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

(1)从大白菜、卷心菜、萝卜和萝卜等十字花科蔬菜中分离到几种含硫植物保卫素。这些植物保卫素以油菜素、环油菜素和螺菜素为代表，以吲哚核的存在为特征，附属物中含有一个或两个硫原子。(2)对十字花科植物保卫素和硫代葡萄糖苷进行了时程研究。在紫外线照射的组织中，吲哚硫代葡萄糖苷和植物保健素的水平均增加，而在未照射的对照组织中，只有前者增加。在紫外线照射和未照射对照组织中，脂肪硫代葡萄糖苷的水平都显著降低。油菜素和吲哚硫代葡萄糖苷的结构特征表明两种吲哚之间存在密切的生物合成关系。(3)利用紫外光照射的萝卜和氚-13&gt；C标记的前体研究了十字花科植物保卫素的生物合成途径：色氨酸是吲哚环的生物起源；这些植物保卫素的甲基硫代基团的甲基部分来自蛋氨酸；分子重排可能参与了从先知素到油菜素的合成途径；在组织中，苄基异硫氰酸酯转化为油菜素类化合物表明，由吲哚硫代葡萄糖苷或直接从色氨酸合成的吲哚1-3-基甲基异硫氰酸酯，将是油菜素生物合成的关键中间体。(4)将人工2-甲基油菜素加入紫外线照射的组织中，导致吲哚和吲哚衍生物的形成，这表明3-羟基吲哚或2，3-二羟基吲哚是环油菜素、二氧油菜素和螺油菜素的常见中间体。(5)提出了从色氨酸到十字花科植物外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.