Xanthones and Other Constituents of Vismia parviflora

Vismia parviflora, planta da família Guttiferae, é uma espécie da tribo Vismeae encontrada na região de Ouro Preto MG. Dos extratos benzênico e etanólico dos galhos e etanólico dos frutos de um especimen desta planta, cromatografados em sílica gel, foram isolados sitosterol, ácido betulínico, lupeol, friedelina, β-friedelinol, ácido chiquímico, ácido 3,4-diidroxibenzóico, quercetina e as antraquinonas madagascina, ácido crisofânico, vismiaquinona-A e vismiaquinona-C, além das xantonas 1,7-diidroxixantona e 1,5-diidroxi-8-metoxixantona. Estas substâncias tiveram suas estruturas elucidadas com base nos seus dados espectrométricos de IV, UV, EM e RMN de H e C uni-(1D) e bidimensional-(2D).


Introduction
According to Engler 1 , 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 studied 4 , 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][6][7][8][9][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 xanthones 11 .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 1 H-NMR spectra of both 1 and 2 showed , absorptions at: δ 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 δ 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 1 H-NMR of compound 1 showed three orthoand metacoupled hydrogens at δ 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 13 C-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 1 H-NMR showed two ortho coupled hydrogens at δ 6.85 and 7.32 (d, J = 7.3 Hz, H-7 and H-6 respectivelly), besides the singlet at δ 3.89 (3H, s, OCH3).The 13 C-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-8 12 , 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 anthraquinones 13 .The 1 H-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 δ 7.23 -7.61 (H-4) and 6.59-7.06(H-2), besides the methyl group at C-3 in δ 2.4 and a chelated hydroxy group at C-1 for all of them.The 1 H-NMR spectra of compounds 4 and 5 showed signals compatible with a γ, γ'-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 δ 7.34 (s, H-5).For compound 6 the 1 H-NMR spectra showed signals in accordance with the presence of a ∆ 1 -isopentenyl side chain at C-7, a methoxy group at δ 3.93 and an aromatic hydrogen at δ 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.