Previously, we found (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) to be a selective inhibitor of root gravitropic bending of lettuce radicles at 5 μM, with no concomitant growth inhibition. Here, we describe a structure-activity relationship study of ku-76 to determine the essential structural features for the inhibitory activity. A series of ku-76 analogues was synthesized and the key features of ku-76 that are necessary for inhibition of lettuce root gravitropic bending were determined. The (2E,4E)-, (2Z,4Z)- (2E,4Z)- analogues were inactive, and 4,5-saturated and 4,5-alkynyl analogues also did not show inhibitory activity, demonstrating the importance of the (2Z,4E) diene unit. The aromatic ring was also crucial and could not be replaced with an alkyl chain. Derivatives in which the carboxylic acid was replaced with amides, alcohols, or esters were much less potent. These results suggest that the (2Z,4E)-diene, the carboxylic acid moiety, and the aromatic ring are essential for potent inhibitory activity against gravitropic bending.

中文翻译：

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(2Z,4E)-5-phenylpenta-2,4-dienoic acid 抑制根向重性的基本结构特征

之前，我们发现 (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) 是 5 μM 生菜胚根根向重力弯曲的选择性抑制剂，没有伴随的生长抑制。在这里，我们描述了 ku-76 的构效关系研究，以确定抑制活性的基本结构特征。合成了一系列 ku-76 类似物，并确定了 ku-76 抑制生菜根向重力弯曲所必需的关键特征。(2E,4E)-, (2Z,4Z)- (2E,4Z)- 类似物是无活性的，4,5-饱和和 4,5-炔基类似物也没有显示出抑制活性，证明了（ 2Z,4E) 二烯单元。芳环也很重要，不能用烷基链代替。羧酸被酰胺、醇、或酯的效力要低得多。这些结果表明 (2Z,4E)-二烯、羧酸部分和芳环对于有效抑制向重力弯曲的活性是必不可少的。