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。