9 ラセミ型epoxyisoprenoidsの菌類による代謝の化学(続)

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We have previously shown the metabolic transformation of (±)-epoxy-farnesol by Helminthosporium sativum yielded optically active diol-metabolites (Fig. 1). Interestingly, these compounds were derived from both enantiomers of the substrate through stereoselective hydration of the racemic epoxide. We wish now to report our further advances on this subject in four parts. (1) The stereoselective hydration mechanism of the racemic epoxide was investigated by metabolizing three isotope-labbeled substrates,i.e. (±)-, (-)-(^<18>O)-, and (±)-(10-D)-10,11-epoxyfarnesols. The scheme shown in Fig.2 has been proposed. The optical purity of (-)-diol-metabolites was determined by nmr method using chiral shift reagents(Eu-csr). (-)-Methyl 10,11-dihydroxyfarnesoate (-)-5b, (α)_D-14.1°, was determined to consist of 86.5% of S-(-)- and 13.5% of R-(+)-enantiomers. (2) Metabolic transformation of racemic 10,11-epoxyhomofarnesol by H.sativum was carried out. Seven optically minus compounds were characterized. Among them, (-)-C_<17>-juvenile hormone, (α)_D-12.8°, was obtained. Its (+)-enantiomer, (α)_D+11.7°, was chemically derived from (-)-10b. The metabolic pathway was shown in Fig.3. (3) In our searching a fungus which can convert the racemic epoxide into (+)-diol, we noticed Collectotrichum nicotianae. By metabolizing (±)-methyl 10,11 -epoxyfarnesoate, we have succeeded in obtaining its (+)-dihydroxy-derivative as expected. (4) During the study for fungal transformation with H. sativum, we found that t,t-epoxyfarnesol was partly isomerized to its c,t-isomer. Mechanism of the trans-to-cis isomerization was investigated. When (1-D_2)-t,t-epoxyfarnesol was isomerized with the fungus, the obtained c,t-isomer lost almost one atom of D as shown in Table 2. Thus, the mechanism via an aldehydic intermediate has been presented as shown in Fig.5. This finding seems to offer a useful method to know a direct precursor in biosynthesis of prehelminthosporol, a normal product of the fungus, by differentiating t,t-farnesol from its c,t-isomer. A preliminary examination using (1-D_2, 2-^<14>C)-t,t-farnesol has been tried.
天然有機化合物討論会の論文
1973-10-01

9 ラセミ型epoxyisoprenoidsの菌類による代謝の化学(続)

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