98(P-12) アブラナ科植物ファイトアレキシン、スピロブラシニンのアキラル条件下における光学富化現象及びその絶対立体化学(ポスター発表の部)

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Phytoalexin production is believed to be a part of a plant's chemical and biochemical defense mechanisms. Our former phytoalexin studies of several economically important cruciferous vegetables revealed that they produce sulfur-containing indole or indole-related compounds. We reported previously isolation of the first oxindole phytoalexin, spirobrassinin (1), from Pseudomonas cichorii-inoculated Japanese radish (Rhaphunus sativus). However, the absolute configuration of natural (-)-1 has not yet been determined. In this paper, we describe about chiral syntheses and determinations of the absolute configurations of 1 and its oxygen analog (2). and also about unusual enantiomeric enrichment phenomena under achiral chromatographic conditions. Racemic 1 and 2 prepared from isatin were enantioresolved by a chiral auxiliary method giving (+)-1, natural (-)-1 and (+)-2, (-)-2, respectively. Detailed chiral analysis of (-)-1 isolated from P. cichorii-inoculated turnips (Brassica campestris) revealed that its enantiomeric excess (ee) was not 100%. Moreover, ee of two natural spirobrassinin fractions separated by non-chiral chromatography were considerably different (98% ee and 83% ee). To clarify this phenomenon, chromatographic separation of partially enriched (+)-1 (artificial mixture, ca. 50% ee. Unnatural type) with non-chiral HPLC system was performed. This showed a more dramatic ee movement depending on its fractions (99% ee〜6% ee). The phenomenon called the enantiomeric enrichment is an extremely rare example about a natural product. The absolute configurations were unambiguously determined by X-ray crystallography of (1'S,4'R)-camphanoyl derivatives of (+)-1, (-)-1 and an urea derivative of (+)-2 prepared from (S)-(-)-α-methylbenzyl isocyanate. It showed both (-)-1 and (-)-2 have S configurations. Their CD spectra supported these results. The nature of 1 suggests to us a difference in biological activity between the racemate and both of the enantiomers. However, no significant differences between the chemical species were expressed in antifungal bioassay against Bipolaris leersiae in vitro.
2000-10-01

98(P-12) アブラナ科植物ファイトアレキシン、スピロブラシニンのアキラル条件下における光学富化現象及びその絶対立体化学(ポスター発表の部)

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