P-36 Xanthanolide類の合成とアレロパシー活性(ポスター発表の部)
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概要
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The xanthanolides were isolated primarily from the Xanthium (family Compositate). Recently, xanthanolides have been found to exhibit interesting biological profiles such as antimalarial and antitumor activity, inhibition of farnesylation of the human lamin-B as well as allelopathic activity. Due to their limited availability, there have been few investigations on xanthanolides as allelochemicals. Herein, we report the synthesis of sundiversifolide (4), isolated from the exudate of germinating sunflower (Helianthus annuus L.) as an allelopathic compound, along with its allelopathic activities and determination of the absolute configuration. We also report the synthesis of xanthanolides such as xanthatin (1), 8-epi-xanthatin (2), dihydroxanthatin (3) and diversifolide (5). Synthesis of sundiversifolide (4) is as follow: The key seven-membered ring construction was achieved by an intramolecular acylation of an organolithium species, and then the γ-lactone moiety was formed from a butenolide, prepared by the one-pot condensation of a α-hydroxyhemiacetal with Ph_3P=CMe(CO_2R). The absolute configuration of natural sundiversifolide (4) was determined by HPLC analysis using a chiral column and allelopathy assay. 8-epi-Xanthatin (2) was synthesized from the sundiversifolide precursor 22 by α-methylenation of the lactone, followed by cross metathesis with methyl vinyl ketone. Xanthatin (1), dihydroxanthatin (3) and diversifolide (5) were synthesized by the inversion of C-8 stereochemistry, which was carried out by the oxidation-reduction method. The ^1H and ^<13>C NMR spectra of synthetic 5 did not match those of the natural material reported by Kuo. We concluded that the correct structure of diversofolide is 11-epi-sundiversifolide (32).
- 2008-09-01
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