C3 unit addition reaction accompanied by formation of C-C bond in phytotoxin biosynthesis of phytopathogen.

Sorokinianin是由引起小麦和其它草的斑点病或根腐病的病原体的Bipolaris sorokiniana的菌株（OB-25-1）产生的植物毒素。推测该毒素由一个长蠕孢酚型倍半萜和一个C_3部分组成。先前进行的饲养实验表明，sorokinianin是由prehelminthosporol通过包括添加TCA循环的成员、脱羧和内酯化的反应合成的。以L-[羟基-^<18>O]苹果酸为碳源的饲养实验表明，C_3单元的直接前体不是苹果酸/丁二酸，而是富马酸/丁二酸。本研究的目的是鉴定在将富马酸/琥珀酸加入到prehelminthosporol后形成的产物。为此，我们<14>从B.sorokiniana培养在含有^ C标记葡萄糖的培养基上制备了^ C标记的前蠕虫孢子酚（1.7 mg，比放射性35 KBq/mg）<14>。在用^<14>C标记的前蠕虫孢酚和^3H标记的琥珀酸孵育菌丝体得到的组分中，我们发现了一个同时具有^<14>C和^3H放射性的组分。然后，我们分析了相同的馏分在冷运行中获得的放射性同位素实验后，通过GCMS乙酰化和甲基化。

Sorokinianin is a phytotoxin produced by a strain (OB-25-1) of Bipolaris sorokiniana, a pathogen causing spot blotch or foot and root rot diseases of wheat and other grasses. This toxin is assumed to be composed of a helminthosporol-type sesquiterpene and a C_3 portion. The feeding experiments conducted previously suggested that sorokinianin was synthesized from prehelminthosporol by reactions that include the addition of a member of the TCA cycle, decarboxylation and lactonization. A feeding experiment with L-[hydroxy-^<18>O] malic acid indicated that the direct C_3 unit precursor was not malic acid/oxalacetic acid but fumaric acid/succinic acid. The aim of this research is to identify the product formed just after addition of fumaric acid/succinic acid to prehelminthosporol. For this purpose we prepared ^<14>C labeled prehelminthosporol (1.7 mg, specific radioactivity 35 KBq/mg) from B.sorokiniana cultured on the medium containing ^<14>C labeled glucose. Among the fractions obtained from the mycelium incubated with both ^<14>C labeled prehelminthosporol and ^3H labeled succinic acid we found a fraction which had both ^<14>C and ^3H radioactivity. Then we analyzed the same fraction obtained in the cold run as in the radio isotopic experiment by GCMS after acetylation and methylation.