Selective Phytotoxic Effects of Sesquiterpenoids from Sonchus arvensis as a Preliminary Approach for the Biocontrol of Two Problematic Weeds of Wheat.

The objective of this study is to find new selective allelochemicals for managing two problematic weeds redroot pigweed ( Amaranthus retroflexus ) and common lambsquarters ( Chenopodium album ) with minimal negative effects on wheat, thereby facilitating the development of eco-friendly botanical herbicide. Three new sesquiterpenoids, sonarvenolide A-C ( 1 - 3 ), and nine known sesquiterpenoids ( 4 - 12 ) were isolated from Sonchus arvensis . Compound 1 was a rare peroxide-substituted eudesmane-type sesquiterpenoid, and compound 3 was a rare iphionane-type sesquiterpenoid. Notably, compounds 1 , 3 , 4 , 6 - 8 , and 11 showed selectivity phytotoxic activity. In particular, compounds 1 , 3 , and 4 exhibited excellent germination inhibitory effect on A. retroflexus (IC 50 = 32.0-129.0 μM), higher than that of the positive control triasulfuron (IC 50 = 141.7 μM), and compound 4 showed excellent inhibition on C. album (IC 50 = 82.0 μM), higher than that of triasulfuron (IC 50 = 100.9 μM). In addition, compounds 1 , 3 , and 4 showed allelopathy to the growth of two weeds, which were more potent than or close to that of triasulfuron. Furthermore, these compounds were not toxic to wheat even at a high concentration (1000 μM). Structure-activity relationships (SARs) revealed that the presence of peroxides or the absence of hydroxyl at C-5 in the eudesmane-type sesquiterpenoids could strengthen the inhibitory activities. The discovery of selective allelochemicals provides not only a new choice to control two problematic weeds of wheat but also new natural lead compounds for herbicides.