6-acetonyl-N-methyl-dihydrodecarine, a new alkaloid from Zanthoxylum riedelianum

SHORT REPORT

6-acetonyl-N-methyl-dihydrodecarine, a new alkaloid from Zanthoxylum riedelianum

Carromberth C. Fernandes^I; Paulo C. Vieira^II; Virgínia C. da Silva^III; Evandro L. Dall'Oglio^III; Luiz E. da Silva^III; Paulo T. de Sousa Jr.^III,*

^IDepartamento de Ciências da Natureza, Universidade Federal do Acre, 66915-900 Rio Branco-AC, Brazil

^IIDepartamento de Química, Centro de Ciências Exatas e de Tecnologia, Universidade Federal de São Carlos, 13565-905 São Carlos-SP, Brazil

^IIIDepartamento de Química, Instituto de Ciências Exatas e da Terra, Universidade Federal de Mato Grosso, 78060-900 Cuiabá- MT, Brazil

ABSTRACT

A new benzophenanthridine alkaloid, 6-acetonyl-N-methyl-dihydrodecarine was isolated from Zanthoxylum riedelianum roots together with lupeol, 6-acetonyldihydrochelerythrine and 6-acetonyldihydroavicine. The structures were established from the IR, MS and NMR spectral data, including 2D-NMR experiments.

Keywords: Zanthoxylum riedelianum, Rutaceae, benzophenanthridine alkaloids

RESUMO

Um novo alcalóide benzofenantridínico, 6-acetonil-N-metil-diidrodecarina foi isolado das raízes de Zanthoxylum riedelianum juntamente com lupeol, 6-acetonildiidroqueleritrina e 6-acetonildiidroavicina. As estruturas dessas substâncias foram estabelecidas com base na análise dos dados espectrométricos de IV, EM e RMN incluindo experimentos 2D.

Introduction

The Zanthoxylum genus (Rutaceae) is composed by more than 200 species and largely distributed around the world.¹ Chemically, this genus is characterized by alkaloids,^2-7 cumarins,^5,6,8 lignans,^4,9,10 amides^11,12 and terpenes.^5,6,13,14 Ongoing studies have shown that Zanthoxylum exhibit a range of biological activities such as antichagas,² tripanocidal,⁹ antiplasmodial,⁷ anti-HIV¹³ and antiinflammatory,^8,10 as well as anti-helmintic.¹²Z. riedelianum is used in folk medicine as a decoction against different types of inflammations, rheumatism and skin stains.¹⁵ Previous works reported the identification of terpenes from the essential oil¹⁴ and lignans from the leaves and the stem bark.¹⁰ In this work we report the isolation and structural elucidation of a novel benzophenanthridine alkaloid, namely, 6-acetonyl-N-methyl-dihydrodecarine (1), together with two known alkaloids 6-acetonyldihydrochelerythrine (2) and 6-acetonyldihydroavicine (3) from the roots of Z. riedelianum.

Experimental

General procedures

Melting points were uncorrected. IR spectra were recorded on FTIR-Bomem-MB/100 model spectrophotometer using NaCl film. NMR spectra in CDCl₃, were recorded on Bruker ARX-400 (400 MHz for ¹H and 100 MHz for ¹³C); Bruker AC-200 (200 MHz for ¹H and 50 MHZ for ¹³C) and Varian-Mercury 300 (300 MHz for ¹H and 75 MHz for ¹³C) spectrometers, using tetramethylsilane (TMS) as internal standard. Electron Ionization Mass Spectra (ESI-MS) was undertaken employing a Quatro LC-Micromass UK model spectrometer. Optical rotations were determined on a Perkin-Elmer 341 polarimeter. CC: silica gel (Merck 70-230 mesh ASTM); TLC: silica gel G 60 and silica gel 60 PF₂₅₄ (Merck) were used to analyze the fractions collected from column chromatography (CC) with visualization by UV (254 and 366 nm), Dragendorff's reagent and exposure to iodine vapor.

Plant material

Zanthoxylum riedelianum (Engl.) was collected in Rio Manso Highway, km 22, Chapada dos Guimarães, Mato Grosso State, Brazil. A voucher specimen (No. 24.080) was deposited at Universidade Federal de Mato Grosso Central Herbarium.

Extraction and isolation

Dried roots (3.0 kg) were powdered and extracted with hexane and methanol by maceration at room temperature. The macerates were concentrated under reduced pressure to yield the extracts A (21.5 g) and B (200.5 g) from hexane and methanol, respectively. The extract A was partitioned with hexane, dichloromethane, ethyl acetate and methanol. Solvents were removed under reduced pressure and the dichloromethane residue (8.2 g) was submitted to column chromatography, carried out in a gradient system from hexane, dichloromethane, ethyl acetate, acetone and methanol as mobile phase. The 174 collected fractions were reunited in 30 fractions. Fraction 10 (1.0 g) afforded the triterpene lupeol (170.0 mg, mp 162.5-164.2 °C). Fraction 25 (200.0 mg) was submitted to preparative TLC with dichloromethane-methanol (2:8), affording the alkaloid 6-acetonyldihydrochelerythrine (2, 30.0 mg, mp 171.6-173.0 °C).

The extract B was partitioned successively with hexane, dichloromethane, ethyl acetate and methanol. The dichloromethane residue (530.0 mg) was submitted to column chromatography performed in a gradient system with hexane, dichloromethane, acetone and methanol as mobile phase. The 243 collected fractions were reunited in 33 fractions after TLC comparison. Fraction 4 (190.0 mg) was submitted to preparative TLC eluting with dichloromethane-methanol (1:9), affording the alkaloids 6-acetonyl-N-methyl-dihydrodecarine (1, 60.0 mg, mp 186-188 °C) and 6-acetonyldihydroavicine (3, 57.0 mg, mp 184-185 °C).

Brown amorphous solid. -5.625 (CHCl₃; conc. 0.014 g mL^-1). IR (NaCl film) ν_max/cm^-1: 3396, 1708, 1615, 1610, 1516, 1425, 1296, 1239. ¹H NMR (CDCl₃, 400 MHz) and ¹³C NMR (CDCl₃, 100 MHz) (Table 1). ESIMS/MS: m/z (rel. int.) 391 [M+H]⁺.

Results and Discussion

The well known natural compounds lupeol,¹⁶ 6-acetonyldihydrochelerythrine (2)¹⁷ and 6-acetonyldihydroavicine (3)¹⁸ were identified mainly by ¹H and ¹³C NMR spectral analyses, comparing with previous literature data.^16-18

Compound 1 presented a positive test with Dragendorff's reagent, indicating it to be an alkaloid. The IR spectrum presented bands at 3396 (ν_OH), 1708 (ν_C=O)_, 1615, 1516 cm^-1 attributed to aromatic rings. The positive ESI-mass spectrum of 1 showed a quasi-molecular ion at m/z 391 [M+H]⁺ pointing out to a molecular formula C₂₃H₂₁NO₅. The ¹H NMR spectrum of 1, exhibited signals corresponding to six aromatic hydrogen, characteristic of a benzophenanthridine system.¹⁸ Accordingly, the aromatic region from compound (1) ¹H NMR spectrum exhibited signals of two pairs of one-hydrogen doublets (δ_Η 7.01 (H-9) and 7.54 (H-10); 7.72 (H-11) and 7.51 (H-12)) and two one-hydrogen singlets (δ_Η 7.10 (H-1) and 7.51 (H-4)) indicating the presence of four aromatic hydrogens in ortho position and two isolated hydrogens. The ¹H NMR spectrum also displayed signals of methylenedioxide group at δ_Η 6.05 (2H, AB system), hydroxyl group at δ_Η 5.30 (s, 1H), a methoxyl group at δ_Η 3.95 (s, 3H) and the N-methyl group at δ_Η 2.65 (s, 3H). In addition to the benzophenanthridine signals, the presence of an acetonyl group at C-6 was indicated by a methyl singlet at δ_Η 2.02 and the AMX system with δ_Η2.25 (J 3.5 and 15.2 Hz) and 2.66 (J 10.9 and 15.2 Hz), respectively, and δ_Η 5.0 (J 3.5 and 10.9 Hz), corresponding to the coupling constants between H-6 and the acetonyl methylene hydrogens in the ¹H NMR and ¹H, ¹H-COSY spectra. The ¹³C NMR spectrum also confirmed the acetonyl moiety with signals at 207.6 (C=O), 31.5 (COCH₃), 46.5 (-CH₂CO). Through the chemical shifts observed in the ¹³C, ¹H-gHSQC spectrum, it was possible the attribution of each carbon and its respective hydrogen (Table 1). The cross peaks observed in the HMBC spectrum showed long-range couplings from H-6 (δ_Η 5.0) and H-3' (δ_Η 2.02) with C-2' (δ_C 207.6), confirming the connection of the acetonyl moiety with C-6. Further correlations were observed between OCH₃ (δ_Η 3.95) with C-7 (δ_C 151.3), as well as H-9 (δ_Η 7.01) and H-10 (δ_Η 7.54) with C-8 (δ_C 144.9) and C-10 (δ_C 119.7), indicating that position 8 is substituted; finally, N-CH₃ (δ_Η 2.65) with C-6 (δ_C 54.8). The absence of the methoxyl group in C-7 moves away the effect of the oxygen atom in C-6, justifying its largest chemical shift (δ_C 60.2) in compound 3, when compared with the correspondent δ_C 54.8, attributed to C-6 in compound 1; thus revealing Δ_C = 54.9-60.2 = -5.3 ppm as γ effect. Therefore, the structure of 1 was established as 6-acetonyl-N-methyl-dihydrodecarine, a decarine derivative.¹⁸ Previous publications,^17,18 however, reported the isolation of the unstable parent alkaloids avicine and nitidine. Although acetone derivatives of avicine and nitidine have been reported in the literature,^19-21 as well as acetone aducts of two other benzophenantridine alkaloids,^22,23 it is controversial, however, whether those acetone derivatives are really present on the plant extract or were isolated as artifacts, due to the greater stability of the acetone aducts as compared to the parent alkaloids avicine and nitidine.

Acknowledgments

The authors are grateful to CNPq, FAPEMAT and Centro de Pesquisa do Pantanal (CPP) for scholarships and financial support, as well as to Dr. A. Gilberto Ferreira, UFSCar, for the 400 MHz NMR spectra.

Supplementary Information

Supplementary data of alkaloids structures as 1 and 2D ¹H and ¹³C NMR spectra are available free of charge at http://jbcs.sbq.org.br, as PDF file.

Received: December 5, 2007

Web Release Date: December 12, 2008

FAPESP helped in meeting the publication costs of this article.

SUPPLEMENTARY INFORMATION

• 1. Talapatra, S. K.; Dutta, S. K.; Talapatra, B.; Phytochemistry 1973, 12, 729.
• 2. Ferreira, M. E.; Nakayama, H.; Arias, A. R.; Schinini, A.; de Bilbao, N. V.; Serna, E.; Lagoutte, D.; Soriano-Agatón, F.; Poupon, E.; Hocquemiller, R.; Fournet, A.; J. Ethnopharmacol. 2007, 109, 258.
• 3. Hu, J.; Zhang, W. D.; Shen, Y. H.; Zhang, C.; Xu, L.; Liu, R. H.; Wang, B.; Xu, X. K.; Biochem. Syst. Ecol. 2007, 35, 114.
• 4. Rahman, M. M.; Islam, M. A.; Khondkar, P.; Gray, A. I.; Biochem. Syst. Ecol. 2005, 33, 91.
• 5. Arruda, M. S. P.; Fernandes, J. B.; Vieira, P. C.; da Silva, M. F. G. F.; Pirani, J. R.; Biochem. Syst. Ecol. 1992, 20, 173.
• 6. Oliveira, E. L.; Freitas, P. C.; Guedes, M. L. S.; Velozo, E. S.; Rev. Bras. Farmacogn. 2002, 12, 29.
• 7. Jullian, V.; Bourdy, G.; Georges, S.; Maurel, S.; Sauvain, M.; J. Ethnopharmacol. 2006, 106, 348.
• 8. Chen, I. S.; Lin, Y. C.; Tsai, I. L.; Teng, C. M.; Ko, F. N.; Ishikawa, T.; Ishii, H.; Phytochemistry 1995, 39, 1091.
• 9. Bastos, J. K.; Albuquerque, S.; Silva, M. L. A.; Planta Med. 1999, 65, 541.
• 10. Lima, L. M.; Perazzo, F. F.; Carvalho, J. C. T.; Bastos, J. K.; J. Pharm. Pharmacol 2007, 59, 1151.
• 11. Chen, I. S.; Chen, T. L.; Lin, W. Y.; Tsai, I. L.; Chen, Y. C.; Phytochemistry 1999, 52, 357.
• 12. Navarrete, A.; Hong, E.; Planta Med. 1996, 62, 250.
• 13. Cheng, M. J.; Lee, K. H.; Tsai, I. L.; Chen, I. S.; Bioorg. Med. Chem. 2005, 13, 5915.
• 14. Guy, I.; Charles, B.; Guinaudeau, H.; Ferreira, M. E.; Arias, A. R.; Fournet, A.; Pharm. Biol. 2001, 39, 152.
• 15. Guarim Neto, G.; Plantas Utilizadas na Medicina Popular do Estado de Mato Grosso, Associação Brasileira de Educação Agrícola Superior: Brasília, 1996.
• 16. Mahato, S. B.; Kundu, A. P.; Phytochemistry 1994, 37, 1517.
• 17. Julián, A.; Delgado, G.; Rev. Soc. Quim. Mex 2001, 45, 189.
• 18. Nissanka, A. P. K.; Karunaratne, V.; Bandara, B. M. R.; Kumar, V.; Nakanishi, T.; Nishi, M.; Inada, A.; Tillekeratne, L. M. V.; Wijesundara, D. S. A.; Gunatilaka, A. A. L.; Phytochemistry 2001, 56, 857.
• 19. Arthur, H. R., Hui, W. H.; Ng, Y. L.; J. Chem. Soc 1959, 4007.
• 20. Gopinath, K. W.; Kohli, J. M.; Kahn, M. S. Y.; Kidwai, A. R.; Indian J. Chem 1963, 1, 99.
• 21. Fotie, J.; Bohle, D. S.; Olivier, M.; Gomez, M. A.; Nzimiro, S.; J. Nat. Prod 2007, 70, 1650.
• 22. Desai, P. D.; Govidachari, T. R.; Nagarajan, K.; Visvanathan, N.; Indian J. Chem. 1967, 5, 41.
• 23. Ng, K. M.; Gray, A. I.; Waterman, P. G.; Phytochemistry 1987, 26, 3251.

Publication Dates

• Publication in this collection
  27 Feb 2009
• Date of issue
  2009

History

• Accepted
  12 Dec 2008
• Received
  05 Dec 2007