Simplification of Natural β-Carboline Alkaloids to Obtain Indole Derivatives as Potent Fungicides against Rice Sheath Blight

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.

Efficacy of Bacillus subtilis XZ18-3 as a Biocontrol Agent against Rhizoctonia cerealis on Wheat

“…Mycelia of R. cerealis were treated with sterile filtrates for 24 h. The mycelia were stained with 10 µM DCFH-DA solution (Beyotime, Shanghai, China). After incubation at 28 • C for 30 min in the darkness, the samples were observed and photographed using fluorescence microscopy [24].…”

“…All experiments were performed in triplicate and antifungal activity was determined by the Oxford cup method mentioned above. The antifungal activity of sterile filtrates was calculated using the following equation [24]:…”

Chemoselective N-acylation of indoles using thioesters as acyl source

“…Acylation of indoles frequently takes place at the C3 position because of the relatively strong electron cloud density. As N-acylated indoles are a widespread motif in many pharmaceuticals and natural products [6][7][8], selective N-acylation of indoles is very important. However, this process often requires unstable and reactive acyl chloride, which results in a poor functional group tolerance.…”