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A comparative study on the effect of arturin (1), ovatifolin (3), deacetylovatifolin (5), and their 1-acetoxyarturin (2), 8-acetoxyovatifolin (4), 1,10-epoxyovatifolin (6), and 11,13-dihydroovatifolin (7) derivatives, isolated from Podanthus ovatifolius and Podanthus mitiqui, on the seedling growth, germination, and respiration of several monocot and dicot weedy target species was carried out. In addition to the inhibitory activity on the bleaching of crocin induced by alkoxyl radicals, these compounds also displayed scavenging properties toward DPPH in TLC autographic and spectrophotometric assays. The results indicate that ovatifolin (3), deacetylovatifolin (5), epoxyovatifolin (6), dihydroovatifolin (7), and the CH(2)Cl(2) extract interfere with pre-emergence of seedlings at the level of respiration. These compounds appear to have selective effects on the radicle and shoot growth of Physalis ixocarpa and Trifolium pratense. Their allelopathic effects are comparable to those of parthenolide, a know natural growth inhibitor.

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