Previously, researchers at Zakusov State Institute of Pharmacology used an original strategy for designing pharmacologically active dipeptides based on non-peptide drug structures to prepare the dipeptide ligands of 18-kDa translocator protein (TSPO) N-carbobenzoxy-L-tryptophanyl-L-isoleucine amide (GD-23) and N-phenylpropionyl-L-tryptophanyl-L-leucine amide (GD-102) that showed anxiolytic activity in standard behavioral tests. The present work reports GD-102 analogs with the reverse amino-acid sequence, i.e., N-phenylpropionyl-L-leucyl-L-tryptophan methylamide (GD-140), N-phenylpropionyl-L-leucyl-L-tryptophan (GD-139), N-phenylacetyl-L-leucyl-L-tryptophan amide (GD-141), N-phenylpropionyl-L-leucyl-L-tryptophan methyl ester (GD-138), and N-phenylpropionyl-L-leucyl-L-tryptophan amide (GD-136). Open-field (OF) tests of mice after i.p. administration showed that the newly synthesized dipeptides were less active than GD-102 (0.01 – 0.1 mg/kg). Dipeptide GD-140 showed anxiolytic activity at doses of 0.1, 0.5, and 1 mg/kg; GD-139, 0.5 and 5.0; GD-141, 1 and 5. Dipeptide GD-138 at a dose of 0.1 mg/kg reduced locomotor activity of animals in the OF test. GD-136 was inactive in the dose range 0.1 – 5 mg/kg. Molecular docking studies demonstrated that the studied compounds could be placed at the TSPO binding site of ligand PK 11195 (PDB ID: 2MGY). Also, π-stacking of the phenyl groups of dipeptides GD-136, GD-139, GD-140, and GD-141 with Trp107 of the receptor was revealed. For dipeptides GD-140 and GD-102, π-stacking with Trp95 was also detected. GD-138 did not exhibit π-stacking with either Trp107 or Trp95. It was concluded that the key interaction affecting the manifestation of anxiolytic activity was π-stacking of the dipeptide ligand with Trp95 of the receptor. The Trp-Leu sequence was preferred over the Leu-Trp sequence for the TSPO dipeptide ligands.

中文翻译：

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18-KDA 转运蛋白的亮氨酰色氨酸配体的合成与结构-活性（抗焦虑）关系分析

此前，Zakusov 州立药理学研究所的研究人员采用原创策略，基于非肽药物结构设计具有药理活性的二肽，制备 18-kDa 易位蛋白 (TSPO) N-羧基苯甲氧基-L-色氨酸-L-异亮氨酸的二肽配体酰胺 (GD-23) 和 N-苯基丙酰基-L-色氨酸-L-亮氨酸酰胺 (GD-102) 在标准行为测试中显示出抗焦虑活性。目前的工作报告了具有反向氨基酸序列的 GD-102 类似物，即 N-苯基丙酰-L-亮氨酰-L-色氨酸甲酰胺 (GD-140)、N-苯基丙酰-L-亮氨酰-L-色氨酸 (GD- 139)、N-苯乙酰-L-亮氨酰-L-色氨酸酰胺(GD-141)、N-苯丙酰-L-亮氨酰-L-色氨酸甲酯(GD-138)和N-苯丙酰-L-亮氨酰-L -色氨酸酰胺 (GD-136)。ip 后小鼠的开放场 (OF) 测试 给药显示新合成的二肽的活性低于 GD-102 (0.01 – 0.1 mg/kg)。二肽 GD-140 在 0.1、0.5 和 1 mg/kg 的剂量下显示出抗焦虑活性；GD-139、0.5和5.0；GD-141、1和5。在OF测试中，0.1mg/kg剂量的二肽GD-138降低动物的运动活性。GD-136 在 0.1 – 5 mg/kg 的剂量范围内是无活性的。分子对接研究表明，所研究的化合物可以放置在配体 PK 11195 (PDB ID: 2MGY) 的 TSPO 结合位点。此外，揭示了二肽GD-136、GD-139、GD-140和GD-141的苯基与受体的Trp107的π-堆积。对于二肽 GD-140 和 GD-102，还检测到与 Trp95 的 π 堆积。GD-138 与 Trp107 或 Trp95 均未表现出 π 堆积。得出的结论是，影响抗焦虑活性表现的关键相互作用是二肽配体与受体 Trp95 的 π 堆积。对于 TSPO 二肽配体，Trp-Leu 序列优于 Leu-Trp 序列。