Synthesis, evaluation of insecticidal activity, and crystal analysis of cis-nitenpyram analogs bearing 1,4-dihydropyridine
A new series of nitenpyram analogs were designed by introducing 1,4-dihydropyridine to fix the pharmacophore (-C=C-NO2) into the cis-configuration, as confirmed by X-ray diffraction. Crystal structure analysis showed that there was a homoconjugation effect on these cis-nitenpyram analogs, and a huge conjugated system comprising the 1,4-dihydropyridine scaffold and the ester group at the 3 position. Preliminary bioassays showed that most of the target compounds exhibit good insecticidal activities (>80 %) at 100 mg/dm3 against Aphis medicagini, while a 4-fluorophenyl cis-nitenpyram analog afforded the best activity, with >90 % mortality at 20 mg/dm3. These excellent insecticidal activities imply that this huge conjugated system results in an enhanced π-π interaction between the molecule and amino acid residues in receptors. Further studies on the mode of action of one of these cis-nitenpyram analogs and structural modifications are in progress.
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