Treatment of indole-3-carboxylic acid with phosphorus trichloride and subsequent reaction of the obtained acid chloride with potassium thiocyanate afforded indol-3-ylcarbonyl isothiocyanate (13). Its treatment with sodium hydrogensulfide in the presence of methyl iodide lead to the corresponding methyl dithiocarbamate, an oxo derivative of brassinin (oxobrassinin, 14), which by methylation with methyl iodide afforded brassenin B (8). Corresponding 2-isomers, 21 and 23, were obtained by an analogous sequence, starting from indole-2-carboxylic acid. During the preparation of isooxobrassinin (21), which appeared to be unstable in the basic reaction medium, also an imidazo[3,4-a]indole derivative 22 has been isolated as an unexpected side product. Related oxobrassinin analogs and their 2-isomers were prepared by treatment of indol-3- and indol-2-ylcarbonyl isothiocyanate with methanol and amines. In the case of isothiocyanate 13, besides the expected products of nucleophilic addition to NCS group (monothiocarbamate 25a and thiourea derivatives 25b-25g), also the substitution products were obtained. Their formation could be explained by partial decomposition of the starting isothiocyanate to an unstable ketene, which reacts with methanol and amines to afford the corresponding methyl carboxylate 26a and carboxamides 26b-26g. Antifungal activity of the prepared compounds has been examined, using the fungus Bipolaris leersiae. All of the compounds exhibited lower activity than phytoalexin brassinin.
将吲哚-3-羧酸与三氯化磷反应,然后将得到的酸氯化物与硫氰酸钾反应,得到吲哚-3-基羰基异硫氰酸酯(13)。在甲基碘存在下,用氢亚硫酸钠处理它,得到相应的甲基二硫代氨基甲酸酯,即油菜硫代氨基甲酸酯(氧代油菜硫代氨基甲酸,14),通过用甲基碘进行甲基化,得到油菜硫代氨基甲酸B(8)。类似的序列从吲哚-2-羧酸开始,得到相应的2-异构体21和23。在制备异氧代油菜硫代氨基甲酸(21)的过程中,它在碱性反应介质中似乎不稳定,还分离出一种意外的副产物咪唑并[3,4-a]吲哚衍生物22。通过用甲醇和胺处理吲哚-3-和吲哚-2-基羰基异硫氰酸酯,制备了相关的氧代油菜硫代氨基甲酸酯及其2-异构体。在异硫氰酸酯13的情况下,除了预期的亲核加成产物(单硫代氨基甲酸酯25a和硫脲衍生物25b-25g)外,还得到了取代产物。它们的形成可以通过起始异硫氰酸酯部分分解为不稳定的酮烯,后者与甲醇和胺反应,形成相应的甲基羧酸酯26a和羧酰胺26b-26g。使用真菌Bipolaris leersiae检测了所制备化合物的抗真菌活性。所有化合物的活性均低于植物抗生素油菜硫代氨基甲酸。