Bioorganic Chemical Studies on Novel Sulfur-Containing Phytoalexins Produced by Crucifers

(1)几种含硫植物抗毒素已从十字花科蔬菜中分离出来;大白菜、卷心菜、萝卜和芜菁。这些植物抗毒素以油菜素、环油菜素和螺油菜素为代表，其特征是存在吲哚核，其附属物含有一个或两个硫原子。(2)利用紫外线照射和未照射的芜菁根组织，对十字花科植物抗毒素和硫代葡萄糖苷进行了时程研究。吲哚硫代葡萄糖苷和植物抗毒素的水平在紫外线照射的组织中增加，而只有前者在未照射的对照组织中。脂肪族硫代葡萄糖苷的水平显着下降，在紫外线照射和非照射的对照组织。油菜素和硫代葡萄糖苷的结构特征表明两种吲哚类化合物之间有密切的生物合成关系。似乎需要额外的通道来诱导植物抗毒素的合成。(3)使用UV照射的芜菁和氘或13 C标记的前体研究十字花科植物抗毒素的生物合成途径<13>：色氨酸是吲哚环的生物来源，这些植物抗毒素的甲基硫基的甲基部分来自甲硫氨酸，从色氨酸到油菜素的途径中可能涉及分子重排;异硫氰酸苄酯在组织中转化为油菜素型化合物表明，通过吲哚芥子油苷或直接从色氨酸合成的吲哚1 -3-甲基异硫氰酸酯，是油菜素生物合成的关键中间体。(4)将人工2-甲基芸苔素施用到UV照射的组织中导致吲哚氧基和吲哚啉衍生物的形成，表明3-羟基吲哚啉或2，3-二羟基吲哚作为环芸苔素、二氧芸苔素和螺芸苔素的共同中间体。(5)提出了从色氨酸到十字花科植物抗毒素的生物合成方案。

(1) Several sulfur-containing phytoalexins have been isolated from cruciferous vegetables ; Chinese cabbage, cabbage, radish, and turnip. These phytoalexins, represented by brassinin, cyclobrassinin, and spirobrassinin, are characterized by the presence of indolic nucleus with the appendage containigone or two sulfur atoms.(2) Time-course studies of cruciferous phytoalexins and glucosinolates have been carried out using UV-irradiated and non-irradiated turnip root tissues. Both of the levels of indole glucosinolates and phytoalexins increased in the UV-irradiated tissue whereas only the former did in non-irradiated control tissue. The levels of aliphatic glucosinolates decreased markedly both in the UV-irradiated and non-irradiated control tissues. Structural features of brassinins and indple glucosinolates suggest close biosynthetic relationships between two types of indoles. Additional parhway seems to be needed to induce the synthesis of phytoalexns.(3) Biosynthetic pathway to cruciferous phytoalexins was investigated using UV-irradiated turnip and deuterium- or ^<13> C-labeled precursors : Tryptophan is a biological origin of the indole ring ; methyl portion of the methyothio groups of these phytoalexins originates from methionine ; molecular rearrangement would be involved in the pathway from tryprophan to brassinin ; transformation of benzyl isothiocyanate into brassinin-type compound in the tissue suggests that indo1-3-ylmethyl isothiocyanate, synthesized via indole glucosinolate or directly from tryptophan, would be a key intermediate in the biosynthesis of brassinin.(4) Administration of artificial 2-methylbrassinin into UV-irradiated tissue resulted in the formation of an indoxyl and an indolenine derivative, suggesting 3-hydroxyindolenine or 2, 3-dihydroxyindole as a common intermediate to cyclobrassinin, dioxibrassinin, and spirobrassinin.(5) A biosynthetic scheme starting from tryptophan to cruciferous phytoalexins is proposed.