RESUMO
Six known pentacyclic triterpenes possessing oleanane, lupane, or taraxerane-type skeletons were isolated from the leaves of Sebastiania adenophora (Euphorbiaceae) and are reported for the first time in this species. These compounds include 3-epi-beta-amyrin, beta-amyrinone, 3-epi-lupeol, lupenone, taraxerol, and taraxerone. Structures were elucidated by comparison with literature data. The bioactivities of these compounds were tested on the root growth of Amaranthus hypochondriacus, amaranth (Amaranthaceae), Lycopersicon esculentum, tomato (Solanaceae), and Echinochloa crus-galli, barnyard grass (Poaceae). All six triterpenes were selectively bioactive. An important stimulatory effect was observed on amaranth root growth (23% to 56%) for almost all tested triterpenes (250 microg/ml). These triterpenes significantly inhibited the root growth of barnyard grass (28% to 78%) and tomato (23% to 49%). Aqueous leachate and organic extracts of S. adenophora leaves significantly inhibited the root growth of all test species. The possible ecological role of the allelochemicals isolated is discussed.
Assuntos
Euphorbiaceae/química , Folhas de Planta/química , Triterpenos/farmacologia , Triterpenos/químicaRESUMO
Bioactivity-directed fractionation of the methanol extract of the roots of Ratibida mexicana resulted in the isolation of two bioactive sesquiterpene lactones, isoalloalantolactone and elema-1,3,11-trien-8,12-olide. Both compounds caused a significant inhibition of the radicle growth of Amaranthus hypochondriacus and Echinochloa crus-galli, exerted moderate cytotoxic activity against three different solid tumour cell lines and inhibited significantly the radial growth of three phytopathogenic fungi. Isoalloalantolactone also caused the inhibition of ATP synthesis, proton uptake and electron transport (basal, phosphorylating and uncoupled) from water to methylviologen, therefore acting as a Hill's reaction inhibitor. The lactone did not affect photosystem I but inhibited photosystem II. The site of inhibition of isoalloalantolactone is located in the span of P680 to QA redox enzymes because the uncoupled electron transport from water to silicomolybdate and, from DPC to DCIP are inhibited approximately to the same extent.