93(P08) アレロパシー活性を有するHeliannuol類の不斉合成(ポスター発表の部)

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Helianane type of sesquiterpenoids heliannuol A-D and heliespirone A has recently been isolated by Macias from the extracts of Helianthus annuus L. and shows an allelopathic activity. Unprecedented and fascinating chemical structures and characteristic biological profiles of these molecules have made them the attractive synthetic targets. In the course of our synthetic studies, we have completed the first enantiocontrolled total syntheses of heliannuol A and D. Starting from the iodide 2, the prochiral diol 4 was converted into an optically pure monoacetate 5 by employing chemoenzymatic asymmetric acetylation. Sequential deoxygenation and chain elongation via the sulfone 8 provided 10, which was oxidized with CAN to afford curcuquinone. The quinone was then treated with sodium hydrosulfite to give curcuhydroquinone. At this stage, the absolute configuration of the benzylic tertiary stereogenic center of 5 was determined to be S. S-(+)-Curcuhydroquinone thus obtained was converted via 6 steps into an enantiomerically pure epoxide 13, which was exposed to 5% NaOH solution for 24h at room temperature to give a chromatographically separable mixture of 8-14 and 7-membered cyclic ether 15 in 6% and 93% yield, respectively. Finally, acidic hydrolysis of 14 and 15 produced heliannuol A and D, whose spectral properties were completely identical with those of natural products. Since the signs of optical rotation of the synthetic materials were reverse to those of natural products, the absolute configurations of heliannuol A and D were established to be (R, S) and (R, R), respectively.
天然有機化合物討論会の論文
1998-08-31

93(P08) アレロパシー活性を有するHeliannuol類の不斉合成(ポスター発表の部)

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