Germination and growth inhibitory sesquiterpene lactones and a flavone from Tithonia diversifolia
1994
Inhibitory effects of two sesquiterpene lactones tagitinin A, tagitinin C and a flavonoid hispidulin isolated from Tithonia diversifolia were determined on germination of radish, cucumber and onion seeds. The flavonoid hispidulin was more toxic to the crop seeds tested and the activity of tagitinin C was weaker than that of tagitinin A and hispidulin. Seventeen derivatives have been prepared from tagitinin A and C by chemical transformation and their phytotoxicity has been compared with the parent compounds (all at 250 micromolars) using radish seeds. The structural requirements related to their biological activity have also been delineated.
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