Plant diseases caused by phytopathogenic fungi are a serious threat in the process of crop production and cause large economic losses to global agriculture. To obtain high-antifungal-activity compounds with novel action mechanisms, a series of 4-substituted mandelic acid derivatives containing a 1,3,4-oxadiazole moiety were designed and synthesized. In vitro bioassay results revealed that some compounds exhibited excellent activity against the tested fungi. Among them, the EC50 values of E13 against Gibberella saubinetii (G. saubinetii), E6 against Verticillium dahlia (V. dahlia), and E18 against Sclerotinia sclerotiorum (S. sclerotiorum) were 20.4, 12.7, and 8.0 mg/L, respectively, which were highly superior to that of the commercialized fungicide mandipropamid. The morphological studies of G. saubinetii with a fluorescence microscope (FM) and scanning electron microscope (SEM) indicated that E13 broke the surface of the hyphae and destroyed cell membrane integrity with increased concentration, thereby inhibiting fungal reproduction. Further cytoplasmic content leakage determination results showed a dramatic increase of the nucleic acid and protein concentrations in mycelia with E13 treatment, which also indicated that the title compound E13 could destroy cell membrane integrity and affect the growth of fungi. These results provide important information for further study of the mechanism of action of mandelic acid derivatives and their structural derivatization.

中文翻译：

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新型4-取代扁桃酸衍生物的设计、合成、体外抗真菌活性及机理研究

植物病原真菌引起的植物病害严重威胁着作物生产过程，给全球农业造成巨大的经济损失。为了获得具有新作用机制的高抗真菌活性化合物，设计并合成了一系列含有 1,3,4-恶二唑部分的 4-取代扁桃酸衍生物。体外生物测定结果表明，一些化合物对测试的真菌表现出优异的活性。其中，E13对赤霉菌（G. saubinetii）、E6对黄萎病菌（V. dahlia）和E18对核盘菌（S. sclerotiorum）的EC50值分别为20.4、12.7和8.0 mg/L，这大大优于商品化杀菌剂mandipropamid。G.的形态学研究 saubinetii 的荧光显微镜（FM）和扫描电子显微镜（SEM）表明，随着浓度的增加，E13 破坏了菌丝表面并破坏了细胞膜的完整性，从而抑制了真菌的繁殖。进一步的细胞质含量渗漏测定结果表明，E13处理后菌丝体中的核酸和蛋白质浓度急剧增加，这也表明标题化合物E13可以破坏细胞膜的完整性，影响真菌的生长。这些结果为进一步研究扁桃酸衍生物的作用机制及其结构衍生化提供了重要信息。从而抑制真菌繁殖。进一步的细胞质含量渗漏测定结果表明，E13处理后菌丝体中的核酸和蛋白质浓度急剧增加，这也表明标题化合物E13可以破坏细胞膜的完整性，影响真菌的生长。这些结果为进一步研究扁桃酸衍生物的作用机制及其结构衍生化提供了重要信息。从而抑制真菌繁殖。进一步的细胞质含量渗漏测定结果表明，E13处理后菌丝体中的核酸和蛋白质浓度急剧增加，这也表明标题化合物E13可以破坏细胞膜的完整性，影响真菌的生长。这些结果为进一步研究扁桃酸衍生物的作用机制及其结构衍生化提供了重要信息。