Identification of Structural Features of Hydrocinnamic Acid Related to Its Allelopathic Activity against the Parasitic Weed Cuscuta campestris

Abstract

Cuscuta campestris is a parasitic weed species that inflicts worldwide noxious effects in many broadleaf crops due to its capacity to withdraw nutrients and water directly from the crop vascular system using haustorial connections. Cuscuta campestris control in the majority of crops affected is non-existent, and thus, research for the development of control methods is needed. Hydrocinnamic acid occurs naturally in the rhizosphere, playing regulatory roles in plant–plant and plant–microbe communities. The toxicity of hydrocinnamic acid against C. campestris was recently identified. In the present work, a structure–activity relationship study of 21 hydrocinnamic acid analogues was performed to identify key structural features needed for its allelopathic action against the seedling growth of this parasitic plant. The findings of this study provide the first step for the design of herbicides with enhanced activity for the control of C. campestris infection.

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

“…The inhibitory activity of derivative compounds with halogenated substituents on the aromatic ring (namely, compounds 18 – 21 ) was increased when compared with trans -cinnamic acid ( 1 ). This finding agrees with a previous study where halogenated substituents increased the activity of the parent compound hydrocinnamic acid ( 2 ) against C. campestris growth [ 26 ] but disagrees with Nishikawa et al [ 28 ], who report similar or slightly less activity for halogenated analogs when compared with the cis -isomer of cinnamic acid. In our work, the growth inhibitory effect of halogenated derivatives was dependent on the type of halogenated substituent and its position.…”

“…In our work, the growth inhibitory effect of halogenated derivatives was dependent on the type of halogenated substituent and its position. On one side, when considering the substitution in the para position, the most phytotoxic compound was that containing the largest and more electronegative halogen Br ( 21 , Figure 3 D) > Cl ( 20 ) > F ( 19 ), confirming the activity of equivalent halogenated substituents in hydrocinnamic acid reported by Moreno-Robles et al [ 26 ] and cis -cinnamic acid reported by Nishikawa et al [ 28 ]. In addition, when comparing the results of compounds containing the same halogen in different positions, the one with a Cl atom in the meta position (compound 18 , IC 50 = 461 µM) presented enhanced phytotoxicity when compared to the para -substituted isomer (compound 20 , IC 50 = 955 µM).…”

“…These results suggest that there is a certain requirement for lipophilicity to be in a certain range for bioactivity with a medium-high CLog P value needed (1.873–3.122), in agreement with Lipinskii’s rule of 5 [ 25 ]. In a previous work, a SAR study was carried out with hydrocinnamic acid ( 2 ) derivatives, where it was also found that CLog P values for active compounds against C. campestris growth were defined in this range [ 26 ]. Even so, adequate lipophilicity is not enough to induce inhibition, since other compounds fulfilling this requirement have shown moderate or poor activity, such as compound 1 or compounds 12 – 15 .…”

Effects of Piper betle L. Extract and Allelochemical Eugenol on Rice and Associated Weeds Germination and Seedling Growth

“…The methyl group substitution at C-4 of the benzene ring increased the activity, but the hydroxyl group at C2–4 decreased the activity of phenylpropanoid dihydrocinnamic acid against parasitic weed ( Cuscuta campestris Yunk.) [ 29 ]. Among the six coumarin analogs synthesized from eugenol, 8-methoxy-2-oxo-6-(prop-2-en-1-yl)-2H-chromene-3-carboxylic acid presented the highest phytotoxic activity against lettuce seedlings ( L. sativa L.).…”

Insights into the Phytopathogenicity of Alternaria alternata Isolated from Infected Pears (Pyrus communis) in Italy: Enzymatic Activity and Production of Non-Host Toxins

“…Regarding the dibenzopyronederivatives alternariol (3) and alternariol 4-methyl ether (4), the higher necrotic effects showed by compound 3 could be explained by the hydroxyl group placed in the position where compound 4 presents a methoxy group, hinting that polar groups could have a positive effect on the necrosis-inducing activity, due to the capacity of forming H-bonds [50]. For both compounds, found herein as necrotic-causing toxins on lemon fruits, but inactive on pear fruits (host and non-host species), other previous studies reported activities of interest.…”