Bioguided isolation of an antifungal compound from Trichocline reptans (Wedd.) Hieron (Asteraceae)

SOLEDAD DEL CORRAL; SARA M. PALACIOS; MARÍA C. CARPINELLA

Congreso; I Congreso Latinoamericano de Química Ecológica; 2010

Previously, in a screening of 100 native plants, we have found that the ethanolic extract of Trichocline reptans was the most effective in the inhibition of Fusarium verticillioides (MIC bioautography on TLC= 0.03mg/spot). The active principle, isolated by column chromatography guided by antifungal assays, resulted to be Xanthotoxin (1). This compound showed a MIC liquid media= 0.1mg/ml against F. verticillioides. In that chromatographic separation, two other coumarins 2 and 3, were also isolated, and taking into account that the T. reptans extract also showed antifeedant and germination inhibition activity, these three compounds were also assayed for these activities. The extract of T. reptans showed 97% inhibition of feeding of Spodoptera frugiperda (L II) at 500µg/cm2, with an effective concentration 50 (CE50) of 95.5µg/cm2. Compound 1 and 3, afforded CE50 of 34.4 and 19.4µg/cm2, respectively, against the same insect. As germination inhibitor, T. reptans extract showed 100% germination inhibition (at 5mg/ml) of Panicum miliaceum (monocotyledonous) and Raphanus sativus (dicotyledonous) with CEg50 of 0.24 and 0.45mg/ml, respectively. The assay of 1 and 3 against P. miliaceum resulted in a CEg50 of 0.15 and > 0.75mg/ml, respectively, while no inhibition was observed for these two compounds against R. sativus up to 0.75mg/ml. These results demonstrate that the ethanolic extract of T. reptans have different pesticidal activities being the antifungal one the most relevant. It is also shows that coumarin 1 is the only antifungal compound and it together with 3, are also involved in the antifeedant and germination inhibitory activities of T. reptans.                      1                                                2                                                3