Abstract
The increasing resistance of rice sheath blight caused by Rhizoctonia solani highlights the need for highly effective and environmentally benign agents. Natural β-carboline alkaloids were simplified to obtain a series of indole derivatives, and their fungicidal activity and preliminary mode of action against R. solani were also evaluated. The initial hit indole (7) displayed significant fungicidal activity with an EC50 value of 25.56 μg/mL, and was selected for further optimization. Importantly, compound 55, the most active compound, had an EC50 value of 0.62 μg/mL, and approximately 300-fold more potent than validamycin A (EC50 = 183.00 μg/mL). In vivo bioassay also demonstrated that compound 55 showed better fungicidal activities than validamycin A. Moreover, the mechanism studies revealed that compound 55 not only caused remarkable morphological and structural alterations of R. solani hyphae, but also induced the loss of mitochondrial membrane potential and interfered with DNA synthesis. Therefore, compound 55 showed superior fungicidal activity against R. solani, and the elucidated mode of action supported the potential application of compound 55 against rice sheath blight.
Highlights
Rice sheath blight, caused by Rhizoctonia solani Kühn, is one of the most serious rice diseases worldwide [1], and has led to devastating loss in rice production—up to 50% under favorable conditions—and causes quality issues [2,3]
Chemistry yield through coupling of indole-2-carboxylic acid and various amines with HCTU as a coupling synthesis of intermediates and target compounds were performed as shown in the reagent
Indole-2-carboxylic acid was treated with diphenylphosphoryl azide (DPPA)
Summary
Rice sheath blight, caused by Rhizoctonia solani Kühn, is one of the most serious rice diseases worldwide [1], and has led to devastating loss in rice production—up to 50% under favorable conditions—and causes quality issues [2,3]. Structural modification or simplification of active lead compounds from natural products has proven to be a successful way to fungicides with new modes of action,structural such as most are not optimally ideal for direct usediscover because of these weak activities [10]. Among natural product-based fungicides, alkaloids their saturated analogues, successful way to discover fungicides with new β-carboline modes of action, such and as strobilurins fungicides. C, and obtained a potent fungicidal template indole attractive for further simplifications. Of indole compounds wasindole systematically scaffold with an opening of ring C,relationship and obtained a potent fungicidal template scaffold [18]. The structure-activity relationship (SAR) of indole compounds was systematically evaluated and Molecules 2020, 25, 1189 the preliminary mechanism of action was elucidated
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