Design, Synthesis, and Study of the Insecticidal Activity of Novel Steroidal 1,3,4-Oxadiazoles

Abstract

A series of novel steroidal derivatives with a substituted 1,3,4-oxadiazole structure was designed and synthesized, and the target compounds were evaluated for their insecticidal activity against five aphid species. Most of the tested compounds exhibited potent insecticidal activity against Eriosoma lanigerum (Hausmann), Myzus persicae, and Aphis citricola. Compounds 20g and 24g displayed the highest activity against E. lanigerum, showing LC50 values of 27.6 and 30.4 μg/mL, respectively. Ultrastructural changes in the midgut cells of E. lanigerum were detected by transmission electron microscopy, indicating that these steroidal oxazole derivatives might exert their insecticidal activity by destroying the mitochondria and nuclear membranes in insect midgut cells. Furthermore, a field trial showed that compound 20g exhibited effects similar to those of the positive controls chlorpyrifos and thiamethoxam against E. lanigerum, reaching a control rate of 89.5% at a dose of 200 μg/mL after 21 days. We also investigated the hydrolysis and metabolism of the target compounds in E. lanigerum by assaying the activities of three insecticide-detoxifying enzymes. Compound 20g at 50 μg/mL exhibited inhibitory action on carboxylesterase similar to the known inhibitor triphenyl phosphate. The above results demonstrate the potential of these steroidal oxazole derivatives to be developed as novel pesticides.

The Insecticidal Efficacy and Physiological Action Mechanism of a Novel Agent GC16 against Tetranychus pueraricola (Acari: Tetranychidae)

“…Naturally, insecticidal agents control insects through a variety of mechanisms, including contact, stomach, repellent, fumigant, and systemic methods or through food intake prevention or oviposition inhibition, etc. [ 40 , 49 , 51 ]. Zhang et al (2013) found that the A. vera L. leaf acetone extract had contact acaricidal, repellent, fumigant, and oviposition inhibitory activities against T. cinnabarinus [ 51 ].…”

“…Zhang et al (2013) found that the A. vera L. leaf acetone extract had contact acaricidal, repellent, fumigant, and oviposition inhibitory activities against T. cinnabarinus [ 51 ]. Ma et al (2021a) reported that 1,3,4-oxadiazoles possessed excellent contact activity and weak systemic activity against E. lanigerum [ 49 ]. Here, a study of the mode of action demonstrated that GC16 had contact activity against T. pueraricola , similar to the mite contact activity of botanical extracts from A. vera and Artemisia annua [ 51 , 55 ].…”

“…Undoubtedly, investigating the action mechanisms of pesticides against pests is an important strategy to develop new prospective pesticides. To explore the action mechanism, SEM, TEM, cuticle permeability, enzyme activity, gene expression profile, and RNAi are generally analyzed [ 49 , 52 , 53 , 58 , 59 ].…”

“…It has been previously reported that the steroid PSNW targets the midgut cells of Mythimnazus separata Walker by destroying the cell membrane and mitochondria [ 63 ]. In addition, the target site of the steroid 1,3,4-oxadiazole was demonstrated to be the mitochondria and nucleus in the midgut tissues of Eriosoma lanigerum [ 49 ]. Mitochondria are the powerhouses of the cell and mitochondrial dysfunction is related to oxidative homeostasis and lipid and energy metabolism [ 50 , 64 ].…”

“…Sample preparation was the same as that described above. A previous method was modified as appropriate [ 47 , 48 , 49 , 50 ]. Samples were fixed overnight at 4 °C using 2.5% glutaraldehyde in 0.1 M PB (pH 7.4).…”