Insect kinins are endogenous, biologically active peptides with various physiological functions. The use of insect kinins in plant protection is being evaluated by many groups. Some kinins have been chosen as lead compounds for pest control. We previously reported an insect kinin mimic IV-3 that had insecticidal activity. And by introducing a strong electron withdrawing group (-CF₃) on the benzene ring (Phe²), we discovered a compound, L₇, with better activity than lead IV-3. In this work, taking L₇ as the lead compound, we designed and synthesized 13 compounds to evaluate the influence of position 4 (Trp⁴) of insect kinin on insecticidal activity, by replacing the H atom on tryptophan with -CH₃ and -Cl or substituting the indole ring of tryptophan with the benzene, naphthalene, pyridine, imidazole, cyclohexane, and alkyl carboxamides. The aphid bioassay results showed that the compounds M₁, M₃, and M₅ were more active than the positive control, pymetrozine. Especially, replacing the side chain by an indole ring with 4-Cl substitution (M₁, LC₅₀ = 0.0029 mmol/L) increased the aphicidal activity. The structure–activity relationships (SARs) indicated that the side chain benzene ring at this position may be important to the aphicidal activity. In addition, the toxicity prediction by Toxtree, and the toxicity experiments on Apis mellifera suggested that M₁ was no toxicity risk on a non-target organism. It could be used as a selective and bee-friendly insecticide to control aphids.

中文翻译：

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昆虫激肽模拟物可作为蚜虫的潜在控制剂：Trp4 的结构修饰

昆虫激肽是具有多种生理功能的内源性生物活性肽。许多团体正在评估昆虫激肽在植物保护中的应用。一些激肽已被选为害虫防治的先导化合物。我们之前报道了一种具有杀虫活性的昆虫激肽模拟物IV-3。通过在苯环（Phe ² ）上引入强吸电子基团（-CF _{3 ），我们发现了一种比铅}IV-3活性更好的化合物L ₇。在这项工作中，我们以L ₇作为先导化合物，设计并合成了 13 种化合物来评估第 4 位（Trp ⁴)的昆虫激肽对杀虫活性的影响，通过用-CH ₃和-Cl取代色氨酸上的H原子或用苯、萘、吡啶、咪唑、环己烷和烷基甲酰胺取代色氨酸的吲哚环。蚜虫生物测定结果表明化合物M ₁、M ₃和M ₅比阳性对照吡蚜酮更具活性。特别是，用具有 4-Cl 取代的吲哚环取代侧链 ( M ₁ , LC ₅₀ = 0.0029 mmol/L) 增加了杀蚜活性。结构-活性关系（SARs）表明该位置的侧链苯环可能对蚜虫活性很重要。此外，Toxtree 的毒性预测和意大利蜜蜂的毒性实验表明，M ₁对非目标生物没有毒性风险。它可以作为一种选择性和对蜜蜂友好的杀虫剂来控制蚜虫。