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New dihydropyrone derivates and further antitumour compounds from Conyza canadensis
Canadian horseweed [Conyza canadensis (L.) Cronq.], a cosmopolitan plant of Asteraceae, has been used traditionally to treat diarrhea, dysentery and arthritis. Its decoction was also applied for cancerous diseases in North America [1,2]. As a part of our comprehensive screening programme for Hungarian Asteraceae species [3,4], the in vitro antitumour effects of lipophilic and aqueous extracts made from the aerial parts and the root of Conyza canadensis were tested by the MTT assay. The n-hexane extract of the root inhibited markedly the growth of three human tumour cell lines (HeLa, MCF-7 and A-431), whilst the chloroform extract of the root showed moderate antiproliferative activity. Here we report the activity-guided isolation and structure elucidation of compounds responsible for antitumour effects of the horseweed root. For the fractionation of the n-hexane and chloroform extract different chromatographic methods were used. Two new natural compounds, E-conyzapyrone and Z-conyzapyrone having an unusual C-10 dihydropyrone structure were isolated through antiproliferative assay guidance, together with a rare C-18 fatty acid (9,10,12-trihydroxy-10E-octadecenoic acid), and apigenin from the chloroform extract. From the n-hexane extract the C-10 acetylene derivates 4Z,8Z-matricarialactone and 4E,8Z-matricarialactone, triterpenes (friedelin, epifriedelanol, taraxerol, simiarenol) and sterols (stigmasterol, sitosterol, spinasterol) were obtained. The structure elucidation was carried out by extensive NMR and MS studies. Pharmacological analysis of the isolated compounds revealed that acetylene-type compounds have the most significant cell growth inhibitory potency with IC50 1.10–4.74µg/ml. E-conyzapyrone and Z-conyzapyrone exerted moderate antiproliferative activity with IC50 7.83–17.05 and 6.98–12.05µg/ml, respectively.
Acknowledgements: Our investigation was supported by the Hungarian Scientific Research Fund (OTKA 72771).
References: 1. Grünwald, J., Brendler, T., Jänicke, C. (Eds.) (2000) PDR for Herbal Medicines. Thomson.
2. Hartwell, J. (1968)J. Nat. Prod. 31: 71–170.
3. Réthy, B. et al. (2007) Phytother. Res. 21: 1200–08.
4. Csupor-Löffler, B. et al. (2009) Phytother. Res. 23: 1109–15.