Study of dracaena angustifolia - Trần Lê Quân

122 Journal of Chemistry, Vol. 42 (1), P. 122 - 124, 2004 STUDY OF DRACAENA ANGUSTIFOLIA I - NEW SPIROSTANOL SAPOGENINS FROM ROOTS AND RHIZOMES Received 15-1-2003 TRAN LE QUAN,1 TRAN KIM QUI,1 SHIGETOSHI KADOTA2 1College of Natural Sciences, National University–Hochiminh City, Hochiminh City 2Institute of Natural Medicine, Toyama Medical & Pharmaceutical University, Toyama, Japan #$a ch% liên l&c: GS. TS. Trn Kim Qui Trng i h c Khoa h c T nhiên Tp. HCM. 55D Trn Phú, Q.5, Tp. HCM in thoi: 08-835-4421 SUMMARY The MeOH extract of Nam ginseng (roots and rhizomes of Dracaena angustifolia) afforded three new spirostanol sapogenins, named namogenins A-C (1-3). Their structures were determined on basis of spectral analyses and chemical methods. I. INTRODUCTION Dracaena angustifolia Roxb. (Dracaenaceae) is locally known as Nam ginseng (ginseng from the South) in Quang Nam province. Its underground parts are used as tonic and for treatment of leukemia.1 In our continuing studies on Vietnamese medicinal plants, we have examined the constituents of Nam ginseng (D. angustifolia) and isolated three new spirostanol sapogenins. This paper reports the isolation and structure elucidation of these new compounds. 123 II. RESULTS AND DISCUSSION Air-dried roots and rhizomes of D. angustifolia were extracted successively by refluxing MeOH, 50% aqueous MeOH and water to give MeOH, MeOH-H2O and H2O extracts, respectively. The MeOH extract was subjected to Diaion HP-20 column chromatography (CC). The MeOH eluate was further separated by a combination of silica gel and ODS column chromatographies, and normal- and reversed-phase pTLC, to afford three new compounds, named namogenins A-C (1-3). Negative-ion HRFABMS of 1 displayed a quasi-molecular ion at m/z 461.2859, indicating the molecular formula C27H42O6. The 1H NMR spectrum of 1 showed signals ascribable to two tertiary methyls and three secondary methyls, while the 13C NMR spectrum of 1 showed thirty-five signals (Table 1). Analysis of the COSY and HMQC spectra, together with the molecular formula, suggested 1 to be a spirostane-type steroid, but the 1H and 13C NMR signals ascribable to ring F appeared as pairs of signals, indicating that 1 was a C-25 epimeric mixture. Since its isolation was very difficult, as reported for similar epimeric mixtures,2 and could not be done, the structure of 1 was elucidated by spectroscopic analysis of the epimeric mixture. Table 1. 13C NMR Data (
) for Compounds 1-3 in Pyridine-d5. 1 2 3 1 78.2 78.2 78.2 2 43.6 43.6 43.7 3 68.1 68.1 69.1 4 44.0 44.0 44.1 5 139.8 139.8 139.8 6 124.9 125.0 124.9 7 26.4 26.9 26.4 8 37.5 36.8 37.5 9 44.4 44.5 44.4 10 43.9 43.9 43.9 11 23.2 23.6 23.2 12 27.2 32.7 27.2 13 48.1 44.8 48.2 14 88.2 86.8 88.3 15 40.6 40.1 40.6 16 90.5 81.9 90.8 17 91.2 59.9 91.2 18 21.0 20.4 21.0 19 14.0 13.9 14.0 20 45.2a 45.7b 42.5 45.1 21 9.9a 9.5b 15.2 9.9 22 109.6a 110.0b 110.0 109.8 124 23 32.2a 26.7b 26.5 33.6 24 28.9a 25.8b 26.3 28.7 25 30.4a 27.4b 27.6 144.2 26 66.8a 65.0b 65.0 64.9 27 17.3a 16.3b 16.3 108.8 a,b Data for the 25R- and 25S-epimers, respectively. Analysis of the COSY and HMQC spectra indicated the disappearance of the methine carbons assignable to C-14 and C-17, but instead of them, 13C NMR spectrum showed signals of two quaternary carbons at
88.2 and 91.2. Thus, C-14 and C-17 seemed to have hydroxyl groups, which were confirmed by the HMBC correlations of H3-21 and H-16 with the quaternary carbon at
91.2 (C-17) and of H3-18 with both quaternary carbons at
91.2 (C-17) and 88.2 (C-14). The
-orientation of 14-OH and 17-OH was deduced by a comparison of the 13C NMR data with that of (25R)-spirost-5-en-3
,14
,17
-triol (ophiogenin).3 Thus, 1 was determined to be a mixture (1:1) of (25R)- and (25S)-spirost-5-en-1
,3
,14
,17
-tetrol, which were named as (25R)- and (25S)-namogenin A, respectively. O HO HO O OH OH 3 O HO HO O R OH 25 1 2 R = OH, 25R,S R = H, 25S H H H H1 3 6 9 11 13 14 16 17 20 22 23 24 26 27 18 19 21 Negative-ion HRFABMS of 2 indicated the molecular formula C27H42O5, one oxygen atom less than 1. The 1H and 13C NMR spectra of 2 were similar to those of 1, indicating 2 also to be a spirostane-type steroid. However, the signals ascribable to ring F protons and carbons appeared as only one set, and the chemical shifts of H3-27 (
1.06) and of C-23 to C-27 (Table 1) suggested 2 to be a 25S-spirostane-type steroid.4,5 The 13C NMR spectrum of 2 revealed a highfield shift (
59.9) of the oxygenated quaternary carbon assigned to C-17 in 1. Thus, C-17 was considered to be a methine group, which was confirmed by the 1H-1H connectivity deduced by the analysis of the COSY and HMQC spectra and the HMBC correlations of the methine carbon at
59.9 (C-17) with H3-21 (
1.17), H3-18 (
1.18) and H-16 (
5.10) and of the quaternary carbon at
86.8 (C-14) with H3-18 (
125 1.18). Thus, namogenin B was determined to be (25S)-spirost-5-en-1
,3
,14
-triol (2). The molecular formula of namogenin C (3) was determined by negative-ion HRFABMS to be C27H40O6, two hydrogen atoms less than 1. The 1H and 13C NMR spectra of 3 were almost the same as those of 1 (Table 1), except for the appearance of signals for an exo-olefin (
H 4.79, 2H;
C 144.2, 108.8) and the disappearance of the signals of a secondary methyl (CH3-27) and a methine (CH-25). Thus, 3 was considered to be a 25,27-dehydro derivative of 1, which was supported by the HMBC correlations of the exo-olefinic protons (
4.79, H2-27) with C-24 (
28.7) and C-26 (
64.9). Thus, namogenin C was determined to be spirosta-5,25(27)-dien-1
,3
,14
,17
-tetrol (3). III. EXPERIMENTAL SECTION General Experimental Procedures. Optical rotations were measured on a JASCO DIP-140 digital polarimeter at 25 °C. NMR spectra were recorded on a JEOL JNM-LA400 spectrometer in pyridine-d5, using TMS as an internal reference. FABMS and HRFABMS was performed using a JEOL JMS-700T mass spectrometer and glycerol was used as matrix. Plant Material. Nam ginseng (roots and rhizomes of D. angustifolia) were collected in Quangnam Province, Vietnam, in November 1998. Extraction and Isolation. Air-dried roots and rhizomes of D. angustifolia (440 g) were extracted by refluxing with MeOH, MeOH-H2O and H2O successively to give MeOH (78 g), MeOH-H2O (77 g) and H2O (5.5 g) extracts, respectively. Part of the MeOH extract (70 g) was subjected to Diaion HP-20 CC and eluted with H2O and then MeOH to give a MeOH fraction (7.2 g). The MeOH fraction was then chromatographed on silica gel with CHCl3-MeOH-H2O (14:6:1) to give 7 fractions. Fraction 1 (1.5 g) was again chromatographed on silica gel to give 3 subfractions. Subfraction 2 (520 mg) was separated on normal- (CHCl3-MeOH-H2O, 14:6:0.5) and reversed-phase (MeOH-MeCN-H2O, 2:2:1) pTLC to afford 1 (10 mg), 2 (11.6 mg), 3 (1.6 mg). A Mixture (1:1) of (25R)- and (25S)-Namogenin A (1): colorless amorphous solid; [ ]D 25 –69.2° (c 0.6, MeOH); 1H NMR (C5D5N)
5.70 (1H, d, J = 5.4 Hz, H-6), 4.78 (1H, m, H-16), 4.03 (1H, dd, J = 10.1, 2.7 Hz, H-26 of 25S-isomer), 3.93 (1H, m, H-3), 3.85 (1H, dd, J = 11.7, 4.2 Hz, H-1), 3.49 (2H, m, H2-26 of 25R-isomer), 3.28 (1H, br d, J = 10.1 Hz, H-26 of 25S-isomer), 2.23 (3H, d, J = 7.1 Hz, H3-21), 1.42 (3H, s, H3-19), 1.20 (3H, s, H3-18), 1.06 (3H, d, J = 7.1 Hz, H3-27 of 25S-isomer), 0.68 (3H, d, J = 5.4 Hz, H3-27 of 25R-isomer); 13C NMR, see Table 1; FABMS m/z 126 461.3 [M-H]–; HRFABMS m/z 461.2859 (calcd for [M-H]– 461.2904). Namogenin B (2): colorless amorphous solid; [ ]D 25 –74.5° (c 0.8, MeOH); 1H NMR (C5D5N)
5.71 (1H, d, J = 5.5 Hz, H-6), 5.10 (1H, m, H-16), 4.05 (1H, dd, J = 10.8, 2.6 Hz, H-26), 3.33 (1H, br d, J = 10.8 Hz, H-26), 3.92 (1H, m, H-3), 3.84 (1H, dd, J = 11.5, 4.0 Hz, H-1), 2.82 (1H, m, H-17), 1.43 (3H, s, H3-19), 1.18 (3H, s, H3-18), 1.17 (3H, d, J = 7.2 Hz, H3-21), 1.06 (3H, d, J = 7.0 Hz, H3-27); 13C NMR, see Table 1; FABMS m/z 445.3 [M-H]–; HRFABMS m/z 445.2956 (calcd for [M-H]– 445.2954). Namogenin C (3): colorless amorphous solid; [ ]D 25 –29.8° (c 0.6, MeOH); 1H NMR (C5D5N)
5.72 (1H, d, J = 5.1 Hz, H-6), 4.83 (1H, t, J = 6.4 Hz, H-16), 4.79 (2H, br s, H2-27), 4.46 (1H, d, J = 11.9, H-26), 3.97 (1H, d, J = 11.9, H-26), 3.93 (1H, m, H-3), 3.88 (1H, dd, J = 11.7, 4.1 Hz, H-1), 2.43 (1H, q, J = 7.3 Hz, H-20), 2.34 (1H, dt, J = 11.9, 4.6 Hz, H-9), 2.17 (1H, dt, J = 11.5, 4.6 Hz, H-8), 1.44 (3H, s, H3-19), 1.21 (3H, s, H3-18), 1.20 (3H, d, J = 7.3 Hz, H3-21); 13C NMR, see Table 1; FABMS m/z 459.3 [M-H]–; HRFABMS m/z 459.2751 (calcd for [M-H]– 459.2746). REFERENCES AND NOTES 1 Vo V. C. Dictionary of Vietnamese Medicinal Plants, Medicine Publisher, Hochiminh City, 1996, p. 128. 2 Miyakoshi M., Tamua Y., Masuda H., Mizutani K., Tanaka O., Ikeda T. J. Nat. Prod. Vol. 63, p. 332-338 (2000). 3 Nakanishi H., Kaneda N. Yakugaku Zasshi Vol. 197, p. 780-784 (1987). 4 Hoyer G.-A., Sucrow W., Winkler D. Phytochemistry Vol. 14, p. 539-542 (1975). 5 Jaffer J. A., Crabb T. A., Turner C. H., Blunden G. Org. Magn. Reson. Vol. 21, p. 576-579 (1983).