Studies on Fungal Metabolism of Phytoalexins

以异黄酮及其相关化合物为底物，以番茄灰霉病菌和黄曲霉为底物，研究了植物保卫素在真菌中的代谢。研究成果总结如下。(1)7-O-甲基-叶黄酮(1)和7-O-甲基-2，3-脱氢异黄酮(2)都是从相应的异黄酮类化合物中化学衍生而来的；从羽扇豆根中分离得到的托巴唑林(3)和从鱼腥草根皮中分离得到的鱼腥草酮(3)被两种真菌代谢。6-戊烯基化黄酮3的代谢与6-戊烯基异黄酮代谢一致。灰霉菌成功地将4中C-6‘位的戊烯基团转化为相应的环醚。(2)1的主要代谢产物为2，2-二甲基-3-羟基吡喃异黄酮，具有右旋性质。立体化学估计为S构型。(3)化合物2不是被黄曲霉迅速代谢，而是被黄曲霉代谢，生成戊烯基侧链双键上的环氧衍生物和乙二醇。后者的代谢物为S异构体，与环氧化物的酸解产物(立体保留值)吻合较好。因此，确认了环氧基中间体的构型为S。首次证实了芳基化化合物代谢成二氢呋喃或二氢吡喃环醚和/或2，3-二羟基二羟基戊烯基衍生物的环氧基中间体的存在。对白羽扇豆中的异黄酮类成分进行了精确的分析，结果表明，复合羽扇豆异黄酮类化合物的结构表明它们可能是由异黄酮烯基化而成的。羽扇豆异黄酮类的生物来源与其真菌代谢密切相关。

Fungal metabolism of phytoalexins was investigated by using prenylated isoflavones and related compounds as substrates, and Botrytis cinerea and Aspergillus flavus. Research results are summarized as follows. (1) 7-O-Methyl-luteone (1) and 7-O-Methyl-2,3-dehydrokievitone (2) both chemically derivated from the corresponding isoflavones, topazolin (3) isolated from Lupinus luteus and piscidone from the root barks of Piscidia erythrina were metabolized by two fungi. A 6-prenylated flavone 3 was metabolized as 6-prenylated isoflavone had been. The prenyl group at C-6' in 4 was successfully transformed into the corresponding cyclic ether by B. cinerea. (2) The major metabolite from 1 was confirmed to be 2,2-dimethyl-3-hydroxypyranoisoflavone with dextrorotatory nature. The stereochemistry was estimated to be S-configuration. (3) Compound 2 was rapidly metabolized not by A. flavus, but by B. cinerea to yield an epoxy-derivative at the double bond in the prenyl side chain and a glycol. The latter metabolite revealed to be S-isomer with which the acid hydrolyzate (stereo-retention) of the epoxide agreed well. Therefore the configuration of the epoxy-intermediate was confirmed to be S. The presence of an epoxy-intermediate in the metabolism of a prenylated compound into a dihydrofurano- or dihydropyrano-cyclic ether and/or a 2,3-dihydrodihydroxy- prenyl derivative was thus confirmed for the first time.Isoflavonoidal constituents in white lupin (L. albus) were precisely examined and the structures of complex lupin isoflavones suggested that they were presumably produced from prenylated isoflavones via epoxy-intermediates. The biogenedis for lupin isoflavones was thus closely related to their fungal metabolism.