Two Dibenzylbutyrolactol Derivatives and Other Chemical Constituents from Aristolochia peltato-deltoidea

Abstracts

The hexane extract from the aerial parts of Aristolochia peltato-deltoidea Hoehne (Aristolochiaceae) afforded two new epimeric lignans of the type dibenzylbutyrolactol, rel-(8R, 8’S, 9S)-3,4-dimethoxy-3’,4’-methylenedioxy-9beta-ethoxy- and rel-(8R, 8’S, 9R)-3,4-dimethoxy-3’,4’-methylenedioxy-9alpha-ethoxy-lignans-8.8’,9.O.9’, besides a benzofuran neolignan, known as eupomatenoid-7, alpha-tocopherylquinone, beta-sitosterol and stigmasterol. From the chloroform extract were isolated two diastereomeric dibenzylbutyrolactone lignans: rel-(8R, 8’R)- and rel-(8R, 8’S)-3,4-dimethoxy-3’,4’-methylenedioxy-9-oxo-lignans-8.8’,9.O.9’. Chemical composition analysis by GC/MS of the non polar fractions from the hexane extract was also carried out and ten components were identified. The structures of the isolated compounds were elucidated utilizing spectrometric methods.

Aristolochia peltato-deltoidea; Aristolochiaceae; benzofuran neolignan; dibenzylbutyrolactol lignans; alpha-tocopherylquinone

Do extrato hexânico das partes aéreas de Aristolochia peltato-deltoidea Hoehne (Aristolochiaceae) foram isolados duas novas lignanas epiméricas do tipo dibenzilbutirolactol, rel-(8R, 8’S, 9S)-3,4-dimetoxi-3’,4’-metilenodioxi-9beta-etoxi- e rel-(8R, 8’S, 9R)-3,4-dimetoxi-3’,4’-metilenodioxi-9alfa-etoxi-lignanas-8.8’,9.O.9’, além da neolignana benzofurânica eupomatenóide-7, alfa-tocoferilquinona, beta-sitosterol e estigmasterol. Do extrato clorofórmico foram isoladas duas lignanas dibenzilbutirolactonas diasteroisoméricas: rel-(8R, 8’R)- e rel-(8R, 8’S)-3,4-dimetoxi-3’,4’-metilenodioxi-9-oxo-lignanas-8.8’,9.O.9’. A composição química das frações apolares do extrato hexânico também foi analisada por CG/EM. Dentre os componentes detectados, dez foram identificados. As estruturas dos compostos isolados foram elucidadas utilizando-se métodos espectrométricos.

Article

Two Dibenzylbutyrolactol Derivatives and Other Chemical Constituents from Aristolochia peltato-deltoidea

Ana Paula Freitas da Silva^a, Sebastião Ferreira Palmeira Júnior^a, Lucia Maria Conserva^a,* and Giselle Maria S. Pinheiro Guilhon^b

^a

Departamento de Química,Universidade Federal de Alagoas, 57072-970 Maceió - AL, Brazil;

^b Departamento de Química, Universidade Federal do Pará, 66060-060 Belém - PA, Brazil

Do extrato hexânico das partes aéreas de Aristolochia peltato-deltoidea Hoehne (Aristolochiaceae) foram isolados duas novas lignanas epiméricas do tipo dibenzilbutirolactol, rel-(8R, 8’S, 9S)-3,4-dimetoxi-3’,4’-metilenodioxi-9b-etoxi- e rel-(8R, 8’S, 9R)-3,4-dimetoxi-3’,4’-metilenodioxi-9a-etoxi-lignanas-8.8’,9.O.9’, além da neolignana benzofurânica eupomatenóide-7, a-tocoferilquinona, b-sitosterol e estigmasterol. Do extrato clorofórmico foram isoladas duas lignanas dibenzilbutirolactonas diasteroisoméricas: rel-(8R, 8’R)- e rel-(8R, 8’S)-3,4-dimetoxi-3’,4’-metilenodioxi-9-oxo-lignanas-8.8’,9.O.9’. A composição química das frações apolares do extrato hexânico também foi analisada por CG/EM. Dentre os componentes detectados, dez foram identificados. As estruturas dos compostos isolados foram elucidadas utilizando-se métodos espectrométricos.

The hexane extract from the aerial parts of Aristolochia peltato-deltoidea Hoehne (Aristolochiaceae) afforded two new epimeric lignans of the type dibenzylbutyrolactol, rel-(8R, 8’S, 9S)-3,4-dimethoxy-3’,4’-methylenedioxy-9b-ethoxy- and rel-(8R, 8’S, 9R)-3,4-dimethoxy-3’,4’-methylenedioxy-9a-ethoxy-lignans-8.8’,9.O.9’, besides a benzofuran neolignan, known as eupomatenoid-7, a-tocopherylquinone, b-sitosterol and stigmasterol. From the chloroform extract were isolated two diastereomeric dibenzylbutyrolactone lignans: rel-(8R, 8’R)- and rel-(8R, 8’S)-3,4-dimethoxy-3’,4’-methylenedioxy-9-oxo-lignans-8.8’,9.O.9’. Chemical composition analysis by GC/MS of the non polar fractions from the hexane extract was also carried out and ten components were identified. The structures of the isolated compounds were elucidated utilizing spectrometric methods.

Keywords: Aristolochia peltato-deltoidea, Aristolochiaceae, benzofuran neolignan, dibenzylbutyrolactol lignans, a-tocopherylquinone

Introduction

The genus Aristolochia (Aristolochiaceae) is found in wide areas from the tropics to temperate zones and consists of about 300 species¹. In Brazil, there are about 90 species². Some species from this genus have been known to possess medicinal properties^3-4. The species Aristolochia peltato-deltoidea Hoehne, known as "jarrinha", originates in South America⁵ and no chemical or biological studies on this plant have been reported.Hexane and chloroform extracts of the dried aerial parts of a specimen of this plant after chromatographic fractionation afforded two epimeric dibenzylbutyrolactol lignans (1 and 2), two diastereomeric dibenzylbutyrolactone lignans (3 and 4), a benzofuran neolignan (5), previously isolated from A. taliscana⁶, along with a-tocopherylquinone (6), not reported from any Aristolochia species so far, b-sitosterol and stigmasterol. Analysis by GC/MS of the non polar fractions from the hexane extract resulted in the identification of phytol, farnesol, sphatulenol, hedycaryol, a-eudesmol, d-selinene, 9-aristolen-1a-ol, caryophyllene oxide, and methyl and ethyl esters of hexadecanoic and nonanoic acids, respectively.

Results and Discussion

Compounds 1 (major component) and 2 were isolated as a mixture whose separation was not achieved by silica gel chromatography. Low resolution mass spectra, [M] at m/z 400, and comparative analysis of the ¹³C-NMR proton noise-decoupled and DEPT spectra suggested for both compounds molecular formula of C₂₃H₂₈O₆, revealing that the two compounds were isomeric. The IR spectrum revealed absorptions indicating the presence of an aromatic ring, ether linkage and methylenedioxy groups and the absence of carbonyl or hydroxyl functions.

The NMR spectra of 1 and 2 (Table 1) showed signals for methoxyl [1: d_H 3.75 and 3.78 (s each); d_C 55.83and 55.67 (CH₃ each); 2: d_H 3.76; 3.79 (s each); d_C 55.83and 55.67 (CH₃ each)] and methylenedioxy groups [1: d_H 5.85 (s); d_C 100.82 (CH₂); 2: d_H 5.84 (s) d_C 100.71 (CH₂)] and also provided evidence of the existence of two dibenzylbutyrolactol lignans by the presence of multiplet signals for benzylic hydrogens and methine groups (d_H 1.96-2.62), oxymethylene of the tetrahydrofuran system (d_H 3.24-3.90) and aromatic hydrogens (d_H 6.39-6.69). Moreover, the NMR spectra showed characteristic signals for acetalic hydrogens [1: d_H 4.74 (d, J = 1.6 Hz), d_C 109.17 (CH); 2: d_H 4.70 (d, J = 4 Hz); d_C 110.97 (CH)] and for ethoxy groups by the presence of signals for methyl hydrogens [d_H 1.13 (t, J = 6.6 Hz); d_C 15.26 (CH₃) and oxymethylene hydrogens probably submerged in the signals for methoxyl groups and methylene in the tetrahydrofuran system [1: d_C 62.83 (CH₂); 2: d_C 62.69 (CH₂)] as well as the appearance of peaks at m/z 354 in their MS spectra corresponding to the loss of ethanol from molecular ions. Analysis using Dreiding models and observed couplings between H-8 and H-9 [1 (J = 1.6 Hz); 2 (J = 4 Hz)] suggested the relative configurations depicted in formulas 1 and 2 for ethoxy groups at C-9 since their couplings were consistent with the cis- (a dihedral angle of nearly 90°) and trans-configurations (a dihedral angle of nearly 120°), respectively.

The presence of two lignans was also discernable from the ¹³C-NMR spectra (Table 1) which showed the doubling of the signals. Since these spectra furnished different intensities of the signals for both compounds [ratio 2:1 (1):(2)], assignments of the chemical shifts for each lignan were inferred. Noteworthy is the fact that the corresponding carbon chemical shifts for lignans 1 and 2 are very similar, the only significant difference being the chemical shifts of C-8’[1 (d_C 45.81); 2 (d_C 43.29, g-effect by the oxygen atom of the ethoxy group on C-8’)], reflecting the different configuration at the C-9 chiral centre. Considering that 1 and 2 have a cis- and trans-relationship between H-8 and H-9, and trans- and cis-relationship between H-8’ and the ethoxy groups at C-9, respectively, it is consistent to deduce that the relative configurations between H-8 and H-8’ for both lignans are cis. By analogy of the chemical shifts of H-9’ of other 8,8’-trans-dibenzylbutyrolactol lignans containing ethoxy group at C-9 (d_H 3.22-4.20)^7-8, 1 as well as 2, must be cis-oriented since the chemical shifts of H-9’ (d_H 3.24-3.90) revealed an upfield shift (anisotropic effect by the p-system aromatic ring). This fact, suggests that 1 and 2 are epimers.

Of additional interest were the mass spectra which exhibited strong tropilium ions at m/z 135 [1 (100); 2 (71)] and m/z 151 [1 (85); 2 (100)] assignable to methylenedioxy- and dimethoxy-benzyl units, respectively. Besides from the base peaks, the MS spectra also showed peaks with different intensities at m/z 219 [1 (9); 2 (3)], m/z 203 [1 (4); 2 (20)] and m/z 152 [1 (32); 2 (43)] corresponding to the fragments 1a, 1b, 2a and 3a, respectively. Thus, the structures of two epimers were elucidated as rel-(8R, 8’S, 9S)-3,4-dimethoxy-3’,4’-methylenedioxy-9b-ethoxy- (1) and rel-(8R, 8’S, 9R)-3,4-dimethoxy-3’,4’-methylenedioxy-9a-ethoxy-lignans-8.8’,9.O.9’ (2).

The possibility that the lignans 1 and 2 are artifacts is discarded due to the fact that their presence have been confirmed by comparison with the original hexane extract on co-TLC. Lignans containing b- and a-ethoxy groups at C-9 have been isolated previously from some Piper^7-10 and Dacrydium^11-12 species.

The structures of two diastereomeric lignans (3 and 4)^13-17, neolignan eupomatenoid-7 (5)⁶ and a-tocopherylquinone (6)^18-21 were established on the basis of their spectral data and comparison with those of the analogous compounds recorded in previous reports.

Experimental

General experimental procedures

Mps are uncorrected. IR spectrum was obtained as film using a FT-IR/1600 Perkin Elmer spectrophotometer. NMR spectra were measured using a Bruker AC-200 spectrometer at 200 and 50.3 MHz for ¹H- and ¹³C-NMR, respectively. Proton and carbon shifts are reported in d units (ppm) relative to TMS as the internal standard. Mass spectra were recorded in a Hewlett Packard instrument using electron impact (EI) at 70 eV. Qualitative GC/MS analysis was carried out on GC-5890 (Hewlett Packard) coupled to a Mass Selective Detector (Hewlett Packard MSD-5970) controled by a computer ChemStation 50070 C, utilizing a glass capillary column coated with dimethylsiloxane immobilized (12 m x 0.32 mm x 0.25 mm). The column temperature was programmed from 100 to 150 °C at a rate of 5°/min. and Helium was the carrier gas (1mL/min.).

Plant material

Aerial parts of A. peltato-deltoidea Hoehne were collected in Ilha de Maçaranduba, Pará State, Brazil, and identified by a specialist from the Museu Paraense Emílio Goeldi (Belém/PA), where a voucher specimen (MG-0147607) was deposited.

Extraction and isolation of the constituents

850 g of dried aerial parts were successively extracted in a Soxhlet apparatus with n-hexane and 90% ethanol. After removal of the solvents under vacuum, the residues were suspended in 90% and 60% MeOH/H₂O solutions and extracted with n-C₆H₁₄ and n-C₆H₁₄, CHCl₃ and EtOAc, respectively.

The hexane residues were combined (35.5 g) and chromatographed on a silica gel column with n-hexane containing gradually increased amounts of ethyl acetate. Eleven fractions of 150 mL each were collected. Fractions 3-6 (7.8 g) were submitted to qualitative analysis by GC/MS in the conditions previously described. This procedure, after comparison of their mass spectra with those in the data system library and/or retention time and/or co-injection with an authentic sample, resulted in the identification of phytol, farnesol, sphatulenol, hedycaryol, a-eudesmol, d-selinene, 9-aristolen-1a-ol, caryophyllene oxide, and methyl and ethyl esters of hexadecanoic and nonanoic acids, respectively. Fraction 8 (2.3 g) was rechromatographed as described above and furnished a mixture, mp 138-138.8 °C, containing b-sitosterol and stigmasterol (168 mg) after crystalization from MeOH. Fraction 9 (2.6 g) was rechromatographed as previously described and the fractions were combined. Some of them were further purified by gel filtration on Sephadex LH-20 with MeOH to yield eupomatenoid-7 (5, 7.9 mg) and a-tocopherylquinone (6, 13 mg) after preparative TLC [silica gel PF-254, n-C₆H₁₄-EtOAc (9:1)] in three consecutive elutions. Finally, fraction 10 (3.1 g) was dissolved in MeOH and submitted to centrifugation (1 h/7000 rpm). The portion soluble in MeOH (1.3 g) was permeated on Sephadex LH-20 with MeOH. After chromatographic fractionation on silica gel 60 H [n-C₆H₁₄-EtOAc (9:1)] and preparative TLC [silica gel PF-254, n-C₆H₁₄-EtOAc (9:1)] in four successive developments afforded a mixture containing lignans 1 and 2 (19.7 mg).

The CHCl₃ residue (8.2 g) was suspended in aqueous 5 % NaHCO₃ and extracted with CHCl₃. The CHCl₃ layer was taken to dryness (1.1 g) and fractioned on a silica gel column using n-C₆H₁₄ with increasing proportions of CHCl₃. This procedure resulted in the isolation of a mixture of lignans 3 and 4 (38 mg).

Rel-(8R, 8’S, 9S)-3,4-dimethoxy-3’,4’-methylenedioxy-9b-ethoxy- (1) and rel-(8R, 8’S, 9R)- 3,4-dimethoxy-3’,4’-methylenedioxy-9a-ethoxy-lignans-8.8’,9.O.9’ (2)

Yellow oil, IR n _max (cm^-1, Film): 2925, 1609, 1511, 1460, 1445, 1367, 1267, 1147, 1058, 932. ¹H-NMR (200 MHz, CDCl₃, d): Table 1. ¹³C-NMR (50.3 MHz, CDCl₃, d): Table 1. EIMS m/z (rel. int.): 400 (1, 3; 2, 9), 354 (1 and 2, 7), 219 (1, 9; 2, 3), 203 (1, 4; 2, 20), 178 (1, 12; 2, 16), 177 (1, 69; 2, 10), 152 (1, 32; 2, 43), 151 (1, 85; 2,100), 135 (1, 100; 2, 71), 113 (1, 44; 2, 5), 91 (1, 9; 2, 12).

Acknowledgements

This work represents part of the MSc dissertation presented by A.P.F.S. at the Universidade Federal de Alagoas on February 1998. We wish to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) - Programa de Apoio ao Desenvolvimento Científico Tecnológico (PADCT II) for the financial support. The authors are also grateful to the Instituto de Química, Universidade de São Paulo, Museu Paraense Emílio Goeldi for acquisition of NMR and MS spectra and Dr Ruth Rufino do Nascimento for analysis by GC/MS.

Received: May 19, 1998

FAPESP helped in meeting the publication costs of this article

• 1.Mizuno, M.; Oka, M.; Iinuma, M.; Tanaka, T. J Nat Prod 1990, 53, 179.
• 2.Leităo, G.G.; Kaplan, M.A.C. Rev Bras Farm 1992, 73, 65.
• 3.Wu, T.; Ou, L.; Teng, C. Phytochemistry 1994, 36, 1063.
• 4.Priestap, H.A. Phytochemistry 1987, 26, 519.
• 5.Hoehne, F.B. Flora Brasílica 1942, 15, 102.
• 6.Enriquez, R.G.; Chavez, M.A.; Reynolds, W.F. J Nat Prod 1984, 47, 896.
• 7.Badheka, L.P.; Prabhu, B.R.; Mulchandani, N.B. Phytochemistry 1987, 26, 2033.
• 8.Koul, S.K.; Taneja, S.C.; Dhar, K.L.; Atal, C.K. Phytochemistry 1984, 23, 2099.
• 9.Koul, S.K.; Taneja, S.C.; Dhar, K.L.; Atal, C.K. Phytochemistry 1993, 32, 478.
• 10.Parmar, V.S.; Jain, S.C.; Birsht, K.S.; Jain, R.; Taneja, P.; Jha, A.; Tyagi, O.D.; Prasad, A.K.; Wengel, J.; Olsen, C.E.; Boll, P.M. Phytochemistry 1997, 46, 597.
• 11.Cambie, R.C.; Parnell, J.C. Tetrahedron Letters 1979, 12, 1085.
• 12.Cambie, R.C.; Pang, G.T.M.; Parnell, J.C.; Rodrigo, R.; Weston, R.J. Aust. J. Chem. 1979, 32, 2741.
• 13.Sheriha, G.M.; Abouamer, K.; Elshtaiwi, B.Z.; Ashour, A.S.; Abed, F.A.; Alhallaq, H.H. Phytochemistry 1987, 26, 3339.
• 14.Estévez-Braun, A.; Estévez-Reyes, R.; González, A. G. Phytochemistry 1996, 43, 885.
• 15.Lopes, L.M.X.; Yoshida, M.; Gottlieb, O.R. Phytochemistry 1983, 22, 1516.
• 16.McDoniel, P.B.; Cole, J.R. J Pharm Sci 1972, 61, 1992.
• 17.Rücker, G.; Langmann, B.; Siqueira, N.S. Planta Med 1981, 41, 143.
• 18.Schudel, P.; Mayer, H.; Metzger, J.; Riiegg, R.; Isler, O. Helv. Chim. Acta 1963, 46, 333.
• 19.Teresa, J.P.; Urones, J.G.; Marcos, I.S.; Ferreras, J.F.; Bertelloni, A.M.L.; Barcala, P.B. Phytochemistry 1987, 26, 1481.
• 20.Urones, J.G.; Marcos, I.S.; Cubillo, L., Garrido, N.M.; Basabe, P. Phytochemistry 1990, 29, 2228.
• 21.Mayer, H.; Schudel, P.; Riiegg, R.; Isler, O. Helv. Chim. Acta 1963, 46, 650.

Publication Dates

• Publication in this collection
  23 Oct 2002
• Date of issue
  1999

History

• Received
  19 May 1998