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

(1)从十字花科蔬菜中分离到几种含硫抗菌素；白菜、白菜、萝卜和萝卜。这些植物抗毒素以油菜素、环油菜素和螺旋油菜素为代表，其特征是存在吲哚核，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萝卜根组织对十字花科植物抗菌素和硫代葡萄糖苷进行了时间过程研究。在紫外线照射的组织中，吲哚硫代葡萄糖苷和植物抗毒素的水平都增加了，而在未照射的对照组织中，只有前者增加了。在紫外线照射和未照射的对照组织中，脂肪族硫代葡萄糖苷的水平均显著下降。油菜素和硫代葡萄糖苷的结构特征表明两类吲哚之间存在密切的生物合成关系。似乎还需要额外的通路来诱导植物抗毒素的合成。(3)利用紫外线照射的萝卜和氘-或^<13> c标记的前体研究了十字花科植物抗毒素的生物合成途径：色氨酸是吲哚环的生物来源；这些植物抗毒素的甲硫基甲基部分来源于蛋氨酸；分子重排可能参与了从特罗芬到花青素的途径；异硫氰酸苄酯在组织中转化为油菜素型化合物表明，通过吲哚硫代葡萄糖苷或直接由色氨酸合成的吲哚1-3-甲基异硫氰酸酯可能是油菜素生物合成的关键中间体。(4)将人工2-甲基油菜素注入紫外线照射的组织中，可形成吲哚基和吲哚啉衍生物，表明3-羟基吲哚啉或2,3 -二羟基吲哚是环油菜素、二氧化油菜素和螺旋油菜素的常见中间体。(5)提出了从色氨酸到十字花科植物抗菌素的生物合成方案。

(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.