatography to provide 6 fractions. Subfraction 5-4-2 (1.3 g) was purified by repeated silica chromatography and then further purified twice by preparative thin-layer chromatography (n-hexane : EtOAc, 2 : 1) to give 2-hydroxy-4,5,6-trimethoxydihydrochalcone (10; 17.3 mg; Rf 0.48), 1 (3.5 mg; Rf 0.15) and 2 (33.7 mg; Rf 0.38). Fraction 5-4-3 (127.0 mg) was purified on a Sephadex LH-20 column and reversed-phase HPLC (250 × 21.2 mm, H2O/MeOH: 30/70, flow rate: 3.0 mL/min) to give benzaldehyde (11; 15.5 mg; t R 28.6 min) and 5-hydroxy-6,7,8-trimethoxyflavone (12; 1.1 mg; t R 32.9 min). Fraction 5-10 (394.6 mg) was separated by Sephadex LH-20 column chromatography to yield 9 fractions, of which subfraction 5-10-2 (37.8 mg) was further purified on a silica gel column, RP-18 column, and by reversed-phase HPLC (250 × 21.2 mm, H2O/MeOH: 25/75, flow rate 3.0: mL/min) to yield lysicamine (13; 2.8 mg; t R 42.7 min) and artherospermidine (14; 0.8 mg; t R 57.9 min).
[3-3′′]bi-2-hydroxy-4,5,6-trimethoxydihydrochalcone (1): Yellow amorphous solid; UV (MeOH) λ max (log ε) 240 (4.31), 285 (3.88); IR (KBr) ν max 3263, 2945, 1672, 1604, 1460, 1448, 1394, 1288, 1275, 1200, 1068 cm−1; 1H- and 13C-NMR, see [Table 1]; EI-MS m/z (rel. int. %) 555 (10), 567 (12), 583 (14), 598 (33), 612 (100), 630 (16); HREI-MS m/z 630.2473 (calcd. for C36H38O10: 630.2465).
|
1 |
2 |
||||
|
Position |
δ (H) |
δ (C) |
Position |
δ (H) |
δ (C) |
|
1,1′′ |
117.7 |
1 |
132.4 |
||
|
2,2′′ |
148.9 |
2 |
187.5 |
||
|
3,3′′ |
111.1 |
3 |
5.86 (1H, s) |
107.4 |
|
|
4,4′′ |
151.3 |
4 |
157.8 |
||
|
5,5′′ |
140.5 |
5 |
178.4 |
||
|
6,6′′ |
152.7 |
6 |
155.1 |
||
|
α,α' |
3.38 (4H, m) |
40.0 |
α |
3.14 (2H, m) |
37.8 |
|
β,β' |
3.09 (4H, m) |
19.4 |
β |
2.88 (2H, m) |
19.1 |
|
1′,1′′′ |
137.0 |
1′ |
137.0 |
||
|
2′,6′/2′′′,6′′′ |
8.02 (4H, d, 7.6) |
128.7 |
2′, 6′ |
7.96 (2H, d, 7.6) |
128.5 |
|
3′,5′/3′′′,5′′′ |
7.46 (4H, d, 7.6) |
128.9 |
3′, 5′ |
7.46 (2H, d, 7.6) |
129.0 |
|
4′/4′′′ |
7.57 (2H, d, 7.6) |
133.6 |
4′ |
7.56 (1H, d, 7.6) |
133.5 |
|
C=O/C'=O |
202.1 |
C=O |
199.1 |
||
|
4-OCH3/4′-OCH3 |
3.70 (6H, s) |
61.3 |
4-OCH3 |
3.81 |
56.8 |
|
5-OCH3/5′-OCH3 |
3.88 (6H, s) |
61.3 |
5-OCH3 |
||
|
6-OCH3/6′-OCH3 |
4.00 (6H, s) |
61.3 |
6-OCH3 |
3.97 |
61.5 |
|
a Chemical shift values are given in ppm, and J values in parentheses are given in Hz. Assignments were confirmed by 1H-1H COSY, HMQC, and HMBC experiments |
|||||
4,6-dimethoxy-2,5-quinodihydrochalcone (2): Yellow oil; UV(MeOH) λ max (log ε) 243 (4.57), 287 (4.58); IR (KBr) ν max 2091, 1679, 1645, 1452, 1361, 1297, 1240, 1206, 1179, 11 221, 1088 cm− 1;1H- and 13C-NMR, see [Table 1]; EI-MS m/z (rel. int. %) 300 (6), 223 (4), 195 (4), 105 (100), 77 (46). HREI-MS m/z 300.0989 (calcd. for C17H16O5: 300.0998)
#Bioassays
The 3 days bioassays against HepG2, Hep3B, MDA-MB-231, and MCF-7 cell lines were carried out according to procedures described in the literature [19]. Doxorubicin (Sigma Aldrich; purity ≥ 98 %) was used as a reference for the cytotoxicity test. Tested compounds used for biological testing were more than 90 % pure.
#Supporting information
The original spectra for compounds 1 and 2 are available as Supporting Information.
#Results and Discussion
Compound 1 was obtained as a yellow amorphous solid. HREI-MS of 1 showed a [M]+ ion of m/z 630.2473 (C36H38O10), indicating 18 degrees of unsaturation. The IR spectrum showed absorptions for hydroxyl (3264 cm−1) and carbonyl (1672 cm−1) groups. The UV exhibited absorptions at 240 and 285 nm. In the 1H NMR spectrum ([Table 1]), ten aromatic protons at δ H 8.02 (4H, d, J = 7.6 Hz), 7.57 (2H, t, J = 7.6 Hz), and 7.46 (4H, d, J = 7.6 Hz) were assigned to H-2′, H-2′′′/H-6′, H-6′′′, H-4′, H-4′′′, and H-3′, H-3′′′/H-5′, H-5′′′, respectively. Four methylene protons at δ 3.09 and 3.38 were consistent with H2-α, H2-α' and H2-β, H2-β'. Thirty-six carbon signals, including six methoxy, ten methine, four methylene, and sixteen quaternary carbons, were observed in the NMR spectra of 1 ([Table 1]). Among the sixteen quaternary carbons, two were identified as ketone carbons on the basis of chemical shifts at δ C 202.1. The UV, IR, and 1D NMR spectra of compound 1 were similar to those of 2-hydroxy-4,5,6-trimethoxydihydrochalcone (10) and 2-hydroxy-3,4,6-trimethoxydihydrochalcone [20]; however, the methine (δ H 6.36, δ C 97.9) in compound 10 was replaced in 1 by a quaternary carbon (δ C 111.1), indicating that 1 had carbon substitution at C-3/C-3′′. In addition, the molecular weight of 1 was almost 2-fold that of compound 10. Therefore, the data supported the presence of two carbonyl and four ring residues to fulfill the 18 degrees of unsaturation, suggesting the presence of two symmetrical retrodihydrochalcone moieties. All assignments were supported by COSY, HMQC, and HMBC spectra. Therefore, compound 1 was named [3–3′′]bi-2-hydroxy-4,5,6-trimethoxydihydrochalcone (1). This compound comprised two molecules of 2-hydroxy-4,5,6-trimethoxydihydrochalcone linked by a C-C bond between the two B rings.
In previous investigations of the Fissistigma species, several retrochalcones such as 2-hydroxy-3,4,6-trimethoxychalcone, 2-hydroxy-3,4,6-trimethoxychalcene, and 2-hydroxy-3,4,6-trimethoxydihydrochalcone have been described in the literature [16]. The first C α -C α linked dimeric dihydrochalcone, brackenin, was isolated from Brackenridgea zanguebarica [21]. Other dihydrochalcone dimers have been reported as constituents of Verbenaceae [22], Myristicaceae [23], Piperaceae [24], Moraceae [25], Liliaceae [26], and Adiantaceae [27]. No dimeric dihydrochalcone has been previously reported from the Fissistigma species. Compound 1 is the first example described to date of a symmetrical structure in which two dihydrochalcones are linked by a single C-C bond.
The molecular formula of compound 2 was determined to be C17H16O5 by HREIMS (m/z 300.0989, calcd. 300.0998). The UV spectrum showed maxima at 243 and 287 nm. One methine proton (δ H 5.86), two methylene protons (δ H 2.88 and 3.14), two methoxyl protons (δ H 3.81 and 3.97), and five aromatic protons [δ H 7.96 (2H, d, J = 7.6 Hz), 7.57 (1H, t, J = 7.6 Hz), and 7.46 (2H, d, J = 7.6 Hz)] were observed by 1H NMR spectrum. The 13C NMR spectrum indicated the presence of seven quaternary carbons, six methines, two methylenes, and two methyls. The 1H NMR signals were assigned similarly to 10, except for a signal at δ 6.36 in 10, which was shifted to δ 5.86 in 2. In the HMBC spectrum ([Fig. 2]), the typical carbonyl function was confirmed by correlations between H2-α/C=O, H2-β/C=O, and H-2′,6′/C=O. HMBC correlations between H-3/C-2, H-3/C-5 and correlations between H2-β/C-1, C-2 and C-6 demonstrated that the other two carbonyl groups located at C-2 and C-5. The above HMBC correlations and the presence of two downfield carbonyl groups in the 13C NMR spectrum suggested a p-benzoquinone ring rather than an aromatic ring (B ring). Fragment ions in the EI-MS spectrum at m/z 195 and 223 also confirmed that compound 2 belonged to the quinoretrochalcone family. Therefore, the structure of 2 was established as 4,6-dimethoxy-2,5-quinodihydrochalcone. One small group of chalcones characterized as chalcoquinones have been reported from Annonaceae, Leguminosae, and Taccaceae [28], [29], [30]. To the best of our knowledge, 4,6-dimethoxy-2,5-quinodihydrochalcone (2) is classified as a unique retrodihydrochalcone with a p-benzoquinone ring.
Fig. 2 Selected HMBC connectivities of 1 and 2.
The known pharmacological properties of chalcones include antioxidant, anti-inflammatory, cytotoxic, hypoglycemic, antihepatotoxic, antimalarial, and antileishmanial activities [31]. However, there are few reports on the biological activities of retrochalcones. Compounds 1, 2, and 10 were therefore evaluated for cytotoxicity against a series of human cancer cell lines ([Table 2]). Of these, 2 showed selective cytotoxicity against MDA-MB-231 cells (human breast carcinoma).
|
HepG2 IC50 (µM) |
Hep3B IC50 (µM) |
MDA-MB-231 IC50 (µM) |
MCF-7 IC50 (µM) |
|
|
1 |
N. E. |
N. E. |
N. E. |
N. E. |
|
2 |
46.5 ± 0.2 |
28.2 ± 0.9 |
7.1 ± 0.3 |
48.3 ± 0.9 |
|
10 |
N. E. |
N. E. |
53.3 ± 0.2 |
N. E. |
|
Doxorubicin |
8.9 ± 0.1 |
0.8 ± 0.1 |
2.4 ± 0.3 |
1.3 ± 0.2 |
|
N. E.: no effect. HepG2: human hepatocellular carcinoma; Hep3B: human hepatoma cell lines; MDA-MB-231: human breast cancer cell lines; MCF-7: human breast carcinoma |
||||
Acknowledgements
The investigation was supported by a research grant from the National Science Council of the Republic of China (NSC 97-2320-B-039-020-MY3) and a grant from the China Medical University, Taichung, Taiwan (CMU98-N1-25).
#Conflict of Interest
The authors report no conflicts of interest.
References
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Dr. Yu-Hsuan Lan
School of Pharmacy
China Medical University
No. 91 Hsueh-Shih Road
Taichung 40402
Taiwan
Phone: +886 4 22 05 33 66 ext. 51 38
Fax: +886 4 22 06 02 48
Email: lanyh@mail.cmu.edu.tw
References
- 1 Chia Y C, Chang F R, Teng C M, Wu Y C. Aristolactams and dioxoaporphines from Fissistigma balansae and Fissistigma oldhamii. J Nat Prod. 2000; 63 1160-1163
- 2 Wu Y C, Lu S T, Wu T S, Lee K H. Kuafumine, a novel cytotoxic oxoaporphine alkaloid from Fissistigma glaucescens. Heterocycles. 1987; 26 9-12
- 3 Alias Y, Awang K, Hadi A H, Thoison O, Sévenet T, Païs M. An antimitotic and cyctotoxic chalcone from Fissistigma lanuginosum. J Nat Prod. 1995; 58 1160-1166
- 4 Wu Y C, Kao S C, Huang J F, Duh C Y, Lu S T. Two phenanthrene alkaloids from Fissistigma glaucescens. Phytochemistry. 1990; 29 2387-2388
- 5 Chia Y C, Chang F R, Li C M, Wu Y C. Protoberberine alkaloids from Fissistigma balansae. Phytochemistry. 1998; 48 367-369
- 6 Chia Y C, Chang F R, Wu Y C. Two p-quinonoid aporphine alkaloids from Fissistigma balansae. J Nat Prod. 1998; 61 1430-1432
- 7 Chia Y C, Chang F R, Wu Y C. Fissohamione, a novel furanone from Fissistigma oldhamii. Tetrahedron Lett. 1999; 40 7513-7514
- 8 Chia Y C, Wu J B, Wu Y C. Two novel cyclopentenones from Fissistigma oldhamii. Tetrahedron Lett. 2000; 41 2199-2201
- 9 Alias A, Hazni H, Jaafar F M, Awang K, Ismail N H. Alkaloids from Fissistigma latifolium (Dunal) Merr. Molecules. 2010; 15 4583-4588
- 10 David B M, Hélène G, Maurice S. The aristolochic acids and aristolactams. J Nat Prod. 1982; 45 657-666
- 11 Mariano P. 5,6,7-Trimethoxyflavone and 5,6,7,4′-tetramethoxyflavone from Kickxia lanigera. Phytochemistry. 1973; 12 3014-3015
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Dr. Yu-Hsuan Lan
School of Pharmacy
China Medical University
No. 91 Hsueh-Shih Road
Taichung 40402
Taiwan
Phone: +886 4 22 05 33 66 ext. 51 38
Fax: +886 4 22 06 02 48
Email: lanyh@mail.cmu.edu.tw
Fig. 1 Structures of compounds 1 and 2.
Fig. 2 Selected HMBC connectivities of 1 and 2.