Quinolizidine Alkaloids from Sophora alopecuroides

J. Nat. Prod. 2000, 63, 190-192 190 Quinolizidine Alkaloids from Sophora alopecuroides Atta-ur-Rahman,*,† M. Iqbal Choudhary,*,† Khalid Parvez,† Aftab Ahmed,† Farzana Akhtar,† M. Nur-e-Alam,† and Naeem M. Hassan‡ International Center for Chemical Sciences, H.E.J. Research Institute of Chemistry, University of Karachi, Karachi-75270, Pakistan, and Department of Chemistry, University of Baluchistan, Quetta, Pakistan Received July 14, 1999 A new matrine-type alkaloid, 7R-hydroxysophoramine (1), was isolated from the aerial parts of Sophora alopecuroides together with eight known alkaloids, 12β-hydroxysophocarpine (2), sophoramine (3), 14βhydroxymatrine, matrine, sophoridine, sophocarpine, adenocarpine, and baptifoline. The structures of compounds 1-3 were confirmed through single-crystal X-ray diffraction analysis. The plant Sophora alopecuroides L. (Leguminosae) is widely distributed over a large area of the Asian continent.1 Biological studies on the constituents found in this plant have been performed in terms of potential sedative, central nervous system depressant, analgesic, hypothermic,2 antitussive,3 anticancer,4,5 nematocidal,6 antispasmodic,7 antipyretic,8 cardiotonic,9 hypoglycemic,l0 and many other pharmacological activities.11-14 In this communication, studies on S. alopecuroides have led to the isolation of a new alkaloid (1) and several known alkaloids. Among these alkaloids 12β-hydroxysophocarpine (2), 14β-hydroxymatrine, and adenocarpine have not been isolated previously from this species. Results and Discussion Aerial parts of S. alopecuroides were collected from the Baluchistan province of Pakistan and extracted with 80% ethanol. The extract was subjected to solvent-solvent extraction and repeated column chromatography on Si gel to obtain the new alkaloid, 7R-hydroxysophoramine (1) together with seven known alkaloids: 12β-hydroxysophocarpine15 (2), sophoramine 16,17 (3), 14β-hydroxymatrine,18 adenocarpine,19 matrine,20 sophoridine,21,22 sophocarpine4,23 and baptifoline. The structures of the compounds were determined unambiguously using either X-ray diffraction technique or 1D and 2D 1H and 13C NMR experiments in conjunction with the analysis of mass spectral and other spectroscopic data. The molecular formula of the new alkaloid 1 was determined by HREIMS to be C15H20N2O2 (m/z 260.1511). Its IR spectrum (CHCl3) showed absorption bands of hydroxyl (νmax 3236 cm-1), R,β-unsaturated lactam (νmax * Authors to whom correspondence should be addressed. Tel.: +92-21499-0007. Fax: +92-21-496-3373 or 496-3124. E-mail: [email protected]. † University of Karachi. ‡ University of Baluchistan. 10.1021/np990351v CCC: $19.00 Figure 1. HMBC correlations in compound 1. 1540 cm-1 for CdC and νmax 1660 cm-1 for CdO), and trans-quinolizidine (νmax 2928, 2855, 2793, and 2735 cm-1) functionalities.24 The EIMS showed a peak at m/z 243 corresponding to [M - OH]+. The 1H NMR spectrum (CDC13) was very similar to that of sophoramine (3). The downfield protons resonating at δ 7.13 (dd, J13,14 ) 8.9 Hz, J13,12 ) 7.2 Hz), 6.40 (dd, J12,13 ) 7.2 Hz, J12,14 ) 1.2 Hz), and 6.19 (dd, J14,13 ) 8.9 Hz, J14,12 ) 1.2 Hz) were assigned to H-13, H-12, and H-14, respectively. Two other downfield signals at δ 3.99 (dd, J17β,17R ) 14.2 Hz, J17β,5 ) 7.0 Hz) and 3.61 (dd, J17R,17β ) 14.2 Hz, J17R,5 ) 13.0 Hz) could be assigned to H-17β and H-17R, respectively. The lack of any other downfield methine signal indicated that alkaloid 1 might contain a hydroxyl group on a quaternary carbon. The 13C NMR spectra (BB and DEPT) of 1 showed 15 carbon signals with seven methylene, five methine, and three quaternary carbons. The chemical shift of a quaternary carbon (δ 69.3) also indicated the presence of a tertiary hydroxyl group. In the HMBC spectrum (Figure 1), the proton resonating at δ 6.19 (H-14) showed a longrange heteronuclear connectivity with C-15 (δ 163.7), while H-13 (δ 7.13) showed HMBC connectivities with C-15 (δ 163.7), C-14 (δ 118.1), C-12 (δ 104.1), and C-11 (δ 148.5). H-12, resonating at δ 6.40, exhibited HMBC interactions with C-14, C-11, and C-7 (δ 69.3), whereas H-17β (δ 3.99) was coupled with C-15, C-11, C-6 (δ 66.5), and C-5 (δ 25.6). These results suggested that the new alkaloid 1 is of the matrine-type, in which a hydroxyl group is present at the ring junction (i.e., C-7). The structure of 1 was established unambiguously as 7R-hydroxysophoramine by X-ray diffraction methods. A suitable crystal that formed in the orthorhombic space group, P212121, was selected for the experiment. Accurate lattice constants were a ) 7.836(2), b ) 12.021(2), and c ) 14.342(8) Å, with four independent molecules in the asymmetric unit. All unique diffraction © 2000 American Chemical Society and American Society of Pharmacognosy Published on Web 01/19/2000 Quindizidines from Sophora Journal of Natural Products, 2000, Vol. 63, No. 2 191 Figure 3. Computer-generated perspective drawing of the final X-ray model of 12β-hydroxysophocarpine (2). Figure 2. Computer-generated perspective drawing of the final X-ray model of 7R-hydroxysophoramine (1). maxima with 2θ e 135° were collected using θ-2θ scans and graphite monochromated Cu KR radiations (1.54178 Å). A total of 3184 unique reflections was collected, and of those 2361 were judged observed [I > 2σ(I)] and used in subsequent calculations. The structure was phased using direct methods (SHELXTL)25 and refined using full-matrix least-squares techniques with anisotropic heavy atoms and isotropic riding hydrogens to conventional crystallographic residual of 0.0361 (Rw ) 0.0982) for the observed data. A computer-generated drawing of the final X-ray model of 1 is given in Figure 2. 12β-Hydroxysophocarpine (2) was previously isolated from Sophora viciifolia,15 but this is the first report of its isolation from S. alopecuroides. It has not been subjected to X-ray crystallographic structure determination before. Its molecular formula was derived as C15H22N2O2. The structure was established unambiguously by the single crystal X-ray diffraction technique. Compound 2 was recrystallized from acetone-methanol mixture, and a suitable crystal was selected for the study. The crystal formed in the orthorhombic space group P212121 was a ) 5.8140(10), b ) 14.892(3), and c ) 15.189(3) Å, with four molecules (C15H22N2O2) in the asymmetric unit. All unique diffraction maxima with 2θ < 135° were collected using θ-2θ scans and graphite monochromated Cu KR radiations (1.54178 Å). A total of 3047 unique reflections was collected, and of those 2047 were judged observed [I > 2σ(I)] and used in further calculations. The structure was solved by the direct methods (SHELXTL) and refined by full-matrix least-squares techniques to a final discrepancy index of 0.0359 (Rw ) 0.1001) for observed data. A computergenerated perspective drawing of the final X-ray model of 2 is given in Figure 3. Sophoramine (3) is an alkaloid previously isolated from S. alopecuroides17 and many other species of Sophora. The compound 3 was isolated as large colorless crystals, and X-ray diffraction studies were carried out. Cell constants and an orientation matrix for data collection were obtained from a least-squares refinement using the setting angles of 20 carefully centered strong reflections. This corresponded to a orthorhombic, P212121, space group with cell constants, a ) 8.0410(10), b ) 9.419(2), and c ) 16.891(2) Å and four independent molecules (C15H20N2O) in the asymmetric unit. A total of 1591 unique reflections was collected using Cu KR radiations (1.54178 Å) of which 1443 were judged observed [I > 2σ(I)] and used in further calculations. The structure was solved by direct methods Figure 4. Computer-generated perspective drawing of the final X-ray model of sophoramine (3). (SHELXTL) and refined by full-matrix least-squares techniques to final discrepancy index of 0.0454 (Rw ) 0.1500) for observed data. A computer-generated perspective drawing of the final X-ray model of 3 is given in Figure 4. This is the first report of its crystal structure. 14β-Hydroxymatrine was previously isolated from S. tonkinensis,18 whereas adenocarpine was isolated initially from Adenocarpus intermedius and A. parvifolius.26 This is the first report of the isolation of these compounds from S. alopecuroides. Matrine, sophoridine, sophocarpine, and baptifoline have been previously reported from this plant.27-32 These alkaloids were identified by comparison of their spectral data with the reported values. Experimental Section General Experimental Procedures. Melting points were recorded on a Büchi 535 melting point apparatus and are uncorrected. Optical rotations were determined on a polartronic polarimeter. The IR spectra were recorded on JASCO IRA-I IR spectrophotometer. The UV spectra were recorded in CH3OH on a Shimadzu UV 240 instrument. The 1H NMR spectra were recorded in CDCl3 on a Bruker AMX 500 NMR spectrometer at 500 MHz, while the 13C NMR spectra were recorded on the same instrument at 125 MHz. MS were measured on a JEOL HX-110 mass spectrometer. X-ray diffraction studies (compounds 1-3) were conducted on a Bruker (previously Nicolet) P4 diffractometer using Cu KR radiations. 192 Journal of Natural Products, 2000, Vol. 63, No. 2 Plant Material. The aerial parts of S. alopecuroides were collected from the Hazarganji and Khanuzai areas, located in the Baluchistan Province of Pakistan, in June 1992. The plant was identified by the taxonomist Mr. Saeed-ur-Rahman, Assistant Professor, Department of Botany, University of Baluchistan. A voucher specimen (HS # 35) has been deposited in the Herbarium of the University of Baluchistan, Quetta, Pakistan. Extraction and Isolation. The air-dried aerial parts of the plant (10 kg) were crushed and extracted three times with 80% ethanol at room temperature. After evaporation of ethanol under vacuum, the concentrate was dissolved in water, acidified to pH 4, and extracted with CHCl3. The aqueous layer was then basified with NH4OH to pH 8 and extracted with CHCl3. The CHCl3 extracts were dried with Na2SO4 and concentrated in vacuo to obtain the crude base (125 g). This was chromatographed on a Si gel column eluted with petroleum ether (40-60°)-acetone mixtures of increasing polarities, which afforded 7R-hydroxysophoramine (1) (150 mg), 12βhydoxysophocarpine15 (2) (50 mg), sophoramine16,17 (3) (90 mg), 14β-hydroxymatrine18 (15 mg), adenocarpine19 (7 mg), matrine20 (535 mg), sophoridine22 (200 mg), sophocarpine23 (100 mg), and baptifoline26 (trace). 7r-Hydroxysophoramine (1): obtained as colorless crystals from acetone-methanol mixture, mp 204 °C; [R]25 D -87 (c 0.04, MeOH); IR (CHCl3) νmax 3236 (OH), 2928, 2855, 2793, 2735 (trans-quinolizidine), 1660 (lactam CdO), 1540 (CdC) cm-1; UV (MeOH) λmax (log ǫ) 309 (3.84), 233 (3.72), 203 (4.04) nm; 1H NMR (500 MHz, CDCl3) δ 7.13 (1H, dd, J13,14 ) 8.9 Hz, J13,12 ) 7.2 Hz, H-13), 6.40 (1H, dd, J12,13 ) 7.2 Hz, J12,14 ) 1.2 Hz, H-12), 6.19 (1H, dd, J14,13 ) 8.9 Hz, J14,12 ) 1.2 Hz, H-14), 3.99 (1H, dd, J17β17R ) 14.2 Hz, J17β,5 ) 7.0 Hz, H17β), 3.61 (1H, dd, J17R17β ) 14.2 Hz, J17R,5 ) 13.0 Hz, H-17R), 2.74 (1H, br s, H-5), 2.72 (1H, br s, H-10β), 2.47 (1H, br d, J ) 13.6 Hz, H-8β), 2.62 (1H, br d, J ) 10.4 Hz, H-2R), 1.99 (1H, br s, H-6), 1.94 (2H, t, J ) 11.1 Hz, H-2β and H-10R); 13C NMR (125 MHz, CDCl3) δ 163.7 (C-15), 148.5 (C-l1), 138.8 (C-13), 118.1 (C-14), 104.1 (C-12), 69.3 (C-7), 66.5 (C-6), 56.4 (C-2), 56.1 (C-10), 43.7 (C-17), 36.8 (C-8), 26.6 (C-4), 25.6 (C-5), 22.1 (C-9), 20.1 (C-3); EIMS m/z 260 [M]+ (100), 259 [M - H]+ (34), 243 [M - OH]+ (65), 152 (40), 134 (58), 124 (81), 96 (96); HREIMS m/z 260.1511 (C15H20N2O2 requires 260.1525). Crystal Data for 1. C15H20N2O2, MW ) 260.1525, orthorhombic, P212121, a ) 7.836(2), b ) 12.021(2), and c ) 14.342(8) Å, V ) 1351.0(9) Å3, Z ) 4, Dx ) 1.280 mg/m3, Cu KR (λ ) 1.54178 Å), F(000) ) 560, T ) 293 K, R ) 0.0361, Rw ) 0.0982, for 2362 unique I > 2σ(I) (total ) 3184), approximate crystal dimension of 0.25 × 0.25 × 0.30 mm3. Crystal Data for 2. C15H22N2O2, MW ) 262.1681, orthorhombic, a ) 5.8140(10), b ) 14.892(3), and c ) 15.189(3) Å, V ) 1315.1(4) Å3, Z ) 4, Dx ) 1.325 mg/m3, Cu KR (λ ) 1.54178 Å), F(000) ) 568, T ) 293 K, R ) 0.0359, Rw ) 0.1001, for 2047 unique I > 2σ(I) (total ) 3047), approximate crystal dimension of 0.31 × 0.25 × 0.30 mm3. Crystal Data for 3. C15H20N2O, MW ) 244.1575, orthorhombic, a ) 8.0410(10), b ) 9.419(2), and c ) 16.891(2) Å, V ) 1279.29(3) Å3, Z ) 4, Dx ) 1.269 mg/m3, Cu KR (λ ) 1.54178 Å), F(000) ) 528, T ) 293 °K, R ) 0.0454, Rw ) 0.1500, for 1443 unique I > 2σ(I) (total ) 1591), approximate crystal dimension of 0.25 × 0.25 × 0.25 mm3. 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