| Summary: | To improve the proinsecticidal activity and phloem mobility of amino acid–tralopyril conjugates further, nine conjugates were designed and synthesized by introducing glutamic acid to tralopyril, and the length of the linker between glutamic acid and tralopyril ranged from 2 atoms to 10 atoms. The results of insecticidal activity against the third-instar larvae of <i>P. xylostella</i> showed that conjugates <b>42</b>, <b>43</b>, <b>44</b>,and <b>45</b> (straight-chain containing 2–5 atoms) exhibited good insecticidal activity, and their LC<sub>50</sub> values were 0.2397 ± 0.0366, 0.4413 ± 0.0647, 0.4400 ± 0.0624, and 0.4602 ± 0.0655 mM, respectively. The concentrations of conjugates <b>43</b>–<b>45</b> were higher than that of conjugate <b>42</b> in the phloem sap at 2 h, and conjugate <b>43</b> showed the highest concentration. The introduction of glutamic acid can improve phloem mobility. The in vivo metabolism of conjugates <b>42</b> and <b>43</b> was investigated in <i>P. xylostella</i>, and the parent compound tralopyril was detected at concentrations of 0.5950 and 0.3172 nmol/kg, respectively. According to the above results, conjugates <b>42</b> and <b>43</b> were potential phloem mobile pro-insecticide candidates.
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