A New Isoflavone Isolated from Harpalyce brasiliana*
Graça Lúcia da Silvaa, Maria Iracema Lacerda Machadoa,Francisco José de Abreu Matosa, and Raimundo Braz-Filhob**
aDepartamento de Química Orgânica e Inorgânica, Laboratório de Produtos Naturais, Universidade Federal do Ceará, C.P. 12200, 60.021-970 Fortaleza - Ceará, Brazil
bSetor de Produtos Naturais, LCQUI-CCT, Universidade Estadual do Norte Fluminense, 28015-620 Campos - RJ, Brazil
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Uma nova isoflavona denominada harpalicina e quercetina foram isoladas das folhas e 3-hidroxi-4-isopentenil-8,9-metilenodioxipterocarpano e ácido betulínico das raizes de Harpalyce brasiliana. As estruturas foram elucidadas usando métodos espectrométricos, inclusive RMN bidimensional (2D) da nova isoflavona.
A new isoflavone named harpalycine and quercetin were isolated from the leaves and 3-hydroxy-4-isopentenyl-8,9-methyle-nedioxypterocarpan and betulinic acid from the roots of Harpalyce brasiliana. The structures were elucidated using spectroscopic methods, including 2D NMR techniques of the new isoflavone.
Keyword: Harpalyce brasiliana, Leguminosae, flavonoids, triterpene
Introduction
Harpalyce brasiliana Benth. (Leguminosae-Papilionoideae) is a Northeastern Brazilian shrub, called "raiz-de-cobra" (snake root) and used by people for treating snake bites1. Two prenylated pterocarpans, cabenegrins A-I (1) and A-II (2)2, potent antidotes against snake venom, were isolated and identified from a locally well known anti-snake bite medicine named "Específico Pessoa", manufactured and sold in the north and northeast of Brazil and available to plantation workers as an oral antidote. The plant, commonly called "cabeça de negro", which furnishes the extract used in the preparation of this remedy has not been identified so far, being kept secret by the manufacturers. There are about ten plants with the name "cabeça de negro" in South America. Two plants reputed as anti-snake bite medicines occur in the Ibiapaba region in Northeast Brazil: Bredemeyera floribunda Willd (Polygalaceae), called "pacari", and Harpalyce brasiliana (Leguminosae-Papilionoideae). The first contains as its active principle one saponin, bredemeyeroside3.
In this paper we report the isolation and characterization of the new isoflavone harpalycin (3) and the known flavonol quercetin (4), prenylated pterocarpan (5) and triterpene betulinic acid (6) from leaves and roots of a specimen of Harpalyce brasiliana. There are three previous chemical reports about this plant4-6.
]]>Results and Discussion
Chromatographic separation of the ethanol extract from the leaves of Harpalyce brasiliana led to the isolation of the new isoflavone harpalycin (3), as well as the known flavonol quercetin (4). From the roots, 3-hydroxy-4-isopentenyl-8,9-methylenedioxypterocarpan (5) and pentacyclic triterpenoid betulinic acid (6) were isolated.
The known natural products quercetin (4, 5,7,3’,4’-tetrahydroxyflavonol) and betulinic acid [6, 3b-hydroxy-20(29)-lupen-28-oic acid] were identified mainly by their 1H and 13C-NMR spectra and comparison with literature data7,8. 3-Hydroxy-4-isopentenyl-8,9-methylenedioxypterocarpan (5) has been recently reported5,6.
Comparative analysis of the hydrogen broad band decoupled (HBBD) and distortionless enhancement by polarization transfer (DEPT) 13C-NMR spectra9 of 3, in combination with the 1H-NMR (one- and two-dimensional 1Hx1H-COSY), IR [n 3420 (OH), 1660 (conjugated carbonyl), 1620 (conjugated double bond), 1590 and 1500 cm-1 (aromatic ring)] and mass {m/z 382 ([M]+, 70 %), 364 ([M - H2O]+, 12 %), 349 ([M - H2O - Me.]+, 39 %), 311 (3c, [M - C4H7O]+, 100 %), 310 (3d, [M - C4H8O]+, 45 %) and 146 (3e, 18 %)} spectra allowed the deduction of a molecular formula C21H18O7, containing eleven quaternary carbons {ten sp2: one carbonyl (dC 180.08, C-4), five bound to oxygen atoms [dC 159.27 (C-7), 159.09 (C-5), 155.19 (C-9), 147.70 (C-3’ and C-4’)], four non-oxygenated [dC 121.71 (C-1’) 124.47 (C-3), 104.22 (C-6 and C-10)] and one sp3 oxygenated [dC 79.03 (C-2’’], six methine [five sp2: dC 154.70 (CH-2), 122.57 (CH-6’), 109.42 (CH-2’), 108.19 (CH-5’) and 94.22 (CH-8); one sp3 bound to oxygen: dC 66.80 (CH-3’’)], two methylene [dC 101.16 (3’,4’-OCH2O) and 25.02 (CH2-4’’)] and two methyl groups [dC 25.25 (CH3-6’’) and 21.07 (CH3-5’’)]: (C)10 (O)4(C=O) (CH)6(OCH2O)(CH2)(CH3)2 = C21H16O7. The two remaining hydrogens (C21H18O7, m/z 382 [M]+, 70 %) were attributed to two hydroxy groups: (C)10(O)2(C=O)(CH)6 (OCH2O)(CH2)(CH3)(OH)2=C21H18O7. The presence of the two hydroxy groups was confirmed by the singlet signals at dH 2.04 (AcO-3’’) and 2.43 (AcO-5) observed in the 1H-NMR spectrum and dC 170.36 and 20.97 (AcO-3’’) and 169.12 and 21.08 (AcO-5), in the 13C-NMR spectrum of the diacetyl derivative 3b (Table 1). One chelatogenic hydroxyl function was revealed by signals at dH 13.20 and 13.13 (HO-5) in the 1H-NMR spectra of 3 and monoacetyl derivative 3a, respectively. These data and the signals at dH 8.12 (H-2) and dC 154.70 (CH-2) were used to classify this natural product as an isoflavone containing one methylenedioxy and one monohydroxylated isoprenoid moiety (Me2C-CHOH-CH2-) involved in a 3,4-dihydro-3-hydroxy-2,2-dimethylpyran ring, along with the chelatogenic hydroxyl group at C-5 (dH 13.20).
]]> The location of hydroxy group at carbon atom CH-3’’ of the 3,4-dihydro-3-hydroxy-2,2-dimethylpyran moiety was deduced by signals at dH 3.69 (dd, J = 6.8 and 5.6 Hz) and 5.12 (dd, J = 5.1 and 4.7 Hz), observed in the 1H-NMR spectra of 3 and 3a, respectively (Table 1), whose attribution was confirmed by a long range heteronuclear correlation (spin-spin interaction) of the signal at dC 69.76 (CH-3’’) and signals at dH 1.37 (3H-5’’, 3JCH) and dH 1.32 (3H-6’’, 3JCH), observed in the 2D 13Cx1H-COSY nJCH (n = 2 and 3, COLOC)10 spectrum of the monoacetyl derivative 3a (Table 2). This spectrum also showed correlation of the signals corresponding to the hydrogen of the hydroxy group at C-5 (dH 13.13) and quaternary carbon atoms C-5 (dC 160.11, 2JCH), C-6 (dC 102.72, 3JCH) and C-10 (dC 105.39, 3JCH), as summarized in Table 2. Additional long range heteronuclear correlations observed in the 2D 13Cx1H-COSY-nJCH (n = 2 and 3, COLOC) spectrum of 3a are summarized in Table 2, along with the heteronuclear direct one bond coupling revealed by the 2D 13Cx1H-COSY-1JCH spectrum of 3a (Table 1). Thus, the complete assignment of the chemical shifts of hydrogen and carbon atoms of 3a in the 1H and 13C-NMR spectra was accomplished by 2D 1Hx1H-COSY and 13Cx1H-COSY nJCH (n = 2 and 3, COLOC), which confirmed the proposed structure 3 (Table 1 and 2). These assignments were facilitated by application of the usual shift parameters and the observed multiplicities of signals9.
Thus, the structure of the new isoflavone, named harpalycine, isolated from Harpalyce brasiliana was established as 3*,4-dihydro-3,5-dihydroxy-7-(3,4-methylenedioxyphenyl)-2,2-dimethyl-2H,6H-benzo
[1,2-b:5,4-b’] dipyran-6-one (3, 3’’*,5-dihydroxy-2’’,2’’-dimethyl-3’,4’-methylenedioxy
-6,7:6’’,5’’-pyranoisoflavone). Relatively few dihydrohydroxypyranoisoflavones have been described as natural products11,12.
Experimental
]]> General experimental proceduresMps are uncorr. IR spectra were recorded on a Perkin Elmer 1320 or Nicolet 5ZDXFT-IR, in KBr. 1H [400 (3) and 270 (3a and 3b) MHz] and 13C [50 (3) and 67.5 (3a and 3b) MHz] NMR spectra were recorded on a Bruker AC-200 (1H: 200 MHz; 13C: 50 MHz) and WP-270 (1H: 270 MHz; 13C: 67.5 MHz) or Varian UN-400 (1H: 400 MHz; 13C: 100 MHz) spectrometers, in pyridine-d5 (3, 1H-NMR), DMSO-d6 (3, 13C-NMR) or CDCl3 (3a and 3b). EIMS (70 eV) spectra were obtained on a HP-5971 GC/MS instrument.
Plant material
Harpalyce brasiliana Benth. leaves and roots were collected in Guaraciaba do Norte, Ibiapaba mountains, Ceará State, Brazil and identified by Professor Afrânio Gomes Fernandes (Universidade Federal do Ceará, Fortaleza). A voucher specimen (nº 14841) is deposited at the Herbário Prisco Bezerra of the Departamento de Biologia of the Universidade Federal do Ceará.
Extraction and isolation of constituents from leaves
Dried and powdered leaves (6 kg) were extracted with EtOH at room temp and the solvent removed under vacuum to yield 736 g of residue. This residue was chromatographed on a silica gel column and successively eluted with hexane, CHCl3, EtOAc, CHCl3-MeOH (1:1), MeOH and EtOH. The residue (55 g) of the fraction eluted with CHCl3-MeOH (1:1) was suspended in EtOH-H2O soln and extracted with hexane; the residue (23 g) thus obtained was chromatographed on a silica gel column and eluted with hexane, CHCl3, EtOAc and MeOH; the fraction eluted with CHCl3 (2 g) was recrystallized from MeOH to afford 3 (286 mg); the fraction eluted with EtOAc (10 g) furnished quercetin (4, 50 mg) after several runs on a silica gel column.
Extraction and isolation of constituents from roots
The natural products 5 and betulinic acid (6) were isolated from roots as described in Ref. 6.
Harpalycin (3)
Mp 208 - 211° (MeOH). IR nmax (cm-1, KBr): 3420, 1620, 1660, 1590, 1500, 1190, 820. EIMS m/z (rel. int.): 382 ([M]+, 70), 364 ([M - H2O]+., 12), 349 ([M - H2O - Me.]+, 39), 311 (3c, 100), 310 (3d, 45), 146 (3e, 18), 145 ([3e - H.], 13). H1 (400 MHz, C5D5N) and 13C (50 MHz, DMSO-d6) NMR: Table 1.
]]> Acetylation of harpalycin (3)Treatment of harpalycin (3, 100 mg) with Ac2O (4 mL) in the presence of pyridine (1 mL), and usual work-up, produced a mixture of 3a (monoacetyl derivative) and 3b (diacetyl derivative), which were purified on a silica gel column using hexane and hexane containing increasing amount of CHCl3 as eluents.
3’’-O-Acetylharpalycin (3a)
Mp 212-213°. IR nmax (cm-1, KBr): 1730, 1650, 1620, 1590, 1500, 1190 e 800. EIMS m/z (rel. int.): 424([M]+, 6), 364 ([M - AcOH]+, 8), 349 ([M - AcOH - Me.]+, 54), 146 (3e, 44); 145 ([3e - H.]+, 46). 1H (270 MHz, CDCl3) and 13C (67.5 MHz, CDCl3) NMR: Table 1; 13C-1H COSY 1JCH and 13C-1H COSY nJCH (n = 2 and 3, COLOC) NMR (1H: 200 MHz; 13C: 50 MHz): Table 2.
3’’,5-Di-O-Acetylharpalycin (3b)
Mp 203-204°. IR nmax (cm-1, KBr): 1730, 1620, 1590, 1500, 1190, 800. EIMS m/z (rel. int.): 466 ([M]+, 6), 406 ([M - AcOH]+, 2), 364 ([M - AcOH - CH2=C=O]+, 8), 349 ([M - AcOH - CH2=C=O - Me.]+, 100), 146 (3e, 44). 1H (270 MHz, CDCl3) and 13C (67.5 MHz, CDCl3) NMR: Table 1.
Acknowledgments
The authors are grateful to Professor Afrânio G. Fernandes (Botanist, Departamento de Biologia, Universidade Federal do Ceará) for plant identification; to CAPES, PADCT/FINEP and CNPq for financial support and CNPq for a research fellowship (R.B-F). We thank Dr. Victor Rumjanek for reading the manuscript.
]]> References
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Received: May 31, 1999
*This work is part of the M.Sc. Thesis of Graça Lúcia da Silva, presented at the Departamento de Química Orgânica, Universidade Federal do Ceará, Fortaleza, Ceará, Brazil, 1995.
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