Lignans from Arnica species.

From four Arnica species (A. angustifolia Vahl ssp. attenuata (Greene) Maguire, A. lonchophylla Greene ssp. lonchophylla Maguire (flowerheads), A. chamissonis Less. ssp. foliosa (Nutt.) Maguire, A. montana L. (roots and rhizomes)) a total of twelve lignans of the furofuran-, dibenzylbutyrolactone- and dibenzylbutyrolactol-type were isolated. No report on lignans as constituents of Arnica species exists so far. Besides the known pinoresinol, epipinoresinol, phillygenin, matairesinol, nortrachelogenin and nortracheloside, six dibenzylbutyrolactol derivatives with different stereochemistry and substitution at C-9 were isolated and their structures elucidated by NMR spectroscopic and mass spectral analysis.

New triterpene esters from flowerheads of Arnica lonchophylla.

From the flowerheads of Arnica lonchophylla Greene ssp. lonchophylla Maguire (Asteraceae), a variety of mono-, di- and trihydroxytriterpenes of the oleanane, ursane, lupane and dammarane types were isolated and their structures elucidated by EI and CI mass spectrometry and extensive NMR spectroscopic analysis. Most of the compounds are esterified at position 3 with lauric, myristic, palmitic and stearic acids. Several ester derivatives of known triterpenes represent new natural products. The triterpenetriols 20(30)-taraxasten-3beta,16beta,21alpha-triol (arnitriol A) and lupane-3beta,16beta,20-triol, both isolated in the form of their C3-fatty acid ester derivatives, possess hydroxylation patterns which have not been described previously. Besides small amounts of triterpenetriol esters, the lauric, myristic, palmitic and stearic acid esters of arnidiol, faradiol, maniladiol and calenduladiol were also identified in the flowerheads of A. montana (Arnicae flos Ph. Eur.), A. chamissonis ssp. foliosa and A. angustifolia ssp. attenuata. A search for sesquiterpene lactones in the flowers of A. lonchophylla resulted in the identification of small amounts of helenalin and 11alpha,13-dihydrohelenalin.

New dihydrobenzofurans and triterpenoids from roots of Microglossa pyrifolia.

From the roots of Microglossa pyrifolia (Lam.) Kuntze (Asteraceae, tribe Astereae), used in East African traditional Medicine to treat a variety of ailments, seven dihydrobenzofurans and seven triterpenoids (five dammaranes and two 28- nor-oleanenes) were isolated. Their structures were elucidated by spectroscopic (UV, MS and NMR) means. With the exception of the tremetone derivative 1, all of the dihydrobenzofurans found in this drug possess the rare 6-acetyl-5-hydroxy substitution pattern. Dihydrobenzofurans 1 [methyl 2-(5-acetyl-2,3-dihydrobenzo[beta]furan-2-yl)propenoate], 3 (methyl2-(6-acetyl-5-hydroxy-2,3-dihydrobenzofuran-2-yl)propenoate] and 7 (6-acetyl-5-hydroxy-2-(1-hydroxy-2-propenyl)-3-methoxy-2,3-dihydrobenzofuran) as well as the triterpenes 3beta-acetoxy-25-hydroxydammara-20,23-diene ( 9), 3beta-acetoxy-24-oxo-dammara-20,25-diene ( 11), 17beta-hydroxy-3,16-dioxo-28-norolean-12-ene ( 12) and 17beta-hydroxy-3,11,16-trioxo-28-norolean-12-ene ( 13) are new natural products, to the best of our knowledge.

Anti-trypanosomal activity of helenalin and some structurally related sesquiterpene lactones.

The anti-trypanosomal activity of six sesquiterpene lactones (helenalin, mexicanin I, 11alpha,13-dihydrohelenalin acetate, chamissonolide, ivalin and isoalantolactone) against the African Trypanosoma brucei rhodesiense and American T. cruzi was investigated. All tested compounds were found active towards both parasites, the former being generally more sensitive. Helenalin was the most active compound in the series with IC50 values of 0.051 and 0.695 microM against T. brucei rhodesiense and T. cruzi, respectively. The low IC50 value for T. b. rhodesiense indicates that helenalin type compounds may be interesting candidates for further evaluation.