Pinoresinol and 3,4’,5,7-tetrahydroxy-3’-methoxyflavanone from the fruits of silybum marianum (l.) gaertn

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Journal of Chemistry, Vol. 45 (2), P. 219 - 222, 2007 PINORESINOL AND 3,4’,5,7-TETRAHYDROXY-3’METHOXYFLAVANONE FROM THE FRUITS OF SILYBUM MARIANUM (L.) GAERTN. Received 19 April 2006 TRINH THI DIEP , PHAN VAN KIEM2, NGUYEN THUONG DONG1, NGUYEN HUU TUNG2, BUI THI BANG1, CHAU VAN MINH2 AND ALESSANDRA BRACA3 1 National Institute of Medicinal Materials, Ministry of Health 1 2 Institute of Natural Products Chemistry, VAST 3 Department of Bioorganic Chemistry and Biopharmaceutics University of Pisa, Italia SUMMARY From the fruits of Silybum marianum (L.) Gaertn. cultivated in the North of Vietnam, (±)2,6bis(4 -hydroxy-3 -methoxy-phenyl)-3,7-dioxabicyclo[3.3.0]octane (pinoresinol) (1) and 3,4 ,5,7tetrahydroxy-3 -methoxyflavanone (2) were isolated. Their structures were elucidated by analyses of the NMR and mass spectra in comparison with the reported data. This is the first report of both 1 and 2 from Silybum species. I - INTRODUCTION In previous papers, we have reported the isolation and structural elucidation of flavonolignan and flavonoid compositions of the fruits of Silybum marianum (L.) Gaertn. (Asteraceae) cultivated the North of Vietnam and used in the folk medicines [1 - 3]. This paper deals with further investigation of the bioactive compositions from S. marianum. By various chromatography methods, (±)2,6-bis(4 hydroxy-3 -methoxy-phenyl)-3,7dioxabicyclo[3.3.0]octane (Pinoresinol) (1) and 3,4 ,5,7-tetrahydroxy-3 -methoxyflavanone (2) were isolated from the methanolic extract of the fruits from this plant. The structures were elucidated by analyses of the NMR and ESI mass spectra in comparison with the reported data. This is the first report of both 1 and 2 from Silybum species. To the best of our knowledge, no 13C-NMR data of 2 has been reported previously. II - EXPERIMENTAL 1. General experimental procedures The Electronspray Ionization (ESI) mass spectrum was obtained using a AGILENT 1100 LC-MSD Trap spectrometer. The 1H-NMR (500 MHz) and 13C-NMR (125 MHz) spectra were recorded on a Bruker AM500 FT-NMR spectrometer using TMS as the internal standard. Column chromatography (CC) was performed on silica gel (Kieselgel 60, 70-230 mesh and 230-400 mesh, Merck) or YMC RP18 resins (30-50 µm, Fujisilisa Chemical Ltd). Thin layer chromatography (TLC) was performed on DC-Alufolien 60 F254 (Merck 1.05715) or RP18 F254s (Merck) plates. 2. Plant material The fruits of Silybum marianum (L.) Gaertn. were collected in Sapa, Lao Cai Province in June, 2004 and were identified by Dr Nguyen Tap, Department of Botany and Medicinal Plant 219 Resources, National Institute of Medicinal Materials. 3. Extraction and isolation Air-dried and powdered fruits of Silybum marianum (L.) Gaertn. (200 g) were defatted with petroleum and then extracted with methanol. After removal of the solvent under vacuum, the residue (5.8 g) was obtained, which was then repeated chromatographed on silica gel columns to get 1 (5.2 mg) as colorless amorphous and 2 (6.5 mg) as yellow crystals. III - RESULTS AND DISSCUSSION Compound 1 was isolated as colorless amorphous substance, mp. 120 - 121oC. The 1HNMR spectrum showed three peaks of the aromatic protons at 6.89 (1H, d, J = 1.5 Hz), 6.82 (1H, dd, J = 8.0, 1.5 Hz) and 6.88 (1H, d, J = 8.0 Hz) suggesting that the aromatic ring has three substituted positions. Oxymethine proton was evident at 4.73 ppm as a doublet and the methylene groups bearing oxygen atom at 4.24 and 3.88 ppm as two doublet of doublet. A methine proton was observed at 3.10 ppm (multiplet) and methoxy group was confirmed at 3.90 ppm (singlet). The 13C-NMR spectrum of 1 exhibited signals of 10 carbons at 146.73, 145.28, 132.96, 118.99, 114.30, 108.65, 85.90, 71.69, 55.99 and 54.20 as listed in table 1. The partial structures were deduced from the HOMOCOSY and HMQC spectra, and were connected based on long-range correlations in the HMBC spectrum of 1. In the HOMOCOSY, cross peaks between the proton at 3.10 (H-5) and protons at 4.73 (H-6)/ 4.24 (Ha-4)/ 3.88 (Hb-6), and between proton at 6.88 (H-5 ) and proton at 6.82 (H-6 ) were observed. In addition, H-C long-range correlations between the proton at 3.10 (H-5) and the carbon at 85.90 (C-6)/ 71.70 (C-4)/ 132.9 (C-1 ), between the proton at 4.73 (H-6) and carbons at 132.90 (C-1 )/ 118.99 (C-6 )/ 108.65 (C-2 ) confirming the lignan skeleton of 1. The ESI mass spectra of 1 showed an ion peak at m/z 341 [M-H2O+H]+ with strongest indensity corresponding to the molecular formula of C20H22O6. These findings suggested the structure of 1 as shown in Fig. 1. All NMR assignments of 1 were confirmed by detailed analyses of HSQC and HMBC spectra (table 1), which are in good agreement with those reported in the literature [4]. Thus, compound 1 was determined to be (±)2,6-bis(4 hydroxy-3 -methoxy-phenyl)-3,7dioxabicyclo[3.3.0]octane (Pinoresinol), the compound was isolated from Festuca argentina [4]. However, this is the first report of 1 from Asteraceae family. Compound 2 was isolated as yellow crystals suggesting that 2 is a flavonoid. The ESI mass spectrum showed an ion peak at m/z 319 corresponding to the the molecular formula of C16H14O7. The 13C-NMR and DEPT spectra of 2 confirmed the presence of 16 carbon atoms including 8C, 7CH and 1CH3 of the flavanon OH 5' 6' 1' O 3 4 6 5" 4" HO 6" 1" 2" 1 5 H 2 7 2' 4' 6' 3' 1' OCH 3 HO O 7 H 6 8 5 10 4 8 OR1 4' 3' OR2 3 OH O OH 3" O 2 R1 = H, R2 = CH3; 3 R1 = H, R2 = CH3 , 4 R1 = H, R2 = H OCH 3 1 Figure 1: The structures of 1 - 4 220 2' 2 9 5' 2,3 Table 1: The NMR data of 1 C * a,c a,b C * C H HMBC (H to C) (J, Hz) 1, 5 54.2 54.20 3.10 (2H, m) C-2, 4, 1 2, 6 85.9 85.90 4.73 (2H, d, 5.0) C-1, 5, 8, 1 , 2 , 6 4, 8 71.7 71.70 4.24 (2H, dd, 7.0, 9.5) 3.88 (2H, dd, 4.0, 9.5) C-1, 2 C-1, 2 1,1 132.9 132.90 - 2,2 108.7 108.65 6.89 (2H, d, 1.5) 3,3 146.7 146.73 - 4,4 145.3 145.28 - 5,5 114.3 114.30 6.88 (2H, d, 8.0) C-1 , 3 , 4 , 6 6,6 118.9 118.99 6.82 (2H, dd, 1.5, 8.0) C-2, 1 , 2 , 4 3 , 3 -OCH3 56.0 55.99 3.90 (3H, s) C-3 C C-2, 1 , 3 , 4 , 6 of pinoresinol [4], aMeasured in CDCl3, b125 MHz, c500 MHz. Table 2: The NMR data of 2 - 4 C C of 3 [5] C of 4 [6] a,b C of 2 a,c H (J, Hz) 2 147.1 84.3 85.2 5.01 (1H, d, 6.5) 3 136.1 73.0 73.6 4.59 (1H, d, 6.5) 4 176.3 198.0 198.4 - 5 161.2 164.8 165.3 - 6 98.6 97.0 97.4 5.94 (1H, d, 1.5) 7 164.4 167.8 168.9 - 8 93.9 96.0 96.3 5.91 (1H, d, 1.5) 9 156.8 164.0 164.5 - 10 103.5 101.4 101.8 - 1 122.6 129.6 129.8 - 2 112.7 115.7 112.5 7.13 (1H, d, 1.5) 3 149.4 145.6 148.9 - 4 147.9 146.4 148.3 - 5 116.0 115.7 115.9 6.85 (1H, d, 8.0) 6 122.2 120.8 122.2 7.98 (1H, dd, 1.5, 8.0) OCH3 56.2 56.5 3.89 (3H, s) a Measured in CDCl3, b125 MHz, c500 MHz. 221 skeleton. The spin-coupling of three protons of ring C suggested the hydroxyl and methoxyl at C-4 and C-3 . The chemical shifts at 85.2 (CH), 73.6 (CH) and 198.4 (C=O) were very similar to that of the flavanone reported in the literature [6]. The methoxyl group evidenced at C 56.5 (q) and H 3.89 (3H, s). The NMR assignments of ring C of 2 were deduced from those of 3 [5], and the NMR assignments of ring A were compared with that of 4 [6]. All these data led to determine the structure of 2 as 3,4 ,5,7-tetrahydroxy-3 -methoxyflavanone, which is first isolated from Silybum species. Acknowledgements: The authors wish to thank to Mr Dang Vu Luong, the NMR Lab., Institute of Chemistry, Vietnamese Academy of Science and Technology for performing the NMR, and Dr. Nguyen Tap, Department of Botany and Medicinal Plant Resources, National Institute of Medicinal Materials for the plant identification. This study was supported by a 222 grant from the Vietnam-Italia international cooperation project. REFERENCES 1. V. V. Chi. Vietnamese Medical Plant Dictionary, Ha Noi Medicine Pub. (1997). 2. T. T. Diep, N. T. Dong, B. T. Bang, C. V. Minh, P. V. Kiem. Journal of Medicinal Materials, Vol. 10(6), 175 - 178 (2005). 3. T. T. Diep, N. T. Dong, B. T. Bang, C. V. Minh, P. V. Kiem. Journal of Medicinal Materials, Vol. 11(1), 9 - 13 (2006). 4. B. Vermes, O. Seligmann and H. Wagner. Phytochemistry, 30(9), 3087 - 3089 (1991). 5. G. N. Kumari, L. J. M. Rao and N. S. P. Rao, Proc. Indian Acad. Sciences, Vol. 97, 171 (1986). 6. E. Kiehlmann and E. P. M. Li. Journal of Natural Products, Vol. 58(3), 450 - 455 (1995).
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