Antiproliferative Constituents of the Roots ofConyza canadensis

Abstract

Introduction !Canadian horseweed [Conyza canadensis (L.) Cronquist, syn. Erigeron canadensis L., Asteraceae] is a plant species indigenous to America, but is now found globally; it is widely distributed in Hungary. The aerial parts of the plant have been used in different parts of the world to treat several ailments, most commonly diarrhoea and dysentery, and as a diuretic agent. In Chinese folk medicine, horseweed has also been applied for the treatment of wounds, swellings, and pain caused by arthritis [1,2]. Moreover, a decoction of horseweed has traditionally been used to treat cancerous diseases in North America [3]. Previous phytochemical studies revealed the presence of specific C 10 acetylenes [4,5], sesquiterpene hydrocarbons [6], flavonoids [7], and sterols, triterpenes, and sphingolipids [8,9] in this plant species. Recently, a triterpenoid ester, 3β,16β,20β-trihydroxytaraxastane-3-O-palmitoyl ester [5], and phenylpropanoyl 2,7-anhydro-3-deoxy-2-octulosonic acid derivatives were isolated [10]. Analysis of the essential oil of horseweed revealed 25 constituents, including monoterpenes, sesquiterpenes, and acetylenes, among which d-limonene predominated [11]. In the course of the search for antiproliferative compounds from the Asteraceae family, lipophilic and aqueous extracts of different parts of C. canadensis have been assayed on human tumour cell lines (HeLa, MCF-7, and A431). The n-hexane phase of the methanol extract of the root inhibited markedly the growth of the cells (62.4-70.1 %) at 10 µg/mL, and the CHCl 3 phase of the methanol extract of the root demonstrated at the same concentration moderate antiproliferative activity (39.3-47.9 %) [12]. The present investigation was aimed at the identification of compounds responsible for the anticancer effects of horseweed root. Activity-guided isolation, structure elucidation, and pharmacological analysis of two new C 10 dihydropyranone derivatives and various known C 10 acetylenes, triterpenes, sterols, a hydroxy-fatty acid, and apigenin are reported (l " Fig. 1). Abstract !Bioassay-guided fractionation of the n-hexane and CHCl 3 phases of the methanol extract of the roots of Conyza canadensis (L.) Cronquist led to the isolation of two new dihydropyranones named conyzapyranone A (1) and B (2), and the known 4Z,8Z-matricaria-γ-lactone (3), 4E,8Z-matricaria-γ-lactone (4), 9,12,13-trihydroxy-10(E)-octadecenoic acid (5), epifriedelanol (6), friedeline (7), taraxerol (8), simiarenol (9), spinasterol (10), stigmasterol, β-sitosterol, and apigenin. The structures were determined by means of ESIMS and 1D and 2D NMR spectroscopy, including 1 H-1 H COSY, NOESY, HSQC, and HMBC experiments. The isolated compounds were evaluated for their antiproliferative activities and were demonstrated to exert considerable cell growth-inhibitory activity against human cervix adenocarcinoma (HeLa), skin carcinoma (A431), and breast adenocarcinoma (MCF-7) cells. Some of the active components, including 2, 4, and 10, proved to be substantially more potent against these cell lines...

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