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Phytochemical Constituents of Bletilla striata and Their Cytotoxic Activity
Phytochemical Constituents of Bletilla striata and Their Cytotoxic Activity
Natural Product Sciences. 2014. Jun, 20(2): 91-94
Copyright © 2014, The Korean Society of Pharmacognosy
  • Received : May 02, 2014
  • Accepted : June 06, 2014
  • Published : June 30, 2014
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About the Authors
Kyeong Wan Woo
Natural Products Laboratory, School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Korea
Jong Eel Park
Natural Products Laboratory, School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Korea
Sang Un Choi
Korea Research Institute of Chemical Technology, Teajeon 305-600, Korea
Ki Hyun Kim
Natural Products Laboratory, School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Korea
Kang Ro Lee
Natural Products Laboratory, School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Korea
krlee@skku.edu

Abstract
Column chromatographic separation of the MeOH extract from the tubers of Bletilla striata yielded seven phenolic components including four phenanthrenes, 3,7-dihydroxy-2,4-dimethoxyphenanthrene ( 1 ), 3,7-dihydroxy-2,4,8-trimethoxyphenanthrene ( 2 ), 9,10-dihydro-4,7-dimethoxyphenanthrene-2,8-diol ( 3 ), and 9,10-dihydro-1-(4'-hydroxybenzyl)-4,7-dimethoxyphenanthrene-2,8-diol ( 4 ) and three stilbenes, gigantol ( 5 ), 3',4''-dihydroxy-5',3'',5''-trimethoxybibenzyl ( 6 ), and batatasin III ( 7 ). Their structures were determined on the basis of NMR spectroscopic data. Among them, compound 2, 3 , and 6 were reported for the first time from this plant. The isolated compounds ( 1-7 ) were tested for cytotoxicity against four human tumor cell lines in vitro using a Sulforhodamin B bioassay.
Keywords
Introduction
The tubers of Bletilla striata (T HUNB .) Reichb. F. (Orchidaceae) have been used for treatment of tuberculosis and pneumonorrhagia in Chinese traditional medicine. 1 Previous phytochemical investigation on this plant reported the isolation of phenanthrenes, stilbenes, bibenzyls, and flavonoids. 1 - 4 Pharmacological studies with some of these compounds reported to antimiotic and antimicrobial activities. 3 , 5 As a part of our continuing search for biologically active compounds from Korean medicinal plants, we investigated the CHCl 3 soluble fraction of B. striata and recently reported the isolation of spirostanesteroidal derivatives with cytotoxic activity. 6 In this study, we further isolated seven phenolic derivatives, including four phenanthrenes and three stilbenes ( 1 - 7 ) from the CHCl 3 soluble fraction. The identification and structural elucidation of these compounds were based on 1D, 2D NMR and MS data. The isolated compounds ( 1 - 7 ) were tested for cytotoxicity against four human tumor cell lines in vitro using a Sulforhodamin B bioassay. Here, we report the isolation and structural elucidation as well as the cytotoxic effect of phenolic derivatives.
Experimental
General experimental procedures − Silica gel F 254 plates (Merck) and RP-C 18 F 254s plates (Merck) were used for TLC. Spots on TLC were detected by UV light and/or by heating after spraying with 10% H 2 SO 4 in C 2 H 5 OH (v/ v). Si gel 60 (Merck, 70 - 230 and 230 - 400 mesh) and RP-C 18 silica gel (Merck, 230 - 400 mesh) was used for open column chromatography. Low pressure liquid chromatography was carried out on a Merck Lichroprep Lobar ® - A Si 60 (240 × 10 mm) columns with a FMI QSY-0 pump (ISCO). Semi-preparative HPLC used a Gilson 306 pump with Shodex refractive index detector. NMR spectra were recorded on a Varian UNITY INOVA 500 NMR spectrometer operating at 500 MHz ( 1 H) and 125 MHz ( 13 C), with chemical shifts given in ppm (δ). FAB MS spectra were obtained on a JEOL JMS 700 mass spectrometer. IR spectra were recorded on a Bruker IFS-66/S FT-IR spectrometer.
Plant materials – The tubers of B. striata were perchased from Kyungdong herbal market, Seoul, Korea, in June 2011, and were identified by one of the authors (K.R. Lee). A voucher specimen (SKKU-NPL 1106) was deposited in the herbarium of the School of Pharmacy, Sungkyunkwan University, Suwon, Korea.
Extraction and isolation – Dried tubers of B. striata (3.6 kg) were extracted three times with 80% MeOH under reflux. The resulting MeOH extracts (568 g) were suspended in distilled water (800 ml × 4) and then successively partitioned with n -hexane, CHCl 3 , EtOAc and n -BuOH, yielding residues of 3 g, 42 g, 51 g and 159 g, respectively. The CHCl 3 soluble extract (40 g) was chromatographed on a silica gel (230 - 400 mesh, 700 g) column eluated with CHCl 3 : MeOH (50 : 1 – 1 : 1) to obtain seven fractions (A-G). Fraction B (5.6 g) was separated on a silica gel column (Hexane : CHCl 3 : MeOH= 4 : 5 : 0.1 – CHCl 3 :MeOH = 50 : 1) to afford ten subfractions (B1-B10). Subfraction B6 (292 mg) was further separated on an RP-C 18 silica gel column with 50~100% MeOH and purified over an RP-C 18 semi-prep. HPLC using a 250 mm × 10 mm i.d., 10 μm, Econosil RP-18 column (Alltech) with a solvent system of 70% MeOH (1 L, flow rate; 2 mL/min) to yield compound 2 (12 mg, Rt = 17.0 min). Subfraction B8 (709 mg) was separated on an RP-C 18 silica gel column with 60~100% MeOH and purified over an RP-C 18 semi-prep. HPLC (55% MeOH) to yield compound 3 (10 mg, Rt = 15.0 min). Subfraction B9 (439 mg) was separated on an RP-C18 silica gel column with 60% MeOH and purified over an RP-C 18 semi-prep. HPLC (65% MeOH) to yield compounds 1 (23 mg, Rt = 16.0 min), 5 (44 mg, Rt = 13.0 min), and 6 (8 mg, Rt = 22.0 min). Fraction D (4.0 g) was separated on a silica gel column (CHCl 3 : MeOH= 20 : 1 – 1 : 1) to afford eleven subfractions (D1-D11). Subfraction D5 (392 mg) was further separated on an silica Lobar A ® -column (CHCl 3 :MeOH = 50 : 1) and purified over an RP-C 18 semi-prep. HPLC (60% MeOH) to yield compounds 4 (10 mg, Rt = 14.0 min) and 7 (5 mg, Rt = 19.0 min).
3,7-Dihydroxy-2,4-dimethoxyphenanthrene (1) –Yellow gum; IR ν max cm −1 : 3385, 2939, 2835, 1621, 1478, 1354, 1294, 1228, 1164, 1125, 1075, 927 and 678; FAB-MS m/z 271 [M + H] + ; 1 H-NMR (500 MHz, CDCl 3 ): δ 9.27 (1H, d, J = 9.0 Hz, H-5), 7.52 (1H, d, J = 9.0 Hz, H-9), 7.39 (1H, d, J = 9.0 Hz, H-10), 7.14 (1H, d, J = 2.5 Hz, H-8), 7.12 (1H, s, H-1), 7.09 (1H, d, J = 9.0, 2.5 Hz, H-6), 3.97 (3H, s, 4-OCH 3 ), 3.87 (3H, s, 2-OCH 3 ); 13 C-NMR (125 MHz, CDCl 3 ): δ 154.8 (C-7), 147.7 (C-2), 144.5 (C-4), 139.9 (C-3), 134.2 (C-8a), 128.0 (C-5), 127.0 (C-10), 125.8 (C-10a), 124.3 (C-9), 123.0 (C-4b), 119.1 (C-4a), 116.1 (C-6), 111.1 (C-8), 105.0 (C-1), 58.6 (4-OCH 3 ), 55.2 (2-OCH 3 ).
3,7-Dihydroxy-2,4,8-trimethoxyphenanthrene (2) – Yellow gum; IR ν max cm −1 : 3379, 2943, 2833, 1619, 1481, 1454, 1299, 1216, 1107, 1032, and 676; FAB-MS m/z 300 [M] + ; 1 H-NMR (500 MHz, CDCl 3 ): δ 9.16 (1H, d, J = 9.0 Hz, H-5), 7.82 (1H, d, J = 9.0 Hz, H-9), 7.63 (1H, d, J = 9.0 Hz, H-10), 7.30 (1H, d, J = 9.0 Hz, H-6), 7.09 (1H, d, J = 8.5 Hz, H-1), 4.05 (3H, s, 8-OCH 3 ), 3.98 (3H, s, 4-OCH 3 ), 3.94 (3H, s, 2-OCH 3 ); 13 C-NMR (125 MHz, CDCl 3 ): δ 147.9 (C-2), 146.2 (C-4), 144.6 (C-7), 141.3 (C-3), 140.1 (C-8), 127.7 (C-10), 127.0 (C-10a), 125.7 (C-4b), 123.8 (C-8a), 123.2 (C-9), 119.1 (C-4a), 117.6 (C-5), 116.7 (C-6), 104.9 (C-1), 60.2 (OCH 3 ), 58.6 (OCH 3 ), 55.2 (OCH 3 ).
9,10-Dihydro-4,7-dimethoxyphenanthrene-2,8-diol (3) – Yellow gum; IR ν max cm −1 : 3445, 2940, 2838, 1598, 1482, 1441, 1277, 1158, 1084, 1013, 973, 874, 813, and 542; FAB-MS m/z 273 [M + H] + ; 1 H-NMR (500 MHz, CD 3 OD): δ 7.68 (1H, d, J = 8.5 Hz, H-5), 6.74 (1H, d, J = 8.5 Hz, H-6), 6.39 (1H, d, J = 2.5 Hz, H-3), 6.31 (1H, d, J = 2.5 Hz, H-1), 3.85 (3H, s, 7-OCH 3 ), 3.80 (3H, s, 4-OCH 3 ), 2.72 (2H, m, H-9), 2.59 (2H, m, H-10); 13 C-NMR (125 MHz, CD 3 OD): δ 158.2 (C-4), 156.4 (C-2), 145.6 (C-7), 141.8 (C-8), 140.9 (C-10a), 126.7 (C-4b), 124.4 (C-8a), 119.3 (C-5), 115.7 (C-4a), 108.0 (C-6), 107.1 (C-1), 98.1 (C-3), 55.2 (OCH 3 ), 54.7 (OCH 3 ), 30.2 (C-10), 21.4 (C-9).
9,10-Dihydro-1-(4'-hydroxybenzyl)-4,7-dimethoxyphe nanthrene-2,8-diol (4) – White amorphous powder; IR ν max cm −1 : 3360, 2941, 2838, 1595, 1511, 1490, 1444, 1278, 1022, 877, 826, and 533; FAB-MS m/z 379 [M + H] + ; 1 H-NMR (500 MHz, Pyridine- d5 ): δ 8.16 (1H, d, J = 8.5 Hz, H-5), 7.41 (2H, d, J = 8.5 Hz, H-2', 6'), 7.13 (2H, d, J = 8.5 Hz, H-3', 5'), 6.96 (1H, d, J = 8.5 Hz, H-6), 6.83 (1H, s, H-3), 4.42 (2H, s, H-1a), 3.73 (6H, s, 4, 7-OCH 3 ), 3.10 (2H, m, H-9), 2.93 (2H, m, H-10); 13 C-NMR (125 MHz, Pyridine- d5 ): δ 156.6 (C-4, 4'), 155.9 (C-2), 146.1 (C-7), 143.2 (C-8), 140.5 (C-10a), 132.5 (C-1'), 129.8 (C-2', 6'), 127.8 (C-4b), 125.4 (C-8a), 119.7 (C-5), 118.4 (C-1), 116.6 (C-4a), 115.8 (C-5'), 108.9 (C-6), 99.0 (C-3), 55.6 (4, 7-OCH 3 ), 30.7 (C-1a), 26.6 (C-10), 22.1 (C-9).
Gigantol (5) – Yellow gum; IR ν max cm −1 : 3359, 2944, 2833, 1600, 1517, 1457, 1219, 1153, 1117, 1032, and 692; FAB-MS m/z 274 [M] + ; 1 H-NMR (500 MHz, CDCl 3 ): δ 6.84 (1H, d, J = 8.0 Hz, H-5''), 6.68 (1H, dd, J = 8.0, 2.0 Hz, H-6''), 6.63 (1H, d, J = 2.0 Hz, H-2''), 6.32 (1H, brd, J = 2.0 Hz, H-6'), 6.27 (1H, brd, J = 2.0 Hz, H-4'), 6.27 (1H, brd, J = 2.0 Hz, H-2'), 3.83 (3H, s, 5'- OCH 3 ), 3.74 (3H, s, 3''-OCH 3 ), 2.80 (4H, m, H-1, 2); 13 C-NMR (125 MHz, CDCl 3 ): δ 161.0 (C-5'), 156.9 (C-3'), 146.5 (C-3''), 144.7 (C-1'), 143.8 (C-4''), 134.0 (C-1''), 121.2 (C-6''), 114.5 (C-2''), 111.5 (C-5''), 108.4 (C-2'), 107.0 (C-6'), 99.3 (C-4'), 56.1 (OCH 3 ), 55.5 (OCH 3 ), 38.4 (C-2), 37.4 (C-1).
3',4''-Dihydroxy-5',3'',5''-trimethoxybibenzyl (6) – Yellow gum; IR ν max cm −1 : 3358, 2945, 2832, 1452, 1032, and 695; FAB-MS m/z 305 [M + H] + ; 1 H-NMR (500 MHz, CDCl 3 ): δ 6.39 (2H, s, H-2'', 6''), 6.35 (1H, m, H-6'), 6.28 (1H, m H-4'), 6.27 (1H, m, H-2'), 3.88 (6H, s, 3'', 5''-OCH 3 ), 3.78 (3H, s, 5'-OCH 3 ), 2.84 (4H, m, H-1, 2); 13 C-NMR (125 MHz, CDCl 3 ): δ 160.8 (C-5'), 156.5 (C-3'), 146.8 (C-3'', 5''), 144.4 (C-1'), 132.8 (C-1''), 132.7 (C-4''), 108.0 (C-2'), 106.9 (C-6'), 105.1 (C-2'', 6''), 99.0 (C-4'), 56.2 (3'', 5''-OCH 3 ), 55.4 (5'-OCH 3 ), 38.2 (C-1), 37.9 (C-2).
Batatasin III (7) – Yellow gum; IR ν max cm −1 : 3358, 2945, 2833, 1698, 1455, 1155, 1116, 1032, and 659; FAB-MS m/z 244 [M] + ; 1 H-NMR (500 MHz, CDCl 3 ): δ 7.14 (1H, m, H-3''), 6.75 (1H, d, J = 8.0 Hz, H-2''), 6.65 (1H, dd, J = 8.5, 2.0 Hz, H-2'), 6.65 (1H, brs, H-2''), 6.32 (1H, brs, H-6'), 6.25 (1H, brs, H-2'), 3.75 (3H, s, 5'-OCH 3 ), 2.84 (2H, m, H-1), 2.79 (2H, m, H-2); 13 C-NMR (125 MHz, CDCl 3 ): δ 161.1 (C-5'), 156.7 (C-3'), 155.7 (C-3''), 144.6 (C-1'), 143.8 (C-1''), 129.7 (C-5''), 121.2 (C-6''), 115.5 (C-2''), 113.1 (C-4''), 108.1 (C-2'), 107.0 (C-6'), 99.3 (C-4'), 55.4 (5'-OCH 3 ), 37.8 (C-1), 37.5 (C-2).
Cytotoxicity assay – A sulforhodamine B bioassay (SRB) was used to determine the cytotoxicity of each compound against four cultured human cancer cell lines. 7 The assays were performed at the Korea Research Institute of Chemical Technology. The cell lines used were A549 (non small cell lung adenocarcinoma), SKOV-3 (ovarian cancer cells), SK-MEL-2 (skin melanoma), and HCT15 (colon cancer cells). Doxorubicin (Sigma Chemical Co., ≥ 98%) was used as a positive control.
Results and Discussion
Compounds 1 - 3 , 5 , and 7 were identified as 3,7-dihydroxy-2,4-dimethoxyphenanthrene ( 1 ), 8 3,7-dihydroxy-2,4,8-trimethoxyphenanthrene ( 2 ), 9 9,10-dihydro-4,7-dimethoxyphenanthrene-2,8-diol ( 3 ), 10 gigantol ( 5 ), 11 and batatasin III ( 7 ) 11 by comparing the 1 H-, 13 C-NMR, and MS spectral data with the literature values. Compounds 2 , 3 , and 6 were isolated for the first time from this plant. The following describes the structural elucidation of compounds 4 and 6 , since the 13 C-NMR spectral data were not yet reported.
Compound 4 was obtained as a white amorphous powder. FABMS, 1 H- and 13 C-NMR data gave a molecular formula of C 23 H 22 O 5 . The 1 H-NMR spectrum of 4 indicated the presence of seven aromatic protons at δ 8.16 (1H, d, J = 8.5 Hz, H-5), 7.41 (2H, d, J = 8.5 Hz, H-2', 6') and 7.13 (2H, d, J = 8.5 Hz, H-3', 5'), 6.96 (1H, d, J = 8.5 Hz, H-6), and 6.83 (1H, s, H-3), two methoxy protons at δ 3.73 (6H, s, 4, 7-OCH 3 ), and three methylene protons at δ 4.42 (2H, s, H-1a), 3.10 (2H, m, H-9), and 2.93 (2H, m, H-10). The 13 C-NMR spectrum demonstrated the presence of 23 carbon signals, consisting of two methoxy carbon signals at δ 55.6, and three methylene carbon signals at δ 30.7, 26.6, and 22.1, and 18 aromatic carbons signals. The 1 H- and 13 C-NMR spectra implied that compound 4 could be a phenanthrene derivative. 12 In the HMBC spectrum, the correlations between the methylene protons (δ 4.41, H-1a) and the aromatic carbon (δ 118.4, C-1) were observed, indicating that the benzylic –CH 2 – moiety was attached at C-1 ( Fig. 2 ). The methoxy position was also confirmed to be C-4, C-7 by HMBC cross peaks of C-4/ 4-OCH 3 and C-7/7-OCH 3 . On the basis of the further comparison with literature values, the structure of 4 was determined to be 9,10-dihydro-1-(4'-hydroxybenzyl)-4,7-dimethoxyphenanthrene-2,8-diol. 13
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The structures of 1 - 7 from B. striata.
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Key COSY () and HMBC () correlations of compounds 4 and 6.
Compound 6 was obtained as a yellowish gum. From FAB-MS ( m/z 305 [M + H] + ) and 1 H- and 13 C-NMR spectral data, the molecular formula of 6 was deduced to be C 17 H 20 O 5 . The 1 H-NMR spectrum exhibited the presence of five aromatic protons at δ 6.39 (2H, s, H-2'', 6''), 6.35 (1H, m, H-6'), 6.28 (1H, m H-4'), and 6.27 (1H, m, H-2'), three methoxy protons at δ 3.88 (6H, s, 3'', 5''-OCH 3 ) and 3.78 (3H, s, 5'-OCH 3 ), two methylene protons at δ 2.84 (4H, m, H-1, 2). The 13 C-NMR spectrum exhibited the presence of 16 carbon signals, including twelve aromatic carbons, two methoxy carbons (δ 56.2 and 55.2), and two methylene carbons (δ 38.2 and 37.2). Above NMR data suggested that 6 was a stilbene. 14 The methoxy positions were confirmed to be C-5', C-3'', and 5'' by HMBC cross peaks of C-5'/5'-OCH 3 , C-3''/3''-OCH 3 , and C-5''/5''-OCH 3 ( Fig. 2 ). Based on further comparison with published data, the structure of 6 was identified as 3',4''-dihydroxy-5',3'',5''-trimethoxybibenzyl. 13
Cytotoxic activities of compounds (1 - 7) isolated fromB. striata
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aIC50 value of compounds against each cancer cell line, which was defined as the concentration (μM) that caused 50% inhibition of cell growth in vitro.
The isolated compounds ( 1 - 7 ) were tested in vitro for cytotoxicity against four human tumor cells using the SRB assay. The stilbene type ( 5 - 7 ) showed considerable cytotoxicity against the tested cells with IC 50 values of 5.28 – 24-51 μM, but the phenanthrenes type ( 1 - 3 ) were inactive (IC 50 > 30.0 μM) except for the compound 4 . According to the substituted pattern in ring B of stilbenes, the cytotoxic activity exhibited different as shown in Table 1 .
Acknowledgements
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2012R1A5A2A 28671869). We are thankful to the Korea Basic Science Institute (KBSI) for the measurements of NMR and MS spectra.
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