Optimization of the KK5 Scaffold and Biological Evaluation of KK5 Derivatives to Identify Potent Strigolactone Biosynthesis Inhibitors

Strigolactones (SLs) are germination stimulants for root-parasitic weeds, such as Striga spp., Orobanche spp., and Phelipanche spp., which cause significant damage to agricultural crops. Manipulation of SL biosynthesis using SL biosynthesis inhibitors can suppress the damage caused by these root-parasitic weeds. Therefore, in this study, we aimed to optimize the structure of the previously reported SL biosynthesis inhibitor KK5 and evaluate the effects of its derivatives on SL biosynthesis. A structure-activity relationship study revealed that 4-(2-phenoxyethoxy)-1-phenyl-3-(1H-1,2,4-triazol-1-yl)butanone (KeIKK5) inhibited 4-deoxyorobanchol biosynthesis in rice more potently than KK5. Additionally, germination assays revealed that KeIKK5 treatment inhibited the germination of root-parasitic weeds. Overall, our data highlight KeIKK5 as a potent SL biosynthesis inhibitor that suppresses the damage caused by root-parasitic weeds.