Coumarins and Alkaloids from the Stems of Metrodorea Flavida

Article

Coumarins and Alkaloids from the Stems of Metrodorea Flavida

Ana Cristina S. Baetas, Mara S.P. Arruda*, Adolfo H. Müller, and Alberto C. Arruda

Departamento de Química, CCEN, Campus Universitário,

Universidade Federal do Pará, 66075-900 Belém - PA, Brazil

Uma nova cumarina , a 5,6-metilenodioxi-7,8-dimetoxicumarina, foi isolada a partir dos galhos de Metrodorea flavida, juntamente com outras cumarinas e alcalóides conhecidos. As estruturas das substâncias isoladas foram definidas por análises de seus dados espectrais , bem como por comparação com dados da literatura.

A new coumarin, 5,6-methylenedioxy-7,8-dimethoxycoumarin has been isolated from the stems of Metrodorea flavida, as well as known coumarins and alkaloids. The structures of the new and the known compounds were established by spectral data and by comparison with the literature data.

Keywords: Metrodorea flavida, Rutaceae, coumarins, alkaloids

Introduction

In a previous paper, we reported the characterization of a new coumarin, 8-(2,3-dihydroxy-3-methylbutyloxy)-6,7-methylenedioxycoumarin, together with known furocoumarins and a furofuran lignan, which were isolated from the leaves of Metrodorea flavida¹. In continuation of our phytochemical studies on the constituents of this species, we report from the stem the isolation and structural elucidation of a new coumarin 5,6-methylenedioxy-7,8-dimethoxycoumarin (1), in addition to the known compounds: scoparone (2)²; 6,7-methylenedioxy-8-methoxycoumarin (3)³; xanthotoxin (4)⁴; isopimpinellin (5)⁴; imperatorin (6)⁴; braylin (7)⁵; g-fagarine (8)⁶; kokusaginine (9)⁷ ; maculin (10)⁸; syringic aldehyde (11)⁹; rutaecarpine (12)¹⁰; sitosterol and lupeol.

All the compounds were isolated by chromatographic techniques. The structural elucidation of these compounds were based on spectrometric data, especially IR, ¹H NMR and ¹³C NMR, involving comparison with the literature data.

Experimental

Equipment

Mps uncorr. IR were recorded in KBr discs. ¹H and ¹³C-NMR spectra were recorded at 300 and 75 MHz, respectively, in CDCl₃ on a Varian GEMINI 300 instrument and at 400 and 100 MHz, in DMSO, on a Brucker ARX 400 instrument. EIMS were obtained by direct probe insertion at 70 eV.

Plant material

Metrodorea flavida was collected in Paragominas, State of Pará, Brazil, in December 1991. A voucher specimen is deposited at the Herbarium of the CPATU-EMBRAPA, Belém, Brazil.

Extraction and isolation

After drying, stems (231 g) were ground and percolated with hexane and CH₂Cl₂, successively. The concd. hexane extract (3.5 g) was submitted to CC using silica gel 60 Merck (particula size 0.063-0.200 mm) packed in hexane. Elution was performed with a gradient of hexane, Me₂CO and MeOH, affording 22 frs. The frs 3 and 7 after prep. TLC (silica gel and hexane- CH₂Cl₂- MeOH/10:10:0.1) yielded lupeol and sitosterol, respectively.

Fr. 12 was rechromatographed on silica gel using gradients of hexane, CH₂Cl₂ and MeOH. Those frs. containing homogeneous components, as judged by TLC, were combined and the solvent removed. Frs. 12/9-12 and 12/14-17 subjected to prep. TLC on silica gel (hexane-Me₂CO/ 75:25) afforded 6 (31.4 mg) and 12 (7.5 mg) , respectively. Fr.17 was subjected to CC on silica gel eluting with gradients of hexane, CH₂Cl₂, Me₂CO and MeOH affording 9 (3.1 mg).

The CH₂Cl₂ extract (4.2 g) was subjected to chromatographic treatments similar to those used for the hexane extract. Frs. 4-5 afforded a mixture (6.3 mg) of lupeol and sitosterol. The Fr. 7 afforded 6 (4.8 mg). Fr. 8 was rechromatographed on silica gel using gradients of hexane, Me₂CO and MeOH yielding 4 (3.7 mg), 6 (8.1 mg), 7 (5.2 mg) and 12 (1.3 mg). Fr. 9 was subjected to CC on silica gel using hexane, Me₂CO and MeOH at different ratios of increasing polarity to give 7.0 mg of the new coumarin 1, 2 (2.7 mg), 3 (0.5 mg), 4 (6.3 mg), 5 (4.3 mg), 8 (2.3 mg), 10 (3.2 mg), 11 (2.4 mg) and 12 (1.4 mg).

5,6-Methylenedioxy-7,8-dimetoxycoumarin (1). Amorphous solid. ¹H and ¹³C-NMR: see Table 1.

Results and Discussion

The new coumarin 1 was obtained from the dichloromethane extract of M. flavida and showed as a blue color on TLC under UV light 336 nm. Its ¹H NMR spectrum exhibited resonances typical of H-3 and H-4 (d 6.20 and 7.91) of the coumarin nucleus in which C-5 was oxygenated¹¹. The presence of a methylenedioxy group was indicated from the methylene hydrogens signal at d 6.01 (s) and two methoxy groups from the signals at d 4.04 and 3.99 (s, 3H each one). These groups were located at the positions 5, 6, 7 and 8 suggesting one of the possible structures 1, 1a or 1b. Further information concerning the actual positions of the methoxy groups was obtained by analysis of the 1D-NOE difference spectrum. Irradiation of the signal at d 7.91 (d, H-4) didn’t enhance the signals at d 4.04 and 3.99 (2x OMe), which confirmed the placement of the methylenedioxy group at C-5/C-6. This result is consistent with the structure 1. The assignments of the signals of carbons 3,4 and –OCH₂O- moiety in the ¹³C-NMR spectrum were established by HETCOR (¹³C, ¹H-COSY-¹J_CH) spectrum and the attribution of the quaternary carbons was made by COLOC (¹³C, ¹H-COSY-ⁿJ_CH, n = 2 and 3) experiment (Table 1).

This is the first report of the occurrence of one indolopiridoquinazoline alkaloid (rutaecarpine) from the genus Metrodorea. This fact reinforces the taxonomic position of the Metrodorea flavida into the Cusparieae tribe, due to the occurrence of this type of alkaloid in the tribes Cusparieae and Xanthoxyleae.

Acknowledgements

The authors are grateful to Coordenação de Aperfeiçoamento de Pessoal de Ensino Superior (CAPES) and Financiadora de Estudos e Projetos (FINEP) for financial support and to Universidade Federal de São Carlos (São Carlos - São Paulo, Brazil) for ¹H and ¹³C-NMR spectra at 400 and 100 MHz, respectively.

Received: September 9,1998

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Publication Dates

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

History

• Received
  09 Sept 1998