Distribution of coumarins in the tribe Plucheeae, genus Pterocaulon

Abstract

The genus Pterocaulon (Asteraceae) is included in the tribe Plucheeae [1]. About half of the Pterocaulon species have been analyzed previously and many compounds have been isolated: caffeoylquinic acids from P. virgatum [2]; thiophene acetylenes and flavanols from P. virgatum [3]; polyacetylenes from P. alopecuroides, P. balansae, P. lanatum, and P. rugosum [4]; hydroxy-α-caryophyllene from P. serrulatum [5]; flavonoids from P. sphacelatum [6], P. purpurascens [7], and P. alopecuroides [8]; and coumarins from P. balansae, P. lanatum [4], P. purpurascens [9][10][11], P. redolens [12], P. virgatum [13][14][15][16], P. polystachyum [17], and P. alopecuroides [8]. Several species of the genus are used in folk medicine as insecticides and agents against snake bites [15].In this work we investigate the occurrence of coumarins in exudates of the species of Pterocaulon native to Brazil and isolate the most abundant compounds. The taxonomic significance of these compounds is discussed.In Plucheeae the only genus that contains coumarins is Pterocaulon in which 40 different coumarins were previously found in ten species. In this work we analyzed five other species native to South Brazil, and coumarins were found in all of them. These data indicate that these compounds could be considered chemotaxonomic markers for the genus Pterocaulon.Although the species of Pterocaulon exhibit other classes of compounds, coumarins are characteristic of the genus. In Pterocaulon, coumarins can be di-, tri-, or tetraoxygenated, and all of them are 6,7 oxygenated.Pterocaulon alopecuroides and P. polystachyum were studied previously, but in this work we investigated the exudate instead of the extract of the powdered plant. The exudate of P. alopecuroides afforded 5-methoxy-6,7-methylenedioxycoumarin (1) and 7-(2,3-epoxy-3-methyl-3-butyloxy)-6-methoxycoumarin (2), previously found in P. virgatum [13,18]. To our knowledge this is the first report on the occurrence of coumarins 1 and 2 in Pterocaulon alopecuroides. From this plant, the compounds 7-(2,3-dihydroxy-3-methylbutyloxy)-6-methoxycoumarin and 7-(2,3-dihydroxy-3-methylbutyloxy)-5-hydroxy-6-coumarin were previously obtained [8]. This difference could be due to the extraction method employed and to the fact that the plants were collected in different places. Nevertheless, it is worthwhile to state that the plant exudate contained several coumarins of which only the most abundant were isolated.The exudate of P. polystachyum, besides 5-methoxy-6,7-methylenedioxycoumarin (1), afforded three other coumarins, namely ayapin (3), prenyletin (4), and prenyletin methyl-ether (5). These compounds were previously isolated from the chloroform extract of the powdered plant material [17,19].

Quantification of Coumarins in Aqueous Extract of Pterocaulon balansae (Asteraceae) and Characterization of a New Compound

“…Addition of methanol in the dry n -hexane fraction afforded 5-methoxy-6,7-methylenedioxycoumarin. This compound was identified by comparison of HPLC retention time with a standard sample previously isolated from the same plant [10] and by spectroscopic analysis. The whole process is represented in the chromatograms shown in Figure 1.…”

“…The coumarins 7-(2′,3’′-dihydroxy-3′-methylbutyloxy)-6-methoxycoumarin ( 1 ), 5-(2′,3′-dihydroxy-3′-methylbutyloxy)-6,7-methylenedioxycoumarin ( 2 ), 5-methoxy-6,7-methylenedioxycoumarin( 4 ), 7-(2′,3′-epoxy-3′-methyl-3′-butyloxy)-6-methoxycoumarin ( 5 ) and 5-(2′,3′-epoxy-3′-methylbutyloxy)-6,7-methylenedioxycoumarin ( 6 ) were previously described for P. balansae [10,16,20,21]. The compounds were characterized by their molecular ion peaks and fragmentation data and by UV absorption as well as by comparison of their HPLC retention times with published data.…”

“…Addition of methanol into the residue resulted in the formation of an insoluble precipitate which consisted of pure 5-methoxy-6,7-methylenedioxycoumarin. The compound was identified by comparison of HPLC retention time with a standard sample and by 1 H- and 13 C-NMR spectroscopy and the data were compared to those previously published by STEIN et al (2007) [10]. The methanol soluble fraction was submitted to chromatographic methods described below.…”

“…Among the coumarins present in Pterocaulon species, 5-methoxy-6,7-methylenedioxycoumarin, identified in P. alopecuroides , P. balansae , P. polystachyum , P. redolens , P. serrulatum , and P. virgatum [6,7,8,9,10], is the most studied. This compound demonstrated cytotoxicity against glioma cell lines and was able to induce markers of cell differentiation, suggesting a potential therapeutic application in the management of leukemia [11,12].…”

Antifungal activity of some coumarins obtained from species of Pterocaulon (Asteraceae)

“…The compounds were identified by 1 H NMR and 13 C NMR spectroscopy. Details of the isolation procedure and identification of the compounds were described previously (Stein et al, 2005b).…”