Abstracts

Article

Xanthones and Other Constituents of Vismia parviflora

Tanus Jorge Nagemª, and Fernando Faustino de Oliveira^b

^a Departamento de Química, Universidade Federal de Ouro Preto, Campus Morro do Cruzeiro, 35400-000 Ouro Preto - MG, Brazil

^bDepartamento de Química-ICEx, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627 Pampulha, 31270-010 Belo Horizonte - MG, Brazil

Received: August 28, 1996

Introduction

According to Engler¹, Vismia parviflora belongs to the Guttiferae family, subfamily Hyperiocoideae, tribe Vismieae. The Vismia genus consists of small trees inhabiting the tropical and subtropical regions of South and Central America, where they are used in folk medicine as strong purgative, whereas their barks are considered to be tonic and febrifugal^2-3.

Although the chemistry of the Guttiferae family has been widely studied⁴, no more than fifteen species of Vismia have been investigated among the fifty known species. Several species of this genus have been shown to contain xanthones and anthranoides^5-10. In the present study we have identified the chemical constituents from stems and fruits of Vismia parviflora, which have not been reported previously.

Results and Discussion

Fractionation of the ethanol extracts of stems and fruits on silica gel, followed by gel filtration and recrystalization, afforded the isolation the compounds 1-6. The UV spectra of 1 and 2 exhibited absorption bands characteristic of xanthones¹¹. The bathochromic shift observed upon addition of AlCl₃ indicated the presence of a chelated hydroxyl group at C-1 or C-8 for the both compounds 1 and 2. The ¹H-NMR spectra of both 1 and 2 showed , absorptions at: d 7.68 (t, J = 8.1 Hz H-3), 6.75 and 6.97(dd, J = 8.1 and 1,0 Hz H-2 and H-4) for 1 and d 7.63(t, J = 7.30 Hz H-3), 6.72 and 6.94 (dd, J = 7.3 and 1.3 Hz H-2 and H-4) for 2, indicative for both compounds the same three hydrogens vicinal pattern for one of the aromatic ring. In addition, the ¹H-NMR of compound 1 showed three ortho- and meta-coupled hydrogens at d 7.50 (d, J = 8.8 Hz H-5), 7.40 (dd, J = 8.8 and 2.7 Hz H-6), 7.57 (d, J = 2.7 Hz H-8). The OH on C-7 was proposed by the absence of the bathochromic shift of the UV maxima in the presence of sodium acetate, and confirmed by methylation of 1 with an ether solution of diazomethane. The ¹³C-NMR spectra was compatible with 1,7-dihydroxyxanthone 1. The mass spectrum showed peak at m/z 228 (M⁺), which is in accordance with the molecular formula C₁₃H₈O₄. For the compound 2 the ¹H-NMR showed two ortho coupled hydrogens at d 6.85 and 7.32 (d, J = 7.3 Hz, H-7 and H-6 respectivelly), besides the singlet at d 3.89 (3H, s, OCH₃). The ¹³C-NMR was compatible with 1,5-dihydroxy-8-methoxyxanthone. The mass spectrum showed peak at m/z 258 (M⁺, 96%) in accordance with molecular formula C₁₄H₁₀O₅, and the base peak at m/z 240 (M - 18⁺, 100%). The loss of water from the M⁺ is due to the operation of an ortho effect caused by the methoxy substituent at C-8¹², what is in agreement with the proposed structure. (Table 1).

Compounds 3-6, appeared to be 1,8-dihydroxyanthraquinone derivatives based on their UV-Vis and the IR absorptions bands characteristic of anthraquinones¹³. The ¹H-NMR spectra of these compounds showed the same pattern of substitution for one of the aromatic ring, all of them showing two meta-coupling hydrogens, between d 7.23 - 7.61 (H-4) and 6.59-7.06 (H-2), besides the methyl group at C-3 in d 2.4 and a chelated hydroxy group at C-1 for all of them. The ¹H-NMR spectra of compounds 4 and 5 showed signals compatible with a g, g'-dimethylallyl side chain, an O-dimethylallyl at C-6 for 4, whereas 5 has a dimethylallyl at C-7. In addition compound 5 showed a methoxy group at 4.01 and an aromatic hydrogen at d 7.34 (s, H-5). For compound 6 the ¹H-NMR spectra showed signals in accordance with the presence of a D¹- isopentenyl side chain at C-7, a methoxy group at d 3.93 and an aromatic hydrogen at d 7.46 (s, H-5). (Table 2).

Experimental

Plant material, A specimen of Vismia was collected in Três Moinhos district, Ouro Preto city, State of Minas Gerais, Brazil, in March 1986. The specimen was identified by Prof. José Badini, botanic garden of the Universidade Federal de Ouro Preto - Brazil.

Extraction and isolation of the constituents from stems: Air-dried, powdered stems (1,400 g) were extracted with C₆H₆ followed by EtOH. Removal of the solvents gave 9.4 g and 22.0 g as residues respectively. The benzene extract was chromatographed on silica gel (200.0 g), elution was performed with C₆H₆ , EtOAc and EtOH. Several frs. were collected and sepd. into ten groups (A₁-A₁₀), by TLC. A₁ (0.36 g) was purified by rechromatography and recrystalization from acetone yielding friedelin (10.0 mg) and b-friedelinol (7.0 mg). A₇ (0.20 g) was rechromatographed on silica gel (10.0 g), using C₆H₆ , CHCl₃ and EtOAc as eluents, giving sitosterol (24.4 mg,), 1,7-dihydroxyxantone (1,1.5 mg, mp 240-241° from EtOH, Lit.¹⁴ 240-241° from CHCl₃ ) and betulinic acid (15.0 mg). The ethanol extract (22.00 g), was chromatographed on silica gel (450.0 g), with hexane, EtOAc and EtOH as eluents, giving chrysophanic acid (3,8.5 mg, mp 191-193° from acetone), friedelin (12.0 mg), b-friedelinol (8.0 mg), madagascine (4,12.0 mg, mp 149.5-152.0° from acetone, Lit.⁷ mp 154-156°) 1,7-dihydroxyxantone (1,12.0 mg) betulinic acid (15.0 mg) and 1,5-dihydroxy-8-methoxyxantone(2,8.0 mg, mp 228,0-229,8° from EtOH, Lit ¹⁴ mp 230-231° from CHCl₃).

Extraction and isolation of the constituents from fruits: The fruits of Vismiaparviflora, were dried and ground to a powder (56.80 g), which was throughly extracted with EtOH. Removal of solvent gave a residue (16.94 g), which was chromatographed on silica gel (370.00 g) using hexane, EtOAc and EtOH as eluents. Several frs. were collected and sepd. into five groups (B₁-B₅) by TLC. B₂ (0.56 g) was washed with Me₂CO and the insoluble portion (32.2 mg) recrystalized in EtOH giving vismiaquinone A (6, 18.0 mg, mp 197.3-198.7° from acetone, Lit⁸ mp 202-204° from petrol/EtOAc 19:1). The remaining soluble portion (0.40 g), was purified by prep. TLC (layer thickness 1.0 mm), giving vismiaquinone C (5,12.0 mg, mp 212,4-214,6° from acetone, Lit.¹⁰ 215-217° from acetone), and madagascine (4,13.5 mg). B₃ (0.21 g), was recrystalized in EtOH giving chrysophanic acid (3,17.0 mg). B₄ (0.23 g) was rechromatographed on sephadex LH 20 (sigma) with MeOH as eluent, yielding quercetin (23.0 mg) and 3,4-dihydroxybenzoic acid (13.0 mg). B₅ (4.30 g) was washed exhaustively with EtOH, giving shikimic acid (0.52 g).

Acknowledgments

Financial support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Coordenação de Aperfeiçoamento Pessoal de Ensino Superior (CAPES) is gratefully acknowledged. The authors also thank anonymous referee for constructive suggestions.

Publication Dates

History