Structure-Activity Relationship (SAR) Study of trans -Cinnamic Acid and Derivatives on the Parasitic Weed Cuscuta campestris

Yunck. is a parasitic weed responsible for severe yield losses in crops worldwide. The selective control of this weed is scarce due to the difficult application of methods that kill the parasite without negatively affecting the infected crop. -Cinnamic acid is secreted by plant roots naturally into the rhizosphere, playing allelopathic roles in plant-plant communities, although its activity in has never been investigated. In the search for natural molecules with phytotoxic activity against parasitic weeds, this work hypothesized that -cinnamic acid could be active in inhibiting growth and that a study of a series of analogs could reveal key structural features for its growth inhibition activity. In the present structure-activity relationship (SAR) study, we determined in vitro the inhibitory activity of -cinnamic acid and 24 analogs. The results showed that -cinnamic acid's growth inhibition of seedlings is enhanced in eight of its derivatives, namely hydrocinnamic acid, 3-phenylpropionaldehyde, -cinnamaldehyde, -4-(trifluoromethyl)cinnamic acid, -3-chlorocinnamic acid, -4-chlorocinnamic acid, -4-bromocinnamic acid, and methyl -cinnamate. Among the derivatives studied, the methyl ester derivative of -cinnamic acid was the most active compound. The findings of this SAR study provide knowledge for the design of herbicidal treatments with enhanced activity against parasitic weeds.