Synthesis and Reactions of Fused Pyrazolo[3,4-b]Pyridine Derivatives: Insecticidal Activity and Digestive Dysfunction against Mosquito Larvae

5-Amino-4-formyl pyrazole 1 was used as a precursor for the synthesis of 6- aminopyrazolo[3,4-b]pyridine-5-carbonitrile 2, and 6-aminopyrazolo[3,4-b]pyridine-5- carboxamides 3 and 4. Pyrazolo[3,4-bpyridines 2, 3, and 4 were treated with different reagents leading to structurally confirmed heterocycles. Mosquito adult females carry and transmit the causatives of many diseases to humans and other domestic animals. Therefore, their management has become a necessity. Ten of the synthesized compounds were tested for larvicidal activity against second-stage C. pipiens larvae. IR spectra were recorded on Shimadzu-408 infrared spectrophotometer. The NMR spectra were performed on a Bruker AV-400 spectrometer and JEOL ECA II 500 MHz. Mass spectrometry was provided on a Varian MAT 312 instrument in EI mode (70 eV). Lethal concentrations were calculated based on probit analysis. Biochemical enzymes were analyzed using analysis of variance ANOVA with Graph Pad Prism 5. Mean comparisons were analyzed using Tukey's test. Five compounds, 1, 2, 4, 5 and 11 exhibited detectable insecticidal activity as these compounds recorded 154.4, 5.6x10³, 8.4, 135.1 and 697.2 ppm, respectively. Moreover, the effect of these insecticidal compounds on lipids and carbohydrates digestive pathways in the larvae was evaluated by comparing the activities of amylase and lipase digestive enzymes in both control and treated larvae. Compounds 1, 4 and 5 showed an inhibitory effect on both lipase and amylase enzymes. Compound 2 inhibited lipase activity, while compound 11 didn’t affect both enzymes compared with the control. Results showed that the incorporation of pyridine and pyrazole induced significant insecticidal activity against larval mosquitoes. Furthermore, insertion of amino or carbonyl groups into the synthesized compounds enhanced the insecticidal activity. Our findings showed that development of such novel compounds is promising in enhancing the agricultural productivity and management of diseases transmitted by insects.